CIS pressure testing
 

I'm working on a 78 SC CIS system. I have a few questions.
First the symptoms that brought me to want to mess with it are these. Starts o.k. but right after start up it runs rough, popping stalling. After warm up runs good.
So form these symptoms it seems (from the Bosch book) to be a good place to get some info on system pressure during warm up. Hopefully it will give me some insight into what the pressure control regualtor and auxiliary pressure controls are doing during this time.
Question #1: The manual says to pull the fuel pump relay and hot wire it so you can flick it on and off with a switch while your working back there.
a) After studying the wiring diagram and playing around with the relay socket I can't get it to behave as I would expect. Shouldn't there be a lead that is always hot going to one post on the relay? This would be the high current contact that the pump is connected to when the relay flips? Non of the relay contacts at the socket have 12v when the ign switch is off. So what do I jumper to make it go?
b) Isn't the whole point of the jumper that you can run the pump with out heating the elements in the other fuel system controls. Based on the wiring diagram this isn't possible by just jumping relay contacts because the wires for the heatign elements nad the pump are joined behind the panel. So when you hot wire the pump your also hot wiring the heating element and thus defeating the whole purpose becasue as they heat up the system will change the pressure.

Question #2: There is a connector that goes to a littel blue piece on the back of the housing that holds the up draft flapper. It has been disconnected. When I connected it the motor ran worse. I don't see any reference to it in any manual. Now remember this is a 78 ( black K distributor). It doesn't fancy stuff like KE. There shouldn't be any electronic correction devices on the back of the fuel dist area. Here's the other weird part. It doesn't look like much other than a little plug that is screwed to the housing. All I can imagine is that there is a little thermo resistor inside that is giving some temp signal back to something. But if that was it why would it be mounted on the aluminum housing at the flapper valve???? ambient air temp correction? Again no reference to this any where.

So in summary ( holly crap this is a long description) how have others done the fuel pump hot wire? What is the point over just turning the key on if the heaters get voltage anyway. WTF is the little blue connector on the back of the flapper housing?

Can anybody save me the time of all this and give me another diagnosis idea for the warm up sysmptoms?
P.S. I did a good visual inspection in teh beginnign and don't see any cracked vacuum connections or other visual wear/damage.

Thanks,
Adam

U can pull the connectors off of the WUR and aux air reg if u dont want them to heat up.
is the connector u are talking about behind the air flow meter? if it is, i THINK it is there to shut off the fuel pump if the engine is not running...if the engine stops, the plate drops to resting position and shuts off pump for safety reasons...dont hold me to that. look at your wiring diag, you will see it coming off the FP RLY. why it is affecting the way it runs baffles me, cis is not controlled by any electrics other than the cold start valve.

Adam: What manual are you using? Just the Bosch? The Bentley tells you how to jumper the fuel pump on 240-11 and yes, ignition is on for the tests.
The Bentley also gives you the right terminology:
Your "Draft flapper" is the air sensor plate and the switch connected to it is the "Air Flow Sensor Contact" and needs to be connected.
Also, even though you don't have Lambda, a '78 has K-Jetronic CIS and is subject to the correct wiring, especially for WUR, AAR, CSV.

Get the Bentley SC Repair Manual and study it to learn more about CIS and follow the wiring schematic. Check that the wiring is correct and then perform a pressure test according to the Bentley.
It sounds to me that your WUR and/or AAR is not performing right.
The Bosch manual is general about CIS but the Bentley is specific for your SC.

Adam
 

There is a Bentley in the back of the car. I also have the CIS book Pennington wrote on how to trouble shoot CIS if you want me to email the PDF.

Thanks for helping me with this.

Andrew

The blue item is the cold start injector and its connection. The nearby green one is for the shutoff switch that T77911S mentioned.

If you search the archives you will find more info on this system than you thought possible. Jim Williams (I think) has a site w/ a very good explanation of he system and its components. You should also get the Bentley manual as Gunter said.

