HMMWV Doesn't Shut Down With Ignition Switch

[hawk-aggie]

If I understand the response to be "NO" as this is an important starting point with the crazy symptoms.

Got a non runner , but got it running, wont turn off unless one pulls the 5A lead on the fuel cut off solenoid.

Walking it back ... all the obvious connections stated, switch, boxes, alternator and the like covered. ? Factory wiring, NO modifications / hack job going on? I would... and I think you'er wondering what is holding the fuel solenoid energized.

More data time. Monitor the 54A lead (tap into it) while properly connected. Would be interested in the voltage in all states, STOP, RUN, STARTing and back to Stop.
I would like to know the condition of the engine and body connectors ? Rusted, busted, corroded can be suspect. Pictures helpful.

These type of problems are going to require eyes on all connections with prints and understanding. Some obvious and looks like you have ruled them out
? The many box swaps is interesting... BUT then, I am NO fan of smart anything LOL.

HumV wiring is pretty straight forward. Harnesses are well made. One thing that is a bit to troubleshoot is there are splices internal to the design. This make it a little tricky to isolate individual circuits feeding... in this case the IP, but other components share the same. Look at the fan control, TDM, TSU and even the "BOX" We all know those boxes fail and everything goes thru it.

More history of the rig is helpful or just jump in and follow the trail to a can of worm... then success.

I don't like to guess this or that, poking and pulling wires might work???

That's what the Dr. does when one is up on the table, CAMO

>>>>> HUMV ________OWNER >>>>>>>>>>> Good Luck
View attachment 952733

I have more data, but left my notes at the shop. Tried a lot of options, including isolating each wire/cable to the alternator. We started removing the negative battery cable to see if the truck would shut down, before pulling 54A lead. When we had the large positive cable disconnected from the alternator, it did shut down when we pulled the negative battery cable off the post. If it is running when the negative battery cable is removed, it's getting its ground from somewhere else. The issue now is finding where. Maybe the alternator itself. I have 3 working alternators and two working regulators to play with. more info to come later this week.

Bottom line is that the truck is running when the negative cable is removed from the battery.

 

[NDT]

Did you verify the correct number wires are plugging into the correct terminals on the ignition switch? Super easy to mess this up.

 

[hawk-aggie]

Did you verify the correct number wires are plugging into the correct terminals on the ignition switch? Super easy to mess this up.

Yes, the ribbed one is a no-brainer. If the other two were switched, the truck would start in the wait/run position.

 

[Milcommoguy]

Yes, the ribbed one is a no-brainer. If the other two were switched, the truck would start in the wait/run position.

Well that's one way to test the switch ?? Be CLEAR... Truck would not start... BUT would engage / crank over engine. Did it start / engine running ??

Here my thoughts. No magic bullet, quickie fix to chase your gremlin. Ground on battery remove , IMO points to power being supplied from alternator.

I am a little unclear to your statement >>>
" When we had the large positive cable disconnected from the alternator, it did shut down when we pulled the negative battery cable off the post. "
Help me here with the what was going on with the which wire when. What happen with negative?? MY GUESS still running when remove HELP ?

Not pointing a finger of wrong... but logic and documented text can spin the little electron, my brain and story to follow along.

Since this site uses, experience, logic and guessing ... MY next guess you have a shorted diode or a very leaky diode in the alternator. This allows one of the phases to be an electro magnet in this brushless design. You start the truck and alternator is self excites with output and a reference to engine ground when trying to turn it to stop Off. That my abstract thought.

Go back the the hillbilly test of big sparks when connecting the positive battery terminal. Remove the big positive lead on the alternator (tape it back to not short to anything) and test for the big sparks. No sparks?? Then see if truck starts and shuts down with battery normal / SRS switch, normal.

Hummwv really don't require a lot of current to run. Yes, Glow and Start / cranking, but after that little. (all accessories off)

This Fing gremiln is starting to (P eye double S) me off too LOL, CAMO

TOO much FUN OH OH OH I went back and saw where it was running with the negative lead remove. Remove the alternator positive and pun back the negative and start? Last free guess for the day.

 

[TOBASH]

There are several things that I would consider and evaluate.

Somehow, some type of fuel is getting to the diesel engine. Unlike a gasoline engine, you don’t need spark plugs so the engine can keep running when you turn electricity off.

That means that you need to evaluate what the fuel supply is meaning that it could be diesel or you could have a tremendous amount of “blow-by” and you are actually burning engine oil (and that can lead to a runaway engine).

Check to see if there’s any blow-by when you pull off the oil level dipstick. If you have thick oil vapor, that could be a problem.

The other issue is that the fuel cut off at the top of the injection pump is stuck and not functioning properly. That piece at the top of the injection pump is in somewhat of an annoying area, but if you climb on top of your vehicle, you should easily be able to remove that piece and check the solenoid. You can also check the solenoid by applying 24 V across and seeing if it is popping open and closed with an audible click.

If this happens to be the injection pump cut-off solenoid, another temporary fix would be to place a cut-off valve in the rubber fuel supply line that runs to the engine. The advantage is that can also act as a “kill-switch“ to prevent theft.

If this turns out to be significant oil blow-by you will potentially have low oil in your engine, but more importantly you should stop driving that vehicle immediately because you have no way of controlling the engine and it can go out of control.

 

[hawk-aggie]

There are several things that I would consider and evaluate.

Somehow, some type of fuel is getting to the diesel engine. Unlike a gasoline engine, you don’t need spark plugs so the engine can keep running when you turn electricity off.

That means that you need to evaluate what the fuel supply is meaning that it could be diesel or you could have a tremendous amount of “blow-by” and you are actually burning engine oil (and that can lead to a runaway engine).

Check to see if there’s any blow-by when you pull off the oil level dipstick. If you have thick oil vapor, that could be a problem.

The other issue is that the fuel cut off at the top of the injection pump is stuck and not functioning properly. That piece at the top of the injection pump is in somewhat of an annoying area, but if you climb on top of your vehicle, you should easily be able to remove that piece and check the solenoid. You can also check the solenoid by applying 24 V across and seeing if it is popping open and closed with an audible click.

If this happens to be the injection pump cut-off solenoid, another temporary fix would be to place a cut-off valve in the rubber fuel supply line that runs to the engine. The advantage is that can also act as a “kill-switch“ to prevent theft.

If this turns out to be significant oil blow-by you will potentially have low oil in your engine, but more importantly you should stop driving that vehicle immediately because you have no way of controlling the engine and it can go out of control.

The are no vapors coming out of the dipstick tube. The fuel cut off solenoid is functioning. I have tested it. There is a mysterious power source “leaking” just enough voltage/amps to keep the fuel cut off/control box solenoids engaged after the SRS switch is turned off. More likely is there’s something continuing to keep the control box solenoid engaged……. More searching and testing to do.

 

[TOBASH]

Start your Humvee, open the hood, and undo the plug on the engine side of the PCB protective control box/EESS smart box. If the engine stops, then it is possible that your problem is the box. If the engine continues running, then you have some other problem.

 

[Mogman]

The are no vapors coming out of the dipstick tube. The fuel cut off solenoid is functioning. I have tested it. There is a mysterious power source “leaking” just enough voltage/amps to keep the fuel cut off/control box solenoids engaged after the SRS switch is turned off. More likely is there’s something continuing to keep the control box solenoid engaged……. More searching and testing to do.

Do you have an electric lift pump installed?

 

[hawk-aggie]

Do you have an electric lift pump installed?

No, we don't modify our trucks in any way. We get them running, use them for 18-24 months, then sell them as an alternate income stream.