6.5 won’t start

[MrMarty51]

Somewhere, in the 6.5 diagnostics to threads, there's information on what voltages are to be read on the PMD harness. Going to & coming from the PMD.

On the 1994 I made a T harness to red the volts going back to the IP. - I don't like to prove.

When I plugged that harness in. The truck ran and I found out I had a pin in the harness connector, not making contact in the harnesses I had tried previously. I still think it weird that the pin lost connection while being driven down the road.

I have read on several threads about the pins being dislodged in some harnesses.
Thats something I keep forgetting about.
A mighty important factor when it comes to figuring out why these units quit running.
Most shops that give up on these and say it cant be fixed, just dont understand these units.
I know there are times that I get frustrated with My old truck, seems I have a tendency to forget that it is paid for and no matter what happens it will run again.
One thing I did get accomplished, as suggested by several forum members, cant now remember who, but did mount the spare PMD and run the harness for it to the top of the engine. This is the harness that Leroy sells for a direct fit to the Stanadyne grey box PMD. I run the lifetime Dorman and when/if it fails I’ll be able to continue on without getting under the truck, at that moment, only under the hood until more favorable crawling conditions is met.

 

[Tmyers]

The wire was connected, I’ll try it with it disconnected

 

[Rockabillyrat]

Here are the test procedures for a crank no start with fuel to the IP but nothing to the injectors. You really need a scope to diagnose these properly. So you can watch the square wave pattern. But I understand most people don't have access to something like that. Its not a tool I use to often at the shop. But when you need one its a life saver for diagnostic work.

1. Listen to the Engine Shut Off, (ESO) solenoid when the key is turned on.

2. Test for 10+V on the ESO solenoid while cranking, ESO connected, Pink wire.

3. Test for a 0-5 V square wave signal to the fuel solenoid module, pin A, Light Green wire, when cranking.

4. Test for a 0-12 V pulse signal to the fuel solenoid from the fuel solenoid module, pin B, Red wire, when cranking. NOTE: This pulse will appear as a 0-12 V square wave with a 20 V or higher spike, much like a gas engine fuel injector pattern.

5. Test for 12 V and ground to the fuel solenoid module, pins D and F, Pink and Black wires.

 

[Will L.]

To ensure it isn’t the fuel shut off solenoid: unscrew it and try starting it. Since you have the injection lines disconnected- they will just spray a little fuel while cranking.

If you ever do this and it starts- the way to shut off the engine is pinching the 1/4” (soon hopefully clear) return line.

verify cranking rpm. Also the clear fuel line I keep bringing up. They go in order because of the most common failures and it divides the type of failure. If you don’t have a clear line on it currently, this should tell you the previous mechanics didn’t follow procedure. You can simply remove the line and put the end into a catch bottle, crank engine and ensure clean fuel flowing- but can’t ensure the fuel is not aerated- I would guess 20% of nonstarters on long term sitting trucks are aeration problems.

I forgot to mention Mod Mafia sells the fuel tap fitting that gets used in step 3.

Fuel Pressure Gauge Adapter

A fuel pressure gauge is essential to monitoring the health of your fuel delivery system. Mod Mafia makes it easy to add this important gauge to your Hummer / H1…

modmafia.com

Again- my instinct is a dropped ground or maybe bent pin to the pmd at one end of cable or another. Possible cps & optic sensor both toasted…. Something electrical. But wanna throw this out there incase you get stuck and decide to start diag over.

 

[Tmyers]

Thanks for info. Got a lot of things to check. Like I said it’s my 18 year old son’s truck, he getting frustrated but I told him we’ll figure it out eventually

 

[denata]

Do you have the ability to use an oscilloscope or an instrument that can measure the frequency? if there is nothing, then you can use wired headphones, you will just hear impulses. It is necessary to check the pulses from the crankshaft sensor. then check the pulses at the input of the FSD.
Do you need help with electrical diagrams?
For diagnostics, to erase PCM errors, buy the ELM327 USB/Bluetooth version ($5-10). For Windows, the ScanXL application. Allows you to view all parameters of the engine and gearbox just like TECH2, also allows you to read and reset errors. Lots of free android apps to read and reset errors via ELM327.

