Persistent CIS problems

[bluelectron]

My 1982 911SC was a perfectly running car while I lived in Houston. I moved to Calgary last December and have been having persistent CIS problems.

1) Car stalled on highway and was not getting fuel. Towed it home, emptied and cleaned the tank, changed tank screen and fuel pump. This fixed the fuel delivery problem.
2) The car would start cold but would not start it left for 20 mins when hot. At his point I changed the fuel filter, accumulator and all the injectors.
3) Continued to have hot start problems so I took the car in to an indy Porsche mechanic shop in Calgary. They diagnosed that the control pressures were too low and changed the pressure regulator in the fuel distributor. I was told the fuel lines were clogged and they cleaned them and WUR was operating as it should.
4) Now the car does not start when cold or left for 20 min when hot. The shop asked me to push the gas pedal in an inch to start the car. The car starts by cranking with the gas pedal pushed in but I can smell that it is too rich and cold idle is not like before. It would not go over 600-700 rpm during cold starts.

When the car warms up it runs really well. Stronger than ever before.

I know that I should not have to push the gas pedal to start the car. I do not have CIS tester and that was the reason why I took it to a well known mechanic. I bought a CIS tester from Amazon.ca but the quality was so bad that even the fittings within the kit would not smoothly fit each other. Returned it.

I am completely lost and do not know what the problem is or how to solve it. Have an appointment with another well known Porsche shop here. Not sure how good these guys are but I am not sure what I can do at this point. Appreciate any inputs.

[boyt911sc]

Blue,

If you want to learn and understand how CIS troubleshooting is done correctly, stick to this forum. There are plenty of help available. But first, get a decent set of CIS pressure gauge kit. I recommend getting a S&G tool brand. The basic model is more than sufficient for your needs.

This is a mandatory tool for troubleshooting any fuel injection system. If you don’t have one, you are just wasting your time trying to diagnose a fuel injection problem. With your pressure gauge kit, you will be able to check your control (cold & warm), system, and residual fuel pressures. And subsequently be able to evaluate your WUR and FD yourself.

Finding a good mechanic that knows and understands CIS is a dying breed. They are still available but getting fewer as time goes by. BTW, the mechanic who worked on your car is not very familiar with CIS based from your information #3 & #4. Good luck.

Tony

[jjeffries]

You'll want to search for threads about similar problems and pay particular attention to the advice procided by Tony (boytsc911) and Dennis (Timmy2), among other CIS gurus. If you want to work on it yourself, you will need a set of gauges and an ability to check circuits (power, ground, etc). Also, remember that many European cars of the 1970's and 80's used CIS, so what you're looking for in a technician may be a guy with grey hair who's worked on CIS-equipped cars for many years. Best of luck, John

[bluelectron]

Thanks for the advice guys. I am in two minds if I want to keep the CIS or bite the bullet and go Bitz EFI. Either way, I do not see any mechanic who might have the know how to fix the CIS or custom EFI when it breaks. I have already vested enough on new CIS parts so might as well try and fix it.

What does a rich condition during start mean?

[jjeffries]

You'll read many voices on this including those who think CIS should be jettisoned in favor of EFI, and indeed the latter has appeal. But CIS gets a worse rap than it deserves, and is really a quite simpe and elegant system. It was used on all of the big Euro brands, incl. VW, BMW, Mercedes-Benz, Volvo, Audi, which I say in order to show how commonplace it was, and to suggest that a good, older tech with, say, Volvo or VW experience could sort your car and you may be surprised at how easy and inexpensive the fix is. John

[tirwin]

Blue,

What is the temperature in your garage? It’s worth noting the climate differences between Houston and Calgary. CIS is sensitive to temperature.

Let’s talk about what a cold start means. A “normally” operating engine prefers an Air Fuel Ratio (AFR) of 14.7:1. 14.7 parts air mass to one part of fuel mass. When the ratio is less than 14.7:1, say 12:1, it is said to be rich. When it is more than 14.7:1 it is said to be lean. Rich is needed for cold starts and when you have your foot on the go-fast pedal.

An engine needs a richer mixture on cold start for a few reasons.

1) colder air is more dense, so the same volume of air at a lower temp will have more oxygen atoms than the same volume at higher temps. this must be accounted for in the cold start process.

2) fuel is harder to vaporize when it is cold

3) on a cold engine, the injected fuel can condense on the surface of cold parts meaning that less than the ideal amount of fuel is available to burn, so the EFFECTIVE AFR is lower than intended

So on a cold start — when it is actually cold outside — engine management systems need to compensate for this temperature differential and supply more fuel (a richer mixture). Whether it’s carbs or CIS or EFI, the principle is exactly the same. They just go about it in different ways.

CIS is a mechanical system that is heavily dependent on proper fuel pressures to function correctly.

To properly diagnose your CIS system you absolutely must have a fuel gauge like Tony suggested.

The basic tests are:

1) system pressure — making sure there is enough pressure from the fuel pump and fuel distributor

2) cold control pressure — making sure the AFR is correct on a cold start (HIGHLY dependent on outside ambient temperature)

3) warm control pressure — normal operating

4) residual pressure — affects warm starts

Get a set of gauges and do the tests methodically. Guessing is an expensive and a frustrating process.

The primary part of focus is the WUR (warm up regulator).

