Persistent CIS problems
 

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.

Basic CIS troubleshooting...........
 

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

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

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?

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

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.

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 :mad:, 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.

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.

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

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.

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

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

Lots of good info here

http://forums.pelicanparts.com/porsche-911-technical-forum/758788-cis-troubleshooting-dummies.html?highlight=CIS+dummies

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

https://youtu.be/a4fJAfXYxWk

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.
http://forums.pelicanparts.com/uploa...1571063772.jpg
http://forums.pelicanparts.com/uploa...1571063772.jpg

CIS Troubleshooting............
 

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

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

Is this the fuel return line near the 3rd intake runner ?http://forums.pelicanparts.com/uploa...1571088681.jpg

Vacuum line..........
 

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

Picture of a late SC motor........
 

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.

http://forums.pelicanparts.com/uploa...1571090887.jpg

Tony

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?

Testing.........
 

Walt,

The standard CIS pressure fitting is 12-mm x 1.5 and the fittings for the delivery and return lines have 14-mm x 1.5. So you will need an adaptor (12-mm x 1.5/14-mm x 1.5) to connect the CIS pressure gauge kit.

The normal return line will have very low pressure reading and could hardly register on the gauge. But a slightly restricted return line will register something on the gauge. Another restriction also occurs at the WUR’s micro screen filter when the screen gets clogged with dirt or debris.

You need to determine that return line is free flowing before blaming the WUR for excessive control pressure and vise versa.

Tony

A quick test for the return line is attaching a new hose to metal line leaving engine bay and it should be easy to tell as gently blowing into it will prove line is clear.

http://forums.pelicanparts.com/uploa...1571108224.jpg


Here are the specs for your car provided it is US market. Pressures are different for non-lambda cars.

Flow restriction........
 

What if the restriction is occurring some where between the gas tank and the connection to the metal line? You need to test the whole return line from start to end.

Tony

Yes, I am talking about the line back to tank. Another guy watching through sending unit hole or even listening at gas fill hole should see/hear bubbles.

If I understand correctly,
I disconnect the return line to the tank at the location you pointed to.
Attach, a hose to the return line and let the fuel drain into an external container.
Measure control pressures.

I really appreciate the patience of everyone. Forgive my silly questions that may be obvious to most. I am not very familiar with these cars.

Pressure, pressure, whose got the pressure:

The fuel pump produces it - maybe 6 bar/90 PSI? If it is weak enough, you might not be able to hit the system pressure target. Yours is new.

System pressure: the line from the pump, after going through the filter and accumulator, has pump pressure reduced by a regulator in the fuel distributor. This can be adjusted by adding or removing shim washers. Your shop sounds like it did this, though I don't know which way they went. Maybe added one, because your system pressure is too high. Getting it back into spec would be a good idea. If this were mine, I'd remove a washer. I've had a FD apart, have a bunch of books, etc. But it sounds like this would be a challenge for you. Not for a shop with CIS experience, though. System pressure gets sent to the WUR, and also to the fuel injectors.

Control pressure: this is set by the misnamed warm up regulator, which really is the control pressure regulator. Control pressure affects the relationship between the amount of air flowing into the intake ports and the amount of fuel injected. More air needs more fuel, etc. It operates counter intuitively - more pressure means less fuel.

The warm up part of the WUR reduces the control pressure while the engine is cold. When the engine gets going, the WUR pretty quickly increases control pressure. This is why you see the two figures, one for a cold engine, one for a hot.

Cold engines like a richer mixture for starting. That's what this is all about. However, if too rich, there are problems, just like being too lean.

You have measured the cold control pressure and the system pressure. What is the warm/hot pressure? And what is the 10 and 20 minute residual pressure? Easy to measure - you've got the gauge set up. You should do those before moving your gauges to check for return line obstructions. I'd put those way down on the list - pretty hard to have anything partially block a return line.

There are other adjustments here. There is an idle speed screw. If the cold idle is too low, you can increase or decrease the throttle bypass air to lean the mixture - or richen it. That isn't likely to help with the starting problem, where you have to put the pedal down a bit. But could with the idle. Of course, it might mess up the warm engine idle.

There is a screw which affects the relationship of intake air to fuel. When you take the air filter off, and reach into the air box and up on the right side, you can feel a lever. More air flow, the sensor plate moves the lever up, and this increases the fuel flow. A screw semi-buried down inside this side of things, reached from on top between the FD and the rubber boot through a small hole, adjusts the relationship. A shop sets this by using a CO meter, or nowadays more often an air fuel meter. There are techniques to do this at home, so to speak, also. Probably not where your starting problem is, but could be. It is used to get the emissions where they should be, but can be adjusted a bit rich for more power. Too much either way, and you get various problems.

Two additional checks have been mentioned.

--You can check for air leaks by having a smoke test done. If a shop asks what is that, try another shop. If you have air leaks, fix those. If you don't have leaks, one less thing to worry about.

