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6.2 Humvee starts, runs for 5-10 seconds then dies

cabraljf

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To start off I just purchased this Humvee a few weeks ago and it had been sitting for 2+ years gathering dust. I have been trying to breathe life back into the old 6.2 engine ever since. (I have worked on engines and transmissions before but this is my first mechanical injection system I have worked on.)

First I removed the fuel tank and cleaned it out. Installed 2 new batteries. I have replaced the lift pump with a 6.2 lift pump I purchased from Auto Zone. The only difference seems to be the Humvee lift pump uses vacuum and the Auto Zone one does not. I have changed the fuel filter and screen. Installed new 24v glow plugs. Confirmed that they are getting 24v. Changed all 8 injectors. Changed the injection pump, also purchased from Auto Zone. I confirmed that the IP and injectors are working by removing one glow plug at a time and making sure that there is "diesel fog" coming out of the hole when turning the engine over. NOTE: I do not know if the IP timing is set properly (it probably isn't). I have tried setting the IP marks lined up, slightly advanced and slightly retarded and nothing seems to change much.

So this is what happens: I turn the engine over and it will start if I lightly press on the throttle or pull the throttle lock slightly. I will run for 5 to 10 seconds then putter out. It stops as if it is running out of fuel. After it stops I have to turn it over a couple of times then it will start up and die in the same way.

The next thing I am going to try is to go get some clear hose and put it on the return of the IP and see if any air is getting in there. I have already ruled out any pinhole leaks in the gas tank and lines leading up to the lift pump. I used a 5 gallon diesel fuel tank and fed the lift pump from the 5gal tank. The issues were still present.

Is there anything I am overlooking?
 

Andyrv6av8r

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Humvee lift pump uses vacuum and the Auto Zone one does not

Are you referring to the mechanical lift pump on the side of the engine?
 

Action

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Auto Zone sold you a 24v injection pump?
Did you remove and reinstall the pushrod for the lift pump and make sure the lift pump was installed correctly?
 

dmetalmiki

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Some things to check, Could be,
Starts, Has fuel. Runs a while. Stops. No fuel.
Vacuum or blocked pipes?
Fuel in limited supply.
Blocked filters? Piping?
Remove the pipes and blow air through them.
Fuel tank pickup, strainer ,blocked?
check flow from the fuel pump.
 

cabraljf

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"Humvee lift pump uses vacuum and the Auto Zone one does not
Are you referring to the mechanical lift pump on the side of the engine? "
Yes, the mechanical lift pump on the side of the engine.

"Auto Zone sold you a 24v injection pump?
Did you remove and reinstall the pushrod for the lift pump and make sure the lift pump was installed correctly? "
I removed the solenoids from the old 24v IP and put it on the Auto Zone IP. The pump was rebuilt by Delphi.
Yes the lift pump was installed correctly. When open the air bleed screw on the top of the fuel filter fuel comes out. Also it does run for some periods of time so I know that the IP is getting fuel. I have not verified the pressure coming from the lift pump though.

Some things to check, Could be,
Starts, Has fuel. Runs a while. Stops. No fuel.
Vacuum or blocked pipes? - vacuum in the fuel system?
Fuel in limited supply. - Tank has about 9gal in it with cleaner additive
Blocked filters? Piping? - The fuel filter was just installed last week
Remove the pipes and blow air through them. - The only lines I have not done this to are the return lines
Fuel tank pickup, strainer ,blocked? - I did install a new strainer in the tank. Also I have tried to run the engine with the lift pump connected to a 5gal fuel tank and had the same issue.
check flow from the fuel pump. - Is there a flow meter I can use to confirm flow? I have read that some users have measured PSI.
 

Andyrv6av8r

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It went to the vacuum line coming off of the intake. I have it plugged right now.
There is no vacuum on your diesel engine and the fuel pump is mechanical, not vacuum operated. Open or remove the bleed screw at the filter, turn the engine over with the starter and see if you're getting pressure and flow. Or if you don't want to make a mess, remove the hose going into your filter and run it into a container.
 

cabraljf

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That black plastic line is a vent line. When you changed the lift pump, did you also remove the plate behind it? or just the 2 bolts holding the pump on?
The mechanical lift pump works. It filled the fuel filter housing with diesel and I can also open the screw on top of the filter housing and see fuel coming out of it. The only thing I haven't confirmed with the lift pump is the pressure because I don't have a gauge.
 

Action

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I believe one of the TM's states how much fuel should come out of the bleed valve (at the end of the hose by the washer fluid tank) in a set amount of time.
If a lift pump fails on an otherwise properly working HMMWV, it will still run with the IP sucking fuel. It is not ideal, but that won't make it shut off.
Try some clear tube for return line at top of injection pump. You should see flow or if there is air in the system. Don't leave that clear hose on when finished.
 

cabraljf

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Indiana
Update: same starting issue.
What I've done: I attached a fuel pressure gauge to the outlet of the fuel pump and it read about 11psi. I know this doesn't show flow but I will do that next.
I also put a clear piece of tubing on the return line for the IP. There is steady fuel flow when cranking and while it runs for a short while. I only notice a few small air bubbles when I initially crank. No air bubbles while it tries to run. (Pictures are of the pressure gauge setup.)

I also took the cover off of the IP ( where the cold advance and shut-off solenoids are attached). I zip tied the shut-off in the open position. I know it would have resulted in the engine not shutting off with the ignition switch in the off position but the engine died on its own anyway. Also it still has the original ignition switch not the keyed one.

IMG_20210119_164638.jpg
IMG_20210119_164645.jpg
 

Retiredwarhorses

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that’s not an ignition pump, it’s called an injection pump...I would not trust anything like that from a local auto store either.
also, I would assume anything local is 12v and not 24v, unless you swapped top cover, but you could have a weak solenoid and is causing your issue. If it were me? I would send your injection pump out to a good rebuild shop.
 

cabraljf

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Indiana
Update. I went with the company that Andyrv6av8r suggested to rebuild my ignition pump and the truck mostly ran after I installed it. I am now fighting an issue with my alternator and need to address that. The truck seems to run when the batteries are charged. I don't know if maybe the "diesel only" ignition pump from Autozone would have worked or not. The rebuild was cheaper than getting one from Autozone anyway.
 

Coug

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We know what you are trying to say, but there is no such thing as an "ignition pump" and it tends to irritate some people when a completely incorrect terminology gets used repeatedly.
 
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