Another piece of advice is to make sure you have all the correct parts for your model year. It is not uncommon to see cars that have the wrong parts after 30+ years. Whether it was a well-intentioned person who simply didn’t know the differences or a lazy mechanic... the point is, you can chase your tail with the wrong parts.

Suggest you look at my CIS Troubleshooting for Dummies thread. Test procedures and links to parts references are all in there.

Do some reading, get the gauges and then build a test plan. Plenty of people here to help. Ask for help if something doesn’t make sense.

[bluelectron]

Originally Posted by tirwin

Blue,

What is the temperature in your garage? It’s worth noting the climate differences between Houston and Calgary. CIS is sensitive to temperature.

It is about 15C or 60F in the garage. I have never had cold start problems even when it was way below freezing. In fact, I picked the car up from the transporter at the border in February and drove for 3.5 hours in way below sub-zero conditions (-5C).

I have ordered the S&G CIS pressure gauges from Amazon USA , because its in stock there and not here. (I can keep going on about Amazon Canada but will leave that aside for now) Once it gets here I will check pressures and report back.
Thanks all.

[930cabman]

A few years ago I found an Alfa spider project car, 1985 with Bosch L Jet injection. After fooling with every sensor, injector, .... for several months I ditched the entire system and went with a Weber twin carb setup. Simple.

Last year I had the engine of our '75 911S rebuild for $15.k (top end, head studs, ..) it has been running great until I filled her up with Sunoco high test a week ago. Probably not the fuel but now she will not idle, the bucking, severe hunting nonsense. I tried the carb cleaner method with 0 results. I am looking at a smoke generator or CIS pressure tester. I know when these systems are working they are the best for street use, but otherwise can be a source of frustration. Perhaps back in the day more techs were up to speed with these older electronic fuel systems, but these days ???

Good luck, I will bet the problem is reasonably simple, just challenging to locate it.

[T77911S]

its sad to hear a MECH probably just threw parts at it. $$$$

[Walt Fricke]

Once you install the pressure tester for the first time, you can just leave it in the car until you get things sorted out. Wire it to the deck lid hinge or someplace to keep things more or less out of the way. For the control pressure check the valve is open, so it is just like it wasn't there as far as the engine is concerned.

[Dave Kost]

Did your mechanic confirm the Frequency valve was operating properly? First thing you check on 1980-1983 Lambda SC's.

[ClickClickBoom]

CIS is not magic, but must be understood. My CIS car after proper tuning worked perfectly in all conditions. The previous owners mechanic instead of fixing the intake leaks, just continuously increased the fuel every tune up, when I brought the car home and fixed all the leaks the car would barely run. After proper adjustments (CO), it ran like a top. When you moved the car to another altitude, your unmetered air leaks ape likely causing your ills.
911 CIS Primer - Index

[pmax]

Lots of good info here

CIS Troubleshooting for Dummies

... Raw's favorite vid (besides ...)

https://youtu.be/a4fJAfXYxWk

[bluelectron]

I finally got to measure the fuel pressures. With the valve closed the system pressure is 5.5 bar or 80 psi. The cold control pressure with the valve open is around 4 bar or 56 psi. From my understanding these are too high. I suspect the fuel return line is clogged. I read that the fuel return line is behind the 3rd intake but I am not sure which one. Can someone point me to it.

[boyt911sc]

Blue,

Now that you have a fuel pressure gauge, you can start analyzing your control fuel pressure. Start measuring your CCP (cold control pressure) until it stabilizes to WCP (warm control pressure). Run the FP by bridging terminals #87A & #30 (FP relay socket) at 30 sec. intervals until WCP stopped increasing. No longer than 5 mins. And no need to run the motor. Just the FP with a fully charged battery.

To test if your return line is clogged or restricted, disconnect the return line near intake runner #3 and measure your cold control pressure. This test should be done first before doing any fuel pressure test. Disconnect the WUR electrical plug. Check the control pressure. Record the pressure reading. Next, disconnect the return line connection to the gas tank and measure again the control fuel pressure. There should be no significant pressure reading between the two (2) readings. Keep us posted.

Tony

[Paulporsche]

Remember to note the part number of the WUR so we can verify it is correct for your car.

[bluelectron]

Is this the fuel return line near the 3rd intake runner ?

[boyt911sc]

Originally Posted by bluelectron

Is this the fuel return line near the 3rd intake runner ?

Blue,

NO. That’s a vacuum line for the brake booster. Further back, to the left of intake runner #3 are two (2) fuel lines. One line coming from the fuel filter is the delivery line. The return line should be in this area. Take a picture and post it.

Tony

[boyt911sc]

Blue,

The return line is bolted to intake runner #3. Or follow the drain line of the fuel accumulator in your motor to intake #3. See circle for reference.



Tony

[Walt Fricke]

Tony - do the standard fittings on the usual pressure gauge systems fit the connection on the return line? I didn't know that.

Since the return to the tank just dumps fuel to atmospheric pressure, shouldn't there be basically zero pressure with the valve open (return flowing)? Do you really need to try to connect up by the fuel tank, with the possibilities of fuel pouring out?

How often is the return line itself clogged? I'm hard put to see just how something big enough to obstruct a line could get into it.

The WUR has a filter on its exit side - a bunch of tiny drilled holes in the casting itself, it looked like. When that got obstructed on my WUR, control pressure equaled system pressure, which was a tip off for sure of a problem.

Easy enough to clean if you disassemble the WUR. Could that be a possible explanation for the quite high control pressure?