CIS Tuning
 

76 911 CIS 2.7.
Replaced a leaking fuel pump. I think I fixed a problem and uncovered a problem(s).

The engine hunts at idle. And cuts out at first 5Krpm and over the last few days progressively lower - now I get misses at 3Krpm or worse.

Start when cold. But doesn't run very good.

After reviewing some archives here I ordered the LM-1 gas analyzer, and am picking up a can of carb cleaner to go vacuum leak hunting while I wait for the Lm-1 to arrive.

Oh - we live at 8500' elevation and a cold start around here can be 25 degrees or warmer. (I don't even think about it below that temp.)

What else should I be considering?

I had the same problem last summer missing at higher RPM,s. Everything was go with ignition, and made so I made a fuel pressure gauge and found out I was only running 35 to 45 psi of fuel pressure. Replaced the fuel pump and It ran at 75psi. That was the problem. Cis needs that much pressure to run right. My car is a 76 2.7 So I would check the pressure

You are leaning. Sounds like you are starving for fuel. Sounds like a progressive problem which is likely to be the fuel filter and/or the pump.

Don't spend money on the LM1 yet (although it is a great tool). A better tool for you is the CIS fuel pressure tester. And if you haven't replaced you the fuel filter or know if it's replacement, plan on it.

The LM-1 will tell you a great deal (I've got one and really like it), but it won't tell you if you have ingition problems.
In fact it might give you the wrong indication.
If your engine is missing due to ignition, you will have excess hydrocarbons as well as excess O2 in the exhaust because they won't be burned up in the engine.
Since the wide band O2 sensor only measures O2, it will tell you that the engine is running lean when if fact that is not the case.

My point? (besides the one on my head) is that you need to make absolutely sure the ignition is in perfect condition before trying to tune the CIS.

The old jokes goes that 90% of all CIS problems are ingition related ;)

i agree that if you don't know when the fuel filter was last changed, by chance, then definitely replace. typically with a dirty fuel filter a car will start fine, but then begins to cut out after say, 5-10 minutes of driving as the sediment particles in the filter begin to get stirred up and enter the mixture. also, like sammy mentioned, baseline your ignition system. if you use points they could be dirty or starting to close up..points are about the cheapest porsche part there is..get a dwell meter and check them out. also check timing and the operation of what i think you have as a vacuum-retard mechanism like my '74, but am not 100% sure of this. anyway, eliminate the ignition question..and how long has it been since you replaced distr. cap, rotor, plugs, wires? know their history?
ryan

Heard somewhere that 99% of CIS problems were ignition.

LOL, yer right, 99%.
I toned it down to be conservative ;)

Even at 99% it's hard to believe that the first place most look into is the CIS.

Good thoughts all. I've had the car 6 mo. The points, cap, plug wires "look" good. The car ran pretty good until the fuel pump leak. So the only apparent change is the fuel pump replacement. That is why I zeroed in on the CIS.

The LM-1 will be useful for this and other cars too. So I'm glad I ordered it. (I like tech gadgets anyway).

I have a replacement fuel filter (from Pelican of course) waiting to go in the car. I'll search Pelican for a CIS fuel pressure tester.

Thanks for the ideas. This is a great forum!

jim..when you say 'look' good, i guess you know that would come across as mighty subjective. you've gotta have good eyes to discriminate hundredths of an inch differences that can make a substantial difference in points gap - dwell meter time. need an ohm meter to venture a 'guess' as to the condition of plug wires..they don't have to show dry rot on the rubber to be in poor working order. anyway, good luck with the troubleshooting and be sure to let us know what you discover!
ryan

That's why the "look" was in quotes. I knew it was a suspect observation as I typed it. But my deductive reasoning made me think fuel related because the only change I observed was the fuel pump leak and subsequent replacement.

I am impressed with the 99% of CIS problems being ignition. That sounds like a sure thing. So I guess I have to move the ignition parts from my project list on Pelican over to the shopping cart. And... I have to "dwell" on where the timing light is hiding.

i personally think the 99% thing is 'tongue in cheek'..in reality i'd bet the actual figures are closer to 50/50..it's just that cis gets blamed for everything..everything except the issue of the ports deal and the uae..the administration's acting president is catching that.. ;)
ryan

LOL, yes the ignition comment is exaggerated, but for a good reason.
Lots of folks spend big bucks chasing CIS problems only to find out part of the ignition system is at least partly to blame. It is easy to mis-diagnose the cause if ignition is contributing to the problem.

