How to test ignition coils? - Page 3 - PeachParts Mercedes-Benz Forum

kmaysob · #31 07-11-2014, 11:14 PM

there are a mess of tests you can do. is this the 4 cyl or v6? the v6 has a mass air flow sensor on it. if you have the v6, clean this sensor and see if things improve.

really though, without looking at live data, you are just shooting in the dark. if you are smelling raw fuel, it may also be time for new o2 sensors.

MS Fowler · #32 07-12-2014, 07:08 AM

I found the problem on my son's Omni ( yes, MANY years ago!). Cold start, fine, but as it warmed up, it would miss. He drove from Cinnci OH to Richmond, VA for a gig, all in short spurts. Every shop would replace something different, and send him on his way.
I reached down to the distributor while it was running, and got shocked. Found that the module on the side of the distributor was bad. Sometimes mechanics don't take the time to find the underlying problem.

TwitchKitty · #33 07-12-2014, 07:31 AM

Quote:

Originally Posted by Jooseppi Luna

am just going to replace the plug wires, since they are 20 years old and NAPA wires are $35 for a set, but I'd like to try testing the coils so that I don't spend $100 buying three new coils when I am assuming I don't have to.

Check prices at rock auto.

That car might have a MAF. I was assuming it was the older speed density system. Some cars have a MAF and a MAP.

Need a book. I bet you can buy the original factory shop manual for small money on eBay.

High voltage parts mentioned in a couple posts are routine replacements. Test parts, don't guess or throw money at it.

DieselPaul · #34 07-12-2014, 07:01 PM

Quote:

Originally Posted by aklim

Touching and feeling is great for working with women. For injectors, the only complete test is on an injection bench. It will tell you if they are spraying at the correct volume and pattern. Anything else is a SWAG.

You are correct, however whatever injectors GM used are notorious for just pouring fuel out of worn tips. My test would identify horribly bad injectors. If if can't hold fuel in it with the car off its bad. It will not reveal the poor patterns but if you're running pig rich and pissing away fuel that can sometimes find it.

DieselPaul · #35 07-12-2014, 07:02 PM

3.1s are speed density. They didn't get MAFs on 60*s until obd2 I don't think, on like the 3400, 3500, and 3900.

Mölyapina · #36 07-12-2014, 07:36 PM

Quote:

Originally Posted by MS Fowler

I found the problem on my son's Omni ( yes, MANY years ago!). Cold start, fine, but as it warmed up, it would miss. He drove from Cinnci OH to Richmond, VA for a gig, all in short spurts. Every shop would replace something different, and send him on his way.
I reached down to the distributor while it was running, and got shocked. Found that the module on the side of the distributor was bad. Sometimes mechanics don't take the time to find the underlying problem.

I'm noticing a theme in your spark-ignition adventures. How are you still alive

?

INSIDIOUS · #37 07-12-2014, 10:46 PM

Low amperage

MS Fowler · #38 07-12-2014, 11:27 PM

Quote:

Originally Posted by INSIDIOUS

Low amperage

And very quick reflexes....
Its probably a good thing I don't have a heart monitor implant. The docs might be puzzled by all the spikes.

TwitchKitty · #39 07-13-2014, 10:42 AM

Some people like high voltage. They say the psych ward really comes alive during lightning storms.

Mölyapina · #40 08-01-2014, 07:42 AM

OK, so I tested the three front plugs with a spark plug tester, and they check out. I still need to test the rears, but first need to dig the wires out... you need to remove the coils and the ICM and the coil mount etc. to get at them, which is a pain.

I would have done it today, but I ran into another interesting test in which you slip a short length of vacuum hose over each of the coil towers and connect the wires to those, leaving a sliver of the coil tower showing under the vacuum hose. Then, you use a test light to short out one coil tower at a time. If a shorted coil tower does not produce a change in RPMs, that cylinder is misfiring.

First time I did the test, It seemed crystal-clear: all cylinders resulted in a drop in RPMs except cylinder #6, which created no change in idle. Ah-ha! I found the problem cylinder!

...no, wait, I had just forgotten to plug that plug wire back in after running the spark plug tester on it. Brilliant.

I tried the test again after plugging in #6, and all cylinders gave a more-a-less equal drop in revs. Then I realized that the engine wasn't misfiring at that point, and that of course all the cylinders would check out... the misfire then kicked up, so I quickly did the test again, and would say the cylinder fed by the coil tower furthest to right seemed (perhaps) a little suspect, but the misfire abated as I was still testing cylinders, so I can't say for sure whether it was that cylinder or another cylinder.

Today, I'm going to drive around the block, then chock the rear wheels and have my sister sit in the car and put it in reverse in an attempt to force the misfire -- the misfire is generally the worst ~2 minutes after startup when the car is in gear.