You are on the right track. Control pressures are critical for proper system operation. Sounds like your WUR is out of adjustment, especially during the warmup phase. There are articles here on how to adjust it and to make it easily adjustable.

Your AAR may also be not functioning correctly. Member Mystery Train has a writeup on the AAR that shows how to adjust.

The Bentley has charts showing control pressure ranges. If you post what you get, we can tell you if you are in range. Let us know the ambient temp @ startup.

Thanks guys. I'll post more info as I continue to dig into it.
Adam,

Some answers to your questions....
 

Adam,

Some pointers:
#1-A). Connect terminals 87A and 30 of the fuel relay using a jumper; and turn the ignition switch on. With the ignition at off position, there is no 'power' going to terminal 87a.

#1-B). The objective of jumping 87A & 30 is to test run the fuel pump without the engine running and subsequently be able to measure the control and system fuel pressure (cold stage).

For cold start, you want low control pressure reading and high system (delivery) pressure.

TD

TD,
This is what is confusing me. The pump normally works without the motor running. Just turn the key to the on position. So if you are turning the key on to get the jumper to work how is the jumper doing anything different than the relay? I guess the only thing it does is let you have a swith in your hand instead of reaching in and turning the key. Is that it? I thought we were doing it to avoid powering other systems that are switched by the ignition key.

I know that on most CIS cars, the fuel pump relay powers the pump for several seconds, but then switches it off if there is no RPM signal (indicating that the engine has started).

It's a safety feature. The purpose of the jumper is to bypass that feature and let the pump run longer/continuously for testing.

Ah ha! Thank You.

Some confusion....
 

Adam,

Now I realize where we get confused. You have a '78 SC with CIS system installed in your '73 car. The information I posted earlier was for SC CIS systems.

If you can make the fuel pump run by just turning the ignition switch on, then you don't need to connect terminals 87A & 30 to test run your fuel pump.

But what also confused me is that you don't get power on any of the fuel pump relay terminals and yet you claim that the pump is running when the ignition switch is turned ON. This does not make sense at all!!!

So why do you need a jumper set-up to run your fuel pump? Now I am really confused too.

TD

No no. Adam is working on my 78SC
 

Adam is being a great friend and helping me with my SC. I have limited (well Zero) skills and was getting sick over all the money I had to poor into mechanics bank accounts and STILL ended up with a car that was not running right. Adam stepped up to the plate and offered to help me with my car. It's a 78 RoW SC he is working on not a late engine in his 73. Thanks to all who have contributed in helping Adam help me.

Andrew

Now Let's Go to basic.....
 

Adam / Andrew,

First in a normal set-up, the fuel pump in SC car will not run or operate with ignition switch at ON position only. Unless the alternator rotates (driven by the engine), the fuel pump will not deliver fuel. This is a safety feature.

However, you could circumvent this safety feature by using a jumper for terminals 87A & 30 or lifting the sensor plate to energize the fuel pump.

After re-reading your post (Adam's) several times, I will concur with Dr. Gunter's suggestion regarding your WUR and AAR. So hooking up a CIS fuel gauge will give you the control and system pressure (cold stage). You can start with this finding.

Jumping terminals 87A & 30 will not energize the WUR, AAR, nor the CSV. Please someone correct me if I'm wrong because I want to learn too. Thanks.

TD

I'm just starting to figure CIS out, so experts can correct me if I'm wrong, but from what I've read the WUR and AAR get power from the alternator (i.e., car must be running). CSV gets power only when the starter is engaged.

All above applies to 78 SC.

Not quite, guys. The alternator doesn't play a role in this, though of course it only does something when the engine is running. The alternator is always connected directly to the battery, and from the same post that comes from the battery (via the starter, but always connected because on the same connection post) is the not quite so big red wire that heads from the alternator over to the relay/fuse panel in the engine compartment.

