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another GM 6.5 diesel question.

mitch504

mitch504

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I know you guys are tired of me clogging up HEF with pickup truck questions, but...

That same early '99 GMC 2500 with a 6.5 and automatic that I posted about before, since curing the PMD problem the truck has been great for about 6 weeks, then after about a 20 mile hwy run I shut it off for about 15 minutes. When I went to start it, it just spun like there was no power to the injector pump. I plugged in my tested good spare PMD, no change. I opened the bleed screw on top of the filter and got a fountain of fuel with no air, spun it again no change. I checked every fuse inside and out, changed a lighter socket fuse, no change. let it sit a few minutes, spun it for about a minute, it started and ran great. Next 20 times, it started instantly, cold or hot. Then, it spun for a long time, started and ran great. It has done this about once every 2 days since.

I have a GM service manual for this truck on the way, but I thought I'd see if any of y'all had seen this problem, or could give me any idea where to start looking.

Are these engines glow plug sensitive even when hot? maybe my glow plugs aren't energizing?

It's getting to the point if I have to go somewhere I don't want to be stranded, I take my old truck.

Thanks guys,
Mitch
 
R

RZucker

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mitch504 said:
I know you guys are tired of me clogging up HEF with pickup truck questions, but...

That same early '99 GMC 2500 with a 6.5 and automatic that I posted about before, since curing the PMD problem the truck has been great for about 6 weeks, then after about a 20 mile hwy run I shut it off for about 15 minutes. When I went to start it, it just spun like there was no power to the injector pump. I plugged in my tested good spare PMD, no change. I opened the bleed screw on top of the filter and got a fountain of fuel with no air, spun it again no change. I checked every fuse inside and out, changed a lighter socket fuse, no change. let it sit a few minutes, spun it for about a minute, it started and ran great. Next 20 times, it started instantly, cold or hot. Then, it spun for a long time, started and ran great. It has done this about once every 2 days since.

I have a GM service manual for this truck on the way, but I thought I'd see if any of y'all had seen this problem, or could give me any idea where to start looking.

Are these engines glow plug sensitive even when hot? maybe my glow plugs aren't energizing?

It's getting to the point if I have to go somewhere I don't want to be stranded, I take my old truck.

Thanks guys,
Mitch
Click to expand...
Glow plugs aren't needed on a hot engine, in fact they shouldn't come on when the engine is warm. Mine starts cold on a 50 degree morning just fine without waiting for the "wait to start light" to go out.
Just for kicks, check the bleed screw on the pump next time it happens. Also the fuel transfer pump relay could be getting weak, Does the transfer pump sound strong when you turn the key on?
 
mitch504

mitch504

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Andrews SC
That's what I was figuring on the glow plugs, you just never know what weirdness car companies get up to. :D The lowest temp since I've had it has been in the 70s and it started immediately.

The transfer pump sounds good, and when I opened the filter bleed screw, fuel hit the hood, so I am getting plenty of pressure and flow.

I had forgotten about the cold water. That used to be Mack's textbook diagnosis for the early '90s VMAC pumps. They specified 5 gallons of the coldest water available, dumped from an open topped bucket. That used to get me some funny looks from drivers, for sure!

My helper just told me that when it did it to her yesterday, she would spin it a second, switch the key off, repeat. After a bunch of times, it started as soon as she hit the key. Is there a relay that sends power to the PMD? Or to the pump otherwise?
 
Coaldust

Coaldust

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That sounds like a malfunctioning oil pressure/fuel pump switch/sending unit. Once engine oil pressure rises, it allows the transfer pump to operate. Tends to act up when the engine is warm. It was designed as a fail safe in the event of an accident, it would shut off the transfer pump. AC Delco part number D1808A
 
mitch504

mitch504

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Joined
Feb 27, 2010
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Location
Andrews SC
Transfer pump is doing fine, good pressure and flow.

I found a troubleshooting procedure on the internet that seemed reasonable.:rolleyes: When it did this yesterday, I checked and had the voltages he spec'ed on several wires, then unplugged the shut down solenoid. truck immediately started. It would run about 1 second and shut off. It did this twice, I plugged it back in and it has been fine since. Next time I'm going to unplug it first to see if it was that or if it was just time to start.

Good news is, UPS just brought my GM factory service manual.
 
mitch504

mitch504

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Andrews SC
Guys, I really hate to post this, and I am trying to figure out how to whisper on the internet, but, I hate when people don't give updates.

I tried to start it with the stop solenoid unplugged and it ran a second, when it wouldn't fire with it plugged in, as I said in my last post. From that point on, it has been flawless.

According to my GM manual, that's just a regular cut off solenoid, powered all the time, grounded through the ECM when running.

It reset the ECM?

Why would it run unplugged?

We really need the shrugging smiley back.
 
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