Stutter/Stall Issue: Troubleshooting/Confirming PMD Failure?

Hi all,

My vehicle is a 94 Chevrolet K1500 Blazer with SSDiesel Intake and Exhaust. It's got 264k miles on it. Recently I've been having issues with intermittent sharp brief engine drop outs at highway speed and stalling at low speeds. It's not a gradual loss of power but rather an immediate and complete power loss during the events.

The problems started a few miles after a fuel stop, so I initially thought I might have gotten some water in the fuel. But that doesn't seem consistent with the suddenness and completeness of the drop outs, and I haven't noticed any smoking or other symptoms during the events. (The vehicle has a "Water in Fuel" indication that has never illuminated; I couldn't say for sure if it's actually functional.)

The problem has become progressively worse over about 85 miles of subsequent driving. Usually the engine will start right back up if it stalls, but recently it's started to be difficult to restart at times and will run for only a second or two on the first few attempts.

I checked the ECU using GMTDScan Basic, and it isn't throwing any codes or indicating anything else obvious.

From the symptoms, I am suspecting the PMD/FSD. I know this engine had its PMD replaced once previously by a prior owner, but that was about ten years ago. The PMD is still in the original location on this truck.

Are there any other steps I can try to confirm/isolate the problem?

Thanks!

Hi Ryan
First thing i would do considering the history you provided...
Order an new PMD and get an extension harness and heat sink from a reputable source and install,lots of ideas for new locations on this site.Do some reading and pick your location.If you keep the truck you will need a PMD at some point so it's a good place to start.
I would get the new Stanadyne grey PMD,but there are some other ones out there.I didn't have much luck with the others.But some people swear by them.
The test for a PMD is to remove it and find a lake,toss it into the lake,if it floats it's good if it sinks leave it there.:D
The ignition switch is another place to look for problems.
Thomas

Thanks for the pointers Thomas,

That pretty much confirms my impression of the proper approach to PMD diagnosis!

I've owned this truck for about eight years and completely rebuilt the chassis, so a new remote-mounted PMD is probably a good idea on general principles. The drive train on this thing is obviously worn but has been pretty reliable up to this point despite some typical 6.5 foibles.

Good idea about checking the ignition switch though. The closest thing to these symptoms I had seen before was the engine cutting out intermittently when a battery cable was loose.

It's currently got a black Stanadyne on the pump. I had been considering the SSDiesel PMD:

http://www.ssdieselsupply.com/c6_ssd...resistors.html

But the grey Stanadyne seems like an obvious choice. The SSDiesel part could just be the same thing in a different box for all I know. They also have a nice remote mounting/heatsink kit that would make things easy, but is a little pricey.

BEST location is on the inside of the front aluminum skid pan thats right under the radiator.

remove the two bolts at the front xmember and swing the pan down.

Mount the cooler on the inside of the pan and make sure you have enough room to swing the pan and not compromise the harness.

Tie wrap to suit and good to go.

Easy to get to and fairly cool with lots of air movement.

Get a cooler that has a good flat mounting surface for the PMD and use Computer processor heat sink paste between the PMD and the cooler.

Snug the tiny little PMD bolts down in a careful cross X pattern .

Use some blue loctite (sparingly) on those bolts to keep them from loosening.

These are small bolts, so easy does it.

Don't forget the new resistor for the PMD if you need one.

Easy to fish the old one out.


Do not be tempted to mount a PMD/cooler on the intake.

The top of the engine area under the hood is hotter than the blue blazes of hell, worse in the summer, and this is why the PMD's fail.

Great pointers, I appreciate it Robyn! Thanks for the warning about the intake-mounted coolers like the SSDiesel. I also see other posts where folks have had bad results with that idea. The radiator pan location sounds great, guess I just need to find (or make) an extension harness.

Hi Ryan
The extension harness quality is important as well.
You don't want to be solving one problem with another problem.
If Kennedy Diesel still sells them you know it will be a quality product.
If you make your own do some research on the size of wire,and connectors there have been cases that someones extension harness caused problems down the road.Then you will be back where you are now looking for a problem that isn't obvious.
Thomas

As Thomas says, go to John at Kennedy and get the harness, Heat Sink and PMD.
John will take good care of you.
Dave

Quote:

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Originally Posted by DieselDavy

As Thomas says, go to John at Kennedy and get the harness, Heat Sink and PMD.
John will take good care of you.
Dave

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Ditto!

I'm still using the heat sink and extension cable I got from John over 12 years ago. Been through a few PMDs since that time, though.

Casey

Awesome, thanks guys. Looks like they are still available from Kennedy. I'm thinking that and a grey Stanadyne under the radiator like Robyn suggests sounds like the way to go.

Hopefully that will solve my problem; if not, it should solve the problem I'm going to have soon anyhow! :D