Another CIS question...

ohecht · 12-03-2002, 07:55 PM

What condition (rich, lean, other) would cause an audible and irregular miss at idle when the weather is cold, and that disappears as soon as the engine is put under load?

82 SC with CIS.

I do not think it is ignition related, as I have fairly new Magnecors and regularly replace plugs, cap, rotor, etc.

Olivier

bigchillcar · bigchillcar's Garage

I don't think we can assume that it's only mixture related. Could be a fuel pressure problem somewhere, clogged injector or fuel filter, faulty accumulator...we'd probably need more info. Do you have a CIS fuel pressure guage?

But...remember that in cold weather that the air becomes denser and in extremely cold conditions this could possibly translate to creating a slightly lean condition. I've seen the reverse effect occur at high elevation. Air was thinner in Denver than in Miami and my jeep got to the point where it would simply not keep climbing a hill...I had to literally climb out and adjust mixture on the spot. Hope this helps!
Ryan

Hladun · 12-04-2002, 06:29 AM

How serious/frequent is the miss? Cold engines running rich often missfire. The manuals said to tune my 62 XKE so there was an occasional missfire at idle. By occasional I mean a second or two.

ohecht · 12-04-2002, 08:06 AM

I do think it is mixture and temperature related, since I tuned it last on the edge of lean, if I remember correctly.

I do have the pressure gauge, and I plan to testing all the relevant pressures and the WUR (perhaps making it adjustable).

What I hate about CIS is that you have to discipline yourself to only "fix" one thing at a time in order to determine what the real cause is. I usually do a bunch of things together, like fuel filter, plugs, cap and rotor, Techron, etc., so I am never sure what the cure is.

This miss sounds bad at idle (randomly all over the place), but the car has plenty of power right off or idle.

Olivier

Superman · 12-04-2002, 08:34 AM

I'll be replacing the infamous 'green wire' soon, and I have the 20/21 cams in my engine, but I have a little miss at idle too. My car is running fairly rich, but if yours is lean, that could cause the miss. Ideally you would disconnect the O2 sensor, a no-brainer if your CAT is gone or gutted, less of a no-brainer if your CAT is working.

Yes, troubleshooting CIS is a step-by-step process. You can go through the steps, or just enjoy the slight roughness at idle. Both options are reasonable.

Gunter · Gunter's Garage

Check for vacuum leaks. I had similar problem at idle with great performance at higher RPM. My leak was in the vacuum hose where it splits to the Servo and another in the oil breather hose and one more in one of the intake runners. It took a lot of cursing, patience and I found the best way to detect was a small nozzle from an azetheline torch to pin-point the leaks; a fluid starter spray is too general.

sammyg2 · 12-04-2002, 09:50 AM

OK, next time it is idling like crap, pull the air cleaner and filter off and lift the air sensor just a little bit. That will give it more fuel and make it run richer. If it smooths out, there's your solution. Then you just have to figure out which of about 7 different things are causing it to run lean :-)

I would check the hoses and oil filler cap and if they are all right I would use my 3mm allen and give her about 1/8 to 1/4 turn in. That should do it. Your gas mileage might go down a little, but who cares?

DISCLAIMER: yeah, I know this may be a band-aid fix and might cover up a related problem, but if it works, it works. If it doesn't, look for something else.