6.2 humvee engine loss of power.

[Ttchutch]

I'm new to the forum. I hope I put this in the correct thread.
I've got a 91 Suburban 2500 with a Humvee 6.2 diesel in it. I've put over 70,000 miles on the motor and it has always ran great. It has just recently lost power. I've changed the fuel filter, air filter and used some BG fuel injector cleaner and that didn't help. It seems fine leaving from a dead stop but once the RPMs are over roughly 2000 there's no power. Going up a hill is extremely painful. There's a mountain pass near me that I could do 45-50mph and now it only does 25. I usually get right around 20-21mpg. I just went on a 275 mile trip and went through about 35 gallons of fuel. I had to keep it floored on the interstate almost the entire time. Oil pressure was normal, right about 45psi. Temp was normal. And there was not any smoke coming out of either exhaust pipe. And no fuel leaks. I checked my oil and it was fine also.
I replaced both mufflers 15,000 miles ago, but it sounds like I have holes all throughout my exhaust system when I'm on the interstate but I don't.
I could understand going through a ton of fuel if I was towing a heavy load and clouds of black smoke was pouring out of the exhaust but I wasn't and there was not any smoke.
Any ideas of what it could be?

 

[Jozseph]

I'm new to the forum. I hope I put this in the correct thread.
I've got a 91 Suburban 2500 with a Humvee 6.2 diesel in it. I've put over 70,000 miles on the motor and it has always ran great. It has just recently lost power. I've changed the fuel filter, air filter and used some BG fuel injector cleaner and that didn't help. It seems fine leaving from a dead stop but once the RPMs are over roughly 2000 there's no power. Going up a hill is extremely painful. There's a mountain pass near me that I could do 45-50mph and now it only does 25. I usually get right around 20-21mpg. I just went on a 275 mile trip and went through about 35 gallons of fuel. I had to keep it floored on the interstate almost the entire time. Oil pressure was normal, right about 45psi. Temp was normal. And there was not any smoke coming out of either exhaust pipe. And no fuel leaks. I checked my oil and it was fine also.
I replaced both mufflers 15,000 miles ago, but it sounds like I have holes all throughout my exhaust system when I'm on the interstate but I don't.
I could understand going through a ton of fuel if I was towing a heavy load and clouds of black smoke was pouring out of the exhaust but I wasn't and there was not any smoke.
Any ideas of what it could be?

FWIW

Possibly Injector Pump issue.

 

[MtnSnow]

I too would say the fuel pump/Injection pump is probably the culprit of the loss of power with the statements of what and how it is acting.

 

[Ttchutch]

I've been looking at some remanufactured pumps online. Did the military 6.2 use the same pump as the civilian engine?

 

[Jozseph]

Ttchutch, attached are three pages from the GM Factory Manual for the 6.2

Covers Diagnosis Procedure for fuel pumps

View attachment GM 6.2 Diesel Engine pages 7-34-36.pdf

Attached is a PDF copy of the GM 6.2 Factory Service Manual

View attachment GM 6.2 Diesel Engine Manual.pdf

Regards

Joseph

 

[Jozseph]

I've been looking at some remanufactured pumps online. Did the military 6.2 use the same pump as the civilian engine?

Pump have a different specification. There is a list posted that shows model number / specification number of pump to the year engine and use. List is posted on this site try;

http://www.steelsoldiers.com/showthread.php?110581-List-of-Stanadyne-DB2-pumps

 

[rchalmers3]

Interesting symptoms. Would it be too hard to loosen the exhaust flanges and take it for a short drive?

Im thinking the exhaust may be restricted. That would give you most those symptoms.

Rick

 

[Ttchutch]

I have thought of that too. In a couple days I'll pull the exhaust off the manifolds and see if it runs better. I changed the mufflers about 15,000 miles ago but who knows.

 

[Skinny]

What are the odds that both sides fail at the same time?
If the exhaust is restricted causing low airflow, wouldn't it blow black smoke in the upper throttle range?

 

[Ttchutch]

Both sides getting clogged at the same time would be near to impossible. I think I'll still pull the pipes off just to check because it's easy....and who knows. Should I upload a video of what it's doing?

 

[Skinny]

Maybe the fuel return glass ball check valve is plugged?

This all wreaks of fuel delivery issues. Maybe a plugged sock on the tank pickup?

 

[Chaski]

Maybe the fuel return glass ball check valve is plugged?

This all wreaks of fuel delivery issues. Maybe a plugged sock on the tank pickup?

That could be it, also could be something evil like the governor weight retainer ring coming apart if it is still original (no metal "E" tag under one of the three lid screws).

 

[Ttchutch]

What is the governor weight retainer ring?

 

[ODFever]

Just curious - When was the last time you replaced the fuel filter?

 

[Ttchutch]

Changed the fuel filter about a 1000 miles ago and then again over this weekend when the problems became worse. Changing the fuel filter had no effect.

 

[Jozseph]

What is the governor weight retainer ring?

Here is a PDF copy of the DB2 Manual;

View attachment Stanadyne DB2 Operation and Instruction Manual 99009.pdf

The governor weight retainer ring is inside the pump.

Regards

 

[Chaski]

Here is a PDF copy of the DB2 Manual;

View attachment 628525

The governor weight retainer ring is inside the pump.

Regards

That is a good manual, but it is new enough that it does not show the old style urethane governor weight retainer. Here is a picture of the old style retainer with the urethane ring. The ring degrades after a few decades and comes apart.