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98 K2500HD runs rough, possible IP?

GM Guy

GM Guy

Manual Trans. 2WD Enthusiast
Messages
4,838
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Location
NW Kansas and SC Idaho
Hey all,

I scored a 1998 GMC K2500HD RCLB 6.5L auto 4wd. definitely a fixer upper.

It runs very rough, and seems to be missing pretty bad. There is no blowby, so I am hoping it is not in the engine. Vaccum pump locked up and shredded the belt, so I need to change the belt and the vac pump so the computer can at least get a tach signal.

PMD has beeen relocated, harness has all black wires, but the heatsink looks alot like Leroy's. IIRC a black stanadyne PMD. it is in the grille. I switched it out with a known good PMD and it doesnt change anything at all.

Here are the codes:
P0126
P0183
P0251
P0606
P0126P
P0183P

I need to get the belt drive operational, and clean grounds and proceed from there, but I was wondering if anyone has allready been down this road and found it to be a bad IP.

Any input appreciated,
Thanks!
 
also, has anyone seen a harmonic damper cut a hole in the front cover? The outer ring has slid back quite a ways, and I am worried. :)
 
GM Guy said:
also, has anyone seen a harmonic damper cut a hole in the front cover? The outer ring has slid back quite a ways, and I am worried. :)
Click to expand...

Change it NOW!

the 251 and 606 are the only 2 that catch my eye, the others are probably reactionary to the running rough. Since you just bought it, I would do all the grounds and clear codes. Then go from there.
 
I am fixing this truck up on a budget, so no Fluidampr.

So, the choices are:
a good used genuine GM damper
or a new Dorman

What shall the choice be? IMO the GM one still might be better. :)
 
OK, here is what I found on Rock Auto:

$43 Dorman
$45 ATP
$66 AC Delco OE
$142 Dayco Premium
$420 Dayco Race grade.

Obviously the racing one is out, for that price I would do a Fluidampr.

The spare damper I have is on an engine with a hole in the pan, so I figured with a lower end failure, re-using the damper may not be a hot idea. agreed?

So, do you think the Dayco premium is that much better, or should the AC Delco OE grade be plenty good? I really wasnt considering the Dorman or ATP.

I didnt realize they were that cheap, so I am leaning towards the new AC Delco OE grade for 66 bucks, pretty cheap insurance IMO.


Also, Will, you dont have to worry about it being driven with the bad damper. :) Total distance since purchase is about 500 feet total, across a yard to load on trailer, then unload and back up to its current parking spot. Once I saw that shit damper, I determined firing it up to drive to the cement pad in front of the shop is all she is going to do.
 
Last edited:
OK, harvest is over, and I am back from Idaho for a little while, so I am playing on the truck.

Batteries sat un-hooked for a few months, I cleaned all the grounds at the back of the intake, and cleaned up the 4 battery connections, but not the other ends of each cable. di-electric grease and the bolt mod were installed.

borrowed an used alternator from project row, the 96 K2500HD. Just to save time, I went ahead and wired up a 10 guage wire, no fusible link (I get dumb on sunday with no parts stores open.... ) for the charge wire, and I had allready put the new damper and vac pump on 2 months back, so I put in the used alt, hooked up the batteries, and fired it up.

It still runs rough. Crap.

It runs smoother than it has since I owned it. Yay

I didnt melt anything with my non- fusible link wire. Yay!

So I checked codes again, and it must have apparently kept the P0183P stored, but nothing else. It was not an active fault, but a stored fault (according to the 29.95 harbor freight code reader)


Also, another tidbit of info, it had red diesel in it, a few months ago when I worked on it, I pulled it up to the tractor, ran a hose to the tank, and hotwired the LP and drained the tank, dumped in 5 gal. of clear, ran the LP to drain the the tank, repeated one more time, and then changed the filter, putting a bunch of Stanadyne lubricity formula in, dumped 5 gal. of clear in, and parked it on the cement pad in from of the shop, where it has sat since.

So, a dyed optic sensor is a possibility. If this is so, will running it and flushing a bunch of additive and clear fuel through it help it out, or is it screwed?

Finally, one or both t-stats appear to stick, as I had warm coolant in the radiator, and it never got much above the bottom line. Can someone refresh my memory if the IP plays with timing only above a certain temp?
 
So, What is everyone's opinion on how to proceed? Will air in the fuel cause the stumbling?

It hesitates, stumbles, and almost sounds like its backfiring when you listen to the right side near the turbo. When you accelerate, it has smooth spots, then rough spots. For example, it is smooth at 1K RPM, but stumbles at idle. It is a little tricky to find 2K, but I can maintain 2K RPM once I find it.

IMO no worse than a few of the higher miled pumps we have in the fleet as far as holding 2 grand.

The low temp is not helping matters, but I dont think its an immediate concern. It appears the block heater is dead, so I would like to do it at the same time as t-stats, and maybe wait till spring, and yank the radiator to boot and get it all cleaned up.

Surely a bad crank sensor would just cause it to die, correct? What about the FSO? would a failing one have a tough time staying open and be trying to starve it all the time?

Any input appreciated!
 
air in fuel will cause it to stumble. saw one recently that only had air in the system at about 2k plus rpm. no air at idle. it also held 3 psi at the same time. bypassed the entire fuel system and still had air. evidently a failing IP can make it's own air.

a bad crank sensor won't cause it to die as it will run on the OS. it can make it stumble buck and snort in no particular order tho.
 
OK, found one air leak, PO installed a new Delphi LP not long ago, and did not get it tight on the suction side.

I tore it apart and changed o-rings and put it back together, still runs like crap. I took it for a little road test, and when I tromp on it, it will blow black and kick it sideways (sanded dirt road, so not that impressive) , so I think its getting plenty of fuel flow. :) seems to blow smoke longer than usual, and the vac controlled WG is definitely working, at idle it will hold it tight, cant move the WG at all.

Upon returning from road test, it will now stumble worse at idle, actually dropping under 500 RPM to the point the computer will bump the fuel a little to get it sped back up.

Basically across the entire RPM band, it will stutter, worse at certain RPMs, and no stumble at certain RPMs.

Do you guys think that a stretched timing chain can be screwing up the timing this much?

Should I bother swapping out Crank sensors with a good used one?

I still need to get a clear line on the return off the pump, kinda tight in there with the dual t-stat. :)
 
Air is the #1 troubleshooting step.
Sounds like bad injectors otherwise.

Air filter and all good?
 
Thanks for the input guys, much appreciated!

unplugging the CPS will result in lots of cranking to get it running, correct? If so, would it be best to fire it up and let it warm up a tad, then shutting down, unplugging, and then re-starting? And if it runs fine upon res-start, its the CPS?

WW, air filter looks fine, a tick dirty, but nothing bad. filter restriction guage has not budged. never checked the turbo. It does not whine under load, but the black smoke will clear up and it seems to have good power, so I am confident it is free and making boost, but I will double check.

With it idling, I also put a bolt on the top of the FSO solenoid and it pulled a little bit due to the electromagnet. Not very hard, but it did pull.

I am honestly suprised that its running so crappy and has not tripped a code. SES light seems to be working more normally, wont come on after shutting off then trying to fire right back up, but will come on on initial key on.
 
I'd make sure to check air in fuel, remove the optic sensor, check sensors, check timing, then it might start costing ya (ip or injectors)...
 
I could have sworn I had some clear tubing laying around, but I guess not.

5/16, correct? or is it 3/8? I would go and look, but the wind is howling and its in the 20s.
 
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