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FSD/PMD an experiment

Turbine Doc

Turbine Doc

Just Another Diesel Guy
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Gautier, Ms./Anywhere Southern USA
This is from the old site I thought I had posted before here but could not find it this morning wanting to point Chessie to it as a reference point of prior experimentation posted back in 2004.


6-27-2004

I have a little experiment I have been thinking on, that I finally got around to doing with the infamous FSD, maybe old ground already covered maybe not.


In Jan 04 I had a FSD "go bad", shut me down on the highway on a return trip from my hunting camp about 2 hours into the 2.5 hr return trip, outside temp was 50F, FSD mounted on a cooler was cool to the touch but would not let the truck start, it had stumbled a couple of times before shutting down, 1 restart then no start. At the time that FSD had about 50K on it, swapped to the new spare I carry and came home. New spare has about 10 K mi on it.


I got home and cleaned up the Bad FSDs transistor mount studs , nuts, to remove any oxidation that might be present, and re-torqued to 10" lb, I slaved it in and truck started right up, it became my spare.


With all the debate it's heat, its loose fasteners, I decided to run an experiment but did not get to it today. Bad FSD reinstalled at 84200, now at 84212mi no problems, will long road test tomorrow.


I took "bad" FSD and; reinstalled it on the cooler, but I 1st filed a small groove in it's base to accommodate a thermocouple wire that touches one of the transistor bases just to see how hot these things actually get and how long will this "bad" one hang in there.


My cooler is mounted on drivers side fender in pocket/bracket where a gassers washer fluid tank goes.


My engine was warm I had been road testing brakes after installing new stainless braided brake lines, I had run it for about 15 minutes. I only have 1 thermocouple so I don't know under-hood temp, ambient air was 80 F.


1st run was 15 minutes with engine at idle, hood down FSD at 96F starting went to 144.8 F in 15 minutes


I shut down the engine for 25 min and temp had dropped to 119.3


I restarted engine and drove for 10 min city traffic 0-50 mph temp varied 135-139


Shut down for another 6 min temp went to 131, restarted and within 4 min 40 sec temp rose to 151.6


Shut down engine after 6 min of driving 0-50 and engine was 150.7


After 42 minutes FSD had cooled to 129.3


After 2 hr 10 minutes FSD was 116 deg


Truck restarted FSD 7min 45 sec 116F up to 133 F 0-50 driving approx 2 miles


shutdown for evening FSD after 30 min back to 118


Will collect more data in AM, I'll also be collecting some numbers on IP PMD location later
 
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Okay I made a run yesterday 6-27-04 to my hunting camp I collected some interesting data. Basically the truck ran for 8 hrs start and stop hi way and woods crawling in 4wd . (Edit transistor after overnight was 100F)


I have 2 latest gen FSDs (34583s) the "resurrected one" as of yesterday had 343 mi on it, I put another 70 miles on it today so I'm up to 413 since retorqueing transistor nuts. Yesterday it was 88F outside today 91. Engine max temp was 192F and fuel temp was 140-144F


With temp probe in transistor cavity, and FSD cool plate mounted on driver side fender as before test I recorded following data:


After 85 minutes of driving temp at hi-way speed 70-75 transistor 135- 150, I shut off truck temp dropped to 147 after 7 min shutdown I restarted the truck after 3 minutes temp peaked up to 170.


Temp gradually reduced after 8 minutes back to 151 and varied 138-150 depending on speed for remainder of the trip 0-75mph about an additional 1.5 hr. total of about 2.5 hr of heated engine/FSD.


Once at the camp I had to shift to 4H gear crawled thru woods, stopping here and there to clear old dead falls across the road, the truck was left idling during time to clear falls, about 30 minutes on camp road I arrived at my cabin, 0-10 mph driving FSD temp was 213.5 and slow rising .1 deg every 3 sec when I shutdown.


