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Discussion Starter #1
98 sierra 2500 4x4 6.5l td, when shifting in and out of OD engine will rev to redline and then drop out.(almost undriveable at 100 km/hr) Suspected tranny, dealer said Torque converter fryed, took it to Tranny shop for 2nd opinion, they say engine has problem with rpm control, ie Rev problem can be induced in any gear and even when parked. Any suggestions?
 

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Well I would question the tranny shop, the reason I say this is if the tranny is doing it's job the engine cannot have wild upward surges, because the tranny would hold it down, if it is providing power to the ground properly. The tranny is the resistance, the engine is working against, so the only way for a wild surge while driving is for the tranny to let go, for a moment. Now why does the engine surge that is anther question, it could be the computer or the IP on its way out, but think about it this way, if you floor the truck does the tranny let go and let the engine RPM's skyrocket?? No the truck sppeds up but it is gradual.
 

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Last winter I had one of our trucks come in for this wild RPM thing and it was the Injection Pump. These IP's are "drive by wire".


Symptoms were in neutral slowly push accelerator to 1200 and she would take off to 4000 with no more pedal movement. In the snow I could duplicate with poor traction.


Warranty covers you to 120,000 miles or 11 years (special policy #00064D). GM updated this policy in May '03.
 

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Discussion Starter #4
Right on Charlie.


1st Dealer still insisted fault was tranny, I took truck to private shop they said Injection pump. took it to another dealer, they are replacing the IP on warrenty right now. reconfirms that 2nd opinions are a good policy for us consumers.


Another point is that the fuel tank was rusted, filter and float bowl full of rust as well. Although not sure if this contributed to the IP problem.
 

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I am concerend that you may have both a weak tranny and the engine problem, because even if the engine is running wild the tranny should hold it down, because on the road there is resistance to the engine reving. Lets think about this for a second, if you floor your truck while running down the road at say around 60 MPH what does the truck do normally, it most likely will shift out of TCC lockup, and maybe out of OD, but the engine should never run wildly to redline unless the tranny is slipping or something else in the driveline is faulty.


Did you have any codes with it, because a few people have had the APP sensor problem, as mentioned by CharlieP. they get dirty and are no longer a linear curve, rather a realy unreliable landslide, that could cause the uncommanded reving, but should not be the cause of the tranny slipping alowing the engine to redline.





This is just my thinking out loud, and by all means if they are willing to replace the IP under warranty than get it, but don't be suprised if that doesn't fix it, but at least you will have the new IP
Edited by: CAT 3406
 

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It just happened to me !!!
2000 gmc 1t crew,it was doing the same thing.
Today it would just barely run and gmc has it
now. It's the injection pump going bad!!!!!!
David n5vxu


PS lAST WEEK MY TRUCK 962500, BLEW A PISTON
Edited by: David
 
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