Good morning all, looking for some advice on a 1991, F150, automatic, 5.0. The truck won't start, doesn't try to start, cranks fine.

Checked the resistance in the coil wire, it is good. (New wires)

No spark coming out of the coil while cranking (once I let off of the key I get a one spark, discharge, dang that hurts.)

I replaced the coil, same symptom.

I checked with a test light on the negative side of the coil to ground, I get a flashing light, the book says should be strong light. I don't know how to measure strong.

Pulled the distributor, took off ignition module, took to Advance, checked good. ( I did not check stator, since I had a flashing light figured it was working). Reinstalled distributor, at most one cog off, but all my marks lined up.

I tried to run self test (which I ran succesfully a couple of weeks ago when it was running), the self test will not start, check engine light does not come on the dash either.

I've read it might be the fuse for the PCM which is in the power distribution box, can't find box.

Any advice?

Thanks

 

try starting fluid.

the distribution box in in engine compartment.

i will post what fuse to look for after i go out to my truck.

ok, under powertrain control module, fuses: 9 and diode 12, and relay 1.

check fuse 22 also, it is a bunch of things.

 

On a 91, look for yellow Fuse Link (link N, hot all the time), and check your EEC Power Relay for hot at the red/lt.green wire for power in (from your ignition switch, check KOEO)

Thats a start.

 

Did you try replacing the ignition module?

 

he said he had it checked and it was ok.

i agree, it still could be the problem.

 

I found this online for eecIV No Spark Condition:

1. Loosen distributor holding bolt with ½" wrench, remove plug from coil, turn ign on, while holding the coil plug ~ ¼" away from the coil tower, rotate distributor left-right-left....if spark doesn't arc from coil to plug…goto 2...if spark arcs from coil to plug…check condition of distributor rotor and cap, replace and recheck.

2. Place ignition key in on, with the 12-vdc test light connected to a good ground, probe the (+) terminal at the coil (Red/Lt Green wire)...if test light is off ….the ignition switch or 20 GA fuse link might be the problem, need to trace power wire....if test light is on…goto 3.

3. Place ignition key in on, with the 12-vdc test light connected to a good ground, probe the (-) terminal at the coil (Tan/Yellow wire)...if test light is off….replace coil and recheck….if test light is on….goto 4.

4. Place ignition key in on, with the 12-vdc test light connected to a good ground, probe the (-) terminal at the coil (Tan/Yellow wire), rotate distributor left-right-left and check test light, if test light blinks….replace coil....if test light does not blink…goto 5.

NOTE: Rotating the distributor with the ign on, generates a PIP pulse, this will also activate the fuel pump relay and pulse injectors (system assumes startup logic).

5. Ign On, backprobe or disconnect TFI module, and check with test light, pin #4 (ICM Power)…if test light is on….goto 6…..if test light is off….TFI Ign On wire has an open that needs tracing and repair.

 

check the wires going to the fuelpump and ecm relay, my 88 had a pulled wire a p.o. put a screw in and it came out resulting in same problem as u. If the computer isnt getting power,the fuel pump wont run and i dont think there is any power to the ign or anything, cause u have no check engine lite and u cant run self test

 

I recently had a similar problem, replaced the coil and would have never thought the second coil was also faulty had it not been for the step by step process I posted above

 

Where is step 6?

 

damn, how'd that get lost...I'm at work now so I'll have to guess that it says replace ecm (i've never had to go that far) I'll check tonight and if it's something else I'll post it tonight....sorry

 

if u have no check engine light when u turn on key, and if u cant jump the self test to run fuel pumps, check those relay

 

I appreciate everyone's quick reply, I've been anxious to get home and check it out.

From what I've read I went with checking the relay's first. My relays are not in a distribution box, just laying on the drivers side fender well (someone didn't like it?)

On the relay with red/lt green (I'm assuming the EEC Power relay from schematic, there is 12 volts with key on. On the red wire (power to EEC?) there is only 3.4 volts. When I turn the key in the run position, I hear no relays "click" on. Bad relay? Can I jumper Red/lt green to red (without frying puter or anything?) <---to confirm bad relay

Update.....Looking at the wiring diagram it looks like once the EEC relay engages it fires the fuel pump relay with the red wire, so I wanted to verify the fuel pump relay was getting just 3.4 volts, it was. When I went to turn the key off I noticed the Check Engine light was on (which it hasn't been on at all). I turned off the key and back to run, light still on. I check voltage, red wire at fuel pump, 12 volts, cranked it, it started, I thought WTF?

Do relays get flaky? Do I have a bad wire? Should I replace the relay? Don't want to get stranded?

Thanks

Thanks for your replys.

 

thats what mine did. I checked over the wires cause they too were just laying there. noticed the drywall screw they had screwed into the plug. I think mine was a black wire. i just drilled out the plug and put a terminal i could plug in after the plug was installed till i find a replacment

 

Same symptoms, I replaced the distributor, problem solved. Had a roadside service guy go through the checks and tell me my module was OK also.

Good luck,


Dave