Sick CIS - diagnostic suggestions?

[phaques]

I guess this is going to be the winter I learn to work on my CIS...

Here's what happened, and then I hope some of you CIS magicians will have some idea where I should start (my car is an 83SC with the stock 3L):

At VIR this past weekend, I ran low enough on gas during a session on track to gulp some air - and other bad stuff, I'm afraid - into my fuel system. Two times I think the motor sucked air. Immediately after the second time, the car started running like cr*p. Back firing under load, throttle cutting out and in under load, rough running and backfiring at idle, engine stopping and then hard to start, and everybody who listened to it agreed it sounded like it was running on only a few cylinders.

I let the car idle for about 10 mins, and then took it out in the next session - after adding new gas - and limped around the track for about 4 laps, car burping, backfiring, and running terribly.

At idle, I removed spark plug wires one by one to see what effect that had, and in apparently four of the six cylinders, it had almost none.

I took off the fuel filter and drained it to see what was inside, and I swear it looked like apple cider - dark and full of lots of particles of stuff. No water separating out though, as far as I could see. This filter has less than 8K miles on it, and is about 18 months old. I tried to salvage the filter by filling it backwards with clean gas, sloshing it around, and dumping it out the inlet side - waste of time. I re-installed the filter, started the car with great difficulty, and drove it around the paddock to the horrified stares of everybody I drove by, and then coaxed it onto the trailer and came home.

So...my assumption is that the car sucked some gunk into the fuel system when I ran it too low on gas. And my question is..

What would you do, and where would you start?

[KFJ]

First thing I would do is get a new filter. :p After that I'd check the spray pattern on each of the injectors. Bentley has the procedure, but basically it is pull injector out of runner, stick in glass jar, run fuel pump (ignition on, lift sensor plate) and check for nice cone shaped flow pattern. Since you are obviously getting some fuel through, I would think the issue is at the non-functioning cylinders. Since it is likely fuel, I'd start with the injectors. If you find any that aren't flowing normally, you can either have them cleaned or there are a couple of people that have had success using carb cleaner and compressed air (very low PSI).

Note - I've had a couple of instances on track where the engine was starved for fuel without any issues - air isn't a problem as the fuel system is not a closed system. Gunk in the filter on the other hand is a problem.

[hoophead]

...At idle, I removed spark plug wires one by one to see what effect that had, and in apparently four of the six cylinders, it had almost none...

The 911 engine runs amazingly well on just 5 cylinders. You should remove one wire, then remove a second to see if it makes a difference on a particular cylinder.

[Jase007]

I ran low enough on gas during a session on track to gulp some air - and other bad stuff, I'm afraid - into my fuel system.

I would bet [and I don't bet on anything BTW] that you sucked up 25 years of crap from the bottom of the fuel tank.

1. put a new fuel filter on it
2. disconnect neg terminal
3. open hood
4. remove fuel level sender
5. shine light into gas tank and see what you have in there after 25 years :shock:

CIS needs GOOD fuel pressure from tank through $$$$ high PSI fuel pump to dirtribution unit. Hopefully, the fuel filter saved the crap from getting to the fuel distributor.

Pull fuel injectors and drop into clear bottles for test is also easy to do as Kirk J mentioned.

Good luck.

[cmartin]

If that doesnt work, drain out the cider and start with some fresh petrol.

Good luck, we've all been there.

[Noah]

Just to add one point to the good advice above, it's possible that you have blockage at the injectors, but it's also possible you have blockage at the fuel distributor. If, for example, you have two injectors that aren't spraying well, before you replace them, detach them from their respective fuel lines and do another flow test of just the lines. You might have gotten crap in the FD. If that's the case, each of the six fuel ports has a tiny screen in it (the fuel line banjo bolts are 12mm, and the screens are under the banjo bolts).

But if you do find you might have blockage in the FD, post here first. They're very, very, very delicate.

[Trak Ratt]

definitly drain and flush tank. then disco line at filter asd runs some good stuff through, then new filter, disco at distribuer and run good stuff. Repeat a each juction. Fire hazard so...!

[type954]

this thread will be very important to me also to help learn about CIS. my fault is that the engine will high idle ~1400-1600 rpm when hot. i was told to suspect the warm up regulator. any comments/questions?

