I have a 95 suburban 6.5 turbo and im having issue with it dyeing when I give it gas. It idles fine and starts up strong no problems there however once i start giving it gas and it hits about 1500 rpms the motor dies. I took it to a local shop and they said it was the PDM/FSD. Ive replaced the PDM with a relocation kit as we as all parts the computer was saying had faulted and ive cleared the codes. Now there are no codes registering but it still idles and starts fine but continues to die once I give it gas. Any one experience this?

 

I have no direct experience with this problem, but I do have a 94 K2500 pickup with a 6.5.

My first question is, do you have a fuel pressure gauge? Inadequate pressure may, or may not be your problem, but it can be a big problem for the 6.5.

The following description is for a 94, and I think it is relevant for a 95 also. 94 and 95 have different locations for relays, and some differences in wiring, although both are OBD 1 (on board diagnostics 1). I'm assuming you don't know much about the 6.5 and am therefore going into more detail. If you are more knowledgeable then please forgive me and laugh at me instead.

In the valley of the motor, near the back and on the drivers side, is the oil pressure sensor (OPS). The OPS has two functions, sending signals to the dash gauge panel to show what the oil pressure is, and on a separate circuit (as soon as oil pressure hits the magic mark) it sends power to the electric fuel pump (lift pump, or LP) (this is overly simplified as there is more details involved). The factory stock wiring is rather small and can't always adequately power up the LP. This can, over time, damage/destroy the circuitry inside the OPS that is supposed to send power to the LP.

This then requires the injection pump (IP) to suck the fuel up to it (instead of receiving it from the LP), stressing the IP. This stress can shorten the life of the IP, and reduces the needed fuel for the IP.

The LP is mounted to the frame under the drivers seat. It looks like a fuel filter, except it will have two wires going into it. The black one should be ground and the other 12V +. Check this out, making sure you have a full 12V there. It is possible to not have full 12V because of a damaged OPS, making it difficult for the LP to operate properly.

Also on the back of the motor, and in the valley, is the fuel filter (or fuel filter manager, or FFM). There will be one fuel line going into it, and two coming out of it. Both go into the motor valley and under the intake manifold, making it harder to see where they go. One of them goes to the IP, and the other goes to a drain valve (water drain), usually attached to the thermostat housing.

The following is from another web site ( http://www.thetruckstop.us/forum/ ) dedicated to GM diesels.

"At the filter manager drain, snake into your cab on long hose a test gauge, make positive to not pinch off the hose and dead/static head the reading, at idle with good stock pump 5-6 psi is normal, go for drive, at hiway cruise speed 70 mph 3-4 psi is strong lift pump, 2-3 psi is good lift pump but has some weakness, if lift will not sustain 1.5 psi or better, get a new one.

Then do an acceleration test on hard acceleration it is preferable to maintain > 1 psi, it may dip below that but once at desired settled out speed, lift needs to recover quickly to 1.5 psi or better, if it remains less than 1.5 or takes more than about 5 second to recover to cruise psi observed before accelerating, either lift is bad or tank sock is dirty."

To do this pressure test you will need a combination vacuum/pressure gauge, several feet of quarter inch fuel line, and possibly a couple small worm screw clamps. The gauge can be purchased inexpensively at Harbor Freight, or elsewhere.

Do the fuel pressure test and LP 12V test and let me know the results before purchasing any replacement parts, as there are several directions to go, depending on the results of the tests.

Don

 

Thank you Don for the advice. I am pretty experienced in auto mechanics how ever not as much with this motor. Luckily this means I know exactly the parts your talking about and where to check. Your tips give me a couple great spots to check. The shop I took the truck to ensured me the LP as well as the injection pump and the injectors were all operating strong and well and showed no problems. They are also the same shop that told me it was a bad PMD. Which have replaced and there has been no change so its hard to know what they acutely checked and didn't. Again thanks for the input I will be checking these things myself.

 

Since you have experience with mechanics here's another forum for GM diesels.

6.5L Diesel Engine - Diesel Place : Chevrolet and GMC Diesel Truck Forums

Both forums have some very knowledgeable members. Take some time to read on both, especially the FAQ threads. You will definitely gain a lot from both.

By the way, I'm still interested in the results of your testing. Keep us posted.

Don