==The frequency valve system, which works with the oxygen sensor to fine tune the mixture so your air/fuel ratio is very close to 14.7 for complete combustion, is part of the equation. If it is disconnected you can experience hard starting. I learned this when putting a 3.0 into my 2.7. The 2.7 CIS didn't have this feature, and I figured I didn't need it, so didn't put it in. Once I hooked it all up, even though I didn't have an oxygen sensor yet, the car started much better.

The white circle is the frequency valve.

http://forums.pelicanparts.com/uploa...1571175609.jpg

You can reach back there to make sure it is plugged in. With the engine running, you can reach it to feel with your fingers if it is vibrating or not. It should vibrate. You could remove the connector with the engine running to see if it feels different, and again when you reconnect it. If it vibrates, one less thing to worry about fixing your starting problems. If it doesn't vibrate, well that's a whole different line of troubleshooting.

Since the car runs great when warmed up, I don't think anything especially bad is going on that would be quite expensive to fix.

But give us the hot control pressures, and the residual pressure figures.

Tony knows these systems almost by heart, and differential diagnosis should work with enough pertinent information. He's a methodical engineer numbers guy, so give him the numbers.

Pressure, pressure, whose got the pressure:

The fuel pump produces it - maybe 6 bar/90 PSI? If it is weak enough, you might not be able to hit the system pressure target. Yours is new.

System pressure: the line from the pump, after going through the filter and accumulator, has pump pressure reduced by a regulator in the fuel distributor. This can be adjusted by adding or removing shim washers. Your shop sounds like it did this, though I don't know which way they went. Maybe added one, because your system pressure is too high. Getting it back into spec would be a good idea. If this were mine, I'd remove a washer. I've had a FD apart, have a bunch of books, etc. But it sounds like this would be a challenge for you. Not for a shop with CIS experience, though. System pressure gets sent to the WUR, and also to the fuel injectors.

Control pressure: this is set by the misnamed warm up regulator, which really is the control pressure regulator. Control pressure affects the relationship between the amount of air flowing into the intake ports and the amount of fuel injected. More air needs more fuel, etc. It operates counter intuitively - more pressure means less fuel.

The warm up part of the WUR reduces the control pressure while the engine is cold. When the engine gets going, the WUR pretty quickly increases control pressure. This is why you see the two figures, one for a cold engine, one for a hot.

Cold engines like a richer mixture for starting. That's what this is all about. However, if too rich, there are problems, just like being too lean.

You have measured the cold control pressure and the system pressure. What is the warm/hot pressure? And what is the 10 and 20 minute residual pressure? Easy to measure - you've got the gauge set up. You should do those before moving your gauges to check for return line obstructions. I'd put those way down on the list - pretty hard to have anything partially block a return line.

There are other adjustments here. There is an idle speed screw. If the cold idle is too low, you can increase or decrease the throttle bypass air to lean the mixture - or richen it. That isn't likely to help with the starting problem, where you have to put the pedal down a bit. But could with the idle. Of course, it might mess up the warm engine idle.

There is a screw which affects the relationship of intake air to fuel. When you take the air filter off, and reach into the air box and up on the right side, you can feel a lever. More air flow, the sensor plate moves the lever up, and this increases the fuel flow. A screw semi-buried down inside this side of things, reached from on top between the FD and the rubber boot through a small hole, adjusts the relationship. A shop sets this by using a CO meter, or nowadays more often an air fuel meter. There are techniques to do this at home, so to speak, also. Probably not where your starting problem is, but could be. It is used to get the emissions where they should be, but can be adjusted a bit rich for more power. Too much either way, and you get various problems.

Two additional checks have been mentioned.

--You can check for air leaks by having a smoke test done. If a shop asks what is that, try another shop. If you have air leaks, fix those. If you don't have leaks, one less thing to worry about. Air leaking in past where the air flow is measured messes up the air fuel ratio.

==The frequency valve system, which works with the oxygen sensor to fine tune the mixture so your air/fuel ratio is very close to 14.7 for complete combustion, is part of the equation. If it is disconnected you can experience hard starting. I learned this when putting a 3.0 into my 2.7. The 2.7 CIS didn't have this feature, and I figured I didn't need it, so didn't put it in. Once I hooked it all up, even though I didn't have an oxygen sensor yet, the car started much better.

The white circle is the frequency valve.

http://forums.pelicanparts.com/uploa...1571175609.jpg

You can reach back there to make sure it is plugged in. With the engine running, you can reach it to feel with your fingers if it is vibrating or not. It should vibrate. You could remove the connector with the engine running to see if it feels different, and again when you reconnect it. If it vibrates, one less thing to worry about fixing your starting problems. If it doesn't vibrate, well that's a whole different line of troubleshooting.

Since the car runs great when warmed up, I don't think anything especially bad is going on that would be quite expensive to fix.

But give us the hot control pressures, and the residual pressure figures.