The fuel pump is controlled for safety purposes by a switch actuated by the air flow measuring plate (or whatever you want to call it). When that plate moves up it breaks a contact, which allows the fuel pump relay to actuate when the ignition switch is in the run position. That's why pushing up on the plate will cause the fuel pump to come on in the run ignition position. But when the ignition switch is in the start position, this interlock is bypassed and the fuel pump runs no matter what the plate and its switch are up to.

There is one odd thing about this interlock. I think that the NC position of the fuel pump relay is the one that powers the fuel pump from the switched ignition source. But when the interlock switch is closed, this powers the relay (which gets its ground via the interlock switch), moving the relay contact to the NO position, where it gets its current from the starter control circuit. Once the air flows through the system the interlock switch opens, the relay relaxes, and power flows to the fuel pump from the ignition switch until either it is turned off, or the interlock closes due to the engine stalling or whatnot. One reason I am pretty sure I have doped this one out properly is this: if I pull the plug from the interlock off, and turn on the key, the fuel pump will run. This can be easier than figuring out how to bypass things with a piece of wire stuck between the proper contacts on a dummy relay up front if you want to test the fuel pump. Especially if you don't want to lift the air plate, which will spray fuel out of the injectors.

The CSV indeed gets its current via the starter circuitry (if the thermo time switch allows it a ground), because it is neither needed nor wanted at any other time.

I had to look up the rest to be sure I remembered it correctly: The WUR (aka control pressure regulator), the aux air slide, and also something I don't recognize called the "temperature valve" (all of which I believe are "heaters" for bimetalic strips) are powered by the "output" of the fuel pump relay. Which means no juice to them unless the fuel pump is running (or should be, if it is working), but conversely they should always powered when the engine is running (or the starter is engaged, for that matter).

Dunno how this relates to the initial issue, though. But one hopes knowledge is power.

Walt

Thanks Walt! Appreciate the knowledge.

No, no, NO.....The pump isn't normally running with ignition on.
O.K. Adam is helping out Andrew by looking at his '78 SC.
Good intentions but............
What concerns me is that , with all respect, Adam doesn't really know his way around the '78 CIS.
When he asks WTF is the blue "thingy" in the back of the TB, and "Draft flapper" I have to say hmmmmm............
The sensors (Blue and green) have to be connected!
In your case, Andrew, I would check the AAR by taking it out and applying 12 V to it. When cold, the halfmoon is open. With 12V applied, it closes after a few minutes.
Next, jumper the pump and check the fuel system pressure.
If the WUR is suspect, check the control pressure according to the Bentley.
But, before anything, look at the wiring schematic and check the wiring from the starter solenoid to the timer for the Cold Start Valve (CSV)
Then make sure that the connector to the CSV has not been mixed up with the connection to the WUR. They have the same kind of plug and they have been mixed up in the past.

In Engineering, we trouble-shoot by elimination, i.e. find out what components in the system work.
Andrew, I suggest that you find someone who really knows the CIS for the SC's. Bad advise is worse than no advise.
Adam is well-meaning but, going around in circles and guessing
isn't going to do it.
It took me more than a year, and a couple engine rebuilds to have a good basic understanding of a Porsche engine.
The learning process never stops.
Adam, I hope you're not offended by me speaking bluntly; the best help you can offer is to help Andrew to find someone with more expertise.

Friendly greetings. SmileWavy

walt,
good expianation.
the thermo time valve (not SWITCH which is part of the CSV) is connected to the vacuum line between the WUR and throttle body. it too has 12v applied. when COLD the valve opens and vents the WUR to atmosphere but blocks off the vacuum from the throttle body. when WARM, after about 30sec, it connects the WUR to the throttle body. its amazing what u can figure out with a 9v batt and a vacuum tester. the connections are important, the bottom one goes to the WUR, middle to throttle body.
when the ign. key is first turned on, the FP will run for 5sec then shut off until the motor is cranked and the "plate" lifts off its resting point allowing the FP to run again.
power to the WUR, AAR and thermo valve(if u have one) all come from the same source as the FP...the FP relay.

We'll Gunter that's allot of input! At first I was just going to let your criticism go but you went on long enough that I'm to entised to not respond
I'll do it in pieces so you don't miss anything.



