95' 7.3 crank but no start...sometimes - Ford Powerstroke Diesel Forum
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Old 10-17-2013, 09:52 PM
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95' 7.3 crank but no start...sometimes

I'm working on a 95' 7.3. Truck has 350k on it, I've owned it about a year and it's always ran like a raped ape. Always fired right up at the turn of the key.

The hpop was leaking really bad so I replaced it with a good used one that was re sealed. And ever since the truck never started the same, it cranks a little longer before firing and sometimes it will just crank and crank with no start but it would eventually fire up and run great.

I was driving into town today and it was running great, then all of the sudden it began running sort of rough and lost some power and the check engine light emedietly came on. So I putted it back home-about 5 miles, and just shut off in the driveway, and absolutely would not try to fire.

Checked codes with a small obd II scanner and no codes were stored. Checked it with a badass scanning system. Buddy of mine had and it was unable to connect with the truck but found 125 system codes.

After a few minutes of head scratching I tried to start it and it cranked for a good 30 seconds and finally fired up and ran normal. I let it warm up and then shut it off, then started it up right after Snd it started normally and idled for about 1 minute and shut off on its own and wouldn't fire up again. When it was running I had no check engine light.

I am getting 8psi at the shraeder valve on the fuel bowl, I have no clue what it could be and was hoping for some help!
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Old 10-17-2013, 10:00 PM
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While the truck is running, you should be getting at least 45 psi of fuel pressure. You may have a dead/dying fuel pump.
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Old 10-18-2013, 07:44 AM
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Okay, does the shraeder valve read off of the mechanicÓl pump or the in-tank pump? From what I understand the mechAnical cam-driven pump only outputs betwene 6 and 9 psi.
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Old 10-18-2013, 08:05 AM
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Originally Posted by mattswan267 View Post
Okay, does the shraeder valve read off of the mechanicÓl pump or the in-tank pump? From what I understand the mechAnical cam-driven pump only outputs betwene 6 and 9 psi.
No in-tank pump just a mechanical one in the valley of the engine. its a 2 phase pump. Check this out it may help Diagnosing a 7.3 no start
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Old 10-18-2013, 08:19 AM
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So the mechanical pump is the only fuel pump on the truck?
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Old 10-18-2013, 08:46 AM
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So the mechanical pump is the only fuel pump on the truck?
Yes its right behind the fuel bowl. It has 2 chambers. the upper one is a lift pump and pumps fuel into the bowl, then the lower chamber takes it from the bowl and pressurizes it around 55-65 psi and runs to the fuel rails.

This is what it looks like
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Old 10-18-2013, 11:04 AM
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Okay so I should see 35 psi at the shraeder valve on the regulator? I went to start the truck this morning and it started up like normal and ran normal for about a minute and then it shut off and wouldn't start at all. I'm not sure what that means.
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Old 10-18-2013, 11:13 AM
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Originally Posted by mattswan267 View Post
Okay so I should see 35 psi at the shraeder valve on the regulator? I went to start the truck this morning and it started up like normal and ran normal for about a minute and then it shut off and wouldn't start at all. I'm not sure what that means.
Yes 35-45 and 55-65 while running and make sure your reading cranking pressure as theres no pressure with just the key on.
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Old 10-18-2013, 11:31 AM
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Ok so, why would it run for about 60 seconds and shut off. It seems odd that it would need 55 psi to run and it emediatly jumps back to 8 psi when it shuts off. Could the fuel pump intermittently work? Or is it a it's good or it's junk deal?
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Old 10-18-2013, 12:02 PM
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Originally Posted by mattswan267 View Post
Ok so, why would it run for about 60 seconds and shut off. It seems odd that it would need 55 psi to run and it emediatly jumps back to 8 psi when it shuts off. Could the fuel pump intermittently work? Or is it a it's good or it's junk deal?
Well no i never said it needs 55 psi to run. it can run with nearly zero psi. 55-65 is just what its supposed to be. Pressure and volume(flow) are 2 different things. Im gonna guess whats happening is you have a weak fuel pump and its able to pressurize the fuel after enough cranking which then lets the truck fire then it starts using the fuel at a rate the fuel pump cant quite keep up with and kills it after awhile when the fuel flow runs out.
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