Tony knows these systems almost by heart, and differential diagnosis should work with enough pertinent information. He's a methodical engineer numbers guy, so give him the numbers.

"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."

When it comes to CIS injection, I find that most shops do not seem to know much more than we do and the they seem to make the most simple problems more complicated and expensive too.

Cheers,
Joe
87 Carrera

:)


"The standard CIS pressure fitting is 12-mm x 1.5 and the fittings for the delivery and return lines have 14-mm x 1.5. So you will need an adaptor (12-mm x 1.5/14-mm x 1.5) to connect the CIS pressure gauge kit."

FYI - I have this adapter fitting in stock if anyone needs one.

Len.Cummings @ verizon.net

:)

Exactly. Not saying there aren't good shops out there but the only sure-fire way to figure it out is by the size of the check you write.

If not for CIS most shops would be out of business. Almost seems like a $cam.

Huh. Interesting. That's not been my experience. I do think where you live and the size of the market makes a big difference. Some people may not have a lot of choices. Some places here would turn away an old aircooled car. But it is always changing as some of the guys who cut their teeth on these cars are retiring. I see blank stares from the younger guys. Or they are looking stuff up on the Internet like the rest of us.

There's no substitute for experience.

I disconnected the fuel return line and connected it to an external container for recycling the gas.
System pressure 78psi, about the same as the previous test with the return line connected to the cars’s tank. This tell me the return line is not blocked.

Now here is the twist.
The cold control is 0.5 bar or 7 psi. The cold control pressure was 3.9 bar or 57 psi. I don’t understand how the control pressure can change so much. I will do additional test again tomorrow with the return line connected back to the tank.

Locating where flow restriction..........
 

Blue,

The cold control is 7 psi. with the return line disconnected and goes up to 57 psi. when connected, as per your test. This simply indicates flow restriction some where along the fuel return line going back to the gas tank. This is the reason why you need to test the complete return line to locate the culprit. There are several connections in the return line, either test the line/s using compressed air or fluid to locate it.

You have a partially blocked return line. To demonstrate how the restriction affects your old control fuel pressure is gradually closing the valve to 70%~80% closed and you will replicate your problem.

Tony

Update with new pressures
 

I remeasured all the pressures again after blowing the return line with compressed air.

Temperature in the garage was 13.5 C (Its already cold in Calgary :( )

Here are the pressures.

First disconnected WUR Electrical connection.

System Pressure: 5.4 Bar
Cold Control Pressure with WUR electrical disconnected: 0.6 Bar

After about 30s, reconnected the WUR electrical connection and watched the pressure rise

Time (min) Pressure (Bar)
0.0 0.6
0.5 0.6
1.0 0.9
1.5 1.2
2.0 1.5
2.5 1.7
3.0 2.2
3.5 2.9
4.0 3.4
4.5 3.6
5.0 3.6

So my cold control pressure is very low, from the charts should be between 1.6 and 2.0 Bar.

Here are the residual pressures.
Time (min) Pressure (Bar)
0.0 3.2
0.5 3.0
1.0 2.8
1.5 2.7
2.0 2.5
3.0 2.2
4.0 2.0
5.0 1.9
10.0 1.7
15.0 1.7
20.0 1.65

I think my first control pressure test posted before was incorrect. I had the electrical connection to the WUR connected and I was measuring hot control pressure instead.

I first plan on removing one shim from the fuel distributor and recheck all the pressures. If I understand the system correctly this should not affect the cold control pressure. But it should drop the system pressure.

Next, remove the WUR and try to push the pin outward. I am not sure if I want to drill and tap a screw into it or open the WUR and push it out.

Am I going in the right direction or is there anything else I should check first.

DO NOT push out the pin on WUR.You will just upset factory specs,and maybe introduce other issues once this is solved.Take WUR apart, and clean,making sure not to drop top hat.Clean screen.This maybe a cause.

I saw a few posts where drilled and tapped to make an adjustable WUR. I thought I could use a C-clamp to push the pin out a little bit, re-assemble the WUR and use c-clamp to put the pin in to get the desired settings.

I removed two shims from the fuel distributor and the system pressure has dropped to 4.9 Bar. Right where it should be. There was no change in control pressure.

if you do this your simply masking a problem elsewhere.The system is finely balanced.Same goes for people chasing pressures, when they havent even done a smoke test.
Personally,Id get the WUR off and clean it.Dont forget to use new copper washers, or aneall the old ones.

I managed to remove the WUR and check but in the process this happened.
http://forums.pelicanparts.com/uploa...1571540267.jpg
The return line was twisted and in my stupid attempt to straighten it, the line broke. Also found that one of the bolts holding the WUR was sheared. Whoever removed the WUR before clearly didn’t know their way around.

Just looking for something positive here. The inside of the WUR looks extremely clean. Maybe the mechanic I took the car to, cleaned the WUR.
http://forums.pelicanparts.com/uploa...1571540564.jpg

I could not find the part number for the WUR return line. Looks like I am stuck till I replace this line.