divil

Would you ever replace a working ignition coil? Can it "wear" (probably not the right word) so that it affects performance but still works reliably?

I am chasing a problem where my car feels a bit sluggish, both on and off boost. It feels ok at very low throttle, but once I open it up a little more, the response is just a bit weaker that I expect. It's intermittent, but when the problem is there, it's at both part throttle and WOT. I am running out of things to test. From all the troubleshooting I've done, I'm leaning away from it being a boost or fuel issue. Among eleventy million other things, I have replaced the distributor cap/rotor, plugs, and the plug leads are about 2 1/2 years old. But I've never touched the coil.

Most info I've found suggests that they either work or don't, and if the car runs you don't bother with the coil. But some people claim to have experienced an improvement in an already running car. If I could fix my problem for the price of a new coil I'd be ecstatic...on the other hand, it might be a complete waste.

refresh951

What plugs are you running Gap?

divil

I'm using Bosch Super Plus plugs. I forget what the gap was set to, but I looked it up and checked/set them with a feeler gauge when I installed them.

azbanks

When my coil went out, the car started shutting off or failing to start very erratically. I didn't really notice a drop in performance.

rude944

Coils can crack, and then usually they will "leak" spark, across carbon trails. Spray it with water from a mister to see if there is a tattletale misfire and light show. In fact, do this with all your ignition leads... In the dark.

Check to see if there is proper resistance between the two circuits. I think Clarke garage has the procedure. Coils don't seem to fail as often as people replace them.

divil

I forgot to mention, the resistances checked out just fine according to the Clark's Garage test. I also cleaned the contacts - there was some white powdery corrosion in the high voltage connector, the others weren't too bad. I'll definitely try that with the water though thanks!

Tom M'Guinn

Intermittent sluggishness would not make me think coil, but I suppose it's possible. Can you just borrow one to see if that works?

Intermittent sluggishness that would make me think more about bad connections somewhere, especially if the issue is all or nothing -- i.e., it either runs perfectly normal or it runs sluggish, with nothing in between -- is that what you have? A friend, for example, had cracked colder joints in the KLR which was causing the car to switch over to the WOT maps from time to time, but otherwise ran fine. Very difficult to track down since everything checked out. Maybe give the harness, dme/klr solder joints, and all the electromechanical stuff (TPS, AFM, etc) a good once over to see if they are failing) -- to the extent you haven't?

divil

Yeah I am thinking about the coil just because of the other things I have eliminated. The DME and KLR are the other prime suspects at this point. I have had another set of computers in my car, and I didn't think it ran any better, but I still plan to open them up and have a look. I can't read into the test I did before too much, since those units were old too, and I have fixed a few other things on my car since then.

I have driven with a voltmeter hooked up to the WOT signal and it seemed to be working correctly but the KLR could still be causing other issues. I thought it might be pulling ignition timing due to a fault.

As regards it being all or nothing...it's very difficult to say, but I think it can vary by degrees. Sometimes I'll be convinced there's a small difference...and then it will stay the same for so long I'll become convinced I just just imagined it. Then out of nowhere it will change. I won't lie, it has made me question my own judgement often!

Tom M'Guinn

Sorry about that -- been there and know how frustrating it can be. You might also check the knock sensor and it's connector -- it can cause screwy behavior too...

divil

Replaced...the old one and it's harness looked so bad I was convinced I'd found the problem. But replacing them both (along with the fuel injector harness) didn't help.

Tom M'Guinn

Just throwing darts, but I once had a bypass valve that would stick open occasionally, which seemed to perfectly imitate an intermittent electrical issue...

divil

Which part is that exactly?

Tom M'Guinn

Aka, blow-off valve, aka diverted valve -- black canister thing off throttle side intercooler pipe...

divil

Oh that guy...yeah I took that off and tested it pretty thoroughly. I was suspicious of it's behavior and posted a thread about it, but in the end I came to the conclusion that it was working. It would allow some leakage with the top port open, but with any pressure at all on the top it would seal up nicely. Still if it was occasional like in your case that could easily have slipped by. I'll keep that in mind.

I yanked the DME and KLR to take a quick peek at the boards. I did find some strange looking discoloration. I wonder if it could be water damage, because I did have a leaking battery tray before.

Here's the KLR - these yellowish marks are all over the board:






And here's a few things that looked odd in the DME. First, the half of the solder joints on the big ribbon cable had what looks like burned flux on them. I have seen this before on circuit boards but never really knew if it's bad or not:




And this looked really weird to me - what is this stuff is on the big transistor (coil driver?)? It looks similar to the stuff in the previous pic, but I've never seen it quite like this before:

divil

Actually this thread seems to suggest that the stuff on the board normal, just left over flux that is not cleaned off.