I popped the hood to get some surface temps, after removing temp probe from FSD cavity the cool plate surface/fins was 185F 4 min after shutdown, temp on intake manifold was 178F after 10 min FSD plate was same.


I restarted the truck about 1 hr later for return trip this time with temp probe on intake at hi-way speed 70-75; intake temp was 187 within 15 minutes, FSD Plate/fins very cool 108-113 F, engine compartment at hi-way speed 160F just above engine aft of IP.


I relocated temp probe to base of the inactive PMD still installed there, (I have 2 spares 1 in glove box and 2nd like new on IP). temp at it's base at hi-way speed within 7 minutes went 153F to 169 F following the shut down to change location, I ran for another 40 minutes with probe here.


I then stopped with engine idling then slow drive for 2 miles @ 30 mph max IP/PMD was 165, FSD cooler surface temp was 138F


Initial conclusions from this are the FSD cooler does reduce transistor temp, with good airflow FSD even cool to touch. Further away from engine is better, probably outside engine bay is best. Right now I only have 1 set of transistor cavity readings, to nail this down some more I'll move the cool plate to the intake manifold and run same test with temp probe in transistor cavity.


Then I might move to the IP but it's such a PITA to get the PMD swapped over, last test I'll run is on a long extension into the cab to see if harness length is a contributor. I might also get a second temp probe from Sears so I can make better comparison without "skewing" result from frequent hood openings.


I think as we have found in past 2 fail modes at work heat itself 213 + on a transistor is darn hot, and loosening of mounting from heat/cool contraction/expansion reducing "clamping force" and giving poor ground to transistor base.


stay tuned folks more to follow.
 
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8-4-2004

Update,
1325 mi and still going, put to ultimate test weekend before last, as hot under the hood as I've seen since I've owned this truck.

Towing my backhoe home from camp est. 18K towed weight 6K GN trailer, 12K backhoe; 101F 100% humidity MS day 50 mi short of 170 mi trip lower IC hose popped off for 2nd time that day just prior to cresting top of huge bridge(not sure of the incline at least 6 deg grade) I-65 South just 20 mi North of Mobile AL. "Dolly Parton" bridge to some, because of 2 side by side humps you get the idea.

Went from 45mph to 10 mph nearly instantly like loosing half an engine without any turbo boost, fortunately I had enough fwd momentum to make it over the top.

After getting arms burnt 1st time I fixed it that day I decided no more big hills left I'd finish drive home without turbo, I did not have temp probe with me but it was so hot under hood nothing could be touched for long, burns on arm still have light scab coming off.

Major Wrong decision to limp home that way, while I had no long hills left, I did have many little ones with long pulls in them; ever try to pull 18K stopped with basically 1/2 an engine; it ain't purty, once rolling I was able to hang in about 40-50 mph.

Getting rolling or climbing grade was hard part 5-10 mph and a long string of P/O-ed folks behind me, fortunately I was on back farm roads at the time this was happening folks sort of used to it.

H20 was getting hot up to 225F, trans fluid in pan was 200, EGT was 900 post turbo, IAT 250. when on the throttle hard making plenty of black smoke, I looked like one of those tractor pulling sleds(Guess I was one sort of).

I made the rest of the trip home windows down, heater on max hot to pull off some heat, and when buddy following radioed "heavy black smoke" backed off throttle, no sense in wasting the fuel it weren't doing no good making smoke.

All in all I survived, but at the end of the trip I was wrung out. Without the mods in my sig I doubt it would have been possible, the 83mm in Heath reflash I saw on the scanner makes heaps of black smoke without the turbo assisting.

Someone in another thread asked how tight to torque the FSD transistor nuts, using a quality in lb torque wrench and progressive torque I torqued to 10 in lb, I used progressive torque 2-4-6-8-10 in lbs as material under transistor is somewhat compressable, so rather than load up one side stage torqued, so far so good.

Will keep posted as time goes on.
 