---------
Good intentions but............
What concerns me is that , with all respect, Adam doesn't really know his way around the '78 CIS.
-------

TRUE! not yet!

---------
When he asks WTF is the blue "thingy" in the back of the TB, and "Draft flapper" I have to say hmmmmm............
---------

My original post was after I referenced a generic Bosch book. It didn't mention the "draft flapper" switch or have it in any pictures. Overall I figured I would ask a few questions here to the "friendly" Pelican community before I went on looking at other resources.
"draft flapper" Come on I didn't have the book in front of me and didn't want to go look it up. "draft flapper" " draft flapper" "draft flapper" Come on it sounds cute.

----------------
In Engineering, we trouble-shoot by elimination, i.e. find out what components in the system work.
--------------

Bachelors and Masters in Mechancial Engineering. Curently run a testing lab that develops Ion Implant equipment. Built entire EFI system for my 73 from scratch. Including designing a high flow air box (made form fiberglass), machined CIS intake runners to take electronic 18lb injectors, made stainless steel fuel rails and plumbing, and the control system. Wrote code in Dynamic C and used a robotics control board as brain.

-----------------
Andrew, I suggest that you find someone who really knows the CIS for the SC's. Bad advise is worse than no advise.
Adam is well-meaning but, going around in circles and guessing
isn't going to do it.
-----------------
I'm not really sure that looking at the system for 30 minutes and asking a few quick questions about a wiring schematic and a blue sensor not in my book is really going around in circles. Dont' worry if I end up going around in circles you'll know because going in circles makes me nautious. I'll send you a picture when it happens.

------
It took me more than a year, and a couple engine rebuilds to have a good basic understanding of a Porsche engine.
--------
I don't mean to return the negative attitude but "It took more than a year to understand how a Porsche engine works"??? Dude glass houses and throwing rocks!
Not rocket science!

---------------
The learning process never stops.
Adam, I hope you're not offended by me speaking bluntly; the best help you can offer is to help Andrew to find someone with more expertise.
-------
Ayway I'm really not that mad just having fun since you started it. I'm rubber and your glue. But seriously I thought I would have some fun learning from you guys instead of just reading books. Not as rewarding as I thought so far! Very rarely have books made fun of me. Actually the only time is when I read " I'm o.k. but you have allot of problems to solve" I found the author to be kinda arrogant.


As you guys can tell I'm taking it slow and asking allot of questions to make sure I don't make mistakes and learn as much as I can. I'm also doing this for selfish reasons not just to help Andrew. I know EFI and have rebuilt my share of Webers too so CIS was the next fuel system to check off from the learning list. This is my first chance to get to learn about CIS and I am excited to do it. I knew it was a very simple system in operation and part count. Not very intimidating. I just want to pull on the experiences that others have had and enjoy the conversation. I like the community part of car stuff. It's one of the reasons I do it. So don't worry Andrew is in good hands. It will just be a faster and more rewarding process if you want to share info and things that you have learned.

BTW I'm not claiming that I won't make mistakes. I've had a llot of awesome hospital visits and have actually used a fire extinguisher in distress. Wahooooooo!
Good story-
Once I was flushing out an EFI fuel Inj system with Xylene acid. I was rushing and changed the plumbing real quick becasue I didn't want the regulator bypass to go where it was going. In doing it quick without thinking about it I made it so the system ran at full pump ressure (100psi). Inejector blew off and sprayed me in the face with 100 psi Xylene. Took the doctors 20 minutes with suction cups on my eyes flushing saline to get all the acid out. No sight damage.
Actually I should have saved that story for another time. I think I had you guys believing in me up to this point. crap! I'll save the story about the fire department and police closing off my neighborhood becasue they got a call of an "explosion followed by a column of flame" I thought it was cool. They didn't! Crap I did it again. Scratch that.


