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very rough running when hot

backwoodsdiesel

backwoodsdiesel

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This problem is getting on my nerves and I could use some suggestions as to what to try next..


The truck starts and runs great, after sitting all night. The trip to town is about 40 mins.. starts acting up just around that long.

Will miss and fish bite a bit.. if I don't let it cool off.. it will begin to feel plugged up.. more throttle making it worse, until eventually it can barely idle, and has actually stalled a couple times now. Tough to restart at that moment.

If at any point I shut it off and let it cool.. all goes back to normal, for a short time.

I've replaced the lift pump, and Oil pressure switch.. thought it was better, and is.. but problem remains.

The FSD was remotely mounted over a year ago.. could it be the FSD already? I still have the IP mounted one.. suppose I could eliminate that easily enough...

any suggestions would be greatly appreciated.
 
Try pouring water on the IP and cooling it off. If it runns better then I would think that the problem is IP
 
yikes, I've been fearing that one.. :(

ballpark figures for a new/rebuilt pump? and I doubt I can install it myself..
 
ah, sorry
98 chevy 2500 4x4 ext cab/short box

no check engine light is coming on

I'll have to have a buddy check for codes stored.. if any.

no smoke to speak of.. other than cold winter starts when I don't plug her in long enough.
no change in smoke that I can see..at least
 
Try doing the simple IP test.

Slowly Bring RPM from idle (in park) to 2,000 RPM's. Hold it for af ew seconds, and try to SLOWLY bring it back down. The test part is seeing if it is capable of SLOWLY dropping back down to idle. They are touchy, so it will take a few times, but its very easily possible if its a healthy IP.
 
well, backwoods, that is exactly what mine was doing, and i just put an IP in last weekend. but i am surprised that there are no codes. when you say it feels plugged up, does it feel like it lost power right now, and sounds different?
 
Can you say snotty sock syndrome!:puke: The coincidence is that by the time your truck is warmed up, the fuel capacity has limited itself to the point of starvation. Had the same problem, eventually the truck wouldn't even run for more than a few seconds. Let it sit over night and it drove for about 20 miles, then died. Had to tow it home. Sounds like what you have, and it was worse when the truck was hot.
 
mfgguru said:
Can you say snotty sock syndrome!:puke: The coincidence is that by the time your truck is warmed up, the fuel capacity has limited itself to the point of starvation. Had the same problem, eventually the truck wouldn't even run for more than a few seconds. Let it sit over night and it drove for about 20 miles, then died. Had to tow it home. Sounds like what you have, and it was worse when the truck was hot.
Click to expand...

Real time fuel gauge in cab would rule this in or out instantly. Snotty sock syndrome through me for a loop too, all that pressure eventually sucks that stuff until it clogs the truck to the point of stall. After stall, LP turns off whether key off or what have you, and the crud releases off the sock. Starts again... same boat. I can tell when this happens crack the fuel filter bleeder and it hisses. I had gauge on it, and it was vacuum -7.

Veg_out's sig says it all, IMHO every 6.5 needs real time fuel gauge. I agree. It basically cuts diagnosing problems in half instantly by a quick glance of a gauge.

May or may not be his problem, but a must have for all 6.5ers... Can't wait for mine.... I'm ditching the sock all together for a servicable filter sitting right before the walbro, which can pull through it, unlike stocker joke pumps. I never want to see the inside of my fuel tanks again.
 
A plugged fuel cap can cause the same symtoms. Try running with the cap loose.Free
 
backwoodsdiesel said:
The FSD was remotely mounted over a year ago.. could it be the FSD already? I still have the IP mounted one.. suppose I could eliminate that easily enough...

any suggestions would be greatly appreciated.
Click to expand...

Depends on where you remote it. The intake is NOT remote enough.
 
ty folks, this gives me a few more things to think about.

I am able to idle to 2000rpm, and bring it down slow, but takes a very gentle foot till down near 1600.. then she is very easy to bring down.

The FSD is remoted by the front of the drivers side wheelwell..behind a battery.

The problem first happened after 3hrs of driving hwy speeds back in December...

Now it seems to happen with less time at 100km/hr or so..

weird thing is .. it seems worst, turning into my road, about 12km from home. The first bit is an incline.. by the top of the hill... despite carrying me 40km back from town decently enough over larger and steeper hills.. by the top of this slow climb she is chugging. If I continue.. within a few minutes or so, she is barely driveable.

I know if I bring it to a shop, it won't do it at the moment he drives it.
 
"Barely driveable" is that means the engine stall or the engine still running?

There is a Diagnostic Checklist in the sticky part of the 6.5 section that may help you check some stuff to help you eliminate things methodically.

On the FSD, my suggestion is to remote it all the way out of the engine compartment. I am not trying to create a discussion on this but you can search about it.
 
This last time it happened.. there was a point where the speedo was locked at 60km/hr, the tach also seemed frozen, and she was barely chugging at idle, if that is familiar to anyone.
 
JMJNet said:
"Barely driveable" is that means the engine stall or the engine still running?

There is a Diagnostic Checklist in the sticky part of the 6.5 section that may help you check some stuff to help you eliminate things methodically.

On the FSD, my suggestion is to remote it all the way out of the engine compartment. I am not trying to create a discussion on this but you can search about it.
Click to expand...

My wire is long enough, but I live in the bush and feared it getting smashed up by rocks or chunks of ice.

Its running barely, but no response from throttle.. sometimes it feels like it wants to catch.. but just can't in various spot through throttle travel.

It finally stalled as I pulled into my driveway, which is an incline. Seems demand of power just makes it worse.
 
Since you don't have or don't want to hook a fuel pressure gauge up to see your data. Try undoing the fuel tank to lift pump inlet line and blow compressed air into the tank with fuel cap removed.

Defanately sounds like a clogged sock / fuel delivery problem that gradually gets worse as you go.
 
Just want to make sure, the replacement OPS is an ACDelco OPS?

Try what Matt is suggested to see if it gets better.

I put my FSD under the bumper open to the ground with the heatsink facing to the ground.
I went to my dad's in the backwood of Alabama with gravel road. The house was not even on the map.
It was fine. Inside the engine compartment is too hot after shutdown, it is soaking the heat.
Don't have to do it but you may have to buy one of those FSD again soon.
 
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