93 k2500 6.5 no start when hot

[mark g]

i have a 93 6.5t that i just bought from the original owner. it runs and drives great till its gets hot. it will start immediately but if you wait 20 minutes it will not. i have read some of the posts on the subject but still need some input. thanks.
i have verified operation of the lift pump. cranking speed is good. oil pressure per gage is present. still no start.
after reading this somewhere i tried spraying the ip with something cool, i used carb cleaner, and the truck started. could this be an internal ip problem?? if there something else i can check before i replace the ip?? milage on the truck is 119k. seems early for ip failure.
previous owner was not helpful, he thought his glow plugs and controller were bad and paid someone to replace them. i have not checked fuel pressure at the filter yet but i can. oil pressure sending unit??? thanks

[DaveBr]

This same issue has happened to me with my 93 2500. Sometimes if I cranked it for what seemed like a very long time it would catch and go and other times I would have to wait untill it was cool enough that the glow plugs would cycle. It went on enough times(30-40) that my lighting fast mind finally clued in that this usually(not always) happened after I had been towing or running the truck hard. Turned out my rad tubes were plugged and the engine was running hot. I did some cooling mods, boost controller and turned up the IP all at the same time. End of problem.

I'm sure the cooling upgrades helped to lower temps which in turn let the IP run cooler, but maybe my IP is getting old and it needed some love. If I would have done these mods one at a time I could help pin point the cause of the failure to start that you are experiencing. I would start with engine temp first. The 93's need a lot of help in that department. I also suggest you change your fuel filter. Cooling mods are in my signature.

[mark g]

thanks for the reply, according to my temp gage my truck runs around 180, even with the a/c on. i actually thought about replacing the t-stat for a warmer 195 reading. im driving the truck this weekend to see if everything else is ok. i have a small oil drip from the filter housing, and i had to replace one of the tiny freeze plugs under the intake runner. i had no idea they were even their!!! thanks, mark

[6.5 Detroit Diesel]

to check if the IP is getting diesel up to the filter, you can either crack the little black knob on top of the filter with the lift pump circuit jumped, or you can crack it with the truck running. You will know right away if you are getting fuel.
I just replaced the IP on my truck, as it exhibited all the symptoms yours does. When you start it cold, how much smoke is coming out the exhaust? After replacing mine, there was almost zero smoke, and the truck will start within 1 second of cranking, regardless of temp.
As for the oil adapter, which is what is leaking, it is 3 rubber rings and a copper one and is really easy to do.

[mark g]

When you start it cold, how much smoke is coming out the exhaust?

thanks for your reply, im getting no smoke at all anytime, when cold its starts within 1 or 2 seconds. thats what puzzles me i drove it 120 miles this weekend with no issues but i didnt have to start it hot. btw, plenty of fuel at the filter when running. i checked that first. oil pressure at 60mph is 40psi. at idle about 25psi or so. temp runs about 180 with the a/c running. outside temp here is in the mid 70's. doesnt the oil pressure switch control power to the lift pump?? thanks, mark

[6.5 Detroit Diesel]

Yes it does control it, as far as I can remember. If your oil pressure is up and running, then the LP is probably running. But I did have mine go out once and the OP read properly. I just wired in a switch with a light that comes on when the LP isn't pumping.

[JohnC]

The oil pressure gauge sender and the lift pump switch are separate functions within the sender.

[daustin]

With the '92-93's the mechanical 4911 IP's have a notorious problem with hot starting issues. The ones which haven't had the head/rotor replaced are bad about not starting hot. If you dribble water on it and it starts, then it's time to look for a rebuild on the pump. Mine did that, and i for a temporary fix turned it up 1/3 turn. Now it hot starts ok, but i know it's IP time and it will revert back to not hot starting before long.
Don

[mark g]

With the '92-93's the mechanical 4911 IP's have a notorious problem with hot starting issues. The ones which haven't had the head/rotor replaced are bad about not starting hot. If you dribble water on it and it starts, then it's time to look for a rebuild on the pump. Mine did that, and i for a temporary fix turned it up 1/3 turn. Now it hot starts ok, but i know it's IP time and it will revert back to not hot starting before long.
Don

how hard is it to turn the pump up? any ideas on what a rebuild should cost? ive seen ebay sellers exchange for as little as 350! ive also read that the core is more valuble than the rebuild itself.
thanks, mark

[6.5 Detroit Diesel]

To turn it up, if you look on the drivers side toward the bottom, there is a little triangular plate. That has to be taken off to access the little key inside. I did mine when it was outside of the truck, so I don't know any tips for doing it inside the truck.

[daustin]

I did mine a few months ago, pretty easy the hardest part was looking in the little window with a mirror and barring the engine over at the same time to see when the 5/16" allen screw appears. Turn it 1/8 or 1/4 turn clockwise, no more unless you have pyro gauge. The "triangle" is beneath the throttle arm on the IP, it's about 1" by 1" more or less. That may fix it temporarily, but the issue will be back. Be wary of the flea-bay IP's, most "rebuilds" there don't replace the head/rotor and that's what crapps out in the DB2-4911's.
Don

[DaveBr]

Mark

I would recomend you do not turn up your IP unless you are willing to do some up-grades first. I don't know if your truck is stock or if you have an after market exhaust or not. Let us know and maybe we can help. If you over fuel your engine without a pyro to tell you what's happening you will cook it's goose. If you don't have the 2 TDP manuals for 6.5's get them. Joining this page and buying those manuals is the best money I've ever spent on my rig.

[mark g]

im looking for a pump locally, thanks. worst case ill have to take mine in to get rebuilt. i now know why the previous owner got rid of the truck!! thanks for all the help.

[DaveBr]

Look in the advertisers section of this page for reputable dealers. I would want to know for sure it was my pump before I put out that kind of cash that I could put towards an intercooler.

[93GMCSierra]

The head and rotor on the original pumps were bad, though I would not get rid of the truck for that reason, a newer pump or rebuilding yours with newer internals will fix the problem.
I paid $650 plus my old pump for a local rebuilt, though I have seen them priced as high as $1000 plus core.

[mark g]

there is an update, i found the oil pressure switch to be bad, no lift pump operation after start. i put a mechanical pressure gage in line behind the fuel filter, noticed 5-10 psi when started, then dropped off to near 0. truck still ran fine. i replaced the switch with an ac delco part. pump runs now. ill let you know when i get some more time on the road. thanks, mark

[DmaxMaverick]

That's good news, actually. It means your IP is in good health, mechanically. Tired pumps don't run well, or at all, without the lift pump.

[KingNuzz]

there is an update, i found the oil pressure switch to be bad, no lift pump operation after start. i put a mechanical pressure gage in line behind the fuel filter, noticed 5-10 psi when started, then dropped off to near 0. truck still ran fine. i replaced the switch with an ac delco part. pump runs now. ill let you know when i get some more time on the road. thanks, mark

Mark,

I had the same experience with the OPS dying - after I replaced the IP at around 120K. The truck wouldn't start warm, but started cold just fine. I ended up taking the lift pump power off the OPS with a control harness; problem solved.

John

[93GMCSierra]

on mine I found that replacing the lift pump, which had gone bad, was only a temp fix the head and rotor were already damaged.

[mark g]

well , even after replacing the ops the truck would still not start after a 30 minute drive, shutting down and then trying to restart after 30 minutes or so. the lift pump worked and i even noticed it running for a bit after shut down. i assume this is normal. guess ill start looking harder for a ip. thanks, mark