In fact, here is a direct quote from the factory manual:
"CONTINUOUS INJECTION SYSTEM (CIS)
General Checkout Procedure
Prerequisite for the CIS checkout is a properly functioning ignition system and proper mechanical condition of the engine."

lol..sammy..even the porsche factory manual tries to 'first blame' the ignition! :)
ryan

Souk, Ryan and others,

I will try not to hijack jimavey's thread but I have a few questions.

First, I HAVE searched CIS threads and have a sketchy picture of what I need to do but... I suppose the first question is about this "CIS pressure tester". I hate to be stupid but is there some standard test setup to make or buy? I looked but didn't see anything like it here on Pelican.

Even if it already exists, where would I find an "Idiot's Guide" on how to use it and properly interpret what it is telling me? It is obvious to me that I'd better get competent with CIS if I'm going to own my '76S at a reasonable cost.

Last, my car has fresh plugs, cap, rotor, new braided factory plug wires, new fuel filter, new distributor and rebuilt fuel distributor. So the ignition system "should(?)" be fine. I had the airbox swapped w/ new pop off valve installed as it blew (over 6 mo down time while being painted, it backfired on first attempting to start, I didn't know not to touch the gas pedal when starting, I do now!). After overnight cold, I've got to crank a little to get it to "kick", sometimes stay on the starter a couple of times to get it to actually start. Then it sputters for a few seconds, idles up to maybe 1200-1300rpm momentarily before settling back down to 900-1000 rpm. Idles smooth then, though not at elevated rpm while cold - AAR, right?

Can pull away smoothly when cold with a little extra blipping of throttle. Runs great when warm but my overall impression is that it is rich, it even smells some of fuel. All this would be okay I suppose - I'd rather it started sharply, idled high reliably until warm then, settle down to normal idle. But the problem is if I have to drive along at low speed in traffic it is awkward to try to drive at 25-30 mph as it wants to "buck" if I shift into second. My buddy's perfectly running SC runs fine in second at this same "in between" 1st-2nd gear speed. Is it just a little extra torque from his 3.0 or do I have a problem?

The first part sounds like a too rich mixture issue which is easy to correct, but the cutting out at 5K is ignition.

Unfortunately, looks don't count when dealing with ignition components. High on the suspect list are the highly problematic and expensive to replace shielded Beru ignition cables which rank high in the "looks good" department while hiding from view any evidence of shorting.

Cheers,

Joe

I searched the Pelican search engine for CIS fuel pressure tester and got this link.:
http://www.pelicanparts.com/cgi-bin/ksearch/PEL_search.cgi?command=show_part_page&please_wait= N&make=POR&model=911M&section=TOLtol&page=5&bookma rk=26&part_number=PEL-PP910450

It is the Bosch CIS Tester. So I ordered it.

I also ordered the CIS fuel Enrichment wrench (Pelican # UN-120-1334) I read in the archives that it is a 3mm allen wrench but 5" long.

I also ordered plugs, wires, and a cap. And a Ignitor electronic Ignition (PEL-PT1867) Anyone have a history with this?

I'm looking forward to getting my stuff!

Dan in Pasadena is describing my low rpm symptoms too.

STLRJ's observation about the high end cutting out being ignition is taken note of. MY new plugs/wires/cap, etc should fix that.

jimavey, Thanks. Not sure how I missed that, Dan

The best way to really nail this ignition issue is to stay away from copper core ignition cables (Beru), they give CIS a bad name. Go for carbon core wires.

Cheers,

Joe

I ordered these wires: http://www.pelicanparts.com/cgi-bin/ksearch/PEL_search.cgi?command=show_part_page&please_wait= N&make=POR&model=911M&section=UPrc91&page=15&bookm ark=20&part_number=CE-9192-28-R

I can't tell from the description if they are copper or carbon - anyone know?