Soooooooooooooooo
With all that beign said. I read through the Bently manual last night. Fantastic! Much better than my generic Bosch book. I already have the fuel gauge hooked up and next chance I get will start getting pressure info and diagnosing. I will post what I get for metrics so you guys can help me diagnose. I'm on vacation for a week starting tonight so there will be a pause until then.


Gunter, Kicked any puppies lately that came up to you looking for a pat on the head?
Shazam! Sorry I love a good banter. Don't feel bad.

PS. Good point about the two plugs getting switced, CSV and other blue thingy. I wondered that when I first noticed one was disconnected. I tried to see if I could expose any part of the wire to see insulator color to reference wiring diagram. No luck with a quick glance. What would I be looking at with a meter to tell which is which? My first guess would be that when cranking starter there would be 12v at CSV until RPM kicked on. What is the blue thingy connector ( I know I know it's the draft flapper switch) gonna read? Probably just a steady 5volts or something?

adam,
get in there and start working on the cis. that is the only way u will learn it. its not hard and u cant mess it up like carbs! understand this, cis is based on preasure, to have pressure, u must have flow AND resistance. thats all the WUR is, a variable resistance to flow to change the amount of force pushing down on the center pin of the FD to either allow the plunger to rise a lot= more fuel or not rise as much= less fuel.
vacuum controls the WUR, if u can find a bad one, take it apart and u will understand better how it works. less vacuum allows more fuel to return to the tank= less pressure on the FD, more vacuum restricts fuel returning to the tank thus increaseing prerssure on the FD= less fuel to the engine. if u can understand that, the rest of cis is cake.
get a fuel pressure tester and a vacuum gauge and go to it!

Adam is one of the Smartest guys I know
 

I have the T-shirt to prove it!

Seriously Thanks Adam! and while your at it can you build a supercharger for the car I noticed some empty tuna cans last time I was at your barn?

Have a great vacation!

T77

Right - thermo switch vs valve. The switch is in the left chain housing cover.

I looked, and I'm deuced if I can find a thermo time valve in my '82. The factory wiring diagram says there is one (called it a temperature valve), and you describe its function, but my WUR has only one fabric covered vacuum line coming from it, and that connects directly to a fitting right up at the top of the throttle body. Nothing with any electrical connections involved with that. I just looked. It is hooked up to the WUR in an interesting way: a thicker short piece of tube has a white plastic or porceline part showing at its top - maybe a reducer - where the thinner vacuum line is attached. But no electricity there.

Or is this thermo time valve inside of the WUR itself, so there are two heater elements in there? I may have opened this WUR up once, but I don't recall.

I notice you said "if you have one." Maybe I don't? Not that I'm losing any sleep, as the car starts fine and runs well.

I don't quite see where or how the fuel pump, on turning the ignition on, could run for 5 seconds (pressurizing the system) and then stop until the starter is actuated. My reading of the schematic says it doesn't start until the starter is actuated (at least for the '77-83 CIS). What am I missing here?

Adam - a quick and dirty on CIS is found on Jim Williams' website. He's collected an amazing amount of Bosch specific information. Well, not dirty, and if you go through it all without some background, maybe not that quick. But really really useful.

The best reference I have seen is Probst's Bosch Fuel Injection and Management. Belongs in anyone's library if they like to fiddle with CIS or just understand it. Not 911 specific, but no matter. SAE engineer type with a good writing style, pictures, diagrams.

We futzers may suffer from what must sometimes frustrate the docs. All human bodies are pretty much the same, but lo and behold every once in a while a heart is on the left side instead of the right, or some other surprise variation shows up. I think our beloved 911s may be that way on occasion. Why doesn't my engine have a thermo time valve?

And to complicate things more, in the later SCs there are three of those fancy Bosch plastic connectors back there in the front of the engine where they are hard to see and just begging to be confused: the frequency valve (came in in '80?), the CSV, and the interlock switch. It pays to label when taking the intake off the engine, as in a rebuild.

