Bernie
Amateur Radio Operator - KJ4VOV
For the past few weeks I've started having difficulty starting my '99 GMC C3500 with the HO 6.5TD. There's a couple of issues involved so let me list those and then we can get on to the speculation.
First, about 6 weeks ago I managed to cook my 140amp alternator. The truck is a radio communications truck with full warning lights and I was assigned to follow the last runner for the USMC Historic Half Marathon. The last runner was walking, which meant 5+ hours of cruising along behind at 3 MPH. Even in low that wasn't fast enough to keep the revs up and keep the alternator output up and the load literally cooked it. I could smell it burning inside the cab when it finally died, but still was able to limp the truck home on just battery power after the race was over.
Swapped out the alternator for a new one that same day and I was good to go, or so I thought.
Since then I've been plagued with electrical gremlins such as a lightbar controller that cooked itself, a new LED taillight that half the LEDs died in (to be fair, it seems to have developed a water leak) an LED strobe light that decided to no longer strobe, and a radio that now randomly switches itself off and back on. And every now and then the truck has trouble starting. It cranks fine, but will not start.
Now, I believe the issue with the no start is heat related, because I've noticed that when it happens it's always when I've tried to start the truck after it'd been running for awhile then shut off and left sit for about a half hour. Yeah, I can hear you all thinking... "PMD dude! Classic symptoms!" and I'll tell you, that's what I've been thinking myself but... (you knew there was a but coming...)
The original PMD died about two years ago, and was replaced with a remote mount kit from SSDiesel (yeah, on the plenum, but I simply cannot mount it anywhere outside the engine bay, no room with all the lights and speakers out there) and that worked fine for a year, until it failed (runaway) last fall. That was one of the FS PMD's that were known for failing as runaways and I got credit for it and a new gray unit replacement Since then, it's run fine with no more PMD issues. Now, because it's still mounted inside the engine bay I agree that it's subject to more heat, but my understanding is that the gray units can take it, especially when on a heatsink, so I'm willing to give it the benefit of the doubt. Now, today, just a couple of hours ago, I had to run to Costco. Since I had a trailer attached I left the truck parked at the far end of the lot, sitting in the hot sun (99 deg) while I went in, grabbed three items and came back out. Total time, about 30 minutes. Tried to start the truck and while it cranked just fine, it would not catch. At that point, just to eliminate the PMD as the culprit, I opened the hood, let the slight breeze blow through, then poured a bottle of cool (not cold) water over the heatsink and the PMD to cool it even further. The truck still would crank but not catch. Waited a little longer, poured a second bottle of water over the PMD and also over the IP and tried again. Crank but no start. Then I thought maybe my lift pump (original) had packed up, so I cracked the air bleeder on the filter and switched the ignition on for a minute. I couldn't see it spurt from that position, but judging by the amount of fuel that came out and ran over the filter housing, and the fact I could hear the pump clicking, I figured it wasn't a dead lift pump. After twenty minutes of crank a bit, rest a bit then crank some more I eventually wore down the batteries and called the wife at home to come out with her truck. When she got there half an hour later we jumped my truck, gave it time to charge the batteries a bit, then cranked it again. Still no start. I then pulled the air cleaner and had the wife crank it while I gave it a shot of WD40 into the intake, just to see if it would try to catch. Nothing. The wife then went inside to get herself a Coke and while she was gone I let the batteries charge up a bit more, then gave one fairly long crank (long enough I worried about cooking the cables or the starter) and all of a sudden it caught and ran. Little bit of black smoke that cleared right up. The truck then idled there for 15 minutes waiting for the wife to come back out, with the hood closed, in the sun, with the A/C on and the gauge reading 195, never faltered, or stumbled, just idled perfect. When she came out I drove it home and it ran fine all the way, no complaints. Now, this is the third time in the past two weeks that the truck has done this. Each time was under similar conditions, and one of those times also requiring a jump, but this time was the longest period during which it wouldn't start. Each time has been a little bit longer too, come to think of it.
Now, before you offer ideas, and I'm open to all of them, bear in mind this is a pretty new PMD, on a heatsink, and it was water cooled to no effect, so I really do not see this being a PMD problem, but I'm still open to the idea and still wracking my brain trying to figure out where I could mount it outside the engine bay that isn't already occupied by lights, horns or speakers. In back of the bumper is, literally, full. I could not fit half a pack of cigarettes back there, let alone a PMD on a heatsink.
