Throttle either On or Off, rough idle, hard 1-2 shifts

[Black6.5L1TON]

Well Im still haveing fits with the 6.5 TD in my 1998 3500 silverado 4x4. I love this truck but its driving me nuts and no one around here know anything about them so Im going at this blind with no real diesel knowledge. First off, I have the FSD heat sync relocation kit and the fuel filter was just replaced about 4,000 miles ago. But when I start my truck when its cold it idles rough and at about 1100rpm and revs very fast. Once its warmed up it idles at 700-750rpm but if you give it just a tiny bit of throttle it revs up to 1500 then hangs at 1200 and then drops back down to 750rpm. Then when I drive away with neerly no throttle input at all it violently revs to 3000rpm and shifts into 2nd hard. It feels like it has 1000ftlbs of torque!! Then once your out of the road there is no grey area in the throttle. Either your accelerating or your coasting. Once it starts to warm up you can cruise at a steddy 10mph. Then it will slowly creep up to a 20mph cruise, then 30, 40 and so on. But in the mean time Im suffering from whiplash as it lurches back and forth between hard acceleration and coasting. Also most of the time when its accelerating hard it is putting out a good amount of black smoke. Its very frustrating and embarrasing sence I just payed $7500 for this truck and now everyone I know thinks my truck is a pile of crap (which is isnt, its VERY nice and has some very nice options). Please help me figure this out. Thanks everyone for your help.

Jeremy

[nathan]

the throttle on these trucks int cable running to an injector pump it is an electronic resistor that sends voltage to your ecm. in short i bet you need a new go peddle.

[Husker 6.5]

Well Im still haveing fits with the 6.5 TD in my 1998 3500 silverado 4x4. I love this truck but its driving me nuts and no one around here know anything about them so Im going at this blind with no real diesel knowledge. First off, I have the FSD heat sync relocation kit and the fuel filter was just replaced about 4,000 miles ago. But when I start my truck when its cold it idles rough and at about 1100rpm and revs very fast. Once its warmed up it idles at 700-750rpm but if you give it just a tiny bit of throttle it revs up to 1500 then hangs at 1200 and then drops back down to 750rpm. Then when I drive away with neerly no throttle input at all it violently revs to 3000rpm and shifts into 2nd hard. It feels like it has 1000ftlbs of torque!! Then once your out of the road there is no grey area in the throttle. Either your accelerating or your coasting. Once it starts to warm up you can cruise at a steddy 10mph. Then it will slowly creep up to a 20mph cruise, then 30, 40 and so on. But in the mean time Im suffering from whiplash as it lurches back and forth between hard acceleration and coasting. Also most of the time when its accelerating hard it is putting out a good amount of black smoke. Its very frustrating and embarrasing sence I just payed $7500 for this truck and now everyone I know thinks my truck is a pile of crap (which is isnt, its VERY nice and has some very nice options). Please help me figure this out. Thanks everyone for your help.

Jeremy

Plug into your ALDL. With the OBDII system and a reader, it will tell you right away if your throttle pedal position sender is fried. If you don't have a reader, go to your trusted mechanic and let them scan it for the code. Odds are it is the sender, my 94 had some major electrical probs. that the previous owner "fixed" by removing the bulb from the SES light! Bad TPS was one of them. Use to be able to get just the position rheostat for 50 bucks from the dealership and replace the faulty one(s). Can't anymore, but Walt has the pedal assembly for less than the dealers! LOL

Allen

[christja]

If you have an Auto Zone near you they will "loan" you the OBD-II Code reader for free. Ive used it before on my wife's car.

[dieselturbo]

sounds like the go pedal ,i agree. mine used to shut down on the highway- i would be cruising along and then no pedal. i pull over and the engine is at idle- no pedal response.. shut off ,disconnect battery and it would work again-- got me home, bought a repro off ebay - its been working fine for past 25,000 miles.