Walt

walt,
i have a wireing diag. that shows 78-on, i shows a thermo time valve (TTV), I dont know what to tell ya if u dont have one( its not inside the WUR). maybe someone took it off ?? mine is on the left side of the motor close to the WUR. maybe look for a flat black connector not being used. if u dont have one and u if u are suppose to, it will run too lean when cold ( popping and sputtering) now that my cams are timed right, my car starts a little slow, but when it does ther is no popping or backfiring.
my WUR also has the white plastic piece.
here is a pic of mine, sorry it is so bad

there was no option on that screen for an upload.http://forums.pelicanparts.com/uploa...1163816162.jpg

Hope this helps
 

Walt: Check your left chain cover. There shoud be a Thermo Time Switch (TTS) with 2 electrical connections. The TTS looks like a small spark plug and is screwed into the cover.
Here is how it works: When you turn the key to start, the yellow wire from the ignition lock wired to the Solenoid, energizes the Solenoid; engine cranks. At the same time, the second yellow wire on the Solenoid is wired to the TTS, energizes the TTS and for a few seconds the TTS sends 12V to the Cold Start Valve (CSV)
Meaning: At the moment of start/cranking, there is a continuous current from ignition lock to Solenoid-TTS-CSV.
As the engine starts, the Airflow Sensor Plate lifts off, allowing the Airflow Sensor Contact to ground the Fuel Pump Relay: NOW the pump runs, not before. It all happens within a few seconds.
The pump should NOT run with just ignition on; if it runs, the ASC is not functioning.
The WUR is mounted on #2 intake runner, left side between #1 & #2.
I would be very surprised if you don't have one because in order for the stock CIS to function, the WUR, AAR, AAV are essential.
There is also a Deceleration Valve: adjustable for '78-'79, but solid for '80-'83.
After '80, the Lambda system required a Frequency Valve, OX sensor and brain.

That picture above is NOT a WUR, AAR, AAV, Decel.Valve or Frequency Valve, it looks like a vacuum switch related to emission control?

My humble apologies to Adam. I should have recognized from his replies that we are dealing with genius, a real wizzard.

Andrew: Your engine will hum in no time. :D

sorry gunter, u are talking about the thermo time SWITCH, the thermo time VALVE is what its name implies, a VALVE that blocks the vacuum to the WUR when the engine is cold.

until i got in there and took things off, the thermo time VALVE and SWITCH confused me along with the aux. air VALVE and aux. air REGULATOR.

my FP RLY was bypassed by the previous owner so my FP runs all the time, but on all fuel injected cars i have worked on, and i use to do it for a living for a short while, the fuel pumps ran for about 5 sec. then shut off until the motor started. is there someone out there that has one working properly that can varify if this is the case with 911's. turn the key to ON and listen for the FP.

i people are taking them off for what ever reason, or even hooking them up backwords could account for excsive backirieing during cold startup. just a thought. once i figured out what it did, i hooked it up right and now mine starts up fine, with no backfiring. although i dont remember if it was hooked up wrong to begin with. mine use to spit and pop like crazy, but i also did some other things at the same time.

Gunter,
Your such a sweety "genius, wizard" I'm glad you saw the fun in my reply and weren't offended. Your very knowledgable and I appreciate your input.


I can't wait to be done with vaca and get some pressure readings so we can start seeing what the prognosis is.
Just a funny thought I had. Remember how I said the draft flapper (never gonna stop calling it that now) sensors was disconnected, and I think one of you guys said that is what is referenced by the relay to keep the pump running after starting. We'll maybe it was left off becasue that is an easier way to keep the pump running during diagnosis than hot wiring the relay. Just a thought. Anybody confirm that the pump does shut off if key is on and car is not started? Saw some debate on that.

PS. Got a PM asking a question. No " I'm OK But You Have Alot of Problems to Solve" is not a real book. I was thinking of writing one with that title about marriatal counseling. It would go with a collection.
"I'm F*&ed up because of you! Improving your adult relationship with your parents"
"Guess who just bought a gun? A guide to moving ahead at the work place"
" Five places you shouldn't be dressed as a clown. A tour of war memorials"

You are correct, I was describing the Thermo Time Switch.
The reason why I kept referring to it as TTV is that some people make up their own terminology and I thought that this was the case here. I'll edit my reply accordingly.