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8-4-2004

This was my response to a member asking about fans added to the sink when under hood, and commiserating about my trouble I was having at the time

Nuthin I could not handle, just one of those things that happen, partly my fault, I went cheap on the clamps, t-bolt clamps IMO only way to go everything else is second best. Especially if you plan on running at elevated boost levels, I was peaking 12-13 psi.


As far as fans go; yes they would help, but blowing hot engine compartment air across them will only produce limited result but better than no flow when stopped or crawling along going slow.


I'm thinking of a Heath bumper mount kit, or toying with idea cutting a hole in the fender and having heat sink fins protrude into wheel well area (Triggerman's Idea over at TDP). I'm on the fence about locating in the cab under the AC duct what if AC is broke or it's too cold, hot transistor and cold air may not be a good idea.


Better maybe to use outside air which be closer to transistor operating temp but still enough delta to transfer heat. It's been a while since I looked at my thermodynamics notes from turbine school so I might have it all wrong here, but from my Navy days on water to steam, oil, &; bleed air heat exchangers if we put too much cold water in the coolers we actually over-temped and hammered/cold shocked the condenser.


Can we cool the heat sink too much and actually reduce a heat sinks capability to dissipate heat, I don't know just thinking out loud, from my discussions with Bill Heath his results show that cab mounted FSD were not as long lived as his bumper mounted ones maybe this is why.


Another possibility since we now have found that loose transistor mount screws can be a contributor in sporadic FSD operation, maybe as a result of large temps swings that would come from cold AC air vs cooler ambient air may be exercising and loosening fasteners over time. Also what about condensation causing connection contact point oxidation, as nuts try to maintain bonding plane especially in location as MS with 60+% humidity year round.


I think there are several fail modes for the FSD no one fix addresses all, and depending where you live may also impact results. Heat #1 problem, loose fasteners #2, combined heat and loose over time #3, faulty/weak transistor # 4, corrosion/gnd plane problems#5 order of occurrence a guess on my part from reading posts here and TDP over the years.
 
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8-5-2004

This was my reply to a member asking about salt & water intrusion note the date some have been running nostril mounted since then

With the right sealing compound risk of water intrusion should be minimal, Bill Heath says he ran his submerged in water for a while just to prove to himself his would work (he is using a proprietary compound though).


I'd try maybe in bumper holes fins in air stream, FSD mounted opposite from air side, verify proper torque on transistor nuts and FSD to cooler screws, then seal seam at joint between the 2 with hi-temp rtv, GE type 106 red is a good one we use to hold turbine compressor shrouds in place, Permatex red looks to be very close to that, be sure bonding surface is oil free before applying it.
 
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8-7-2004

Another comment same member asking again about water:

Olee I doubt water intrusion will be a problem with the connector if you have a proper GM Weather-Pak connector, it wiil be tight those are the same connectors used under your trucks frame that hook up everything, lights, lift pump, trans, 4x4 transfer case, if water & muck under there does not get in those you won't have a problem on the FSD.
 
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8-15-2004

Broke it again, made it 2300 mi before it quit again; when I got up to drive back the morning after our wild ride; the truck fired and died 1st attempt, I swapped to my spare PMD and it started right up, on a whim I reinstalled the "suspect" PMD the truck restarted, I drove it to the front of the hotel about 300yd and shut down, when I tried to restart no joy; crank no start. I drove home with the spare on the fender mounted FSD cooler, I haven't started to TS the suspect FSD yet, need my good tq wrench from the office.
 
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8-17-2004

Okay it's "fixed" again (suspect FSD) haven't driven anywhere yet, but started restarted about 10 times in the driveway revving engine up and down. Now reinstalled at 86987 mi will see how long it lasts.


I goofed I did 2 things at same time & now don't know which "fixed it" I should have tried one before the other. 1st thing I did was read the calibration resistor, I got intermittent reading (don't know if it was me trying to hold FSD and read pins at same time or oxidized pins).


