Sick CIS - diagnostic suggestions?
 

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?

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.

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.

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.

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

Good luck, we've all been there.

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.

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...!

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?

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

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. :)