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hi idle

D

dbergeron001

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iv got a 1997 GMC 3500hd with a 6.5 turbo in it that i just picked up. the fuel that was in it was terrible. i sucked out all the bad fuel cleaned the tanks fresh fuel new fuel filter. lift pump is working. it isn't the PDM. the engine starts good. as soon as it starts engine goes to 1200 rpms and surges to 1400-1500 rpms. the throttle is very touchy. if you push on the brake or push in on the clutch the surging stops and idles at 1200 fairly smooth. there isn't any codes. live data looks good but but its not idling so cant check timing the throttle pedal is reading correctly. it will idle at 700 RPM once in a while but if you touch the throttle it goes back up and sometimes goes WOT. im guessing the injector pump has something sticking in it but im hoping that some one has seen this before and its something stupid that ive over looked. before i go dump 1200 into a new pump.
 
Welcome to the forum @dbergeron001 it sound like something in the IP. can you read live data on your scanner? check the APP sensor for any erratic data. you mention it's not the PMD, have you connected a spare to verify? (mounted to a heatsink of course). replace the 1/4" return line from the IP to the return steel line (looks like an upside down U shape hose about 6 inches long) with a clear hose from the hardware store so you can see if any air is getting in the fuel system.

you can also pull the top of the IP off carefully (the part that houses the connector for the optic sensor) and just look in there to see if you see any varnish or corrosion in with the fuel. DO NOT stick or prod anything in there. there is a very delicate reluctor that the optic sensor reads, if that gets damaged, it's a replacement IP for you.

other than the above mentioned things, it suspect would be the IP. I will let others with more experience and knowledge chime in before you do anything. just one thing to note, pull the turbo intake hose off or something so that if I goes WOT and won't shutdown with the key you can choke it and stop the run a way condition before it goes boom on you.
 
I did swap the pdm. Made no difference.i haven't put on clear hose off the return yet. I did have the pick up and return in a gallon jug and there was no air bubbles there. There. Were there isn't any codes I'm assuming it's something mechanical. I did see any erratic data. App sensor?
 
Welcome.

So, was there any signs of fuel bugs? Black or green goo in the fuel filter?

Get the clear line on there- that is huge, there is a reason that is step #1 in Stanandyne’s book as well as GM.

I’m gonna be chicken little saying the sky is falling and jump to things that will be positive now and positive after the ip gets replaced.

Buy one of the pressure sensor adapters that screws into the inlet of the ip and get a pressure gauge in the dash. Going under 1 psi under any condition is detrimental. Desired pressure is 8-14 psi. Hint- the factory lift pump brand new is enough to get the truck out of warranty period and thats about it. For your current problem you just need to maintain over 1 psi. Long term get something like the fass for their great pump and filter system. The cost of the gauge pays for itself in extending life of the injection pump.

I would use a double dose of the stanandyne (or 2 stroke) lube additive in the tank. (If you had a db2 I would be telling you run straight atf- but ds4 can’t withstand it.)
 
APP sensor is the accelerator pedal position sensor. these trucks are drive by wire and all the go pedal has is a triple stacked into one sensor with a bunch of wires there, not throttle cable!
 
Will L. said:
Welcome.

So, was there any signs of fuel bugs? Black or green goo in the fuel filter?

Get the clear line on there- that is huge, there is a reason that is step #1 in Stanandyne’s book as well as GM.

I’m gonna be chicken little saying the sky is falling and jump to things that will be positive now and positive after the ip gets replaced.

Buy one of the pressure sensor adapters that screws into the inlet of the ip and get a pressure gauge in the dash. Going under 1 psi under any condition is detrimental. Desired pressure is 8-14 psi. Hint- the factory lift pump brand new is enough to get the truck out of warranty period and thats about it. For your current problem you just need to maintain over 1 psi. Long term get something like the fass for their great pump and filter system. The cost of the gauge pays for itself in extending life of the injection pump.

I would use a double dose of the stanandyne (or 2 stroke) lube additive in the tank. (If you had a db2 I would be telling you run straight atf- but ds4 can’t withstand it.)
Click to expand...
Fuel was bad I'd say extremely old smells like varnish. And it was brown. The tank was full of it. I sucked it all out sucked it out of the fuel filter housing. I made up some hoses and connected to were the pick up screws onto the fuel line. I than took a clean can with new fuel and run the lift pump with a jumper wire. Let the filter housing fill as I sucked out the fuel. Once good cleaning fuel was getting to the housing I put in a new filter. I than run the lift pump until clear fuel was coming out of the return line . Once it was clear I put both the suction line and return line in the same jug and started the engine. I also put injection cleaner in the fuel. On the strong side. Can't remember the name something like cetron.
 
Ok hopefully not bugs (fuel algae) is in there. It is usually described as muddy. Can be green, dark brown or black.
I would absolutely drop and gasoline clean the tank, full line flush and replace injectors if you have to replace the injection pump. Actually hold off doing any lift pump improvements until sure this is not algae. Think of it like a contagious sick person and each component of the system is a different person. BTW this sickness is often deadly to pumps and injectors. Many people don’t even try cleaning tank when they get it, they buy that new also.
 
The tanks are empty clean and dry right now. I was able to pressure wash them out the rear one is plastic and I got my arm in there and was able to wipe it dry. The other tank is steel I thought it was toast but it cleaned up nice. I lifted the front of the truck up about 50 inches so as I pressure washed it everything would run to the back of the tank and I had a air operated pump sucking out all the crap as I washed tank. I'm pretty confident it's clean. I'm pretty fussy. The pickup tubes are junk so I'm waiting for new ones to show up. Once I get them I'm putting new fuel in and some kilz. If there's any algae left that will kill it.
 
do the gasoline wash out on the tanks. the reason for the gasoline is to kill off any growth in the diesel. just get it all out before installing and trying to run it to the engine.

think of the gasoline as hand sanitizer for our hands for bacteria.
 
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