engine surge/louder diesel sound

[jeff4re]

I've been experiencing sporatic engine surges followed by an abnormally loud diesel sound. The truck doesn't run well when this happens. Sometimes it's when the engine is cold and other times when it's hot. If I turn off the engine then re-start it, the problem goes away temporarely.

I recently replaced the air, oil, fuel filters, vacuum pump, and alternator. The FSD was replaced at 60K miles.

Any Ideas???

Jeff
98 AMG Hummer 6.5L TD
81K miles

[markrinker]

First things first - are you getting a SES dash light, are any trouble codes set?

Will the truck do this at idle, or only under load?

It sure sounds like you are experiencing widely varying fuel delivery and/or boost pressures, which would point to a failed lift pump and/or weak injection pump, or a leak in the vaccuum controls for the wastegate.

Are you sure that everything was buttoned up properly when you replaced the vacuum pump? Did this problem start after its replacement?

Replacing the lift pump would be an inexpensive (under $100) experiment as well, after verifying that you indeed have good control at the wastegate...

[catmandoo]

under a hundred man the last lift pump i bought was 140.00 for the ac delco (i won't use anything else)

[jeff4re]

Hey Mark thanks for the reply...

To answere your questions...

1. yes, the check eng. light comes on every time the engine surges. I do not have the scanner to check the codes. The problem occurs at idle and under load but its more difficult to detect under load. It occured 3 times today from start up through the first 10 minutes of operation. All 3 times I shut down the engine and restarted it to clear the problem. After the 3rd time it ran fine.

2. The lift pump & FSD were replaced at 60K miles. Do they usually go bad that quick and how would I test the lift pump?

3. When I replaced the Vaccuum pump there was only one vaccuum line to remove. I inspected the line and reconnected it the same way I removed it. I've double checked the lines and found no signs of trouble.

4. The surge problem had occured prior to me changing the Vaccuum Pump but not as often.

It sounds like the problem is either the wastegate, lift pump, or injection pump. Is there a way to test these items individually and do they need to be tested when the problem is occuring?

Thanks for the help.

[markrinker]

Get a scanner on it and let us know what codes you are getting. There is no dependable way to isolate the problem, based on your description.