As to the vacuum devise (TTV) in the picture:
I have not seen one before.
Not on '77, '78, '80, or '82 engines that I worked on.
The Bentley SC Repair Manual makes no referrence to this TTV.
I would consider removing it and running the vacuum lines straight from the WUR without it.
Bosch # for '77 WUR is 0 438 140 033. Is that your number?

Re the pump: No, it should not run when you turn on the ignition; not even for 5 seconds. If it does, someone misadjusted, or disconnected, the Airflow Sensor Switch.

Re quote " No pressure without flow": Hydraulics certainly can have pressure WITHOUT flow.
The CIS has the check valve on the pump, and the accumulator, to maintain pressure for quite a while after shut-off.
When there is flow, resistance to flow will increase pressure.

doc,
you are correct in saying there does not have to be any FLOW to have pressure, but there must be a source trying to provide flow, as in the accumulator, even though its volume is very limited.
but i still stand behind my statement.
there is no "flow" in the case of the accumulator, thats because the resistance has overcome the max force the accumulator can provide and max pressure has been reached!
so if u want to pick my description apart, thats fine, next time i will say "a source for flow".
when i look at your statement, "When there is flow, resistance to flow will increase pressure", it doesnt sound any better or more correct than what i said, in fact, does the resistance necessarily have to INCREASE pressure, or does it just CREATE pressure? sometimes when YOU understand something, putting it in writing is not always that easy. so lets not turn this thread into an argument between you and me, that is not why we are here. i apologize to the rest of u out there.

here is a line from the web site below:

In '77, a vacuum switch, or thermo valve, was included to further enrich the mixture during cold starts.

http://members.rennlist.com/jimwms/CIS/CIShome.html

T77 - thanks for the picture. Looks like it mounts on a boss cast on a left side intake runner. My '82 engine does not have this thermo time (or temperature, as the factory wiring diagram calls it, or vacuum switch) valve. The boss I am thinking of has a stud which holds a metal stamping which is broken, but it isn't like the holder in the picture, so it was used for something else. And no spare electric connector or snipped and taped off wires.

Gunter has a wider range of SC engines he has worked on and hasn't seen it. Sounds like this is maybe a California modification (or maybe they didn't have it?) or something? The vacuum line from my WUR runs straight to the throttle boddy. Was that way when I purchased the engine used, but there was no indication that the engine had been modified anywhere. The only time it hasn't run well (other than when fuel pumps have worn out) was when I first ran it without the frequency valve system and its little computer. Hard starting, bad idle, all cured by adding the rest of the system.

Could it possibly be something superceded when the mini-brain and FV were added? The FV is capable of some extra cold start enrichment. Aichile, Frere, and Anderson didn't help me on this fine point of CISology. The Parts and Technical Reference Catalog shows the "Thermovalve" as being used from '77 -'79, but not thereafter. Next time I have my SC engine out maybe I'll be smart enough to take some pictures of the front side of it for the hard to see parts.

Cliff - actually, after you let your car sit over night there is little or no pressure in the fuel system. The spec for the system shows pressure decreasing with time with the engine off, just not too quickly. Doesn't seem to matter cold - the pump pressurizes it instantly, it seems, and the CSV maybe requires very little pressure and I think that is what a cold engine starts on. It is hot starting (when the ThermoTime switch disables the CSV) that the pressure accumulator (and check valve)is needed for.

Just why the pump doesn't promptly pressurize a hot system (with a failed accumulator) enough to start it with only a few revolutions instead of instantly (and hence would not be too much bother) is one part of this I don't understand, though I don't have to understand it in order to know what to test and fix.

Gunter - Are you in agreement that disconnecting the airflow sensor switch WILL cause the the fuel pump to run with the ignition on but the engine not running (no air flow)? I know mine is that way. I now use an altered relay up front for this because it is easier to reach, but in the past I just pulled the plug back on the engine.

