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97 hummer has 6.5 turbo diesel engine lost power, doesn't do over 2500rpm

S

shellieman

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was going down road when notice a lost in power, figured fuel filter, so change it and it wouldn't start, fuel pump wasn't coming on, so put new fuel pump on, running again but still wont run over 2500 rpm, engine light is on check code, throwing on code twice one mil and one pend, code# p0251, I am thinking injection pump! but don't want to just spend that kind of money on a guess and be wrong,, its hard to start for first start and pours black smoke, when running seems find could be a little louder not sure! any one with any ideals, thanks for any help I get
 
Clear the codes, and see if they come back. Foam from lack of fuel and air may have tripped this. Remove the Optical filter harness and see if that is the cause if the codes come back.
 
I have cleared codes a couple times and bleed the lines,, where is Optical filter harness
 
Some more info would be helpful. starting with any modifications to the engine or fuel system there may be, ie relocated PMD. Maintenance history. How familiar with the fuel system are you? Did you check the Lift Pump pressure? What are you running for fuel, do you put anything in it? Do you drain the water from the filter manager, at least before changing the filter?

You may not have an OS filter, but if so it would be connected to the OS on top of the IP.
Fixing truck 004.jpgFixing truck 001.jpgOS_harness_filter.jpg
 
Pmd has been relocated! the truck is really my brothers but I am trying to help him out, since I am the one mechanically inclined just not a diesel guy, he change filter and no he didn't drain water, said he drain where filter goes! the hummer is all stock except for the moving of the pmd. he is only running diesel and no he does not put anything in it, it has dual tanks and has problem on both tanks,,
 
My suggestion would be to check the lift pump pressure. look in the stickys of the 6.5 technical library for the OPS and LP troubleshooting thread.

Also, if using #2 ULSD he needs to add a lubricant to the fuel, such as 2-stroke oil or Non-detergent SAE30 lubricating oil

the p0251 code puts you in limp mode which is why it feels underpowered. That is the Optical Sensor in the IP coding, it is a timing reference. Could be from air in the fuel or contaminants. Check for air leaks as well, which happens so much more often with a failed lift pump. If you live in rust belt try inspecting on top the fuel tank to see if the steel fuel lines are all rotted. The rubber lines under the intake can get rotted too. The optic sensor has to see through the fuel, air bubbles cause all kind of issues

What kind of tool are you using to read codes? Do you have access to a scanner? Do you know what the timing is set to? It is the TDCO value
 
The coding part is in the injection pump, but air in the fuel can also cause it to happen. Is the code immediate after clearing? The rest of the stuff is all need to know anyway to maintain the vehicle, and contributes to failure of the IP.
 
shellieman said:
we put a new fuel pump on it
Click to expand...

You still need to verify the fuel pressure, just like on any carbeurated or fuel injected gas engine. There could be restrictions or can get weak pumps.

shellieman said:
yes when you clear code and unhook scanner and start it, it throws the code again
Click to expand...

Sounds like it would be electrical failure of the OS, but its always good to check everything first. For checking air most people put clear line on the IP return outlet and watch for bubbles.
 
anyway to test the OS, if we have good fuel pressure,, oh what would be consider good fuel pressure on this,, thanks again for all the help
 
That LP and OPS troubleshooting thread should explain it all, that is a very important part of keeping these eninges running right. The pressure shoud be like 8psi at the water/fuel drain port, when running the LP with engine off or while idling. It shouldnt cause any problems as long as you have 5psi though when the engine is running. having pressure eliminates possibility of an air intrusion post fuel pump. But still possible there is air intrusion pre pump.

No real tests for the OS. Although you can try unplugging it and plugging it back in. Sometimes the clips on the connectors are broke and it comes loose. If you unplug the OS and run the engine it should run the same as it does now. If you unplug the crank position sensor the truck shouldnt even start if the OS is bad.
 
shellieman said:
did not find no leaks anywheres!!!
Click to expand...

Air leaks do not show up as external leaks. Fuel can't leak out while air is leaking in...

Did you bypass the filter as Buddy has pics of shown? This would be remove that short harness and plug the connector directly into the IP.

4 PSI is low. In my experience this has happened when there is a lot of air in the system from replacing an engine. You could have other causes including a plugged sock etc. Did you purge the fuel filter by the vent on top?

Any water from the drain? How does the fuel look?
 
no I didn't bypass os filter, will that help,,, we purge the hole system! fuel looks good see no water or any other contaminates,,have my fuel pressure guage hook to it and releasing pressure to watch for air through there, but was good,,it could be 5 psi hard to tell on mind,,
 
You would be looking at replacing the Optical Sensor. There are some used ones cheap on ebay last I checked, no guarantees they work, but real cheap. Swapping an OS is easier than the whole IP, and cheap remanned IPs are not necessarily new internals either. Cheapest IPs out there are like $500, although some are skeptical of them. If you can find a new OS may be a few hundred bucks.

As WW said, air leaks wont show and might not leave a huge bubble that would appear from bleeding. This is because an air leak pre pump would be a vacuum so you wont seen any fuel leaks, except after you shut down they may weep a little. Rotted steel lines coming out of the fuel tank are notorious for that. To see air bubble would need to watch the fuel flowing and see if there are tiny bubbles in it.
 
The P0251 refers to the "injection pump cam system"

This issue is probably the end of the road for the IP.

How many miles on the rig ??

With 4 PSI to the IP I dont think the issue is fuel delivery.

I would start planning for an IP replacement.

Missy
 
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