Anybody know the procedure for testing the old style GM coil? (the ones we have in our cars). I've narrowed my idle problems down to one of a few things. Either a vaccum leak (gonna have the motor "smoked" to find out), the ignition coil (unlikly I would think, but it's what my flow chart suggests), or the IDle control system. Anyhow, I just need to know the test procedure if anyone knows it (I can't find it in any of my service manuals at the shop).

 

I don't know the testing procedure for our cars, but I thought I would mention something I learned about testing coils. Resistance values for OEM coils is not necessarily the same as those for aftermarket coils (stock replacements). I was chasing a slight miss on a Toyota once and ended up testing the coil. My Haynes manual gave the testing procedure and it tested out of spec, so I replaced it. Ran the same, so I tested the new coil. It also was out of spec, and all the new ones at O'Reilly's were the same. It seems that coil resistance values are just a general guide, and not really a spec. I ended up fixing the car, but the new coil was a waste of money since the old one was still good.

 

Say Aaron (My name too! Lol), you owuldn't happen to remember what caused the miss would you? I've been trying to track down one myself (more of an irregular idle miss/stumble). I've been through just about everything I can think of short of smoking the motor and trying a new PROM. The scanner data I'm getting is all normal except for the lack of a timing advance number (value reads as "0"), this using a Snap-On MT-2500 scanner. Any ideas, outside of the box?

 

im having some ignition problems too. the coil is basically just a lot of windings of wire resistances will vary. an open reading or short is bad. most auto parts stores can test it. im just replacing mine. $34 for new or $59 for cool mallory at discount auto.

 

autozone will test anything free.

 

I got my MSD GM replacment coil for $40.

 

Aaron, I'm not certain which part that I replaced on that Toyota ended up fixing the problem. The miss was very slight. Could barely feel it even though I was very familiar with the car. After trying the coil, instead of replacing one part at a time I ended up giving it a full tune-up, fuel filter, injector cleaner, etc all at once.
Have you figured out why you are getting no timing advance number? Since everything else checks out, that is probably an indication of where your problem lies. It definitly sounds like a you have a timing problem from the description in your other post. I don't know what exactly the Scan tool reads when checking the timing advance, but components related to timing advance would be the ESC (knock sensor and module) and the EST system, which gets its information from the distributor. Possible culprits could be the knock sensor or module, distributor, or maybe even the ignition module.

 

Yeah, the Distributor and module are both brand new. I don't have a knock sensor (that came one year later). The only thing I can figure that would have effect on timing advance is the PROM. Stranger things have happened I suppose. We shall see. I'm taking it to a specialist Tuesday. It's only money afterall.

 

I did a vaccum test (somthing I hadn't thought of yet), using a nice GM goodwrech Vaccum gauge I picked up at the parts store (15 bux!). Anyhow, the Vaccum was reading where it should be, at between 17-18 in/mg . The only time the needle moved was when the idle bobbled. This rules out a mechanical problem, such as valve leak, timing chain looseness, and sticking lifter. Anyhow, the problem is ignition related, or fuel related, which doesn't rule out the stupid computer goofing around. I'd like to take a moment to remind all of you how neat carburetors are....just a public service announcement (wish to heck I had one).