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Truck stalls or almost stalls after start

3K views 9 replies 2 participants last post by  C7N3M 
#1 ·
Hello,
Very new to the forum so I'm probably in the wrong section.. I have read many of the helpful posts in the past but I couldn't find anything exactly relating my issue.. I apologize if I am repeating a thread..
I have a 2004 lly with 315k on it, very stock.. brand new battery's and starter and fuel lines all the way from tank to cp3 and apparently has a new cp3 according to the guy I bought it from(whom I think I trust lol)
Truck runs strong and has plenty of get up and go..

I bought the truck and the guy said it has a fueling issue so I don't know much of the history of the issue. At first it seemed as though there was constantly air in the fuel lines.. and I couldn't get the truck to start after off for more than an hour it would crank forever and I would give it a small shot of ether and it would fire right up... I suspected a bad filter housing or lines so I put a new system in with an aftermarket sump and inline filter with a primer bulb.. after getting that all primed and free of air(I think) the truck will start every time but it cranks to long(15-20 seconds when cold)(but only a few seconds when warm)(maybe that is normal I don't know)
Now.. my main issue at hand is that when it does start it stalls instantly .. not 1 second later... Right away!. And does not keep cranking if you hold the key turned..so I believe it has technically started. it does that maybe %50 of the time and the other 50 it starts but the the rpms dip very low and it almost stalls but then bounces right back up to normal idle.. I have started and run the truck quite a bit since changing all the lines so I think all the air is out of the system..
I have done the bottle test and got no fuel in my bottle.. so I'm thinking the fuel rail pressure relief is ok..
I am suspecting the fuel pressure regulator on the cp3 now.. it has a bit of a rough idle but nothing crazy
I have been using a Bluetooth obdii reader connected to my phone to watch rail pressures..
When off but key on my rail pressure bounces from 253-279 psi
When on at idle rpm my rail pressure fluctuates from 4023-4562 psi(sitting graphing high and lows for 15mins) my understanding is something closer to 4900 and within 200-300 psi is desirable..
When I give it some throttle in park I have hit over 16000psi (wasn't trying to get as high as possible just gave it a one shot)..

It is running two codes at this time.. maf and a tranny code of some sort other than that it is clean.. tried the 3 key reset.. going to try the 30 minute security reset and check grounds next but I don't think that is what it is?..


Thank you for your time and reading this!.. any and all info is muchly appreciated!
Thanks
-Caleb
 
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#3 ·
Hey thanks alot for the reply.. I will look into the mass airflow sensor code.. might it be confused because it doesn't know the ratio of air to fuel that it is getting?
And yes I'm not sure.. could psi when off not be reading correctly because of a faulty pressure regulator? It also bounces from 253 to 279 back and forth every couple seconds.. I would think that would be more consistent when the engine was not running?..
Thanks
-Caleb
 
#4 ·
I previously tried to clear the maf code when the truck was off and it came back.. I just cleared it while it was running then left it running for a bit.. reved it up, drove it, turned it off and started it multiple times and I cant get the code to come back.. however it still starts the same way...
The maf sits at 38 g/s while at idle fluctuating less then 1.. and I got it over 200 revving it a bit..
Based on that I think the maf is ok?
No codes now.. just the starting issue
Thanks
-Caleb
 
#5 ·
Also the rail psi is sitting between 5350 and 5750 today.. started, checked, turned it off, and started, checked it again multiple times.. maybe because the engine isn't warm yet.. however it doesn't seem like it is in high idle..
Thanks
-Caleb
 
#7 ·
There may be some residual pressure in rail after shut down. I might try bleeding off the rail pressure after shutdown and see if it will read zero. If pressure sensor is off a couple hundred pounds that might cause it to react differently if it constantly reading high.
 
#10 ·
Today a weird new development.. I tried to start it cranking for 15 second intervals probably 10 times and couldn't get it to start.. checked the rail pressure and I couldn't get it over 1500psi.. (my understanding is it needs to be 2500 to start?)
I took the fuel relief valve out to watch the psi reading drop but no fuel came out of the rail and the psi never dropped below 229.. could this be a faulty reading from a faulty pressure regulator? What tells the computer the rail pressure? Is it the regulator or is there a sensor on the rail as well?
I'm going to shim the relief valve and reinstall it..
Still trying to find a gauge and figure out where to hook up to the fuel rail to test pressure..
I have a compression tester.. I will check compression of the engine while trying to start it.. I assume I can use the glow plug hole?..
Also tried the security reset.. didn't help..

Thank you
-Caleb
 
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