Reving problem

[tom lovinggood]

Hello--I own an '86 M1009 in excellent condition with 55K. Last summer, I had a new IP installed and it ran perfect up until about a month ago. The problem I am now having is that for reasons unknown, the idle speed on the engine will suddenly increase, then go back to normal idle. Then, the idle speed will slow down, and return to normal speed. This will happen several times and then the engine will quit altogether. I had to have it towed in for the reason to a local GMC dealer who installed the IP last summer. I had just picked it up from a local GMC dealer who had informed that the problem had been fixed and it would be fine. That was not the case as i pulled out of the dealership on my way home, the mystery idling speed problem returned and the engine quite altogether about 1/4 mile from the dealership. They are as baffled as I am. Anyone have any thoughts on this problem? Thanks in advance.
Tom Lovinggood

 

[dougco1]

Is your cold advance solenoid working properly. Mine had the "mind of its own" revving symptoms when "cold started" . Turned out to be a finicky solenoid.

 

[cucvrus]

Disconnect all the green wires on the injection pump and see if that helps. I doubt it but try it anyway. Sounds like an internal injection pump problem. I doubt any of the mechanics that are at the GM dealership today even saw a 6.2 diesel. I was broke down once and had to go to a local dealer and they didn't even know a thing about the 6.2 diesel. The pumps are usually warranted for a year. I hope that is not the issue. But it could be sucking air or have a weak lift pump also. Very hard to diagnose and assist from afar. I am basically shotgun blasting the issue. Good Luck. Report back. I hope it starts so you can continue the diagnosis. but our local dealer get $105. @ hour to diagnose. I stay clear if at all possible.

 

[tom lovinggood]

Cucvrus--the IP pump I had replaced this past summer was a re -man so, that is totally possible that the part is bad.

 

[cucvrus]

Tom I would still check the lift pump. A far shot but worth a look. The injection pump itself will suck fuel but I would check the lift pump. And if it is a new lift pump it could be an incorrect one. And another thing I just thought of. Is the fuel pump feed line sitting against the frame crossmember? I had one do that and it would allow air in and not leak fuel. It ran like a house on fire and then would just shut down. Check that. If that is touching that crossmember it needs new motor mounts to correct that issue. If you see a mark or the paint worn off the crossmember below that hose the motor mounts are bad. Not to say I know everything. But like I said shot gunning from afar. Good Luck. Report back. Maybe a hit if I'm Lucky