[KFJ]

Could be as simple as idle adjustment, but, before you go turning any screws you have to recognize that CIS is comprised of a bunch of components that all work together as a system. Adjusting one component blindly can lead to adverse effects. So, your high idle could be a stuck Auxiliary Air Valve which could be overcome by adjusting the idle way down, but the car would then run lean (bad). So, what do you do? Testing! Get a cheap fuel pressure gauge ($50 JC Whitney) and test the system and control pressures to make sure they are in spec first (spec is in the bentley). You can test the AAV by sticking it in the freezer and applying 12V. Vacuum leaks (also a potential high idle contributor) can be found using an unlit propane torch with the car running around potential leak points. There is a test for every component in the CIS system.

Problem with CIS is it is a system. The component replacement strategy doesn't work - someone says "sounds like the WUR" or "must be AAV" and you spend large $$ chasing the parts. Test, make small changes to one component at a time, re-test, rinse, repeat...

BTW - this will be helpful for you: http://members.rennlist.com/jimwms/CIS/CIShome.html

[Jase007]

Good link Kirk.

Jim: Charlie and others have posted some threads here on this subject. Search around and when you are ready to test / tune borrow gas analyzer / fuel pressure guages. :)

[Rick Lee]

Guys, this is my old SC. I miss her and want her healthy for when Fax sells her back to me:).

Fax, the WUR is almost new. I replaced it shortly before you bought it. I don't believe the injectors have ever been replaced, though I did mark date and mileage on the fuel filter last time I changed it. FWIW, my lean mixture problem in my 993 was remedied once I got my injectors ultrasonically cleaned. Ran me $164 and was worth every penny of it. I never drained the gas tank, so it may indeed have some gunk down there.

[Cliff Claven]

this thread will be very important to me also to help learn about CIS. my fault is that the engine will high idle ~1400-1600 rpm when hot. i was told to suspect the warm up regulator. any comments/questions?

What kirk says. Could be one or more of several different potential faults. You need to figure out, is it a fuel mix problem or false air problem. This means checking both your mixture (emissions levels) and fuel line pressures under different conditions. The so-called warm-up regulator, more accurately called a control pressure regulator, works (through fuel pressure control) to enrich the mixture on cold start (and on hard acceleration). Auxiliary air valve works to add extra air-flow past the throttle plate on cold start, which also causes higher idle if not shut down on warm-up. AAV can be tested with the freezer test, though it could work fine in the test but still not function properly on the car due to an electrical fault in the circuit that controls it. There are also vacuum lines contolling fuel/air switchs that can influence idle. You just need to start testing.

As for the original question, could very well be clogging in the fuel distributor, which is a major pain in the ass and/or high dollar repair (though possibly a good excuse for investing in carbs).

[phaques]

I bought the Bosch Fuel Injection book by Pobst, which seems to be great. Dropped the fuel tank, rinsed and dried it thoroughly, installed a new fuel pump, pumped gas from the tank through the new pump up to the inlet side of the fuel filter to flush that line, installed a new fuel filter, and started the car to see what I got (hoping I got really lucky..). Car started fine cold, ran fine for 30-45 seconds, then started wah-wah-wahing, backfired, said f*ck you, and died. I'm assuming the pump is fine (since it is new), but I guess I should test flow rate through the filter and in the return line between the pressure regulator and the gas tank. Also, if I had a bench fuel injector tester (hint, hint....RickV?) I could test the injectors.

[Rick Lee]

Fax, I put a new fuel pump in there in Dec. 2004 and I think I gave you the receipt for it. This one is a real head scratcher.

[markwemple]

How was the tank filter. "We" always remember to change the one in the engine bay but I believe yours came with one that was a screen in the tank as well.

[phaques]

Rick,
Thanks - I got a good deal on a basically new pump, so I bought it. But, I never throw any parts out so I'll label your old pump w/date and mileage and stow it somewhere. My diagnostic skills in this area are weak, and I'm baffled. There was quite a bit of visible junk in the tank when I took it out and held my match down in there to look around, but I rinsed it pretty well and blew it dry....my working theory is that I've got a clogged injector or two, but I need to find a way to test them. I may try the quick check method first (run the pump with the car off, stick the injector in a jar while still attached to the distributor).

[phaques]

Tank filter didn't look too bad. No holes, and a rinsed it and blew it dry, and tried to blow any debris out of it.

