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1988 2.9L crank no start, no spark at coil.

Toskin

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Hey guys new to the forum, hoping I might be able to get some help with my crank no start problem.. I’ll start from the beginning..

i have a 1988 Ranger, 2.9L v6 with manual transmission. I initially had a crank so start problem, wasn’t getting fuel. I had tracked it down to being a loose wire going into the plug at the EEC relay causing the fuel pump relay to not fire. I got the plug fixed cleaned up all my wires and truck was running great.
One day, I fired the truck up to let it warm up. Left for 5 min, came back and it was off. I’ve tracked it down to now I’m not getting spark from the coil.

I did some tests at the ICM plug on the backside of the distributor, i probed the #4 wire with my ignition on to test the positive lead. I’m getting 12V. So then I did the same test at the #6 wire which is ground. Probed the wire with ignition on and I’m reading 4.09V. I tore the whole harness apart and found that the wire runs inside of what I think is some sort of insulated tin foil? With 3 other wires from the icm, which are also wrapped in a bare wire. I followed the insulated line all the way back to inside the cab next to my ECM. The ground wire and that bare wire both end up in the cab by the ECM. The bare wire ties into the ring terminal with the ground cable. I cleaned up where It grounds out inside the cab. And probed the wire closer to the battery near my eec relay. And I’m still reading 4.09V

I’m wondering if I’m okay to run a new wire 3” or so from the ICM plug straight to my battery or to a good ground inside the engine bay? And how crucial is that bare wire? The bare wire doesn’t connect to anything near the ICM plug, just cuts off where the insulation stops. It doesn’t appear that there is any other grounds that tie in with the one from the ICM that goes to inside the firewall.

I’m not the greatest with wiring, trying to wrap my head around it. Thanks in advance to anyone that is able to give me some advice or guidance. Owned this truck for far too long with it only running for like a year and a half collectively for me lol.

Thanks again, Justin
 

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franklin2

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There are some very sensitive signals that go to and from the distributor to the computer. That tin foil is shielding these wires from all the noise the ignition system makes. DO NOT ground this shielding on both ends. It should be grounded on one end only. Don't even let the tin foil lay against the engine or anything metal, neatly wrap it and insulate it and let it be grounded only on the one end.

What happens if you ground it on both ends? It's called a ground loop. Some grounding points can be better than other grounding points. If you tie these different grounding points together, a small current can develop in your shielding. This causes noise in the shielding which you don't want.

I know you are doing the right thing and checking your wires and checking voltages. But the TFI module on the side of the distributor has a terrible reputation in the reliability department. So bad, that I would just change it and see what happens. If it doesn't fix it, you can at least have a spare in the glove box. If it hasn't gone out yet, it will eventually.
 

Toskin

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Thanks for the well detailed reply. I figured there was a good reason for the tin foil haha, my next question would have to be.

Because there is such a weak ground through that wire. Would it make sense to pick that wire up from somewhere near the passenger side fender well and make a new ground for it? I did take all the tin foil off to inspect the wire. But considering I’m not getting a strong ground would I be alright to splice a new wire on somewhere in the engine bay and say attach it to the battery or something?
The ICM I have on there is relatively new.. I did replace my entire ignition system a few years ago. (Truck only ran for like 3 months since then) would it be worth it to try and sort out my grounding issue first before throwing the parts at it? Would it hurt to splice in a temporary ground even near the plug itself just to see if that it my problem?

Thank you for the reply, Justin
 

franklin2

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If you wanted to run a new ground wire from that point near the ECM where the shield wire is bolted, and run the new wire all the way out to the battery negative, that would be a ok repair. Running a extra ground wire anywhere else along this shielded assembly is a no no.

It would not be unheard of to have a bad ground to the cab. The cab is mounted on rubber body mounts. The main large ground goes from the battery to the engine block. The engine has rubber mounts, the transmission has a rubber mount and the rear leaf spring bushings are rubber. So there are some important grounding wires here and there.

As I am writing about this, it just occurred to me you have a important computer ground out at the battery. There should be a smaller wire coming off the large battery negative wire, it will run through a connector and then disappear into the computer harness over there. This ground wire and it's connector is notorious for giving trouble because of it's proximity to the battery.
 

Toskin

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Okay I gotcha, so if I was to run a new wire I needs to go back to the same spot through the firewall and connect next to the computer.

I’m going to attach a photo of the ground I think you might be talking about. Don’t mind the rats nest of wires right now lol. I have my ground wires on my battery running to a shut off switch cause my keys are stuck in the ignition (my back yard immobilizer) I did have to splice that wire and connect it to the my shut off. Would that identically cause a bad ground reading to the wire that runs directly to the ICM plug?

My index finger is on the wire I believe you are talking about. I was just about to try testing the ground spot itself That the wire from ICM is running to beside my computer right now and see if I’m still getting the same 4.09V reading
 

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Toskin

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I will rip that electrical tape off and check out my connection aswell after I do this test
 

Toskin

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Okay, so this is a little bizarre… I checked probed the wire just down from where it connects for the ground inside the cab. I was reading 12V I came outside the cab, probed, was reading 12V disconnected the ICM plug from the ICM, checked at that point. Got between 3.95-4.10V.. plugged it back in and I was reading 12V at the plug.. still crank no start no spark.. I don’t understand why, when the plug is off, that it’s not reading the 12V..

I also probed the wire on the backside of my connection cause I have it heat shrinked together. And was also reading proper voltage there. Would this mean that the ICM must be the culprit..?
 

franklin2

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If I am reading your post correctly, the ground screw by the ECM is good if the large wiring plug is plugged into the computer. It's not good if the computer is unplugged. It almost seems like you do have a bad cab ground and the ECM harness ground is grounding the whole cab. That would not be very good and can lead to some melted ground wiring. Why don't you try your experiment and run a temp ground wire from the screw next to the ECM to the battery ground under the hood and see what happens.

I know you are having security problems right now, but it's not great that you are powering down the computer each time you open your anti-theft switch. That means the computer has to wake up and try to re-learn everything each time it's started. It can do it, but it may make it run a little weird each time you start it (when you get it running).
 

Toskin

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I’ve had the computer plugged in for all my tests I’ve done. I’ve only been unplugging it from the ignition control module. When I have the module hooked up with the key on I read 12V at the ground, when I unplug my ICM I read 4V.

So to try my test out, you are saying to add a wire from inside the cab out to the important wire that goes to the computer to the battery? Or should I be splicing in a new connection and run a whole new wire from inside the cab out to the plug at the ICM?

I will also take my shut off plug out for the rest of my tests that im doing, and see if I can maybe figure out how I would wire in a switch to my ignition maybe
 

Toskin

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So I tried my theory out, I ran a wire from the ICM to the ground near my rad support. Tested to see I was getting 12V first with the key on. Which checked out. Tried to turn it over and nothing. I also replaced the ICM itself with a brand new one.
 

edj

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Toskin, I had a similar problem with my electrical... As Franklin2 mentioned in his excellent reply on grounding connections and the foil wrap, there is a single small gauge wire connected at the negative battery terminal. This single wire has another connector before it disappears into the harness and that is responsible for a number of other grounds (up to 4 or 5 according to an electrical schematic I have for the Ranger). That small connector at the battery terminal was bad and when I replaced it with a good connector, that solved my problem.
HTH
 

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