[Black6.5L1TON]

Thats alot guys for the help. Im gonna see what I can find locally. Hopefully I can find a used one for a reasonable price for right now, then buy a new one later on. Funds are kinda short Right now. Thanks again everyone I really appriciate it.

Jeremy

[chevyturbodiesel]

ive have an extra good one for sell email me @ boondockboyz26@hotmail.com if your interested

[Husker 6.5]

Thats alot guys for the help. Im gonna see what I can find locally. Hopefully I can find a used one for a reasonable price for right now, then buy a new one later on. Funds are kinda short Right now. Thanks again everyone I really appriciate it.

Jeremy

Make sure it is the later model pedal assm. if you buy used. Make very sure it is functioning correctly, you won't gain anything swapping one bad for another. When they went fly-by-wire in 94 they had some serious problems with the early pedals. Try runaway engine that revved till it blew!! GM actually shut down the assembly line til engineering dept. could come up with a fix. Early pedals had two position sensors on them that sent two reference signals to the ECM. If one of the sensors failed (which early ones were prone to do) the signal was unbalanced which the ECM read as WOT and BOOM! even if you took your foot off! The fix was to change the proramming in the ECM, and go to a triple redundant sensor, so if one went bad, there would still be two working, and if only one worked, the unbalanced signal would be read as idle, not WOT by the ECM. My 94 was built a couple of months after they restarted production. That's why there is a couple of month gap in the date codes for 94 6.5's. This is according to my local GM guru. We had to make very certain when I ordered my new ECM 3 years ago to get the ECM code and build plate data to ensure the correct version.

[Black6.5L1TON]

Make sure it is the later model pedal assm. if you buy used. Make very sure it is functioning correctly, you won't gain anything swapping one bad for another. When they went fly-by-wire in 94 they had some serious problems with the early pedals. Try runaway engine that revved till it blew!! GM actually shut down the assembly line til engineering dept. could come up with a fix. Early pedals had two position sensors on them that sent two reference signals to the ECM. If one of the sensors failed (which early ones were prone to do) the signal was unbalanced which the ECM read as WOT and BOOM! even if you took your foot off! The fix was to change the proramming in the ECM, and go to a triple redundant sensor, so if one went bad, there would still be two working, and if only one worked, the unbalanced signal would be read as idle, not WOT by the ECM. My 94 was built a couple of months after they restarted production. That's why there is a couple of month gap in the date codes for 94 6.5's. This is according to my local GM guru. We had to make very certain when I ordered my new ECM 3 years ago to get the ECM code and build plate data to ensure the correct version.


WOW!!! THANK GOODNESS you posted this info. I was going to go get the throttle assymbly out of a 94 chevy this afternoon that has a blown motor. I think Ill pass on that one just for the possabilty that it could be an early 94 truck and throttle could be the reason then engine is blown. Thanks very much for the info. Ill have to pass that along to my friends around here who have 6.5s also.

Jeremy

[Husker 6.5]

WOW!!! THANK GOODNESS you posted this info. I was going to go get the throttle assymbly out of a 94 chevy this afternoon that has a blown motor. I think Ill pass on that one just for the possabilty that it could be an early 94 truck and throttle could be the reason then engine is blown. Thanks very much for the info. Ill have to pass that along to my friends around here who have 6.5s also.

Jeremy

No problem, bro. That's the whole point of the 6.5 forum, and why I joined. Knowledge is power they say, so lets all make our 6.5's powerful!

[Husker 6.5]

WOW!!! THANK GOODNESS you posted this info. I was going to go get the throttle assymbly out of a 94 chevy this afternoon that has a blown motor. I think Ill pass on that one just for the possabilty that it could be an early 94 truck and throttle could be the reason then engine is blown. Thanks very much for the info. Ill have to pass that along to my friends around here who have 6.5s also.

Jeremy

No problem, bro. That's the whole point of the 6.5 forum, and why I joined. Knowledge is power they say, so lets all make our 6.5's powerful!