7.3 IDI No start when hot

Nlevine125

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1991 7.3 IDI non turbo. I’m just about out of ideas here. This has been an ongoing problem for quite some time now. Got a truck that will start and run just fine when the engine is cold, but will just sit there and crank without firing when hot. I know that this is a problem sometimes caused by a worn out injection pump. This is a 1 owner truck with 260k miles and was still on the original pump and injectors. As I’m doing a semi-restoration on the truck, I decided I might as well try and fix the no start issue while I was at it. I have replaced the following:

-Injection Pump, stock output purchased from Conestoga Diesel
-Injectors, aftermarket stock replacements from Accurate Diesel
-All injector return lines and cups
-Starter
-Both batteries
-Glow plug relay from Motorcraft
-All glow plugs (AC Delco I believe)

The truck runs great when it’s actually able to start. Way smoother than before, better throttle response and just nicer to drive in general. However, as soon as I shut it off, it will not start until the engine cools down completely, although at times it sounds like it wants to run. I’ve had issues in the past where the truck would suck air into the fuel system and cause the engine to die or not start. That issue has since been fixed and I am 100% certain there is no air in the system. Also, I have the mark on the injection pump lined up exactly with the line on the timing cover. I’m completely out of ideas as to what the problem can be. Any help would be greatly appreciated.
 

gnathv

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lining up the timing marks are to get it running. The pump is probably out of time. Take the AC glow plugs out and install Motorcraft before you regret it. When it cranks and doesn’t start are you getting smoke out of tailpipe?
 

Big Bart

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Ditto start with the timing, these trucks are very timing sensitive. Then you can move on to other tests.

Many heat related starting issues tend to come back to IP issues. Many folks get back a problematic IP rebuild. So if the timing is spot on I would call Conestoga to discuss other things to test. Then return for repair/replace.
 

Nlevine125

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lining up the timing marks are to get it running. The pump is probably out of time. Take the AC glow plugs out and install Motorcraft before you regret it. When it cranks and doesn’t start are you getting smoke out of tailpipe?
No, not getting any smoke out the pipe.


Ditto start with the timing, these trucks are very timing sensitive. Then you can move on to other tests.

Many heat related starting issues tend to come back to IP issues. Many folks get back a problematic IP rebuild. So if the timing is spot on I would call Conestoga to discuss other things to test. Then return for repair/replace.
Should I start by advancing or retarding the timing? Correct me if I’m wrong, but I believe to advance the timing is to tip the top of the pump towards the passenger side of the truck? Also, how common is it to receive a defective pump? I had done quite a bit of research before I purchased a new pump and Conestoga came highly recommended from everywhere I looked. I spoke to the owner and rebuilder at length before I purchased the pump, explaining the issues I was having and he was certain that was the problem.
 

drewr13NJ

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Following this... I have a 92 that was recently sleeved and rebuilt. I have been having similar issues. The truck has 107K mi on it. I got a "new" pump from someone who worked at the Navistar plant in Indy. That being said it was given to me, so I think I got what I paid for. He had a truck with a 7.3 IDI too, but gave me some parts since he no longer has the truck. The pump looks new, but I still have the hot start issues that the original pump had. Brand new E code injectors too. Did many tests; checked lift pump pressure, changed fuel filter. Starts cold with no stalls or stuttering after sitting for several days too, so I doubt it is an air intrusion issue. I have advanced the pump to the passenger side about a dime width, maybe a little more. Smokes a little on start and when I let the clutch out at a stop light, but doesn't really act much different from when the timing marks were lined up. Batteries checked out good and we checked fuel solenoid. Didn't loose power to it while cranking. Both new and old pump start much easier with water poured on front of pump.

My situation is a little different than Nlevine125 since he has a brand new rebuilt pump from a reputable supplier, but there are many similarities. I can start a new thread if you guys think it is appropriate. Any thoughts? Should I pull it off and spend the money to get it rebuilt? I also have access to a eBay "rebuilt" pump for a turbo engine. Think I should stick that on my NA to see if it hot starts better?
 

gnathv

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How long has the pump been sitting before it was installed. May have gummed up from being on the shelf. I’d run a cleaner through it and see if it makes a difference.
 

tradergem

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I thought my IP was having hot start problems recently, but it turned out to be my starter was dying and wasn't cranking the engine over fast enough when hot. Got a new Mitsubishi style starter and the truck starts right up every time even when it was 107* the other day.
 

Big Bart

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Should I start by advancing or retarding the timing? Correct me if I’m wrong, but I believe to advance the timing is to tip the top of the pump towards the passenger side of the truck? Also, how common is it to receive a defective pump? I had done quite a bit of research before I purchased a new pump and Conestoga came highly recommended from everywhere I looked. I spoke to the owner and rebuilder at length before I purchased the pump, explaining the issues I was having and he was certain that was the problem.

Most members find using the alignment marks only gets them close. But from many pictures and my own IP, you will have the pump mark 1-3 dimes widths closer to the passenger side battery when it is timed correctly. (To be more clear the space between the alignment marks will be 1-3 dimes widths apart vs lined up.)

Once you invest in a timing device you will see how sensitive they are to timing. More so than a gasser. Some claim to have a ear for it and maybe they do. But I cannot tell by ear if I am at 10,9,or 8 by listening or driving the truck. Or if the truck is set to 9.5 or 9 degrees. I cannot tell the difference. I can sense it is off 5-8 degrees either way by power or rattle at start up.

Rule #1 for this site, DO NOT ASSUME ANY PART IS GOOD! Countless members bought quality parts or rebuilds that where bad out of the box. You did buy from a reputable shop, but there is always going to be a failure rate on a rebuilt part.(Just less from a pro.) There is also damage that can happen with a part bouncing or vibrating in a truck or plane on its way to you. Or damage or improper installation by the mechanic. It may likely not be the pump, thus why you and Conestoga should discuss. They will want to advise you on some other things to check first. If still an issue I am sure they will agree to a return for testing and potentially replacement.

Stick with it you will figure it out!
 

Nlevine125

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Just a quick update. I have called Conestoga and am waiting on a call back. In the meantime, I have played with the timing on the pump. I’ve both advanced and retarded the timing 1, 2, and 3 dime widths either way, and get no audible change to the motor. It still runs just as smooth with no timing in it as it did advanced or retarded. It also starts the same in the cold. But as soon as the motor gets hot it continues to not start, even with the timing changes.
 

Big Bart

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I am sure Constoga will have some ideas for testing, once completed if still an issue should be more than willing to get it back and test it agian.

It likely could be a bad IP soleniod. Get's hot and stops working electrically, or gets hot and will not slide. The challenge is he likely cannot heat test on his bench.
 

The_Josh_Bear

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To test if it's the classic internal tolerance problem within the IP:
Get the engine hot, then turn it off and pour .5L of room temperature water(not cold!) on the head of the IP. This will cool it off quite a bit and close down those tolerances.
If that's your problem, it'll start up good. And it will make your conversation with Mel a lot shorter! They do great work over there but you never know. It's worth a quick test.

As for the timing: advance it, and yes towards the passenger side. Where you'll hear the difference is with the engine cold. It'll sound loud and rattley like a PSD. Then when the fast idle and timing advance solenoids turn off that sharp rattle will go away and it'll sound normal. That's the spot you're looking for and it'll get you within 2-4* typically.
 
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