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1988 Ranger 2.9 bad ICM?


PowerRanger

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Update:
TFI is getting power and ground. So next I moved onto testing the wire that sends signal to the ignition coil, according to the site I'm reading from, my test light should blink on and off when I crank the engine, however when I attach the test light, the light stays on. And when I have someone crank the engine, it turns off and does not flash at all. What's going on?? I double checked to make sure I'm testing the correct wire (second from the bottom of the harness) and I believe I'm doing it correctly. Any one have any input? This is a brand new TFI module btw.

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PowerRanger

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Update: I put the original TFI back on. I am now back to getting some spark, only when I first turn the key and when I let off the key. The new TFI module didn't make the Ign Coil spark at all so I'm concluding that it was bad. Could my pick up coil be bad?

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Last edited:
adsm08

adsm08

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PowerRanger said:
Update: I put the original TFI back on. I am now back to getting some spark, only when I first turn the key and when I let off the key. The new TFI module didn't make the Ign Coil spark at all so I'm concluding that it was bad. Could my pick up coil be bad?

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Click to expand...
The pickup could be bad. In my final years of 2.9 ownership I had taken to replacing the TFI, coil, and pickup as a set after finding that replacing only a single component seemed to be leading to reduced life of all three.

However, the way this system works is pretty simple.

The coil gets power when the key is on. It gets it's ground through the TFI module. The TFI switches the ground based on signals it sees coming out of the pickup.

The coil, when it has a complete circuit, builds an EM field around it's windings. That field collapses when the circuit is broken, and the EM field collapsing and rushing over the secondary windings is what creates the high voltage spark used by the plugs.

If you have a constant ground to the coil it may spark when the key is turned on and then again when it is turned off without the need to crank the engine to produce a spark.

The next thing I think I would do is get a small bulb in a socket and hook it up to the coil's wires. It should glow dimly and kinda pulse a bit as the engine cranks. If it is on full time with the key on you have a problem with the coil's ground.
 
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PowerRanger

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adsm08 said:
The pickup could be bad. In my final years of 2.9 ownership I had taken to replacing the TFI, coil, and pickup as a set after finding that replacing only a single component seemed to be leading to reduced life of all three.

However, the way this system works is pretty simple.

The coil gets power when the key is on. It gets it's ground through the TFI module. The TFI switches the ground based on signals it sees coming out of the pickup.

The coil, when it has a complete circuit, builds an EM field around it's windings. That field collapses when the circuit is broken, and the EM field collapsing and rushing over the secondary windings is what creates the high voltage spark used by the plugs.

If you have a constant ground to the coil it may spark when the key is turned on and then again when it is turned off without the need to crank the engine to produce a spark.

The next thing I think I would do is get a small bulb in a socket and hook it up to the coil's wires. It should glow dimly and kinda pulse a bit as the engine cranks. If it is on full time with the key on you have a problem with the coil's ground.
Click to expand...
Juat to make sure i read it right, the coil grounds through the TFI, so if should find that I have constant ground ( the tiny bulb would stay on and also flash a little when I crank the engine) how should I go about repairing my ground connection? Would I need to trace back the ground wire from the TFI? Should replace the TFI again and have it tested before I install it to ensure it actually works?

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adsm08

adsm08

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Right, the coil gets ground from the TFI. The easiest way to test the wiring, if you should find a constant ground, would be to unplug the module and see if it goes away. If it does the module, or the pick up are shot.

If it doesn't the wire is chaffed through and grounding somewhere. Can't hurt to have the module tested.
 

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adsm08 said:
Right, the coil gets ground from the TFI. The easiest way to test the wiring, if you should find a constant ground, would be to unplug the module and see if it goes away. If it does the module, or the pick up are shot.

If it doesn't the wire is chaffed through and grounding somewhere. Can't hurt to have the module tested.
Click to expand...
I tried this test as you mentioned above. The light did not come on. I did it with the wires unplugged from the coil. Did I do it right or should I reconnect the wires and back probe the connector? Sorry for all the questions, trying to learn as I go.

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adsm08

adsm08

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Dillsburg PA
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2WD / 4WD
4WD
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31X10.50X15
You did it right. It doesn't really matter if the coil is plugged in or not.

I used to do it with a test light hooked to the battery + and the coil unplugged.
 
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