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95' 7.3 crank but no start...sometimes

3K views 14 replies 3 participants last post by  mattswan267 
#1 ·
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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#4 ·
#6 ·
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
 
#8 ·
Yes 35-45 and 55-65 while running and make sure your reading cranking pressure as theres no pressure with just the key on.
 
#10 ·
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.
 
#13 ·
Make sure it has a real good charge and keep cranking. You have to work all the air out of the system after you open it that much. It helps to prime the fuel bowl too. All air has to be out for it to fire. Trust me it takes some time but it should fire if your getting 45 psi
 
#14 ·
So I changed the crank sensor and it fired right up. I let it run for about 10 minutes and shut it off and let it sit for a couple minutes and it would not start. I checked oil pressure from the ICP port on the head and got a reading of barely 210 psi while cranking (cranking speed is around 250-300 rmp)
 
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