Newbie with a no start

[942dr]

ok, so i have a 94 4.0 4x4. it has been randomly dying on me, and starting up again an hour later.

Well, i have traced EVERYTHING down. when it dies, i have no power at the PCM, hence no power to FP or INJ. well, here is what i have checked

I have power at the #14 diode,30amp fuse. i have power at the red/lg wire coming from the ignition switch, and have power at the coil, when the ignition is on.

i have no power at the FP. MAS, PCM. Im not sure where to look, ive done looked at so many diagrams its driving me nuts.

 

[942dr]

well, silly me. i just realized the ICM isnt built into the coil packs, im assuming this could be an issue if it isnt bolted down, and just zip tied to the radiator support

 

[MrShorty]

Except that a problem at the ICM would not normally prevent you from having power at the PCM, fuel pump, or MAS.

If I were in your place, I'd probably focus my diagnosis at this point at the EEC relay -- make sure it has power, and it is closing when the key is on.

 

[942dr]

Except that a problem at the ICM would not normally prevent you from having power at the PCM, fuel pump, or MAS.

If I were in your place, I'd probably focus my diagnosis at this point at the EEC relay -- make sure it has power, and it is closing when the key is on.

well see, heres what it does. it will fire up fine in the mornin when its cold. if it sits in the sun all day, it wont start, if i drive it, it will run for 20 mins or so, it will die. have to wait for it to cool down again. then it starts right up most the time, sometimes it will take a day before it starts again, but when it does run, it runs flawless

i already replaced the crank sensor, just to be safe.

and i put a new EEC relay in it.

 

[MrShorty]

and i put a new EEC relay in it.

But have you verified that the EEC relay has power and is closing?

 

[942dr]

But have you verified that the EEC relay has power and is closing?

No i havent, not while it wont run. i understand how to check for power, but how do i check to see if its closing, and if it doesnt have power, or isnt closing, what would i be looking into?

 

[MrShorty]

but how do i check to see if its closing,

Basically the same as checking for power to the relay. Move the meter lead to the "downstream" wire after the relay and see if it has power with the key on. If there's 12 V immediatelyt upstream of the relay, but significantly less than 12 V immediately downstream of the relay, then it is not closing. If it's not closing, then we need to look at the wiring between the ignition switch and the relay to see why it isn't closing.

If it isn't getting power, then we need to continue probing upstream between the battery and the relay to figure out where the break in the circuit is.

 

[942dr]

OK, so i tested the eec circuit, i have power, i have ignition power, it is closing. and i also now have power at the PCM. But still no fire.

no fuel pump and no spark

 

[Gadget X]

could it be a problem with your ignition switch? Just a thought.

 

[MrShorty]

OK, so i tested the eec circuit, i have power, i have ignition power, it is closing. and i also now have power at the PCM. But still no fire.

no fuel pump and no spark

I don't know if you are still following this. I've been away a couple of days.

So, you have power at the PCM, but no spark and no fuel pump. One thing these two have in common is the crankshaft position sensor signal (CKP) that is fed through the ICM to the PCM. Have you tried pulling codes (in particular looking for a CKP type code)? Have you verified power at the ICM? Ground at the ICM? CKP is a basic hall effect sensor -- can you verify that the CKP is functional?

Along the way, can you verify that the fuel pump relay has power and is closing?

 

[942dr]

I don't know if you are still following this. I've been away a couple of days.

So, you have power at the PCM, but no spark and no fuel pump. One thing these two have in common is the crankshaft position sensor signal (CKP) that is fed through the ICM to the PCM. Have you tried pulling codes (in particular looking for a CKP type code)? Have you verified power at the ICM? Ground at the ICM? CKP is a basic hall effect sensor -- can you verify that the CKP is functional?

Along the way, can you verify that the fuel pump relay has power and is closing?

yeah its not a DD, so i gave up on it for a few days, lets my mind unravel from all the wire tracing lol.

CKP is new. just replaced a few days ago. does the same thing before and after. i have no verified power at the ICM, thats where im stuck, i cannot find any wiring diagrams for it, none that are worth a crap anyways. But yes, CKP is fine. and i have power at the ECM, but no spark and no fuel. i have no checked fuel relay for power and closing yet. that was my next step. im getting back into it tomorrow afternoon

 

[MrShorty]

Have you tried the diagram in Chiltons? I've found it does a pretty good job for the basic engine management wiring (including ICM power at pin 8 and ICM ground at pin 9).

Another quick test that occurred to me: does the fuel pump relay close if you ground the fuel pump test lead (short end of the trapezoidal self-test connector)?