CIS pressure testing

[T77911S]

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!

[Ferrariguyma]

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!

[Walt Fricke]

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

[T77911S]

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

[T77911S]

there was no option on that screen for an upload.

[Gunter]

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.

[T77911S]

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.

[T77911S]

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.

[adamb113]

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"

[Gunter]

Originally posted by T77911S
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.

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.

[T77911S]

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

[Walt Fricke]

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

[T77911S]

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.

[KFJ_SC]

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.

[CliffBrown]

Originally posted by T77911S
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.

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.

[Walt Fricke]

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

[T77911S]

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

[Gunter]

Originally posted by Walt Fricke
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

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.
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?

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.

[T77911S]

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?

[T77911S]

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

78 WUR on 77