FSD on Heat Sink Toasted

[Franko]

Hello All,

98 4WD 2-Dr Tahoe 6.5TD with 205,xxx miles. K&N air filter, Racor 645. Almost new dual batteries. Almost new fuel lift pump (Autozone E 8012s).

Driving along parkway with my three kids this past Sunday afternoon, just tanked up 20 minutes before. Going uphill so had pedal down a bit to maintain speed, noticed less power available (been meaning to change the Standadyn fuel filter for the past two weeks now).

A little black smoke at first, then more. Engine revs start going up and truck accelerates (not surging), hit the brake pedal enough to slow it down, engine revs settle then begin to go up again and truck accelerates again, hit brake pedal again. Engine starts surging.

Take the next exit where I know there is a gas station and service center next to it. Waiting at stop sign for traffic to thin out while I'm dying because the engine continues to surge widely up and down, hazard lights flashing. Local cop lets me go ahead and we pull up right in front of service center (closed). Shift into Park and engine dies. Guardian angels working full-time, only 8 minutes from home.

Popped the hood and hearing fizzing, see smoke coming from remote-mounted FSD Cooler on upper intake manifold. Bubbling, yes, bubbling out of hole that developed between connector and aluminum heat sink.

Waited for engine to cool down a little (at least half hour). Disconnected both battery grounds. Changed fuel filter while waiting, will wait until I reconnect the pump mounted FSD to bleed air out. Disconnected the wiring harness from FSD Cooler, disconnect ground from heat sink, removed from the intake manifold, checked the harness connector visually which looked intact. Used a Torx bit to remove the FSD from the heat sink, noticed two mounting screws were loose (!@#$%^&*). Should have used thread lock before I installed it. Mental note to retorque regularly in future and use RTV to seal perimeter.

Took another hour for engine to cool down enough to wiggle connector back onto the stock FSD. Bled air from filter.

Told kids to pray and I cranked away. No start. Tried several times while allowing starter to cool down in between cranks (bled fuel from filter, too, just in case). Called wife to pick up kids, called Geico Roadside Emergency to arrange free tow. Flatbed International (nice truck) dropped off Tahoe at local mechanic/friend less than half mile from home.

Went home to retrieve OBD2 reader, no codes. Putting together the following shopping list:

1. FSD/PMD module
2. ECM
3. Fuel cutoff switch
4. Assorted relays
5. Extension harness for FSD/PMD (to get away from heat soak)

What else should we be looking for? That is, other than the DB4. Could this be also mechanical/timing? We love this beauty/beast and need it back. Thank you in advance and Happy Fourth of July!

Regards,
Franko

[Robyn]

A fried PMD will do just what you experienced.

If you cranked the engine while you were bleeding air you could have air in the IP.
Depending on the year of the truck you can place the tranny in drive and then turn the Ign to start and the Lift pump will run without spinning the starter.

94's are a bit different to do though. 95 can be done with the switch and the tranny in D.

********Be sure to set parking brake for safety ********

Was the original PMD on the IP still good or had it failed previous to the install of the remote unit.

The heat sink up top is still too bloody hot of a place. Get an extention harness and mount the sucker down in the front area under the radiator on the inside of the front fold down skid pan.

Let us know

Robyn

[rameye]

I think Robyn hit the mark that there is a fair chance the pump gulped air...gonna have to crack the injectors you can get to and crank till they flow fuel.

After that...with a known good PMD in place it should start.

Cant help but wonder if a legitimately fried PMD couldnt knock the pump internal solenoid out of the picture??

I'll leave that pondering to More power and Kennedy....

[Robyn]

If there are no codes stored I think its just the PMD and the air issue.
Bleed the fliter out good and the pull the line off the IP and bleed it to get air free fuel there then buckle it back up and give it a go.

You may have to crack a couple injector lines though.

[Franko]

If you cranked the engine while you were bleeding air you could have air in the IP.

I bled the new fuel filter a couple of times before cranking -- got a half cup of diesel through clear PVC tubing into an empty soda bottle. Still, will go ahead with bleeding to the IP and to the injector lines I can get to.



Depending on the year of the truck you can place the tranny in drive and then turn the Ign to start and the Lift pump will run without spinning the starter.

