94 Chevy 6.5 diesel stuck on high idle

Nathan (SD) · Apr 25, 2015

Anyone had this happen? Trans won't shift into overdrive either in this mode.

Thanks

Bob · Apr 25, 2015

'94 would be "fly by wire"... electronic gas pedal, unless someone has swapped an older fuel system into it.

If it is "as built", you need to have a look at the trouble codes. Could be a bad electronic footfeed (actually, there's a separate "check throttle" lite for that), or a "PMD/FSD" issue.

Then, the FUN stuff starts... something open or shorted in the wiring harness, or a bad IP, or even the PCM.

I have quite a bit of info/troubleshooting stuff on these, but there's no need to start throwing parts at it without scanning it first to ask it where it "hurts"!

I'm currently working on a '95 on which someone hacked up the wiring harness and ruined the fuse block when all it originally needed was a new ignition switch. FUN!

Bob · Apr 25, 2015

Also, there is a fast-idle provision to the "fly by wire" setup... that involved wiring a switch to certain pins on the PCM for PTO use. Any chance that was ever done and the remnants of it have shorted out?

Deere Scotty · Apr 25, 2015

Only time I had anything to do with the 6.5 was in 1998, took a used 94 for a test drive. Had about 40K on it, & it died along the road in the middle of the drive. I got out opened the hood, didn't touch anything tried to restart it, & it fired right up. Took it back & told them sorry but I cant take a chance; unless they knocked the price of a rebuilt engine with labor off of it. They sent the truck to auction rather than try to fix it! So I was told by salesman later.

Bob · Apr 25, 2015

LOL! That was normal! A simple updated FSD/PMD would likely have fixed it.

mattwillson · Apr 25, 2015

I'd run , not walk away from that piece. If you do want to buy it, you'll need a lot stronger constitution than I.

Nathan (SD) · Apr 25, 2015

No add ons. Bone stock original truck.

bison · Apr 26, 2015

(quoted from post at 11:53:02 04/25/15) Anyone had this happen? Trans won't shift into overdrive either in this mode.

Thanks

igh idle was an option, it involves grounding a pin in the ECM(behind the glove compartment)with a switch in the dash.
I bet the wire from the pin to the switch is shorted somewhere or the brake switch has a problem( hitting the brake pedal should cancel the high idle as long as you keep your foot on it)
I have installed high idle switches in my 3 GMC trucks with the 6.5

I have the pin out of the ECM in my shop,.i can look it up if you want.

Determined · Apr 26, 2015

(quoted from post at 13:53:02 04/25/15) Anyone had this happen? Trans won't shift into overdrive either in this mode.

Thanks

Coolant temp sensor
There is more than one on that engine
Tranny temp sensor
Are you sure it is not going into overdrive as opposed to torque converter not locking up?
Similar feel

Nathan (SD) · Apr 26, 2015

It wouldn't be stuck on high idle if it was a torque convter issue. I am leaning toward temp sensor myself. Should find out tomorrow if thats it.

bison · Apr 26, 2015

(quoted from post at 10:59:36 04/26/15) It wouldn't be stuck on high idle if it was a torque convter issue. [b:e1bc8a8dd8]I am leaning toward temp sensor myself.[/b:e1bc8a8dd8] Should find out tomorrow if thats it.

ust disconnect it,it'll tell you right there.(the CTS for the ECM is on the water crossover), the CTS in the dr side head is only for the temp gauge

94 Chevy 6.5 diesel stuck on high idle

Nathan (SD)

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Bob

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Bob

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Deere Scotty

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Bob

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mattwillson

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Nathan (SD)

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Determined

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Nathan (SD)

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