There is an old saw about CIS that goes like this:

There are three types of CIS guys.

1) The guys with working CIS systems are probably out driving their cars so they won't reply.
2) The guys that tinker with their CIS systems and have them royally screwed up will keep you running in circles with suggestions.
3) The guys that have spent a fortune on Webers will tell you they're great to justify their expenditure to themselves.

All kidding aside :), like many above, before you mess with the CIS, verify the ignition sysem is operaitng correctly, you have good fuel flow and a clean filter, and you have no vacuum leaks.

This chart (http://www.pelicanparts.com/911/technical_specs/911_cis_troubleshoot.htm) can help you figure out your problem. Note many of the suggested "fixes" are not adjustments to the CIS System but to the systems that support the CIS.

To use your CIS Tester effectively, you will need to get the charts or tables that show fuel pressure at various operating conditions. I think you can find these in the factory manual.

Best of luck.

I do not know but many on this board like those wires, they are probably ok.

FWIW, from what I have been able to find out, the most likely failure source of the factory wires is the failure of the resistor inside the Beru connector.

No comment on the clewitt wires, do a search, a few recent posts will pop up. you might want to include "rain" or "water" in the search.

Here's how I troubleshoot a CIS system:
1) After verifying the ignition system is just right, I tape a shop vacuum hose onto the snorkle of my air cleaner so that it only draws in air from outside the engine compartment.
2) Then I do the vacuum leak check. 9this is how i recently found my leaking air box).
I use starting fluid but am not recommending anyone else use it, YMMV do what you want but do it safely, if you burn up or burn up yer car it aint my fault. We're all grown up and as smart as we will get, our safety is our own responsibility ;)

3) If the ignition is good and I am absolutely sure there are no vacuum leaks, I let the engine completely cool down like overnight and hook up the pressure test kit.
The kits usually come with a generic instruction manual but the factory manual does a good job of describing the trouble-shooting process.

4) If the pressure tests are all within specification, I start diagnosing and testing the other individual components depending on the symptoms. Again, I use the factory manual as a guide.

Lots of guys skip step 1, 2, and 3, and go right to step 4.
That's called the shotgun approach and it gets real expensive. Kind of like playing the lottery. they might spend a lot of money with no results, or they might actually find the problem and replace it just by sheer blind a$$ luck. Odds are they won't.

CIS is actually a very simple system and very simple to diagnose and fix, once you have studied it enough to fully understand the components and how they affect everything else, and after you have trained your brain to follow the logical steps.
Skipping steps or cutting corners only leads to frustration.

If you need specific details out of the factory manuals, drop me a PM and I'll see if I can forward them without breaking any copywrite laws ;)

Sammyg2,

Thanks A LOT for the diagnosis process description but (of course) I've got to ask some stupid questions and restate your directions - sorry, I am anal about getting it right!:

I assume the shop vac trick is with the engine not running, apply starting fluid or carbuerator cleaner around any/all connections and "see" where it gets sucked up by the vacuum... whether airbox, hoses, etc.

But then you make the safety comment about use of the starting fluid...how would that be unsafe if the car is not running? Granted starting fluid is flammable as hell, but this is just a general warning right? You're not suggesting somehow using the starter fluid and the shop vac together while the car is running? Geez, I feel like an idiot asking.

Then assuming you don't find any leaks (if you do, address them -a whole other subject in itself - and start again). THEN hook up the test setup sold here, following the directions to determine if you have a lack of fuel or a pressure problem. Barring those problems THEN start with the "factory charts" (where would I get these?) and follow them component-by-component to eliminate each as a cause for your symptoms. Have I got this right?

Apologies to everyone reading this and thinking "what an idiot".

hi dan,
sammy means for the engine to be running..you determine the source of the leak by a sudden increase in rpm's when the carb cleaner 'does its magic' and finds a leak. i've never heard of a method where you do not have the engine running. unless i'm misunderstanding sammy, perhaps..i'm not familiar with the idea of covering the snorkle. maybe i'd better not speak for sammy and let him clarify for you, dan.
ryan

Make sure the points have no transfer of metal from one side to the other, and set them w/ a dwell meter. I like to set them @ 35 or 36 degrees when brand new, As the rubbing block wears down, the gap decreases and the angle goes up gradually to 41 or 42 when it's time for a change.

