I can use some help troubleshooting a mysterious ignition problem.

I have an ’88 F150 4.9L that just died while cruising along the freeway. There was no warning or sporadic behavior, it just died as if you’d turned the key off at 60mph.

After getting it home and checking things out, we found that there was no spark coming from the coil. Ran some of the tests described in the Haynes manual and became convinced that the ignition control module was the culprit.

Replaced the icm and tried firing it up. Still no spark. A few hours later replaced the coil and tried it again. Still no spark.

Of the various diagnostic checks, the one thing that is not checking out is the icm supply voltage check. The voltage at pin 2 of the icm wire harness measured 4 volts rather than 10-11 volts (the pin 2 corresponds with the wire connected to coil TACH).

I am at a loss of what to do next. Have any ideas ?

 

Maybe a bad ignition switch? THere was a recall on them in the late 80's and early 90's.90% of the time it is the ignition module, They fail because they are mounted on the distributor and get too warm. Ford changed the location in 92 to the fire wall. My dads 87 bronco went thru 3 of them in 180,000 miles. They all did the same thing, Just dies. They are $45 bucks a crack at the parts store. He kept one in the glove box at all times

 

You might want to check the pick-up coil which should be located in the distributer. My 88 mustang had a similar episode but the ICM was new. The shop found it was the pick-up coil. Sometimes it is cheaper and easier to just by a neew distributer with the pick-up coil already in it. You might want to test it and then check the prices of parts.
Hope this helps

 

Is it possible that you have reversed the module connector? What you think of as "pin 2" may be the SPOUT signal instead of the "TACH" signal. +4 volts is not an unreasonable value for SPOUT with the truck not running. Try removing the SPOUT jumper and checking the module connector again. If the voltage changes, you have the wrong wire.

The signal labelled "tach" on the TFI (aka icm) module connector runs directly to the coil negative lead. Whatever you see on one end of that wire should be the same as the other.

Pull the gray connector off the TFI module. Turn the key on. Don't attempt a start. Measure the voltage at the coil. Both sides should be +12 volts. If you have +4 volts at either lead of the coil, there is a problem with the wiring.

Probe the gray connector. The TACH wire should be +12 volts, the same as the coil. If it is not, the wiring is bad.

Turn the key off. Plug the gray connector back in. Turn the key on. Probe both sides of the coil. It should STILL be +12 volts on both sides.

Check all your grounds. Bad grounds can cause the TFI system to quit even through the starter spins over fine.

92supercab is right that the pickup coils have been known to fail as well. Without a press and experience it will take you 1 to 2 hours to change the pickup coil. For $50 more than the cost of a new pickup, you can buy a rebuilt distributor with the pickup already installed. Make sure you get the correct distributor gear on a replacement. A truck sof this model year hould have a cast iron gear, not the more common steel gear. Best to pull the old distributor and bring it to the parts counter if you don't know how to tell.

 

I had the same problem and replaced EVERYTHING including computer before I discovered that a hot wire in the harness had corroded to the point I would show 12v but the wire would not pass any current. It was a red/green wire beneath the under the hood fuse box, the break was at a junction where the single wire from the coil split into 3 wires. All I can conclude is that the wire was cut halfway through from the factory because the harness has never been apart. If I had run a jumper from the hot wire on the module to the hot side of the coil to battery it would have started right up.

 

I am throwing in with a couple of the guys that have answered you so far, I'm betting that it is the TFI module. I had that problem happen to me twice on my 1987 F150 in the course of 300,000 miles. Just last week I got an official FORD TFI MODULE CLASS ACTION SETTLEMENT REIMBURSEMENT CLAIM FORM. All I have to do is run down repair records and receipts from 12 years ago and they will send me some money. It was a common problem on that series of trucks.

 

I would check out the PIP sensor in the dizzy, I changed mine out a while back when I was having stalling/dieing problems. It would switch off on the highway like someone had a remote. After ten minutes it would be fine like nothing happened. Search for my thread on pip and you'll find a bunch. It's only a 20$ part and kept it from running. The book didn't have much on how to test it. I used a spark light off the dizzy primary, and when it stalled was getting no spark. Ten minutes later, spark was fine. After replacing the PIP pickup, never stalled on the highway again.
I had to use a 5k lb gear puller to get the dizzy drive gear off, and make sure you don't bend the dizzy wheel sensor part when you're takin it apart.

 

A tip for putting the distributer gear back on is to heat it up with a torch or the stove in my case, then the gear will slip right on, you just have to be fast about it because if it cools to much before you have the roll pin hole lined up it will freeze in place causing you to have to use the puller to get it off again.