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Leaning out passed 5000 rpm

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GettinPaper

10+ Year Contributor
289
0
Aug 31, 2009
Battle Ground, Washington
This is my daily driver that's basically stock other then a 3" turbo back exhaust, ported 7cm hotside and a wide band. Holds 13lbs to redline with no creep, my AFRs are rich until 5000 Rpms and leans to 13ish AFR and loses power.. What would be causing this?? Any help is appreciated, Thanks.
 
can you post a log??
what fuel pump and base pressure are you running

No logger or anything at all, I just put an exhaust and wide band on the car. I am running a walbro 255 10000 miles on it. AFRs are fine at idle and under boost, until 5000 Rpms then I lean out. I am running stock fuel pressure I have no Afpr

In addition did you do the fuel pump rewire mod?

Also it's past not passed. ;)

I know LOL it's my phones autocorrect I was trying my best :)
 
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It sounds like a fuel pressure issue, irrespective of how new/old the Wally is, I've seen them go bad.

You didn't answer anyones questions on whether or not you re-wired it? Did you? Start there.

Second, you mention you have no AFPR, that's a no-no on a Wally 255lph.

I would suggest you head down to Autozone (or local auto parts equivalent) and rent a fuel pressure tester. Hook it up, leave the gauge hanging up by the windshield cowling so that you can read it, and make sure the fuel pressure increases appropriately.

I think you'll find the issue.
 
What symptoms do you have besides the leaning out and losing power? Any bucking or hesitation? In my case it was the 1g MAS that was being overrun. Check out the other "MUST" items the others have posted, but keep this in the back of your mind.
 
You might want to reverse flush your pump, and replace the strainer and filter. If you make a a small paper funnel to tape to the outlet of the pump, and pull the anti drainback valve with a pair of hemostats, you'll find that the pump will flow fuel backwards when you add 12 volts of reversed polarity.

I am not the first person to have good results with a Wally using this method. I got it from an F-body forum, where the OP was leaning out during dyno pulls.

Before doing all this, you might want to make sure the FPR is reading a solid boost source, and doing it's job first.
 
You might want to reverse flush your pump, and replace the strainer and filter. If you make a a small paper funnel to tape to the outlet of the pump, and pull the anti drainback valve with a pair of hemostats, you'll find that the pump will flow fuel backwards when you add 12 volts of reversed polarity.

I am not the first person to have good results with a Wally using this method. I got it from an F-body forum, where the OP was leaning out during dyno pulls.

Before doing all this, you might want to make sure the FPR is reading a solid boost source, and doing it's job

You might want to reverse flush your pump, and replace the strainer and filter. If you make a a small paper funnel to tape to the outlet of the pump, and pull the anti drainback valve with a pair of hemostats, you'll find that the pump will flow fuel backwards when you add 12 volts of reversed polarity.

I am not the first person to have good results with a Wally using this method. I got it from an F-body forum, where the OP was leaning out during dyno pulls.

Before doing all this, you might want to make sure the FPR is reading a solid boost source, and doing it's job first.

The car runs great other then leaning out past 5000rpms so I don't think it's the Maf. How do I go about making sure the fpr is doing its job. Thanks
 
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Fuel pressure should rise as you get into boost on a 1:1 ratio. Get a gauge to check that the regulator is raising fuel pressure
 
I had the same issue in my old car. After changing and checking this that and everything else it turned out that my year old (5k miles) Walbro 255 was dying. It was the last thing I checked cause it wasn't that old. Do you notice if your pump makes any odd noises sometimes? Can you hear it whine or does the whine change tones? Mine would make a real quick screeching for a split second every once in a while. I've also been told the louder the they whine the closer to death they are but don't hold me to that one. My new Walbro 255 that I dropped in was way quieter than my dying one so maybe there is some truth to that.
 
If your FPR wasn't raising fuel pressure then you'd lean out as soon as you hit boost. I'd say either your fuel pump is weak and can't supply enough fuel at high RPM, or you have one or multiple very dirty fuel injectors.
 
If your FPR wasn't raising fuel pressure then you'd lean out as soon as you hit boost. I'd say either your fuel pump is weak and can't supply enough fuel at high RPM, or you have one or multiple very dirty fuel injectors.

I am going to replace my fuel pump this weekend to rule that out just to be sure.. And i'm going to go with a walbro 190 this time.
 
On an afpr there is a port for a gauge. Run a line TEMPORARILY to the cabin and hook it up to a gauge and watch. Your gonna have to watch 2 things at once since you arent logging boost. Not the safest thing. I think i would have a passenger ride along. The stock fpr would only cause you problems(99% of the time) at idle. When in boost it will do its job just fine. There are members, albeit only a few, that do not have afprs. I dont recommend this.

And yes, your maf could indeed be causing it. If its 5000 rpm under any load in any gear then its not the maf. But if its under a certain load then it could be flaking out and sending a lower hz to the ecu thus shortening pulse width time on your injectors.
 
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