A too rich mixture may be a mixture that is simply set that way, or it could be from an out of spec or malfunctioning WUR. A too rich mixture can also cause your low rpm bucking, and can even sometimes cause high rpm cutting out.

On my car, without a cat or O2 sensor, I can judge mixture a number of ways, including tail pipe color. As in the old days, a really black one is too rich.

Too much going on in this thread boys.

All of it has been discussed over and over again. But! Let me try to help...so you don't have to search and pick through 30+ threads :)

To the original poster: did you check the ignition for proper operation?

I'm going to sound harsh, but it'll be good for you..OK? :)

More often than not, someone with a CIS problem will cry out for help, then don't listen or do as they have been advised. Then they cry louder that CIS is terrible and the have just wasted all his money on parts, tools and time.

So! Lets get to basics. Combustion needs air, fuel and an ignition source. It appears you both have all of the components. So let's move along to the quality and quantity of those three.

I have not seen to many CIS engines get sick when using Beru wires. The wires are not that critical. If they pass the resistance test, they will work. Hell, even if they are beyond the resistance numbers they will still work well enough to prevent the problems that you two are having. I did have a friend whose car would cut out at about 5200 RPM even after new wires, new coil, new plugs...all the replaceable parts. Well it was none of those in the end. It was a short in the wiring somewhere in the engine bay! Our cars are old, and they have changed hands over the years. So anything can be wrong. Without you getting your hands dirty, internet help is just not going to get it done.

Now, the original poster (OP) reported having to replace the fuel pump. Was the car cutting out before the pump replacement? Was the fuel tank ever cleaned out? Was the filter ever changed out? Sounds like the car was having driveability issues before the pump was replaced. How bad was it?

OP indicates he's got a fuel filter ready to swap in...so DO IT! OP reported that the missing is occurring at lower and lower RPM over time. A clogged fuel filter or a tank that has debris filled gas will starve the engine. It might not do it right off, but as you circulate the fuel things will get worst. The fact that you went from a 5000 RPM miss to a 3000 RPM miss makes me think you are reducing the flow rate of the system every time you drive your car! The hunting is likely a mixture issue. I'll post a couple of links at the bottom for this.

Dan, since you had your box replaced, it is likely that who ever replaced it missed something. Maybe the cold start injector connect was not seated, or its trigger wire was not wired to the start or maybe something else. They might have had starting issues, and they compensated with a rich idle mixture setting! It's pretty common for a CIS car to have air and fuel settings that compensate for something that should have been fixed! But some wrenches do know enough about CIS to figure out what the real problem is, so they mask the problem by cranking up the mixture or air just so long as it starts and the customer is on their way!

You might even have an air leak (external or internal) since someone has been in your system. The carb cleaner test is simple for detecting an external air leak. And you do need the car idling. The idling car will have its intake plenum under vacuum (downstream of the throttle body). So if the plastic CIS air box/plenum has a crack or a bad seal, the engine will suck in air through that crack or seal...bypassing the normal route. Spraying carb cleaner in suspected areas around the air box/plenum will increase the idle speed since you are inducing more of a combustible mixture into the engine (air and carb cleaner!). There is little danger in doing this, other than to the paint in side your engine bay. Remember you are doing this at idle and most of the engine is still cold, and well below the auto-ignition temperature of the carb cleaner that will run down until it evaporates. You can also do this with propane, like the 5 dollar propane torch you get at the hardware store. With the propane torch (not lighted) you can vent the bottle around the engine. Of course you don't want to stand there with the bottle and fill up your engine bay then light a cigarette. Some common sense is required when working on such things. ;)

Dan, you might have some bigger problems, so I would recommend you start a new thread and provide as much details of your problems as you can.

I've said it before, without the details you can't expect us to help. It's like going to a doctor's office and telling the doc that you hurt while expecting him to give you the cure without any further information. LOL!!! A prescription of loopy pills will do that, but you might not want it.

