96 7.3 Strange starting issues??
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96 7.3 Strange starting issues??
Hey guys I am working on a 96 F250 7.3, I have done so much to this truck and usually can figure out problems. This one has me stumped!
I replaced the IPR, the IPR harness, all new Injector O-rings. It will start, and when you get on it on the freeway, it screams like it has all the power in the world. Runs perfect on the freeway! At idle though, it runs a little rough.
If you let it sit for just a minute, it will fire back up pretty quickly. The problem is when you let it sit for 20-30 minutes or so.
You can crank and crank and it takes forever to build back low pressure oil. Eventually after cranking forever, the oil pressure gauge moves to the middle, and the truck will start up.
Again, runs amazing after getting it started! High pressure oil reservoir is full.
I'm thinking LPOP, PLEASE HELP!
I replaced the IPR, the IPR harness, all new Injector O-rings. It will start, and when you get on it on the freeway, it screams like it has all the power in the world. Runs perfect on the freeway! At idle though, it runs a little rough.
If you let it sit for just a minute, it will fire back up pretty quickly. The problem is when you let it sit for 20-30 minutes or so.
You can crank and crank and it takes forever to build back low pressure oil. Eventually after cranking forever, the oil pressure gauge moves to the middle, and the truck will start up.
Again, runs amazing after getting it started! High pressure oil reservoir is full.
I'm thinking LPOP, PLEASE HELP!
Cargo Master
Joined: May 2011
Posts: 2,623
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From: Rockford IL
Are your oil levels good?
Usually the LPOP on these arent an issue... But I could be wrong.
And you say it just has a rough idle? Like it will stay running, but lopes or idles low?
If that is the case I believe the ICP would be your issue. Unplug it and see if your idle changes. The ICP is located in the driver's side valve cover towards the front of the engine. If standing in front of the truck it would be closer to you than the cab.
Usually the LPOP on these arent an issue... But I could be wrong.
And you say it just has a rough idle? Like it will stay running, but lopes or idles low?
If that is the case I believe the ICP would be your issue. Unplug it and see if your idle changes. The ICP is located in the driver's side valve cover towards the front of the engine. If standing in front of the truck it would be closer to you than the cab.
FOREIGN GURU
Joined: Jul 2006
Posts: 7,655
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From: Celaya, Gto. MX
Hey guys I am working on a 96 F250 7.3, I have done so much to this truck and usually can figure out problems. This one has me stumped!
I replaced the IPR, the IPR harness, all new Injector O-rings. It will start, and when you get on it on the freeway, it screams like it has all the power in the world. Runs perfect on the freeway! At idle though, it runs a little rough.
If you let it sit for just a minute, it will fire back up pretty quickly. The problem is when you let it sit for 20-30 minutes or so.
You can crank and crank and it takes forever to build back low pressure oil. Eventually after cranking forever, the oil pressure gauge moves to the middle, and the truck will start up.
Again, runs amazing after getting it started! High pressure oil reservoir is full.
I'm thinking LPOP, PLEASE HELP!
I replaced the IPR, the IPR harness, all new Injector O-rings. It will start, and when you get on it on the freeway, it screams like it has all the power in the world. Runs perfect on the freeway! At idle though, it runs a little rough.
If you let it sit for just a minute, it will fire back up pretty quickly. The problem is when you let it sit for 20-30 minutes or so.
You can crank and crank and it takes forever to build back low pressure oil. Eventually after cranking forever, the oil pressure gauge moves to the middle, and the truck will start up.
Again, runs amazing after getting it started! High pressure oil reservoir is full.
I'm thinking LPOP, PLEASE HELP!
Post Fiend
Joined: Dec 2010
Posts: 10,121
Likes: 3
From: Orrville, Ohio
I am willing to bet that if you let it sit like that for 20-30 minutes then pull the plug out of the top of the HPOP reservoir, it will be low on oil. It sounds to me like you either have a bad IPR (or the wrong one as has been mentioned above) or a bad backflow valve that is letting the HPOP res drain down. Either way, if you pull the plug in the top of the reservoir and the oil is much lower than 1/2" or so from the top, you're draining all the oil out of the HPO system back into the pan. That will cause the issue you're describing with the hard start and the fact that the HPO system is losing prime and probably has some air in it can cause the rough idle you're talking about as well.
