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GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 29367
Experience:  GM Grand Master Technician 2007. 14 years experience.
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97 GMC: with a 6.5L diesel..problem is intermittent..starts fine..mile

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97 GMC Sierra with a 6.5L diesel. The problem is intermittent so I'm having a tough time tracking it down. It typically starts fine, I might drive for a 1/4 mile or so and the engine will quit, I know I'm still getting battery power because my lights and radio will stay on. This started a couple months ago and it would do this usually when it was first started and it would only do it once every couple weeks. Now it could occur a couple times in a row and then go a few days before it acts up again. The truck will usually start right back up when I turn the key. I had an occurrence where it didn't start for over an hour. I'm assuming that it's an electrical problem intermittently dropping power to the injector pump.
Hello, I'm Cam. Please include all the details about your issue so I can accurately advise you. I cannot see your vehicle so please be detailed.

Do you still have the gray coveron the top of the engine first?
Customer: replied 4 years ago.
Yes the engine has the grey cover on it.
Ok this is likely a heat issue, 99% sure of it. That cover keeps too much heat inside the engine and the pump mounted driver which is the black box on the side of the pump gets too hot and cuts out.
i would get a rebuilt one with a kit to mount the module off to the side out of the engine heat. Check on ebay, they have kits with both for a reasonable price.
Customer: replied 4 years ago.
I suspect it's not a heat issue, our weather here is still pretty cool and the problem typically occurs with in the 1st mile of running, so far it seldom happens later in the day of running around town.
then likely an optical fuel temp sensor in the injector. These are notorious thes having bad pumps.
Customer: replied 4 years ago.
Are you saying there is an optical sensor in the injection pump? If so how do I test it and can that be replaced rather than the entire pump. As per my symptom description, I'll be driving down the road, the engine will stop and while still moving if I put the tranmission in neutral and turn the key for the starter (without turning the ignition off) it will typically start right up. There isn't any hesitation or missing before it quits the engine shutsdown and I just checked this evening and I don'y have any engine codes.
There is no real test.

YEs, these will run like that. these pumps are so bad that Gm had a special policy that covered them for 11 years.
When the sensor fails it will cause the stalling just like the engine was turned off and will start up after.
Basically if the pump is factory then I am 99% sure that is the issue, and also there is little else it can be.
Customer: replied 4 years ago.
I bought the truck used a couple years ago, the pump was replaced by the previous owner's mechanic attempting trying to solve an intermittent perfomance issue, I tracked that problem down to a bad wire for the solenoid for the turbo.
I was looking on another site describing the same problem I'm having and here was a suggestion "noise suppression harness" but I have no idea what they mean by the "noise suppression harness"
That is a harness used prior to 1995 on this so that is not the issue.
Customer: replied 4 years ago.
Where is the relay located that supplies power to the Injector Pump? I'm wondering if I should check that and trace out the circuit, before I look at spending the big bucks for another injector pump.
it gets power from the pink wire off the igntion switch, so basically it gets power with the ignition on and you can verify that yourself easily.
Customer: replied 4 years ago.
That makes it easy, I should be able to run a wire into the cab from the positive wire on the electric motor on the injector pump and leave my volt meter hooked up. If the engines quits and I still have power, then it's probably the pump as you describe?
You also mentioned something about the pump driver, is this something mounted under the grey cover on top of the block? Anyway of testing that unit?
The pump driver module is mouned on the side of the injection pump itself, and yes, your idea for testing the pink is a good way to test. Your logic is sound.
Customer: replied 4 years ago.
Just a couple more questions before I accept and sign off. What does the pump driver module do and just to confirm the pump motor get's it's power directly from the ignition switch?
The pump driver is what actually controls the injection pump. It has a couple large transistors inside.

The switch supplies power to the fuses then the fuse runs to the solenoid.
Customer: replied 4 years ago.
So does the ignition switch power go directly to the pump motor, or does the ignition supply power to the pump driver and the pump driver supplies power to the pump motor?
The pump is not a motor, but the power goes to the driver module and to the shut off solneoid from the same wire in the form of a splice.
Customer: replied 4 years ago.
I could be mistaken, but it looks like my injector pump has an electric motor driving it. From the front of the vehicle on the drivers side, just behind the batter, the injector pump has a unit sticking our of it that looks like a motor with two wires coming out that look like they are about 10 gauge. So I'm assuming that the pump is driven by an electric motor?
That is just how it looks, that small motor is the a stepper motor, only for minor controls.
The pump is physically turned buy the timing gears.
The wires you see are for the fuel solenoid it self.
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 29367
Experience: GM Grand Master Technician 2007. 14 years experience.
GM Tech (Cam) and other Chevy Specialists are ready to help you
Customer: replied 4 years ago.
Thanks, XXXXX XXXXX I could find an after market service manual for this thing, it would certianly save some of the guess work for me.

You've given me enough info rip into it tomorrow.


look into alldataDIY for your vehicle, 15 a year for it, it is not a bad deal.

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