96 Chev 6.5L Turbo - after 20 min starts running rough like it's missing

[jeff6.5]

Hey everyone:

Background:
This truck is a dedicated snowplow—not licensed for the road—and only gets used when needed, usually at low RPM. I previously had starting issues, which I fixed by replacing the FFM and the fuel hoses (thanks again, Will). After that, it started much better, but then it began randomly dying. Replacing the PMD (aftermarket) took care of that problem.

New Issue:
Now I’m dealing with a different problem: after about 20 minutes of running or plowing, the engine starts running rough. This has happened twice. The first time, a couple of weeks ago, it had been running for around 20 minutes when it started coughing small puffs of black smoke, running rough, revving slightly on its own, and even stalled once—though it restarted immediately.

While going through The 6.2L/6.5L Diesel Troubleshooting Guide (1998 edition), I wondered if maybe an injector was going bad.

Naturally, being in NW Ontario, we got hammered with more snow right after the last storm. The next morning, I went out with my fingers crossed, and it fired right up. It ran smoothly for about 20 minutes again… and then the same symptoms returned. This time, it stalled several times but always restarted instantly—sometimes stalling again right away, sometimes just idling very roughly.

Has anyone run into this before? Any theories or suggestions would be greatly appreciated.

 

[MrMarty51]

Hey everyone:

Background:
This truck is a dedicated snowplow—not licensed for the road—and only gets used when needed, usually at low RPM. I previously had starting issues, which I fixed by replacing the FFM and the fuel hoses (thanks again, Will). After that, it started much better, but then it began randomly dying. Replacing the PMD (aftermarket) took care of that problem.

New Issue:
Now I’m dealing with a different problem: after about 20 minutes of running or plowing, the engine starts running rough. This has happened twice. The first time, a couple of weeks ago, it had been running for around 20 minutes when it started coughing small puffs of black smoke, running rough, revving slightly on its own, and even stalled once—though it restarted immediately.

While going through The 6.2L/6.5L Diesel Troubleshooting Guide (1998 edition), I wondered if maybe an injector was going bad.

Naturally, being in NW Ontario, we got hammered with more snow right after the last storm. The next morning, I went out with my fingers crossed, and it fired right up. It ran smoothly for about 20 minutes again… and then the same symptoms returned. This time, it stalled several times but always restarted instantly—sometimes stalling again right away, sometimes just idling very roughly.

Has anyone run into this before? Any theories or suggestions would be greatly appreciated.

Time fir a spare PMD to be installed then report back.

 

[jeff6.5]

Time fir a spare PMD to be installed then report back.

I replaced the defective Stanadyne PMD with a cheap Chinese knockoff from Amazon. I was wondering if that would come back to haunt me. I'll try to locate another or even rebuild the old one. While I have you, what's the deal with the small resistors that slide onto the pins of the PMD harness? What is the purpose of those?

Thanks

Jeff

 

[dbrannon79]

if you still have the old one that you replaced, I know it was randomly shutting off with it, but would it run longer than 20 minutes? if so, mount it to something flat that will protect it from burning out . if you have a spare heat sink use that. connect it up and try it to see if the current symptoms go away.

This will help tell you if it's the jungle site special PMD or something different. next is to replace the return line on the IP with a clear piece if tubing to check for air in the fuel lines.

are you running the PMD on an extension mounted out of the bumper or is the PMD still mounted on the side of the IP? heat is the #1 killer of electronics. having that PMD right in the valley of the engine catching all the heat from the engine, doesn't matter if it's blow freezing outside. your engine will get up to 200 degrees and heat rises, so it's right in the path of lots of heat being anywhere under the hood. otherwise if it's outside one an extension, check the connectors to see if moisture or corrosion has gotten into the plug. your in the snow so I'm sure it has seen some salt too. salt is a good conductor and if there is any moisture in the connector, that can cause many odd issues even kill a PMD.

 

[MrMarty51]

I replaced the defective Stanadyne PMD with a cheap Chinese knockoff from Amazon. I was wondering if that would come back to haunt me. I'll try to locate another or even rebuild the old one. While I have you, what's the deal with the small resistors that slide onto the pins of the PMD harness? What is the purpose of those?

Thanks

Jeff

The resistor is for specific IP calibrations.
9 feeds more fuel and smaller numbers is less fuel.
Stay with whatever number is stamped on Your current resistor.
It is recommended by many members in here to run with a NO.5.
I have three spare PMDs each on their own extended harness behind the front bumper.
I numbered the terminal plugs on each end so if one PMD fails i unplug that one, look at the number, plug in one of the spares. When time and weather permits, get under the truck, unplug the harness with that number, remove that PMD and get another one ordered.
Leroy Diesel and Quad Star Tuning both sells the Flight System PMDs and they pack a lifetime warranty.
Right now I have two Flight System PMDs and one Dorman, Both brands is lifetime and the Dorman is purchased from oriellys. But I’d stick with the Flight Systems but just keep a spare on hand as it takes a couple weeks to get the replacement unit.
I ordered this Dorman immediately after I received the truck, just from what I had read on the form here.
Good thing too, within several days of the Dorman unit arriving the one on my truck failed, weird accelerations, shut downs then rev back up again with copious amounts of black smoke each time it would rev.
Oh yeah too, I believe that maybe Dorman may have bought out Flight Systems but the FS units is stll made in the USA, Last Dorman was still chinesium.