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Old 08-18-2011, 03:52 PM   #1 (permalink)
kshow
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Sudden acceleration. Sometimes surging.

Thanks in advance.
'98 G3500 Extended Van, F vin, 176,XXX mi., 6.5 L TD, Just installed used 4L80E tranni, After market pmd last spring on aluminum fab'd block higher off intake near IP, new turbo boost solenoid, new vacuum pump.

Van has a couple issues that don't happen at the same time. Sudden massive acceleration/over revving accompanied by heavy black smoke oftentimes. Does it at times even in park or nuetral. Does it even with foot off accelerator at times. At other times at speed, van will take off faster than when running normally and putting the pedal to the floor. Has revved so high I shut down for safety, though losing power steering/brakes isn't all that safe either. Will let sit for a moment, and re-start, and sometimes this works, sometimes I have to let it rest longer. I'm getting tired of rolling up to intersections in neutral...

Other issue is rhythmic surging, which started before the sudden acceleration/smoke screening. When this happens, I can be on the throttle and it adds power for a second, then de-powers for 2-3 seconds before adding power again, and of course some good smoke most of the time. It'll only go 10-20 mph in surge mode. So.... we take a rest, fire up and get on the way.

The van only seems to display symptoms when under normal running temp. Never when cold. Some days it won't do it at all, others I'm glad I have a phone for the tow truck.

CODES: P0236 Turbo boost sensor a ckt rng/perform
P0251 Injection pump metering cntrl A
P0756 Shift sol b ckt perf stuck off
these faults were all on before the tranni swap.

Also, van will at times at idle (stop signs) run really, really ROUGH. It shakes the entire 4.25 ton van, and I always expect it to die.

I read the forums, so I think I can expect PMD, IP, or something related to be the culprit. Has anyone had these symptoms??? Please help.
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Old 08-18-2011, 05:29 PM   #2 (permalink)
racer55
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Your PMD is a black one with a notch in one corner where the mounting screw goes right?

Sounds like the "toyota" failure mode of the flight systems PMD's.

Get a proper heatsink and extension cable and move your next PMD outside the engine bay where it is exposed to less temperature and temp swings.

Keeping the PMD cool and at as close to an even temperature or ambient temp as possible gives them the best chance at a long life-it is still a crap shoot though.
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Last edited by racer55; 08-18-2011 at 05:29 PM.
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Old 08-18-2011, 06:45 PM   #3 (permalink)
GbByChubsy
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I am going to be a pessimist here and say you sir need a new IP. All the right signs, but as racer said swap out the PMD first.
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Old 08-18-2011, 07:17 PM   #4 (permalink)
JMJNet
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P0251 is a sign for new IP but then the PMD on intake can be a culprit also.

I am not sure if bad PMD can cause P0251.

So, agree with trying a GOOD KNOWN WORKING PMD.
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Old 08-18-2011, 09:55 PM   #5 (permalink)
kshow
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Does any place "rent" good known pmd's??? Will pay shipping, of course. This truck is my business' only vehicle. If necessary, which remote kits are the best for the pmd? (Extension wiring, pmd...) Thanks.

Has anyone had both of these symptoms at relatively the same time? I drove the van today, and it gave me trouble after startup (after running temp achieved) several times with the over revving & the rhythmic throttle/non-throttle (10 mph max.).

Then, now it seems I need a thermostat, as my temp climbed steadily near the end of my drive to over 210 F, however, she never displayed any of the running issues when it was that hot! What's UP???

Thank you!
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Old 08-18-2011, 10:14 PM   #6 (permalink)
outalne94z71
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since it can be a business writeoff, i would pay the extra and get the 7yr warranty kit from heath diesel
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98 Gmc Sierra Victory Red K3500 Crewcab SLE dually 6.5td(F) fresh 4l80e 4:10 gears fresh gm-8 turbo,3" exhaust from turbo to muffler (no cat),new crate motor with new ip , bumper relocated fsd with hucksdorf diesel heatsink.

88 chevy k2500 7200gvw(short box conversion from long),18" lift 1 ton axle swap(ford d60 with chevy outers) 14 bolt rear with disks and detroit,rather large hunk of iron to power it on gas(currently building a short deck 572), divorced 205 t-case behind a th400 and rollin on cut 44" swamper tsl front goodyear ag 21.5 x16.1 14 ply rear, straight 3" pipe from ceramic long tubes to 5" stacks to make your ears bleed, OFF ROAD USE ONLY
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Old 08-18-2011, 10:21 PM   #7 (permalink)
racer55
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There are times when the excess fuel dumped in and causing black smoke symptom can contribute to high engine temps.
The unburnt fuel in the exhaust is a real heat problem.

Like mentioned the Heath unit is the way to go for dependability and peace of mind/service after the sale.
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Last edited by racer55; 08-18-2011 at 10:22 PM.
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Old 08-18-2011, 10:29 PM   #8 (permalink)
kshow
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When my temp was high, the van was running great,... no smoke at all.
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Old 08-18-2011, 11:32 PM   #9 (permalink)
outalne94z71
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when my dtech went bad it did just like yours, quick revs with black smoke, even disconnected the throttle petal and same reving at startup, swapped to spare stanadyne and ran just fine, hooked dtech back up and it was fine again for a little bit till it took off on me
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98 Gmc Sierra Victory Red K3500 Crewcab SLE dually 6.5td(F) fresh 4l80e 4:10 gears fresh gm-8 turbo,3" exhaust from turbo to muffler (no cat),new crate motor with new ip , bumper relocated fsd with hucksdorf diesel heatsink.

88 chevy k2500 7200gvw(short box conversion from long),18" lift 1 ton axle swap(ford d60 with chevy outers) 14 bolt rear with disks and detroit,rather large hunk of iron to power it on gas(currently building a short deck 572), divorced 205 t-case behind a th400 and rollin on cut 44" swamper tsl front goodyear ag 21.5 x16.1 14 ply rear, straight 3" pipe from ceramic long tubes to 5" stacks to make your ears bleed, OFF ROAD USE ONLY

Last edited by outalne94z71; 08-18-2011 at 11:33 PM.
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Old 08-18-2011, 11:44 PM   #10 (permalink)
zombienerd
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I also had similar issues when my Cardone PMD failed on me. I would let off the pedal on the highway, and it would either accelerate, or barely decelerate, and the only way to get it to slow down was putting it in neutral, or hard braking. Occasionally, after a startup, if I gave it a bit of pedal, it would jump up to 3000+ RPM and spit black smoke like no tomorrow, and not stop until I turned off the engine. Besides that, the truck had no other symptoms. No fishbiting, cruise control still worked, and acceleration was fine.

I replaced the PMD under warranty, and it was fixed.

+1 to making sure your PMD is outside the engine bay. I have mine in an air grille on my aftermarket front bumper. Nice and cool up there
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