First, about 6 weeks ago I managed to cook my 140amp alternator. The truck is a radio communications truck with full warning lights and I was assigned to follow the last runner for the USMC Historic Half Marathon. The last runner was walking, which meant 5+ hours of cruising along behind at 3 MPH. Even in low that wasn't fast enough to keep the revs up and keep the alternator output up and the load literally cooked it. I could smell it burning inside the cab when it finally died, but still was able to limp the truck home on just battery power after the race was over.
Swapped out the alternator for a new one that same day and I was good to go, or so I thought.
Since then I've been plagued with electrical gremlins such as a lightbar controller that cooked itself, a new LED taillight that half the LEDs died in (to be fair, it seems to have developed a water leak) an LED strobe light that decided to no longer strobe, and a radio that now randomly switches itself off and back on. And every now and then the truck has trouble starting. It cranks fine, but will not start.
Now, I believe the issue with the no start is heat related, because I've noticed that when it happens it's always when I've tried to start the truck after it'd been running for awhile then shut off and left sit for about a half hour. Yeah, I can hear you all thinking... "PMD dude! Classic symptoms!" and I'll tell you, that's what I've been thinking myself but... (you knew there was a but coming...)
The original PMD died about two years ago, and was replaced with a remote mount kit from SSDiesel (yeah, on the plenum, but I simply cannot mount it anywhere outside the engine bay, no room with all the lights and speakers out there) and that worked fine for a year, until it failed (runaway) last fall. That was one of the FS PMD's that were known for failing as runaways and I got credit for it and a new gray unit replacement Since then, it's run fine with no more PMD issues. Now, because it's still mounted inside the engine bay I agree that it's subject to more heat, but my understanding is that the gray units can take it, especially when on a heatsink, so I'm willing to give it the benefit of the doubt. Now, today, just a couple of hours ago, I had to run to Costco. Since I had a trailer attached I left the truck parked at the far end of the lot, sitting in the hot sun (99 deg) while I went in, grabbed three items and came back out. Total time, about 30 minutes. Tried to start the truck and while it cranked just fine, it would not catch. At that point, just to eliminate the PMD as the culprit, I opened the hood, let the slight breeze blow through, then poured a bottle of cool (not cold) water over the heatsink and the PMD to cool it even further. The truck still would crank but not catch. Waited a little longer, poured a second bottle of water over the PMD and also over the IP and tried again. Crank but no start. Then I thought maybe my lift pump (original) had packed up, so I cracked the air bleeder on the filter and switched the ignition on for a minute. I couldn't see it spurt from that position, but judging by the amount of fuel that came out and ran over the filter housing, and the fact I could hear the pump clicking, I figured it wasn't a dead lift pump. After twenty minutes of crank a bit, rest a bit then crank some more I eventually wore down the batteries and called the wife at home to come out with her truck. When she got there half an hour later we jumped my truck, gave it time to charge the batteries a bit, then cranked it again. Still no start. I then pulled the air cleaner and had the wife crank it while I gave it a shot of WD40 into the intake, just to see if it would try to catch. Nothing. The wife then went inside to get herself a Coke and while she was gone I let the batteries charge up a bit more, then gave one fairly long crank (long enough I worried about cooking the cables or the starter) and all of a sudden it caught and ran. Little bit of black smoke that cleared right up. The truck then idled there for 15 minutes waiting for the wife to come back out, with the hood closed, in the sun, with the A/C on and the gauge reading 195, never faltered, or stumbled, just idled perfect. When she came out I drove it home and it ran fine all the way, no complaints. Now, this is the third time in the past two weeks that the truck has done this. Each time was under similar conditions, and one of those times also requiring a jump, but this time was the longest period during which it wouldn't start. Each time has been a little bit longer too, come to think of it.
Now, before you offer ideas, and I'm open to all of them, bear in mind this is a pretty new PMD, on a heatsink, and it was water cooled to no effect, so I really do not see this being a PMD problem, but I'm still open to the idea and still wracking my brain trying to figure out where I could mount it outside the engine bay that isn't already occupied by lights, horns or speakers. In back of the bumper is, literally, full. I could not fit half a pack of cigarettes back there, let alone a PMD on a heatsink.