 

[Tmyers]

Thanks denata, don’t have an oscilloscope, will try with out it

 

[denata]

You can assemble a circuit from several wires, a pair of radio components from a toaster. and make the pump spit fuel without the PCM. For pump and FSD testing only.

 

[jrsavoie]

To ensure it isn’t the fuel shut off solenoid: unscrew it and try starting it. Since you have the injection lines disconnected- they will just spray a little fuel while cranking.

If you ever do this and it starts- the way to shut off the engine is pinching the 1/4” (soon hopefully clear) return line.

verify cranking rpm. Also the clear fuel line I keep bringing up. They go in order because of the most common failures and it divides the type of failure. If you don’t have a clear line on it currently, this should tell you the previous mechanics didn’t follow procedure. You can simply remove the line and put the end into a catch bottle, crank engine and ensure clean fuel flowing- but can’t ensure the fuel is not aerated- I would guess 20% of nonstarters on long term sitting trucks are aeration problems.

I forgot to mention Mod Mafia sells the fuel tap fitting that gets used in step 3.

Fuel Pressure Gauge Adapter

A fuel pressure gauge is essential to monitoring the health of your fuel delivery system. Mod Mafia makes it easy to add this important gauge to your Hummer / H1…

modmafia.com

Again- my instinct is a dropped ground or maybe bent pin to the pmd at one end of cable or another. Possible cps & optic sensor both toasted…. Something electrical. But wanna throw this out there incase you get stuck and decide to start diag over.

At some point I always run the return line to a container.

I encountered 2 plugged return lines and that told me what was wrong.
It's a very fast and easy check.

 

[Paveltolz]

I would check a few other points before you start really tearing things down, throwing parts at it.
Remove the fuel line to the IP to ensure there's fuel even getting to it (as suggested by Husker).
Check the PMD Cable as jrsavoie pointed out for the connectors to ensure the pins haven't retracted.
Check the PMD extended cable for continuity to ensure it is still good as some aren't built very well.
With reference to the attached 'PCM-FSD signals and no start....' file (copied from the help stickies), reference voltages should be:

Test to determine working PMD Harness
Pin outs on the PMD Harness
Pin Wire Color Voltage Source/Connection
A Light Green .05 VDC ECM
B Red 0 VDC Fuel Solenoid
C Black 0 VDC ECM
D Pink 12 VDC Underhood Fuse Fuel Sol Fuse (Connects to Shut Off)
E Red 5 VDC ECM
F Black 0 VDC Fuel Solenoid

I have a 97 shop manual I can scan the pages/topics you need. Lemme know as I'm heading out of town Tuesday. Here's a couple of things that you may find useful in the meantime.

 

[Tmyers]

Again, thanks to everyone for all the input! We’ve got a lot to check out. Might be a few days before we have time too, we are farmers and got a lot of hay to make this coming week. I’ll post as soon as we’ve checked some things out. Hopefully to say that it’s started!

 

[jrsavoie]

I would check a few other points before you start really tearing things down, throwing parts at it.
Remove the fuel line to the IP to ensure there's fuel even getting to it (as suggested by Husker).
Check the PMD Cable as jrsavoie pointed out for the connectors to ensure the pins haven't retracted.
Check the PMD extended cable for continuity to ensure it is still good as some aren't built very well.
With reference to the attached 'PCM-FSD signals and no start....' file (copied from the help stickies), reference voltages should be:

Test to determine working PMD Harness
Pin outs on the PMD Harness
Pin Wire Color Voltage Source/Connection
A Light Green .05 VDC ECM
B Red 0 VDC Fuel Solenoid
C Black 0 VDC ECM
D Pink 12 VDC Underhood Fuse Fuel Sol Fuse (Connects to Shut Off)
E Red 5 VDC ECM
F Black 0 VDC Fuel Solenoid

I have a 97 shop manual I can scan the pages/topics you need. Lemme know as I'm heading out of town Tuesday. Here's a couple of things that you may find useful in the meantime.

Also need to check what's going back to the IP.
Checking the extension harness by itself, doesn't guarantee it's making connection.