OK, got a 91 f-150 5.0l 2x4 auto.
6 months ago I installed a factory reman ECM due to alot of issues that ead back to a bad brain box. Truck ran great like it always has. Ran it for about a month and had the ignition switch and key tumbler go bad on me. Replaced both of em(done it many times in it's life) and everything was good. A month later I pulled into my driveway one day and shut it off as usual. Next morning I got in it and it wouldn't start(hopped in my other truck and put it off till later). Well now it's later and I'm trying to bring it back to life(yet again).

KOEO- the check engine light stays on as does the battery light...fuel pump runs like normal a few seconds and then shut's off.

Trying to start- lights stay on, engine turns normally but it won't hit.

I've shot it with ether but got no response, you can smell the fuel being injected and the injectors are firing according to the noid light.

I have zero spark at the coil. The coil's resistance checks OK on primary and secondary, Voltage checks out ok except- when trying to start- the voltage on the coil input isn't intermittant......it's steady at 12V.

I haven't checked nor changed the TFI module on the dizzy yet.

To add to it- I have no accessory power with the key to the back. I never did have it after I changed the switch an tumbler....but it started and ran for a month.

I can't get any codes from the ECM manually nor through my scanner.

So, start at the TFI.....PIP.....or the ignition switch and tumbler(again) Is what I'd like ya'lls opinion on. Or maybe somwhere else I haven't thought of???

Thanks for the input and reading this mess, ANG

 

Try testing with a known good coil. I had a coil go bad that way once.

 

I would have said bad coil plug, they do that.


But you say the CEL stays on all the time so pull the SPOUT and see if you get fire from the coil.
Does your test light flash at the coil while it is cranking?
If it flashes and you get spark with the SPOUT out it would sound like the computer.


If still no spark unplug the EEC computer and see if you get spark.
The Computer can not stop the spark if it is unplugged.


Not able to pull codes, CEL on sounds like another EEC Computer.
I do not understand why you are getting the injectors firing while it is cranking.
This would mean the computer is seeing a PIP train from the distributor (the PIP does not come from the TFI but is in parallel with it).


The battery light will normally be on while cranking.

 

Well I got it to hit and run today.....Pulled he coil off my 88 bronco and swapped em out........still no spark......pulled the TFI module off the brinco and swapped and it started and ran like normal.

New issue- I drove it to my shop and aired up the tires and topped off the fluids. Cleaned out the bed and washed off the exterior. Left the shop and went and got some gas and some lunch.....I drove it about 28 miles or so total today.....after I got back to the shop I pulled up to the door and out of nowhere-----The check engine light came on, idle started fluctuating, and the rpm was very sluggish to throttle response. Looked at the exaust and could see and smell it was very rich. Neither of my scanners would comunicate with the ecm...so I couldn't pull the codes.

Now last time this happened it was the exact same symptoms that finally lead me to the ECM(I was able to get codes from that ecm though)....So I am lead to think I have yet another ECM issue....and if that be the case, WHY????

What is eating the ECM?.......what do ya'll know of that will kill one.

I want to know of things that could potentially kill the ecm, but know that I do not plan on getting an ECM for it this time.....I said last time if it happened again that I would convert it to mass air and perhaps get a tweeker set up for it...But I don't want to spend that money and have the new system damaged or ruinedby somthing else that could be causing this.

On a side note, the only electronics that have ever been messed with on this truck is a radio swap.....I am the second owner and the original owner I knew, and know that he did nothing but drive it. That doesn't mean that I might not have a wiring issue that is shorting the ecm, but that's not where I would start to diagnose it.

 

Well lets see, what can kill an ECM Computer.

1. taking the battery cable off while it is running or anything that would make and brake the battery connection.

2. Something shorting the VREF (5V) wires.

3. If it is a rebuilt maybe they did not fix the problem it came in with.

4. Old caps in the ECM's 5V supply (if you got it from a salvage yard or they were not replaced when it was rebuilt).

5. Alternator runing away with itself (voltage going to high, maybe the "A" wire not making good contact with the B+).

6. Unplugging the ECM with the battery still on (not very likely, I do this all the time while testing computers so I do not have to reset the radio and have not lost one yet but I do have two extra computers for each truck).

 

I was think trying to think of any of the sensors or actuators that could kill it if they shorted or went bad......But They are supposed to built so they don't do that if they go bad....can't think of any?

I would figure there is somthing in the computer.....Supposedly, I bought the very last ecm with that fuel code in the national system according to my dealer. It was a factory reman, and he told me not to mess it up cause he couldn't get another one...supposed to be disscontinued by ford. Not sure whether to beleive it or not, really.

So Bill, know anything about mass air conversion using parts from a pony car or a T-bird?

Not sure which route I'll take yet....the above or fork out the money for the new kit.

 

No I do not know anything about that. I only work with stock Ford Trucks and I have no information on conversions.
Sorry.

But MustangGT221 & Conanski seem to know a lot about this so you might PM them.
They will not let me PM for some unknown reason.

 

How's the power to the ecm? It goes through a relay. Might be intermittent, or dropping voltage on the + or ground side.

Just something quick to check before doing an ecm. Voltage problems could definitely look like a bad ecm.

 

ag,
a couple things to consider. i once had a sluggish response to my throttle as well and mines seems to have a few of those same symptoms as well. one of my first problems was that i had a bad throttle position switch, once a local shop changed that out the difference was AMAZING. also now when it does, i am not positive, but i'm pretty sure its due to water in my gas. tank has a slight leak and even the SLIGHTEST bit of water gets in power drops DRAMATICALLY....i have recently used the STP water remover (comes in a yellow bottle) and everything works itself out ok. not exactly the best cure, but it does work (as per the cost of a new tank,paint, and such). good luck

 

Have you not heard of the water injection system to gain power?

 

I think my eec just took a dump after 2 years of service , though mine was a reman from PartsAmerica...aka Advance auto! but i just ordered a nother one. because they are the cheapest ive found to supply a Mass Air 5.0 E4OD. (WAY1 /f5tf-12A650-JB)