My 91 4-cyl Trooper has had this problem off and on since I bought it 6 years ago. Now it seems to be less intermittent and more semi-permanent. No spark from the coil.

The first time it happened (6 years ago) the first thing I did was check for fuel flow. As soon as I bumped the starter, it was a gusher. Plugged the fuel line back in and it started right up. Well, this method lasted three or four years, and I only had to do it three or four times per year. And I never had a fire!

Then one day it didn't work. I checked for spark, and there was none. As I messed around with connections and such, at one point I forgot and had left the key to "On" while I was jiggling fuses. Heard a "pop" from somewhere in the dizzy area and then the truck was starting again no problem.

After that my "fix" was to jiggle the coil wires at the connector, and it worked every time. Not any more. I replaced the coil years ago to no effect, just did the module and distributor, and still no spark, even using my tried and true "fixes".

So I decided to see if there was a stored code even without the Check Engine Light on. Jumped the ECM wires, turned the key, no CEL. Hey, that's not supposed to happen! Unplugged the ECM jumpers, turned the key to "ON", no CEL. Pulled the cluster, swapped bulbs with the O2 indicator, no CEL.

Now I ride a little low, and many of you know the CEL is the lowest indicator on the panel, so I don't even know if this is a new problem or an indicator of the "intermittent" problem. Is my ECM dead or dying or do I need to buy a test lamp and check out every stinking circuit that can energize the coil? Or maybe just pull the fuse block and replace it?

Went to this thread:

Planet

I found all of the checks you can do for no CEL and always on CEL.

Too bad they didn't help. I was about to resign myself to having it towed when I wondered if there was just a bad ground or connection in the ECM. So I turned the key to "ON', got no CEL of course, then tapped on the ECM. CEL came on, went to "Start" and it started right up.

Good thing I didn't get so disgusted that I used a BFH on the ECM.

Goodonya for persevering and for posting the details of your solution. <img src="/forums/images/graemlins/cheers.gif" alt="" />

Well, I'm still persevering it seems. No CEL (and no start) this morning. Pulled the main relay, which should be called "pain" relay for how hard it is to pull an electical component, and a couple of pins were rusty.

So instead of shining it up and putting it back in, I decided since it's out I'll get a new one. Now I'm waiting on AutoZone store to store delivery.

I'm thinking that it may be the ultimate fix, since it explains both the intermittent problem and the "fixes" I used to use.

I'll keep you guys posted.

OK, swapped the main relay. Worked for a "short" time, and now no start. Again. Now I know to just look to see if the Check Engine Light comes on so I'm not wearing out my battery and starter.

Seems I'm going to have to get a test lamp. Still could be either a balky computer or a bad connection somewhere.

Perhaps this suggests a bad connection or bad earth or a dry joint in, on or near the ECM?

Yeah, it suggests that, but I sure can't find it. Yet. It may take a gallon of kerosene and a match, but one way or the other this will be resolved!

It seems that just the right vibration renews the connection, wherever it is. I checked the ECM chassis ground, and it's OK, but I'll check again. I cleaned the rear mounting bracket with alcohol since a previous owner had spilled a lot of Coke or Dr. Pepper into the area.

I guess that's why Isuzu put a plastic tutu over the connectors.

Now I'm looking at a fault in the ignition circuit. I pulled the main relay again and checked the power to it and it's fine, so I'm now thinking it's the ignition switch circuit that energizes the coil in the main relay. The relay coil ground is OK, but I ran out of time to look at the ignition.

Oh, and the truck never quits once it starts. If it were a bad conection in the ignition circuit the coil would just quit giving spark and the truck would die. Kinda sounding like the ignition switch circuit that energizes the relay coil.

It's been working all day today and yesterday. That hasn't happened in quite a while. I won't declare victory yet. I'm going to wait a week and if I get the CEL to turn on every time I will do my happy dance. Here's my theory of the problem:

The gutters on the right fender under the hood have been clogged for years as evidenced by the crud buildup behind the rubber cushions. The water goes someplace- right to the area of the main relay. This moisture rich environment promotes corrosion, not only of the MR's pins but the sockets in the connector.

By replacing the Main Relay and then removing it a few times to attempt diagnostics, the sockets in the connector got cleaned.

Now the truck starts. Every time.

Anybody know of a product to spray in the connector to prevent this from happening? I know WD-40 drives water away but it can't be that good of a conductor.