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I am willing to bet that if you let it sit like that for 20-30 minutes then pull the plug out of the top of the HPOP reservoir, it will be low on oil. It sounds to me like you either have a bad IPR (or the wrong one as has been mentioned above) or a bad backflow valve that is letting the HPOP res drain down. Either way, if you pull the plug in the top of the reservoir and the oil is much lower than 1/2" or so from the top, you're draining all the oil out of the HPO system back into the pan. That will cause the issue you're describing with the hard start and the fact that the HPO system is losing prime and probably has some air in it can cause the rough idle you're talking about as well.
Reservoir is full, and the HPOP should be getting plenty of oil. There is some aeration in the oil, but if the pickup tube was cracked, wouldn't it run rough at all times? On the highway, when you get on it the truck makes tons of power! It has a harsh/ rough idle, and will sometimes keep dying right after starting it. If it was the HPOP, one would think at WOT the truck would lose power, but it doesn't at all!
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Does the HPOP need pressure from the LPOP even if the HP oil reservoir is completely full? Is the oil pressure gauge able to move while cranking? Even after 10 seconds or more of cranking, the gauge reads nothing. Then after a bunch more cranking, the engine will start, the gauge will jump up and stay, but the truck runs extremely rough and stalls a lot. Then it requires continually restarting it until it will idle on it's own. Even then it will still stall. ICP at idle jumps from 380-550. It surges up and down and seems to have a hard time keeping enough ICP. The HPOP is fine though, WOT it will make around 2500 PSI. Hooked a mechanical gauge directly to it and it shot up over 2000 PSI.
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Fleet Owner
Joined: Aug 2004
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From: AZ
The hpop will be feed by the lpop while cranking. Its staying full so no problem there. After posting I thought that maybe the gauge will not pop up until the key is released after starting. Usually the IPR O rings are bad with what your decribing so I'm at a lost.
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Ok thanks anyways, I appreciate the input! Anyone else have any ideas? Since the truck is keeping the HPOP reservoir full all the time, the only thing I can think of left is to replace the HPOP. DAMN!!!!
Post Fiend
Joined: Dec 2010
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From: Orrville, Ohio
The oil pressure "gauge" on the dash is really nothing more than a dummy light with a needle. It only has two positions; off and right in the middle. I wouldn't base your diagnosis on what you're seeing that gauge do. Based upon the readings you're seeing at the HPOP I doubt that is your issue as well. If the HPO pressures (ICP) are fluctuating that much at idle, I think you should start there. It could be a blown injector o-ring or two, but that generally causes a stumble around 1500 RPM. Does the fuel in the filter bowl look clean? How does the fuel filter look? I know you said the o-rings are new, but they can get cut up during installation occasionally.
The other thing you could do would be to replace the ICP. If you unplug the ICP, does it idle smooth? Is there any trace of oil inside the electrical connection at the ICP? If there is, that generally means it is shot.
The other thing you could do would be to replace the ICP. If you unplug the ICP, does it idle smooth? Is there any trace of oil inside the electrical connection at the ICP? If there is, that generally means it is shot.
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Yes it is a brand new ipr, the correct one as well. Also it has a brand new ipr harness as the old one was in horrible condition. It is keeping the hpop reservoir full at all times, yet doesn't make enough icp without excessive cranking to start. All brand new alliant injector o rings, very carefully installed. Hpop makes good pressure in upper rpm range. Wtf is it???
Post Fiend
Joined: Dec 2010
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From: Orrville, Ohio
Swap the ICP out or try starting it with the ICP unplugged. Regardless of what the HPOP is doing, if the PCM doesn't see 500 PSI of HP oil (using the ICP for this reading) it won't fire the injectors.
Just out of curiosity how fast does it crank over? Is it possible that the starter is weak and not spinning it fast enough, or that the batteries are weak and the voltage is dropping below threshold while you're cranking it?
Just out of curiosity how fast does it crank over? Is it possible that the starter is weak and not spinning it fast enough, or that the batteries are weak and the voltage is dropping below threshold while you're cranking it?
Thread Starter
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Swap the ICP out or try starting it with the ICP unplugged. Regardless of what the HPOP is doing, if the PCM doesn't see 500 PSI of HP oil (using the ICP for this reading) it won't fire the injectors.
Just out of curiosity how fast does it crank over? Is it possible that the starter is weak and not spinning it fast enough, or that the batteries are weak and the voltage is dropping below threshold while you're cranking it?
Just out of curiosity how fast does it crank over? Is it possible that the starter is weak and not spinning it fast enough, or that the batteries are weak and the voltage is dropping below threshold while you're cranking it?