I have a second pair of wires (fused +, -) run to the fuel lift pump which I use for air bleeding the filter.



Was the original PMD on the IP still good or had it failed previous to the install of the remote unit.


It was still good. The IP and PMD were replaced by the dealer at 95,000 (?) and I installed the SS Diesel FSD Cooler at 125,000. I'm just kicking myself for not using thread lock on the bolts that secure the PMD to the heat sink.



The heat sink up top is still too bloody hot of a place. Get an extention harness and mount the sucker down in the front area under the radiator on the inside of the front fold down skid pan.


I'm still kicking myself for not mounting the FSD cooler really remote from the engine compartment. I picked up a couple of Peltier heat pumps (8 amp draw at 14 volts) which I was planning on mounting one Peltier (with a copper heat sink on the hot side) onto the heatsink next to the PMD module to draw heat away from the aluminum heat sink. The other Peltier (with a copper heat sink on the cold side) was going to be mounted on the turbo heatshield to generate voltate/current to power the FSD cooler-mounted Peltier. I'll still do it but with the FSD cooler mounted as you are suggesting - remote from the engine compartment.

Thanks, folks. I'll keep you posted.

[Robyn]

Thats the ticket.
get the PMD out of the crispy zone.

[j_k_auto]

Not to highjack this thread but I am glad I got away from the whole pmd issue. I read about this all the time. Yes you need to get it in the front bumber area.

[JohnC]

If you tried to reconnect the connector to the FSD mounted on the pump, without removing the manifold, there's a good chance you damaged the FSD connector and this would account for your no-start. Ask me how I know this... :mad:

[moondoggie]

Good Day!

Please don't take this wrong, just friendly advice, but Peltiers for FSD/PMDs are only if you like doing that sort of thing, they almost certainly won't make the the FSD/PMD last longer. ;) The consensus seems to be that FSD/PMDs fail due to the extreme ambient temp swings underhood causing expansion / contraction of the packaging, NOT failed semiconductors.

If the FSD/PMD is IM-mounted, they will only help while they're powered, so to work effectively they would have to be powered anytime underhood temps are high, which is when the truck's running, & for a long time after you turn off the key.
If the FSD/PMD is remote-mounted (in front of a battery, on the skid plate, etc), there's no need for a Peltier.Again, no offense intended, I've done LOTS of things that didn't need doing just because I wanted to do it. Plus, maybe it couldn't hurt, eh? Plus, maybe it actually WILL make the durn thing last longer.

Good Luck & Blessings! :D

[Franko]

If you tried to reconnect the connector to the FSD mounted on the pump, without removing the manifold, there's a good chance you damaged the FSD connector and this would account for your no-start. Ask me how I know this... :mad:

Please, I can't stand the suspense... anything is possible, including the possibility that the harness connector itself was damaged (see "bubbling" when the PMD died).

We are popping the lower intake manifold to get to the IP. Just waiting on a PMD we ordered.

Thanks, JohnC. How do you know this???

[Franko]

Good Day!
If the FSD/PMD is IM-mounted, they will only help while they're powered, so to work effectively they would have to be powered anytime underhood temps are high, which is when the truck's running, & for a long time after you turn off the key.


Thanks moondoggie! I agree with the consensus but trying something different is in my blood... I will eventually remote mount the PMD in the bumper hole, maybe with the Peltier setup.

The dual Peltier setup does not require battery power. One Peltier needs power to pump heat away from the PMD. The other generates power if you keep the hot-side hot and the cool-side cool. With the hot-side remaining hot after the engine is turned off, the Peltier will still keep generating power as long as the cool-side is kept cool. The challenge there is how to keep the cool-side cool and I have a couple of ideas that may work (one is to mount it on the exhaust pipe where the cool-side can be exposed to outside air -- can't do this if mounted on the turbo heat shield). Anyhow, this part is fun. Getting the bloody truck to run again is where the REAL fun is.

Thanks again, moondoggie! It is appreciated.

[moondoggie]

Good Day!

Thanks for not taking offense. Personally, I wish I could try this myself, it sounds like fun. :)

Blessings!
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