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Old 09-16-2018, 01:52 PM   #1
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Boosted Car popping and stumbling when accelerating

As of late my 89 fox supercharged hesitates and pops when i accelerate HARD, somewhere around 3500rpm and up. doesn't do it in low rpm accelerations.
I'm at 6lbs of boost and fuel pressure at 50psi. when i accelerate hard, my air fuel ratio goes super lean around 23.00!! 14.7 at idle.
I currently have a 340lph fuel pump PLUS a T-REX secondary external pump running.

do i need more fuel pressure? or is there something wrong with my fuel system?
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Old 09-16-2018, 05:34 PM   #2
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Did it NOT do this when you first installed everything? I’d guess that (although 23 to 1 is waaaay too lean!) you may need more robust injectors to support higher boost levels.
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Old 09-16-2018, 05:55 PM   #3
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Lol melt them pistons yea yea

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Old 09-17-2018, 09:32 AM   #4
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Definitely sounds like a fuel delivery problem.
The first two things to check are the fuel filter, and the fuel pressure regulator.
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Old 09-17-2018, 05:37 PM   #5
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Wow !!!! 23 to 1, How long has this been going on ? Lucky to still be running. Do you have a FP gauge that you can moniter while this is happening to make sure pressure isnt dropping?
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Old 09-18-2018, 12:34 AM   #6
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Originally Posted by Guard 5.0 View Post
Did it NOT do this when you first installed everything? I’d guess that (although 23 to 1 is waaaay too lean!) you may need more robust injectors to support higher boost levels.
It ran fine, lots of power! just until a month and a half ago this started happening. I only drive the car on the weekends and less now because of this problem.
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Old 09-18-2018, 12:40 AM   #7
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Wow !!!! 23 to 1, How long has this been going on ? Lucky to still be running. Do you have a FP gauge that you can moniter while this is happening to make sure pressure isnt dropping?
I installed one last week but its in the engine bay. it read 60psi when first installed it.
keep in mind the problem was still there with 60psi, i just installed it to see where i was at in fuel pressure. so i dropped it to 50 psi and the problems still there. i pulled the vacuum line that goes to the fuel pressure regulator at idle and psi goes up a bit, i guess the fpr is working i guess...

I did notice my fuel pressure goes all the way down quickly and holds no psi when i shut the car off, perhaps theres a pressure leak somewhere?
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Old 09-18-2018, 12:42 AM   #8
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Definitely sounds like a fuel delivery problem.
The first two things to check are the fuel filter, and the fuel pressure regulator.
thats what i was suspecting even though i replaced my fuel filter i guess its worth a check. I've been hearing about a fuel pump or fuel pressure check valve online and maybe it could be bad, i just gotta find the dang thing.
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Old 09-18-2018, 01:12 PM   #9
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There are three places that it could be leaking internally.
On the stock pump, there is a check valve inside of the in-tank fuel pump. Not sure about your aftermarket pump.
The fuel pressure regulator can develop a leak.
A fuel injector can be stuck open.

Can probably rule out the stuck fuel injector, in your case.

You really need to figure out a way to monitor the fuel pressure while driving, and see what it is doing while re-creating the conditions when the pinging occurs. The fuel pressure might be good at idle, but there may be a problem with the fuel volume when the engine is under full load.
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Old 09-18-2018, 01:17 PM   #10
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I just had to replace pumps on my 04 Cobra , ran fine until you got on it like to pass some body , acted like it was running out of gas, changed pumps problem went away , car ran great before this ,
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Old 09-19-2018, 04:27 PM   #11
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You do have the car tuned properly right? You didn't just set the fuel pressure and roll did you?
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