Help! Hard miss under load
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Joined: Aug 2012
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Help! Hard miss under load
Hello all,
I have been lurking and using all the helpful threads here since I got my truck this spring, but I have had one major unresolved issue and am about out of ideas. This is my first diesel and am not a mechanic, but consider myself mechanically inclined. Okay here is the issue:
The truck has a 1997 7.3 mated to the zf5. It idles smooth and accelerates fine in any gear to about 2500 RPM then begins to miss violently. The whole truck shudders like it is running out of fuel, but i have the FPR shimmed and fuel pressure never drops below 60psi or so at any point. If i let off the pedal i can ease it over 2500 rpm but if i put the pedal down too much it begins to shudder and stumble again. In neutral i can rev to redline with no issues.
I have replaced the IPR, CPS, checked fuel pressure and HPOP pressure at all speeds and RPM, visually inspected uppipes and turbo boots for leaks, removed cat, removed VC and checked all injector connections and unplugged each to check contribution. I have removed and inspected every sensor I can find with no luck. This is a constant problem, I have never been able to rev over 2500 under load since i've had the truck and am running out of things to check.
Thanks in advance
I have been lurking and using all the helpful threads here since I got my truck this spring, but I have had one major unresolved issue and am about out of ideas. This is my first diesel and am not a mechanic, but consider myself mechanically inclined. Okay here is the issue:
The truck has a 1997 7.3 mated to the zf5. It idles smooth and accelerates fine in any gear to about 2500 RPM then begins to miss violently. The whole truck shudders like it is running out of fuel, but i have the FPR shimmed and fuel pressure never drops below 60psi or so at any point. If i let off the pedal i can ease it over 2500 rpm but if i put the pedal down too much it begins to shudder and stumble again. In neutral i can rev to redline with no issues.
I have replaced the IPR, CPS, checked fuel pressure and HPOP pressure at all speeds and RPM, visually inspected uppipes and turbo boots for leaks, removed cat, removed VC and checked all injector connections and unplugged each to check contribution. I have removed and inspected every sensor I can find with no luck. This is a constant problem, I have never been able to rev over 2500 under load since i've had the truck and am running out of things to check.
Thanks in advance
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New User
Joined: Aug 2012
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yeah it revs to redline no problem in neutral. and i can get it over 2500 if i really ease on it but if i goose it even a little after 2500 it starts bucking like crazy and feels like its running out of fuel or something
Post Fiend
Joined: Dec 2009
Posts: 15,505
Likes: 18
From: Livoina,La
It's gonna he high pressure oil not keeping up or fuel pressure dropping off.
Id start with getting a fuel pressure gauge hooked up and see what the fuel pressure is doing when it starts bucking
Id start with getting a fuel pressure gauge hooked up and see what the fuel pressure is doing when it starts bucking
Post Fiend
Joined: Mar 2007
Posts: 26,966
Likes: 50
From: Texas
What was your fuel pressure under load when it started bucking? And I'm guessing you checked the engine oil pressure instead of the injection control pressure on the high pressure oil side, but just in case, what was your oil pressure under load when it started bucking?
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IIRC my fuel pressure was around 65 or 70 but i dont remember the exact number, just that it was high enough and didn't drop at all. The reason its so high is because i shimmed the regulator. and i tested the high pressure oil through one of the plugs on the top of the motor next to the valve cover. it maxed out at around 2600 or 2700 and didnt change when it started bucking
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