WTF is happening with my 99 4.6 AWD? HELP ME. PLS.

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1955moose

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Oh well you'll get it off. If not just replace broken part. Never ends does it!


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98RedExp

98RedExp

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Update.

Replaced Spark Plugs
Replaced Coil Packs
Replaced Camshaft Sensor.
Recently Replaced MAFS
Replaced TPS
Replaced both Headers
Has new EGR Tube
EGR Recently Replaced.
Fixed Various Vac Lines.

Still starts up fine sometimes and idles OK, dies out after a long hard rev.
Other times, it hard starts and cranks hard and just BARELY starts up and then runs super rough.

Possibly a bad fuel pump? I am open to hearing suggestions at this point. I have so much time and money out, IDK what to do.
 

1955moose

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Well as some of us old timers have stated time and time again, check fuel pressure at fuel rail. It should be at least 33 minimum. You could have a fuel pump screen that's disintegrated that's struggling to pass fuel through it. Or a weak pump that's on it's last leg. You've replaced all the other culprits. Coils, maf sensor, ran the code checks. Run a fuel test, you can probably borrow the gauge. Exaust leaks will make you lose some power, but as extreme as your problem I would say probably not. I had a 82 mustang gt with a 5.0 liter. When I had an Exaust leak it felt like I was running on 7 not 8 cylinders. But it still ran, didn't die or have your systems. Keep the faith, you've come this far.


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98RedExp

98RedExp

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Well as some of us old timers have stated time and time again, check fuel pressure at fuel rail. It should be at least 33 minimum. You could have a fuel pump screen that's disintegrated that's struggling to pass fuel through it. Or a weak pump that's on it's last leg. You've replaced all the other culprits. Coils, maf sensor, ran the code checks. Run a fuel test, you can probably borrow the gauge. Exaust leaks will make you lose some power, but as extreme as your problem I would say probably not. I had a 82 mustang gt with a 5.0 liter. When I had an Exaust leak it felt like I was running on 7 not 8 cylinders. But it still ran, didn't die or have your systems. Keep the faith, you've come this far.


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The Expy is currently at my best friends and my mechanics house, 120 miles away from me. What should he do to give a proper fuel test at the rail? Edit - It also can idle completely fine after hard starting too.

I ordered an IAC, FPR, Fuel Filter and a New Fuel Pump to be there tomorrow, so hopefully we can clear things up.
 
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1955moose

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Change the fuel filter hook up gauge to Shrader valve up front on fuel rail. If your mechanic friend doesn't know what to do to get proper reading, I'd question his ability. You need to do a pressure test, both off and running. Look online to figure out how. Theirs always a how to video online.


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1955moose

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After hooking up gauge, fire up SUV observe reading, should be 33-42 psi. Leave gauge connected, shut off see if pressure holds. If it drops more than a few pounds, theirs a leak that you guys will have to figure out. The important thing for performance is running pressure. If it's low the SUV will run lean and poor. Keep us posted.


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