UNCJD

Good morning, all:

Reviewing some other posts on this forum, it looks like my resistance on the secondary coil shouldn't be higher than 13,500 ohms, and it's testing out at 15,000 ohms. On the primary side, it shows 1.7. When I short the leads together, it regularly reads 1.4 or 1.5, so the primary resistance isn't way high...because I have to take the meter's internal resistance into account, right?
This is a cheap multimeter (Harbor Freight). Wondering if the secondary is as inaccurate, but I would think 14,998 ohms is still too high on the secondary...unless somebody here can tell me otherwise.
I'm asking this because...
After replacing the tranny mount, I drove the car about 50 miles and it started running like crap. I limped home, and on the way the CEL came on--the code was for the ECT sensor not letting it go into closed loop. Open loop makes sense, since the car smells like gas when it runs (badly, of course) and it has apparently baked my driver's side cat. I replaced the ECT sensor and thermostat, both the most common causes of that particular code, and the car still runs like crap. So I decided to test the coil on that bank. Budget and spousal tolerance being what it is, I didn't want to order another ignition coil if this one isn't actually a problem.
I haven't tested spark because I can only work on this thing early in the morning, and I'm a 1-man operation. Any insight would be much appreciated.

UNCJD

I forgot to mention, the code it was throwing was P0125.

dicer

"Take meter internal resistance into account" ? The meter reads the resistance, why do you think you have to guess whats going on in the meter? Your not working with high frequency stuff here.
1,500 ohms difference, whats more important does it work, you could do the igniter test and prove that.

oldskewel

iTrader: (1)

If I am correct in inferring that you mean when you connect one test lead to the other, where there should be zero resistance, and you read 1.4-1.5 Ohms instead of zero, then ...

First double check that the probes are plugged in securely to the VM, and that the probe tips are clean, so you are not affected by any surface resistance.

If you do that and still are reading 1+ Ohms, you may want to get rid of the VM. That's what I would do. Maybe leave it in your trunk to check battery voltage when needed. But get an instrument you can trust, or you'll be regretting it eventually.

And then more specifically regarding the coil, in my experience with coils, the resistance measurements are for non-conclusive guidance. You of course don't want an open or shorted circuit in there, but as long as there is a finite non-zero resistance, it tells you that your coil may or may not be bad (not helpful, I know). I was having some rough running problems on my '91 a couple of years ago, tried measuring my coils as best as I could, and found nothing conclusive. I ended up buying a new pair since that was easier than anything else I could think of. Placebo effect told me the new ones helped a little, but I later swapped the old ones in and confirmed it ran the same. The top coil (by the ECT) is far easier to swap than the one by the AC compressor.

I still have the ones I took out in case you are interested in using them for troubleshooting, etc.

UNCJD

Thanks for the help, everybody. As I was trying to remove the old driver's side coil, I noticed the cable running from the coil to distributor had been chewed nearly in half. When I just replaced that, the car ran fine. How I missed that before, I don't know. Right now, the car is sitting out there smirking at me, plotting its next move.
How'd the cable get chewed up? A while back, I did the distributor caps and rotors. When I put the spark plug/distrib cover back on, I neglected to thread that crucial cable through the cutout in the plastic. Of course it didn't screw up immediately, but 40-50 miles of movement sawed through it.
Suspect the cat is baked, as it overheated. Tach doesn't work anymore, but its kind of wonky anyway at times--although I think I cooked the sensor when the cat overheated.
Question, though...I have a new oil change in there, expensive synthetic. Would all that unburned fuel dumping when there was no fire have diluted the oil? Should I change it again just to be safe, or am I okay to keep running it? Don't want to waste money, but don't want to be penny wise and pound foolish, either.

dicer

So that 1,500 ohm difference coil is working just fine then?

UNCJD

Close enough for gub'mint work.

Yamae

We need to know the specifications before we worry about.
9.0 - 15.4kΩ (-10 - 50℃)
11.4 - 18.1kΩ (50 -100℃)