[phaques]

Okay, in my searching on the topic, I have found a couple of very good links on this topic. One, http://www.classicsaab.net/library.html contains a link for the COMPLETE Bosche K-Jetronic with Lambda technical manual (first link under the Engine section), but BEWARE, it is 178 Megs and a total hog to download. On the same page is an excellent link for CIS troubleshooting, the second link under the engine section, and a much more manageable download.

[86911TLCAB]

while no expert on this...when i tested my injectors, i pulled all six and stuck them each in a bottle so as to prevent getting unburnt fuel into the engine. Can lead to other undesireable issues...tito

[Cliff Claven]

phaques, what noah said earlier, you need to check the flow to the injectors cuz its very possibly the fuel distributor. when that kind of crud from the tank gets past the fuel filter, it can end up clogging the furel distributor. unfortunately a rebuilt fuel distributor costs big $$$$$. and it's hard to rebuild yourself. could be a good excuse for switching to carbs.

[phaques]

Anybody have a place you like and recommend to send my injectors out to?

[Jase007]

Ivan Arzola at IMA has a full Bosch F.I. tester / cleaner setup.

Merrifield, VA.

Search on here and you'll see several examples of his work ... particularly for electronic FI injectors [911 carerra up, 944 up] which are more involved than the mechanical pop injectors on the CIS cars.

FWIW: I went through my CIS several years ago and simply:

1. new accumulator
2. new fuel filter
3. new injectors
4. got new injector sleeves and outer sleeve O-rings - didn't install ... yet. :)
5. New $$$$ fuel pump
6. flushed tank, was OK.

[Rick Lee]

Ivan did my 993 injectors too. I spent about $1000 tracking down the problem and $160 on cleaning the injectors, which fixed the problem.

[phaques]

I think I may have found a possible solution...I pulled the distributor cap, just to be sure, and the end of the rotor is a grey, charred stub with no portion of the metal contact visible at all...flakes of the plastic rotor head are sitting in the distributor, and the contacts on the cap are heavily worn....maybe this is it all along? I've got new cap and rotor coming in tomorrow, and my fingers are crossed...

[Rick Lee]

That's kinda weird. I changed the cap and rotor when I did plug wires, probably in Dec. '04.

[cmartin]

Check for play in the distributor bearing. Mark it before you pull it, then try to wiggle the shaft inside the housing.

[phaques]

Replaced the dist cap and rotor, which enabled me to start the car, but the rough running, backfiring, and falling off of power under load are still there....

I pulled all the injectors out of their ports and placed them, still attached to the fuel lines, into separate mason jars, jumped the fuel pump relay, and ran fuel through each injector to compare flow rates....#'s 4 and 5 look to be about 10% less than the rest.

I discovered that just about any good diesel engine shop will have bench injector cleaning machine that will clean and test these injectors. the local shop that I dropped mine off with today is going to charge me $50 to clean and test mine. I'll let you know how this pans out....

Also spoke with a helpful local old german mechanic (yes, the mechanic is german and he works on german cars too...lots of Mercedes and Volvos with this same CIS system) who said to pull the fuel lines where they connect to the fuel distributor and fish out the small screens that sit in each port on the distributor and inspect/clean them...

I'll keep you all posted...

Another tidbit - EuroEast seems to have a good price on new injectors - about $39 each.

Rick - you did replace the rotor and cap in 12/04, but they've got about 20K on them since then...and as you know, those ain't highway cruisin' miles, neither.

[phaques]

The Final Resolution...
CMartin was closest to big money...
After taking it to a local mechanic, he found that a small screw on top of the distributor shaft had worked itself loose, and the shaft had become loose enough to chew itself all up. No spark. Voila. Nothing to do with fuel whatsoever. Oh well - now I have a clean gas tank, new pump, clean fuel lines and injectors.....

[HoodPin]

The Final Resolution...
CMartin was closest to big money...
After taking it to a local mechanic, he found that a small screw on top of the distributor shaft had worked itself loose, and the shaft had become loose enough to chew itself all up. No spark. Voila. Nothing to do with fuel whatsoever. Oh well - now I have a clean gas tank, new pump, clean fuel lines and injectors.....

Wow....talk about your magical mystery tour...:p

Glad to hear you were able to resolve the problem, albeit the long way around...But it sounds like the car is ready for another 25 years of abuse. :D

[OldTee]

You have a head. Take small wooden hammer and bang away on it a few times. You earned it.
ARF