Edit: Read these threads if you are a CIS Newbie. Within these threads there are links to other threads and web pages that will help. You must understand how the parts work before you can begin to understand how the system works! You will thank me for being hard on you later :D

http://forums.pelicanparts.com/porsche-911-technical-forum/232089-cis-idle-speed-mixture-setting-without-analyzer.html?highlight=cis

http://forums.pelicanparts.com/showthread.php?s=&threadid=185926&perpage=20&highl ight=cis%20mixture%20idle&pagenumber=1


As for the fuel tester and procedure. I've posted on this before..let em look for the thread. But basically, path between the fuel distributor and the WUR is where you are tapping into. With that part cut off, you are checking the system pressure while the pump is running. With the path open (guage on the path of course) , you are checking the residual pressure after the pump has turned off. With the car running and the path free to flow, you are checking the cold pressure and the control pressure. You gotta start from cold (over night cold) to check the cold pressure. You can watch the pressure increase as the car warms up at idle.

Let me pile on, too. As part of the ignition check, make sure the advance mechanism works smoothly from idle to 6K and returns to its idle position. Observe this with your timing light, and the vacuum line to the distributor disconnected and plugged. If the mechanism has never been serviced it's hard to believe it's still functioning smoothly (mine wasn't).

Souk knows of what he speaks, very good and accurate advise.

I hook up the hose from the shop vac to the intake snorkel on the air cleaner (just the hose, not the vacuum) so that the intake air is coming from outside the engine compartment, and then carefully spray the starting fluid around certain places. I hit the injectors, the rubber intake sleeves, all around the hoses, around the oil tank cap, and under the air box.
If you have a vacuum leak the engine will probably be running lean unless someone has adjusted the mixture to compensate for it.
Spraying a flammable vapor like starting fluid will add fuel and get rid of the lean condition for a second or two, during that time the idle will change and that is the indication of your leak. If you don't hook up the hose to the intake it makes it harder to diagnose a leak because the air cleaner wil ltry and suck in the flammable vapors and the idle will go up. You might think it's a vacuum leak when it isn't.

Carb cleaner works well but is a little harsh on paint and stuff, stating fluid is mostly ether and is not corrosive but is very flammable and makes to act funny if you breath it. I have heard peolle using WD 40, I'm not sure if that works well or not. i hate the stuff. Some folks use a propane torch that is not lit. I stick with what works well for me, the starting fluid.

If you follow the steps and get to the pressure test, I have the correct pressure chart from the factory manual and will make a copy for you.
you have a 76 2.7 liter S engine, right? I assume it is US and not ROW?

I'm the "OP". And I know a heck of a lot more than I used to. I have a plan of attack, parts on the way and its time to start doin'.

I'll keep you posted on progress - its cold here and I can't work on it when I want to. (New shop on the way - maybe by May)

Thanks for the guys!

First, apologies to jimavey...I wasn't trying to hijack and kinda did anyway, sorry. Souk is right, too much happening on this thread. I WILL start my own, but not until I read through all the links/threads provided. For what it is worth, I HAVE searched and I always feel like I am coming into a conversation after missing the first five minutes.

To Souk and Sammyg2, it is obvious to me that you both know what you're talking about which may be my problem in understadning some of your advice. The shop vac hose to the snorkel makes perfect sense - to isolate the incoming air from sorta "ambient" starter fluid flying around the engine compartment - but when you first mentioned the hose trick I didn't make the mental connection that it was the hose alone. Like I said perfectly sensible, I just didn't "get it".

I take no offense whatsoever to your "tone". In fact I don't think you are being harsh at all. You're more patient than I would probably be. For what it is worth, I bought and have been trying to read the book, "How to Understand, Service and Modify Bosche Fuel Injection & Engine Management" by Charles O. Probst. It was recommended in a thread via my search. It is good, though a bit of a slog to get through. The one thing on my mind is that when my wrench had my car smogged for me, it didn't immediately pass. One of the guys in the shop went overto the smog shop and (I think) leaned out the car some. I suspect he reset the mixture by "feel" - which in and of itself has got to be off, probably my problem....but I will continue to do research. Thanks guys for your patience. Dan