Hey fellas,

So I have another thread about getting my truck running and I've been getting *great help*, but it's getting long and the more and more I read threads on here the more I *think* that my PCM is the culprit behind the no start condition and I'd like to just cut to the quick if I can.

So here's why I think that it is bad.

Symptoms:

1. Engine Cranks, won't start
2. No spark
3. No Fuel
4. Check Engine Light is on

Things checked:

1. Engine Codes w/OBD-1 Reader - get nothing at all
2. Power to Coil - Check
3. Flashing 12v Power to Coil - Check
4. Spark Tested coil tower - No Spark
5. Replaced Coil with new coil - Check (Can't check if it sparks now as I'm by myself and can't see the spark tester)
6. Unplugged PCM to check for spark - No spark with old coil, but can't verify bc I can't see the spark tester when cranking it by myself...bugger
7. Jumper from EEC to ground to check fuel pump - relay just clicks
8. Inertia Switch not tripped - Check
9. Removed PCM and took apart - No signs of popped caps or scorches or the like - Reinstalled

Need to check:[LIST=1][*]12v power to fuel pumps (dual tank)[*]Replace Fuel pump relay to verify it's not bad[*]Fuel pumps could just be bad I reckon[*]Get a buddy to check if I have spark at the coil tower[*]Unplug PCM and see if I have spark

Alternate Option:

• Push the darn thing off a cliff

Thanks for reading fellas!

 

You're on the right track. Get a buddy and check for spark but also have your buddy spray in some starter fluid in to the intake to see if it will start that way....then you know it's a fuel issue. You might want to check the fuel pressure, and the distributor and Pip too. Oh, and don't push it off a cliff.

 

I've checked spark by myself before. 1st off, make sure you're not in gear, parking brake on. Then get a new plug and stick it on a ground source. Don't touch any metal on the spark plug (unless you want to feel the power of the spark lol) Have the ignition ON then take a big insulated screwdriver and touch the two posts on the solenoid together. I know it's redneck, but I had to by myself before

 

Matt,
Go to harbor freight and get a remote starter it is like 8 bucks then key on hook one lead to positive battery and pull the small boot of the 12v from the key on the coil attach other lead and press button, voila you can test spark by yourself!


Brian

 

Thanks Bink! My buddy and I will be working on it this Sunday. He and his dad are quite adept so I having a good feeling that we'll have narrowed down the issues come Sunday night. She's safe from the cliff for now...I live in the DFW area so I'd have to have an expensive towing bill to find any suitable cliffs...

I've been whacked my a spark plug before as well...not something I care to experience again

Brian, will do. I need very little reason to go to Harbor Freight and you just gave me a good'n!

 

Explain this one.
The 12v Power to Coil does not flash and comes from the Ignition switch on the column.
The ICM does ground the other side of the coil to ground off and on to fire the coil.

Explain this one also.
What do you call an EEC (ICM, Computer, Test-Plug)?
If you are saying you grounded pin #6 of the self-test plug and the fuel relay clicked and the fuel pumps did not run it is not the PCM/EEC Computer.
If so by it clicking you have proved the the PCM/EEC Power relay is made (picked) and giving power to the coil of the fuel pump relay.
Did you have power with a loading test light at the Inertia switch while the fuel pump relay was picked (made)?

 

Just a thought ........... Check the Neutral Safety Switch, black triangle switch located on the transmission. If not making contact/working won't start. Since the starter turns over maybe not.

 

Subford - I'm certain I'm using the wrong terminology for it and admittedly I was trying to follow along as my buddy was doing the diagnosing, but what I can tell you is that we proved that at the two wire connector that plugs into the coil one of the wires has a constant 12v power source with the key on and the other had a flashing signal 12v when the engine was cranked. I believe this was the wire that receives the signal from the ICM to tell the coil to spark, thus proving the ICM and the PIP sensor are functioning - is that the correct summation?

When I stated the EEC what I was really referring to was the plug where you connect the OBD-1 reader.

This is the test I did:

Again, just so I clearly understand what you stated - because the relays clicked when I did the self test that proves that the PCM is still functioning? If that's the case, why am I not getting any codes off the OBD-1 reader? The CEL is on and, since it's not running, I'd have to suppose that there are a *few* codes?

My buddy did have a Snap-On brand powered test light and he did test the Inertia switch, but I can't honestly remember if we did it while trying to pick (close?) the fuel pump relay circuit. That said, I can do it on Sunday when he's back over.

Can't hurt to take a look, but since I have to push the clutch in to get it to crank I'd assume the safety switches are functioning?

As always everyone, I greatly appreciate your time and feedback!

S/F,

-Matt

 

[QUOTE= Can't hurt to take a look, but since I have to push the clutch in to get it to crank I'd assume the safety switches are functioning?

As always everyone, I greatly appreciate your time and feedback! [/QUOTE]

Never mind I was talking about an automatic transmission neutral safety switch yours is a manual ......... Carry on.

 

Yes that would say that the PIP and the ICM are functioning.
No, when you ground pin #6 of the EEC test plug and turn on the key you are bypassing the PCM Computer. It states nothing about the PCM Computer.
The stored codes come from a running operation. The first part of the self-test (KOEO) is an electrical test of wiring and sensors. It will not give the fuel pump codes that dying fuel pumps do with an running engine.
Note that with the pin #6 not grounded or shorted to pin #2 the power at the Inertia switch will only be there for one second each time you turn the key to the on or run position.

 

good to go

Ok I understand now, thanks for the clarification! Is there any way to do a test on the PCM or am I being dense and not understanding that the previous tests we've done indicate the the PCM is functioning?

Fantastic, thank you!

 

If you are having problems not having fuel pumps running or not getting spark just leave the PCM Computer unplugged.

Then.
Crank the engine and check for spark if the problem is no spark and if you have spark now the PCM Computer is more than likely bad.

Or.
If it was non running fuel pumps that was the problem ground pin #6 of the EEC self-test plug or short it to pin #2 and if the fuel pumps now run with the key in the run position the problem may be the PCM Computer or no ground or power to the Computer.

 

Ok, so I just bought a new battery. With the new battery when I jump the fuel pump the rear pump kicks on but not the front.

i also bought a remote start so I can crank the engine without help. When I did it the first time the PCM was connected but the key was not in the ignition. Result was no spark. I put the key in the ignition (on) and cranked again, still no spark. I unplugged the PCM, still no spark. I also bought a harbor freight logic probe. At both connectors with the key out I get a green LED. I tested with the multimeter and I'm getting 0v at both. With the key on, I get 12.2v at both the white wire (steady) and 12.2v at the red/green wire (steady).

I'm thinking I need to recheck the ICM again. Good news though, now I smell fuel...

 

I have never heard of anyone using a logic probe on a truck. I have a logic probe but use it on TTL circuits to test for highs and lows.

You need a loading test light and not an LED test light to check the power at the Ignition Coil.


/

 

Subford, I definitely chose the wrong light...I was thinking I was getting something similar to what my buddy had; I'm clearly still learning the ropes when it comes to the electrical side of things. I do have a test light and can repeat the procedure it with it. The light should flash when the ignition is on and engine is cranked when testing at the white/tan wire correct?

Do you know how I can check for power or ground at the PCM?