I'd always wondered how it did that, assuming that when the air measuring plate system moved up it closed a switch and completed a relay coil circuit. But careful inspection of the wiring diagram for the fuel pump relay shows how that could be (and thus I think is) wired so that opening the circuit allows the non-starting pump circuit to work.

Walt

walt,
so u could pull the plug off of the back of the AFM and turn the key to ON to run the fuel pump or did u also have to change the relay?

are we back to just figuring out how to make the FP run?

i asked my brother about his 930. he said his FP runs 1 to 2 sec when the key is first turned on.

i may open another thread just to see who has the TTV.

I have a TTV on my 78 SC (euro spec). Mine is not mounted nicely like yours, but exists and is plugged in. I'll snap a picture if you'd like.

Can you provide us with a description of the vacuum hose routing for the TTV, on your motor?

I found a TTV in my garage today and one end looks like it has a restrictor fitting at the end of the hose and the other hose has a T-fitting.

T77 - yes, when I pull the plug on the backside (in terms of reaching way in there to get to it) of the AFM with the ignition in the on position, the fuel pump comes on. Standard red fuel pump relay in place, etc. My car was originally a '77, so the front wiring is from that year, but it did the same thing with the 2.7 as it does with the '83 3.0 replacement, which one would expect from the wiring diagrams, which are the same in this regard.

Cliff - I believe there are at least two styles of throttle body involved here - one with but one vacuum fitting high atop the casting on the rear (of the car) side, and one with two of these one above the other. My car has but the one, so the one vacuum hose from the WUR goes to it.

My WUR has an unused fitting - sticks out the bottom left of the device. A parts diagram showing the Thermovalve shows it connected between a fitting in this location and the lower of the two fittings on the throttle body.

Walt

i am starting a new thread on the TTV. i dont think this is helping adamb113.

Yes, I believe that disconnecting the Airflow Sensor Switch is the same as lifting the Airflow Sensor Plate: The pump will run with ignition on provided the wiring is OEM.
You are right about the TB having different vacuum conections in the back and front for different SC-years because the '78-'79 has an adjustable Decel. valve. and only one vacuum line (Advance) on the distributor.
The '80-'83 has Lambda and 2 lines from the distributor: Advance and retard.
It is my experience, and JW confirmed this, that the '80-'83 engines will run fine with the OX sensor disconnected; everything else stays the same: The Frequency Valve, and the Lambda brain, stays connected. A readjustment of the mixture is required.
Make sure that the relay under the pass. seat is working, it gets power from the same fuse as the interior light.

Accumulator: I think it is there to minimize pressure fluctuations in the system and to maintain pressure for a while to enable hot-starts. The later accumulators have 3 lines to it, the earlier ones have only 2. (No return line to the tank)
An example on how you can have pressure in a system without flow. :D
The accumulator, and check valve on the pump, will keep pressure for quite a while allowing a smooth hot-start.

I would get rid of this TTV and get the appropriate WUR to run the engine without the TTV; just one more item that can go wrong; why bother? :confused:

Many engines don't have it and run fine without it as long as you set it up correctly. :)

In fact, you can start a TTV-delete club. :D :D

CLIFF,
the "T" fitting should go on top of the decel valve, then to the vacuum fitting on the rear of the TB that is below the butterfly. the other end connects to the WUR, top for 76-77 and bottom, or side, for 78-79.

DOC,
the WUR's have different warm-up curves and may even have different control pressure settings. so, i wouldnt do it myself. i will try and post a link to the thread that has talked about this. like i saud before, maybe people are taking the TTV of for what ever reason, then their car starts popping and backfiring when cold. i know that after i hooked mine up correctly it starts and idles whithout all the popping, where as before, it was bucking like a mad horse.

what year did they go to the single vacuum fitting?

here is the link to another thread talking about putting the wrong WUR on.

http://forums.pelicanparts.com/porsche-911-technical-forum/315844-78-wur-77-a.html