PCM Swap Out...
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Joined: Jun 2006
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PCM Swap Out...
I think I am fighting a bad Powertrain Control Module issue.
I drive an 88 F250 with the 300 6cyl. It's a 2WD with fuel injection. When it's running, I really love my old farm truck.
Well, Tuesday morning it stalled out and died just like someone had cut the key off and it would not start again. It would crank and crank just fine, but it never cuaght fire and started. Fuel and air checked out fine, but there was no fire to the plugs. A buddy of mine told me that the Ignition Control Module often caused this problem in older Ford Pick-ups. I changed out the ICM and tested the old one. Sure enough the old one was bad according to the tester machine at the auto parts place. However, the new ICM did not fix the problem. I thouhgt it might be the pick-up module inside the distributor that the ICM plugs into. I even bought one, but I stopped short of installing it.
When I tested for spark from the coil wire to the distributor, I found that it was not firing there either. I checked the voltage on the leads to the coil and they have the full 17-18 volts of juice. I've also checked the fuses under the dash and the inline fuses next to the relay mounted on the firewall.
Now I'm thinking that I'm looking at a Powertrain Contorl Module that might have gone bad. I priced one, but I don't know how much trouble they are to change out. Shucks, I don't even KNOW where the thing is mounted!
Is changing out the PCM a big hairy deal or can Joe Average pull it off? Has anybody done this that has lived to tell about it? Any pointers?
Thanx,
Duece
I drive an 88 F250 with the 300 6cyl. It's a 2WD with fuel injection. When it's running, I really love my old farm truck.
Well, Tuesday morning it stalled out and died just like someone had cut the key off and it would not start again. It would crank and crank just fine, but it never cuaght fire and started. Fuel and air checked out fine, but there was no fire to the plugs. A buddy of mine told me that the Ignition Control Module often caused this problem in older Ford Pick-ups. I changed out the ICM and tested the old one. Sure enough the old one was bad according to the tester machine at the auto parts place. However, the new ICM did not fix the problem. I thouhgt it might be the pick-up module inside the distributor that the ICM plugs into. I even bought one, but I stopped short of installing it.
When I tested for spark from the coil wire to the distributor, I found that it was not firing there either. I checked the voltage on the leads to the coil and they have the full 17-18 volts of juice. I've also checked the fuses under the dash and the inline fuses next to the relay mounted on the firewall.
Now I'm thinking that I'm looking at a Powertrain Contorl Module that might have gone bad. I priced one, but I don't know how much trouble they are to change out. Shucks, I don't even KNOW where the thing is mounted!
Is changing out the PCM a big hairy deal or can Joe Average pull it off? Has anybody done this that has lived to tell about it? Any pointers?
Thanx,
Duece
New User
Joined: Feb 2005
Posts: 9
Likes: 0
I had a similer experiance with an 87 150. it turned out to be a bad connection from the computer relay to the computer. the computer was only receiving 5 volts. the mech that repaired it siad it was fairly comon. Dan.
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Fleet Owner
Joined: Aug 2005
Posts: 23,666
Likes: 301
From: Easton,Ks
I would not go after the PCM yet. Pull out the SPOUT jumper and take your test light and place the point on the NEG (TACH, -) side of the coil. Crank it and see if flashes.
Franklin2 said this in another post but it seams to fit here for no spark.
“The first thing I would check is voltage at the coil + terminal. Before you go on a test run, get the wiring prepared so you can probe the + wire of the coil, with a good clean place on the engine block to hook the ground for the meter or testlight.
The next test would be to probe the negative (or "tach") terminal of the coil. Put the probe on the - terminal, and put the negative of the meter or testlight on the clean engine ground.
The coil is the last part of the ignition system besides the sparkplugs and sparkplug wires. What you are looking for is around 12 volts on the positive of the coil when the key is turned to run, and also when the key is in start.
If that is ok, then do the negative coil terminal test. What you should see here is the testlight or voltmeter blink on and off when the engine is cranked.
If you have + voltage at the coil, and the - of the coil voltage is blinking, then you should have spark”
Franklin2 said this in another post but it seams to fit here for no spark.
“The first thing I would check is voltage at the coil + terminal. Before you go on a test run, get the wiring prepared so you can probe the + wire of the coil, with a good clean place on the engine block to hook the ground for the meter or testlight.
The next test would be to probe the negative (or "tach") terminal of the coil. Put the probe on the - terminal, and put the negative of the meter or testlight on the clean engine ground.
The coil is the last part of the ignition system besides the sparkplugs and sparkplug wires. What you are looking for is around 12 volts on the positive of the coil when the key is turned to run, and also when the key is in start.
If that is ok, then do the negative coil terminal test. What you should see here is the testlight or voltmeter blink on and off when the engine is cranked.
If you have + voltage at the coil, and the - of the coil voltage is blinking, then you should have spark”
Mountain Pass
Joined: Feb 2003
Posts: 136
Likes: 3
If it does indeed turn out to be a bad ECM, then, and this is assuming its in the same spot as my 92, it is locaed on the drivers side firewall. Youll first need to remove the wireing harness from it(10mm, as you turn the bolt it backs the wires off of the pins.) Once you get the wires off theres two nuts, and then its just a matter of slipping it out. You may, however, have to loosen remove the plastic wheel well cowling, as it may be in the way. It is definitely a DIY job.
