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7.3l will not start when hot

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  #1  
Old 07-11-2018, 08:26 PM
MONAVIERONJON
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7.3l will not start when hot

188k on odometer, reman engine. has new ipr, new injector o rings, new valve cover gaskets, fresh oil, new bellowed up pipes, fuel gauge is 63;bs . starts right up when cold, (oil is thicker). bought hits as a non running truck have a scan gauge and seeing the icp range from 500 to 3400 when cranking, unplug icp and still no start. i do have rpm and ill have to follow up with the ipr #.( thinking bad hpop or bad pcm ) since this is a reman engine.drives good until it warms up, will shudder and loose power.
 
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Old 07-11-2018, 08:39 PM
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Not starting warm is usually an IPR, or o-ring issue. If you're really getting over 3,000 psi while cranking, then I'd suspect the HPOP. We've seen remans produce good pressure, but not near enough volume to do anything. If you suspect the HPOP, pull the plug on top of the reservoir or disconnect a line and see how much oil comes out while cranking.

You'll either get, holy cow that was a whole lot more oil than I ever thought, or you'll get just a small dribble of oil. Holy cow = good HPOP, but it can make a mess. You've been warned.
 
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Old 07-11-2018, 09:43 PM
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thankx for the info, is there any theory as to why this might only happen when oil is warm and thinner? im thinking the hpop prolly wasnt remanned ,just the block measured for compression and new rings, something to that effect. This is an engine that has an International reman sticker. Anyway, I have a known good one I most likely will swap . I will try that test first since I park on sand,
 
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Old 07-12-2018, 06:51 AM
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Originally Posted by F350-6 View Post
Not starting warm is usually an IPR, or o-ring issue. If you're really getting over 3,000 psi while cranking, then I'd suspect the HPOP. We've seen remans produce good pressure, but not near enough volume to do anything. If you suspect the HPOP, pull the plug on top of the reservoir or disconnect a line and see how much oil comes out while cranking.

You'll either get, holy cow that was a whole lot more oil than I ever thought, or you'll get just a small dribble of oil. Holy cow = good HPOP, but it can make a mess. You've been warned.
I didn't think that the reservoir got high pressure, only low pressure, am I wrong on that?
 
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Old 07-12-2018, 08:34 AM
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I'd say you are right. LPOP fills HPOP reservoir. HPOP makes high pressure after reservoir. He might be talking about plugs in the head on oil rail.

When oil and engine are hot it increases heat in IPR coil. That cause increase in resistance in IPR coil which takes more voltage and amps to overcome that circuitry can't produce. Take a upside down can of air and spray IPR coil or dump a bunch of cold water on it while it is hot and see if makes a difference. If it does then it is the IPR.
Cooling coil reduces resistance which puts it closer to factory specs and allows it to run until hot again.
 
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Old 07-12-2018, 12:37 PM
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so I let truck cool down overnight and went to start it and all it does is crank. the oil is cold, and the icp fluctuates from 400 to 3500. It acts like it wants to start , IPR in the 14.4 range, thats normal when cranking. I have another truck I can pull the coil from for the ipr although it seems more like the hpop. I guess next Im going to pull off a hpop line going to a rail and see what volume it pushes out. and of course verify there plenty of oil in the reservior
 
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Old 07-12-2018, 06:26 PM
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Originally Posted by Walleye Hunter View Post
I didn't think that the reservoir got high pressure, only low pressure, am I wrong on that?
Nope. Not wrong at all. But fluid follows the path of least resistance. Removing the plug will show volume of oil, at low pressure, but you're right, it won't show if the HPOP is the problem, only if it's an LPOP problem. Disconnecting the hoses is who to test volume on the HPOP. The reservoir plug will still make a mess, but won't help the HPOP.

I've had a lot on my plate lately. Thanks for setting me straight.
 
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Old 07-12-2018, 06:30 PM
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Originally Posted by MONAVIERONJON View Post
thankx for the info, is there any theory as to why this might only happen when oil is warm and thinner?
If it's the IPR, it because the valve gets hot and stops working. If it's o-rings, it's because the thinner oil leaks by faster. If it's the HPOP, I'm not really sure how that mode of failure works where it can still produce full PSI, but not at enough volume to fire the injectors. I suspect the volume needed is just bleeding by and backfeeding through the pump. If that's the case, it follows the same logic as the o-ring issue when warm.
 
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Old 07-12-2018, 07:32 PM
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Instead of swapping hpops, im in the middle of swapping injectrors now, found an easy trick to drain the oil rails , pull injectors and then completely fill and bleed air out of the oil rail and starts first try. These original injectors have 188k , and im thinking something internal in the injectors is worn. prior to yesterday I had oil with a few hundred miles in the oil and a crank and no start, then installed injector o rings, and fresh oil and fired right up and ran for a half hour, then perhaps the fresh oil worked it way through the system and ad me to believe the thicker fresh oil is revealing an internal injector problem that reoccurrred after mixing with older oil and thinning
 
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Old 07-13-2018, 09:37 PM
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Originally Posted by F350-6 View Post
If it's the IPR, it because the valve gets hot and stops working. If it's o-rings, it's because the thinner oil leaks by faster. If it's the HPOP, I'm not really sure how that mode of failure works where it can still produce full PSI, but not at enough volume to fire the injectors. I suspect the volume needed is just bleeding by and backfeeding through the pump. If that's the case, it follows the same logic as the o-ring issue when warm.
Sorrybut that's only half the story. I've rebuilt probably 20 iprs to save money and the coil is the culprit that dies and makes a full replacement needed on 15 - 16 of them.
 
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Old 07-13-2018, 10:38 PM
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must be the heat exposure, just finished my injector swap and fired it up today, tommorrow is test run and will post results
 
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Old 07-14-2018, 07:10 PM
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follow up, results are the same. when truck warms up and the new oil in the hpop res and oil rails is then mixed with the rest of the crank case oil it runs for a short while and then is a crank , no start. the icp begins about 280 and then peaks in the 2800 range, so this next week im swapping a known , good hpop from another motor. tin , nut is snug and the ipr is new. by process of elimination sure appears to be a bad HPOP, have a great weekend, Ronjon
 
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