I have a 1991 F150 with the 4.9 straight six engine. Manual transmission. After the engine runs for a while, it will just shut off as if you had turned the key off. Then it will not restart. I check for ignition at this point and have none. I am using the spark tester that you put a spark plug wire to and clamp it to ground.
So far I have replaced the pickup coil inside the distributor, the module on the distributor, the coil, plugs, wires. None of this fixed it. If the truck sits long enough it will fire right up and the process repeats. Any ideas on a way to test this system? Thanks

 

pull the spout connector and then check for spark.

 

Ok I've located the spout connector. So I remove it then check for spark the same way I've been checking it correct?

 

Still have no spark with spout connector unplugged. Sometimes when I release the key when cranking it will start.

 

Maybe the ignition switch.

 

Yea that's what I'm thinking. Need to figure out how to test it

 

Hi,
I'm the first to want to test parts before replacing but....

On a 25 year old truck and showing certain signs.

If the part is not expensive I will replace with OEM/Motorcraft if available?

Saw this!

help with ignition switch - Ford Bronco Forum

 

It was the ignition switch. I found a table that showed which terminals should have continuity at the 4 different key positions. In the run position, I had high resistance between two of the terminals.

 

Hi,
Good deal!

I would buy a Motorcraft replacement...

Even if I had to order it!!!

 

Correction: An ignition switch did not totally resolve the issue. I replaced it with a new motorcraft switch but this morning the same problem showed up again. Still no spark. So I did more testing of the ICM, PIP, Coil, wiring, ground connections..... and eventually that led me to pulling down the engine computer behind the drivers kick panel. I removed the cover to look at the circuit board and found the problem. The capacitors had leaked out onto the circuit board and damaged it pretty badly in three places. I ordered one and I'm pretty confident this will fix it.

 

No spark with the SPOUT unplugged and the problem was the PCM?
See post #4 above.
Interesting.
I guess we will just have to stick with telling posters to unplug the PCM's plug with a no spark condition in the future.

 

From the wiring diagram I was looking at, pulling the spout connector doesn't completely isolate the pcm from the system. There shows to be ignition ground on one of the pins at the ecm and and also PIP on one of the pins as well.

 

Yes I know, that is why Randy A (rla2005) and I have always said to unplug the PCM but others seem to say just pull the SPOUT out to check for spark.
And pulling the SPOUT works most of the time.

The ground for the whole Ignition is located inside the Distributor.


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