This is a #9 83ohm, on the back side of the plastic holder there was some slight brown discoloration (Heat caused ???). I sprayed the cavity & resistor with Blue Shower contact cleaner & let dry fully before reinstalling resistor in the cavity.


2nd thing I did was re-check torque of transistor nuts, they were looser than the 10" lbs I had torqued them to previously. 1 only took 5" lbs before starting to retorque, 2 took 7"lbs, and the last took 8". All are at 10" lbs again, will see how long they hold up.
 
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8-18-2004

I think it's dead lasted 44K or so mi in it's life time, it moved a grand total of 50' this morning before stalling and stopping and restarting, back to the spare, so unless somebody has better ideas of what to check maybe time for a burial ceremony RIP little FSD
 
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This comment from GMCTD 8-18-2004

Could be Emitter\Base pins have worked loose at the solder-connection to the pcb from heat-cool cycles and the re-torquing procedures.


Might try removing the potting compound around the four leads, resolder the connections.


Emitters are parallel to isolated power via very low resistances, Bases are darlington driven parallel via 390ohms - either way, no workee.


Parallel Collectors (case) are shorted together thru stainless fasteners to pcb circuit, to FSD coil - should measure direct short between cases and fasteners to FSD pin B.


Be good to de-pot that failure for further investigation, after trying the solder re-flow job on the transistors.
 
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9-26-2005

Bumping back to the top again, just saw another post asking hot hot does it get, and how long before I fail.

There is no known when it will fail, some have gone 200+K without failure, but preponderance of evidence has been much lower incidence with those mounted off pump out of engine bay, my choice has been Heath mount on the back side of my license plate, 7yr warranty was final selling point.

From my experience a "used but good" driver is just that with emphasis on used, the driver distress is cumulative IMO, depending on mfr of the transistor and the quality to which they were built to are the reason some last longer than others, if going used but good route even remote mounted, carry a spare, as these things never fail at a good time. That said even with my new store bought Heath driver I still carry a spare, fortunately after a year since installing it, I've not needed it.
 
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10-03-2005

This was my response to someone asking about adding locktite to keep transistor nuts from loosening up:

the base leg of the transistor is carried thru the studs, lock tite would act as an insulator and would not carry current then, you get same problem with oxidation between the stud & nut, which also is corrected by retorque, actually before retorquing you should completely remove the nuts, & then buff them and the transistor bases so you get good electrical bonding contact again.
 
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Okay to today 8-26-2010,

The Heath remote mount installed in 2004 is still chugging along, been on the bumper or in it (Buck stop bumper installed in Jan 2007, and has been inside it since then).

The bumper mount survived multiple trips to winters in VA, MI, PA, NY and points between as well as briefly submerged in flood waters driven through during hurricane Katrina and that was salt-water.
 
Just a thought Tim. Would ample use of dielectric grease be an advantage? Maybe it's in the thread and I missed it.
 
Good info in all those posts doc. Thanks for that. One of the things I was going for was to make it easy to change when it goes bad. I was looking at that FSD heat sink and it looks as if there is room to add a second one to it for a quick change over if the other one quits.The FSD seems to be mounted mostly at one end. Whether it effect the heat transfer from the other is, of course unknown, but probably not a problem. Since the one on this truck is of unknown age/ mileage., it might be a good idea to have a quick change spare. The grey ones are supposed to be improved, but from some posts, maybe only the color was changed.:rolleyes5: I wonder if these fail quicker on trucks that are worked harder since you say temp of transistors increase a lot with increased fuel output. Are Humvees electronic or mechanical? If electronic, are these mounted on the IP on them also? If so, I wonder how they hold up in the heat in Iraq.
 
As usual, a clear, concise, detailed, real world experience, that leads to "just about a unchallengable" verdict on the PMD/FSD and how heat effects this necessary evil demon.

In my opinion this thread sould be a "must read" sticky attached to PMD/FSD.


All in favor?
 
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