Blow-By Test for 6.5L Diesel

Volume 2 Issue 1 - 6.2/6.5 Issues and Answers

I have always been a gasoline engine driver, however I am thinking about buying a used 1995-1998 Chevy or GMC diesel Suburban and need some advice in making a decision. Those I am looking at have more than 150,000 miles on them, which seems like quite a lot to me. How can I know whether the engine is OK? Do I need to have compression tested? Any help is appreciated! Jim – Amarillo, TX

Jim, we recommend that you check for crankcase blow-by vapor flow. This is the best way to determine the health of the 6.5.


Testing the Injection Pump for 1994-2000 6.5L Diesels

Volume 2 Issue 1 - 6.2/6.5 Issues and Answers

Hello, I hope you can help us out. Our 1998 Chevy 6.5 truck has been doing some odd things lately and the shop I took it to, told me it needs a new injection pump, but I am not so sure I believe their diagnosis at least I don’t want to believe it. Here’s the issue: Sometimes when the truck is stopped at a traffic light, the engine will surge against the brake and makes a puff of gray-black smoke when this happens. I thought maybe it could be caused by a bad throttle switch. Hope this is enough for you to go on. Thanks in advance!

Here is a quick and easy way to determine whether the injection pump of any 1994-2000 6.5 C-K truck is working properly.


6.5L Diesel Starting Problems

Volume 2 Issue 1 - 6.2/6.5 Issues and Answers

We hope you can help us with our hard starting 1995 Chevy 6.5 diesel. When the wait to start light comes on and stays on the normal amount of time, it starts fine, like always. Often, the light comes on only very briefly and the start up is not so easy, with a lot of extra cranking. Perhaps this additional problem is related and I include it to help in the diagnosis: The truck often bucks and misses under heavy load. Two shops have diagnosed this as a failed fuel transfer pump. Between the two shops, they have installed 4 new fuel transfer pumps: no help. One shop replaced the engine computer: no change. Another replaced the glow plug relay: no change. Yet another replaced the ignition switch: again, no change. Sure hope you can offer a suggestion! Ray S., Maine

These problems may be related. Here are the things to check out.


How does the fuel lift pump work in the 6.5L diesel?

Volume 2 Issue 1 - 6.2/6.5 Issues and Answers

Can you help me understand how the fuel lift pump works in the 6.5 turbodiesel GM trucks? I’ve talked with several knowledgeable mechanics and get as many answers. I’m confused!

You did not specify the year of your truck and there is a difference between the 1994-1995 and those built later.  In the 1994-1995 models, the lift pump...


Troubleshooting a Heavy Rattle Sound in a 6.5L Diesel

Volume 2 Issue 1 - 6.2/6.5 Issues and Answers

Our 1996 K-2500 GMC diesel has many mechanics stumped; maybe you folks have the answer. Last summer, while traveling through Oregon, we began hearing a rattling sound under the hood. A shop diagnosed it and replaced the air conditioner pump. No change and he threw up his hands and sent us on our way. Another shop in California, decided it was a bad water pump which they replaced. Again, no improvement and in fact, it had gotten louder as time passed by. Of course, the shop couldn’t very well switch the old pump back on, so we were stuck with yet another unnecessary and costly repair. Then, another shop in Mexico diagnosed the problem as being the alternator and this time, the mechanic ‘proved’ his diagnosis by removing the drive belt so we could listen. Sure enough, the rattle was gone when he did that little test, so on with the new alternator. Same old deal. When the drive belt is on the rattle is there and it is getting worse all the time. The engine runs well and has good oil pressure, so we are hoping it gets us back home to northern New Brunswick next September. Can you offer any help?

Most commonly, a heavy rattle, one that sounds like marbles rattling in a tin can is caused by



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