93 k2500 6.5 no start when hot

[mark g]

http://img.photobucket.com/albums/v242/mgerdes/P1010024.jpg
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:confused: 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.
Donhow 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:D

[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:D

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

[mark g]

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
so what did the harness do exactly that the ops is not doing? thanks

[Robyn]

Try dumping a couple quarts of motor oil in the fuel and letting it mix well.
If the issue is better then the IP is just worn out.
The oil will thicken the mix and allow the IP to get up to pressure.

Let us know

Best

Robyn

[mark g]

Try dumping a couple quarts of motor oil in the fuel and letting it mix well.
If the issue is better then the IP is just worn out.
The oil will thicken the mix and allow the IP to get up to pressure.

Let us know

Best

Robyn
thanks, ill try that!!

[Robyn]

It's a cheap diagnostic trick that will do no harm and take little time to do.

If the truck starts up better after the oil is added and run a bit to mix then you know the story.


Best

Robyn

[DmaxMaverick]

so what did the harness do exactly that the ops is not doing? thanks

He may be referring to an electronic lift pump controller, like kennedydiesel sells. It is a solid state solution for pump control. You could also power the pump via a relay. Either of these will greatly reduce the electrical load on the OPS, preventing or delaying its failure. Either solution is a worthy upgrade, and a DIY relay setup is much less expensive.

However, the OPS isn't your problem if your pump is powered with the engine running. The "after run" you experienced is normal. The LP is powered by the OPS, and oil pressure will decrease slowly after shutdown. The pump stops running once the oil pressure is below about 5 PSI.

Robyn offered good advice for testing. Using motor oil is OK for a diagnostic tool, but I do not recommend using it on a regular basis.

[before trying the motor oil]
Once you have a situation when the truck won't start, try pouring about a cup of water, slowly, over the IP. If your no-hot-start is due to a worn pump, the cold water will "shrink" the pump housing (contracts the aluminum housing). This will tighten up the internal clearances. If this "trick" works a couple times, you can bet the pump is just worn out internally.

Another possibility is low compression. During a hot start, the glow plug cycle is disabled. It's possible hot cranking isn't providing enough heat for combustion without the help of the glow plugs. You can test this by a compression test (done on a hot engine). You can also test by disconnecting the GP circuit temp sender during the start, which will force a GP cycle at any temp (simulates a -40°F start).

[mark g]

[before trying the motor oil]
Once you have a situation when the truck won't start, try pouring about a cup of water, slowly, over the IP. If your no-hot-start is due to a worn pump, the cold water will "shrink" the pump housing (contracts the aluminum housing). This will tighten up the internal clearances. If this "trick" works a couple times, you can bet the pump is just worn out internally.

(simulates a -40°F start).
tried that first yesterday after hot soak, no effect. will try glow plug start next time i drive. my engine seems healthy as far as no blow-by, good oil pressure when hot(25-30), little to no oil consumption, and good cold start(yesterday morning was 40). thanks, mark

[DmaxMaverick]

The IP failures generally start out slow, and gain speed (more pumping problems) over time. It will reach a point when it is no longer able to develop pressure, no matter what you do.

In your first post, you said you used carb cleaner to cool the pump, and it worked. Using water does the same thing, only water is not as effective as carb cleaner (a very volatile solvent). It is possible, however remote, the carb cleaner may have help the start in other ways. It is a highly combustible volatile solvent, and evaporates very quickly, especially if applied to a hot engine. If your intake is open to the engine compartment, it is possible the vapors from the cleaner made their way into the combustion chamber (like starting fluid). Try more water, poured more slowly, allowing maximum cooling effect.

Also, low blow-by and low oil consumption is not the only indicator of low compression. There are a number of reasons for low compression, including valve, lifter, timing, cam, head gasket, and the head in general. Blow-by and oil consumption is generally associated with cylinder/piston wear.

Depending on mileage and previous care/maintenance, an original timing chain can cause issues with starts under specific conditions. As the timing chain wears (stretches), the timing retards. You can offset this, somewhat, by physically advancing the pump timing (however, this creates a departure between the cam and pump timing). The same effect seen when the HPCA activates during a "cold" start. If manually activating the HPCA helps with the hot start, it may be as simple as that.

[mark g]

im leaning toward something besides the ip. the truck sure has good power. i feel all 200 horses, even after driving my dmax. i got it hot this morning and let it sit for thirty minutes. any less and it will fire. anyway it would not start , so i cycled the glow plugs for 5 seconds and it started. so what should be my next step:confused: thanks again

[DmaxMaverick]

Much depends on what you are going to do with the truck. Keep it, sell it?

If it's a keeper (no indication it isn't), I'd look at refreshing the time/mileage wear components. Injectors, timing chain, water pump, harmonic balancer, drive pulley (if it's the damper type), fan clutch. Not in any specific order, except you'll want to do everything on the front of the engine at the same time to save a lot of labor. All of this is simple DIY, with lots of help here. In the meanwhile, you can rig up a temporary temp sender interrupt switch (or a GP relay jumper) to get it started when hot. A set of injectors may cure the no-start issue. 120K is about the limit for OEM injectors.

[KingNuzz]

so what did the harness do exactly that the ops is not doing? thanks

It takes the electrical load off the OPS, which doesn't handle the lift pump current well and can fail to provide power to the LP. My experience was that the OPS failed when warm.