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Discussion Starter · #1 ·
I've been battling high idc's so today i checked my fp to see if it was raising 1:1. My first test at 42psi bfp i applied 20psi to the afpr and as expected fp raised to 62psi. I upped the boost source to 25psi and got 66psi fp but no matter how much more boost pressure i added to the afpr it would not raise fp over 66psi. I also tried 45psi bfp and added 25psi to the afpr and got the same 66psi fp. Its a brand new aeromotive afpr. I am also running a rewired walbro 255. Shouldn't the walbro be able to push that much fp under that much boost? I pinched off the return line for a moment and even then i only saw 68-70psi fp. Last summer i replaced the seal on the pump where it meets the sending unit.

I've been battling high idc's (90%) on 650's 2g maf fmic and a s16g at 20psi on 93 octane and was hoping this was the culprit but after seeing the afpr raise the fp accurately up to around 23psi i don't think this is the problem.


I'm looking for any ideas on what might be going on or somethings to look into.

Thanks
 

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On idle if you raise the fuel pressure, does it stop at a certain psi?

I had a similar problem last year, it wouldnt raise above 35psi (vac off) , and was hitting fuel cut every time. Finally found i was missing the plastic spacer which goes in between the pump and fuel line.
 

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Discussion Starter · #3 ·
On idle if you raise the fuel pressure, does it stop at a certain psi?

I had a similar problem last year, it wouldnt raise above 35psi (vac off) , and was hitting fuel cut every time. Finally found i was missing the plastic spacer which goes in between the pump and fuel line.
It was able to hold 50psi base fp without a problem. I am sure that the plastic spacer seal and cap are on the walbro correctly as well.
 

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Discussion Starter · #11 ·
Fix that boost leak.Does your fuel pressure drop on 20+psi boost or stays the same?

i'm not sure i understand your question but when i applied 20psi to the regulator at 42psi bfp the fuel pressure raised 1:1 to 62psi and held fine it was when i applied 25+psi i couldn't get anything over 66psi of fp with the same 42psi bfp. I even upped the bfp to 45psi and applied the same 25psi to the regulator and it only raised up to 66psi again.
 

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Does your fuel pressure drop on 20+psi boost or stays the same?
I meant at 20psi boost and 42 base pressure, Your fuel pressure should be 62psi.
Hook up a fuel pressure gauge to the Afpr and place it where you can see from in the car & do WOT pulls. I would prefer 3rd gear. The fuel pressure should stay at 62psi through out the RPM.
 

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Discussion Starter · #13 · (Edited)
I meant at 20psi boost and 42 base pressure, Your fuel pressure should be 62psi.
Hook up a fuel pressure gauge to the Afpr and place it where you can see from in the car & do WOT pulls. I would prefer 3rd gear. The fuel pressure should stay at 62psi through out the RPM.

How would that be any different than testing it with 20psi from a compressor to the vacuum port while running the fuel pump off the battery? I'd assume with the injectors firing while it was running would play with fp a bit.? I did it that way and it held 62psi fp under the 20psi i feed to it at 42psi bfp. I have thought about trying that but I just don't like the idea of running a fuel line inside the cabin or anywhere outside the engine bay. besides i am more concerned why my wally 255 can't produce more than 70psi of pressure.
 

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How would that be any different than testing it with 20psi from a compressor to the vacuum port while running the fuel pump off the battery? I'd assume with the injectors firing while it was running would play with fp a bit.? I did it that way and it held 62psi fp under the 20psi i feed to it at 42psi bfp. I have thought about trying that but I just don't like the idea of running a fuel line inside the cabin or anywhere outside the engine bay. besides i am more concerned why my wally 255 can't produce more than 70psi of pressure.
The test will tell you if your are loosing fuel pressure up top end. A defective fuel pump would do that. Telling you this from my own experience.
 

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Discussion Starter · #15 · (Edited)
Well i have sort of an update

I did some more testing today and using a c-clamp on the return line i saw 80psi on my fp gauge before i opened it back up quickly. I don't even think i fully closed the line yet either. I fired up the compressor and applied 30psi to the regulator at 42psi bfp and again only saw 66psi. I had an old fp gauge lying around that i swapped out just to see if i could rule that out and sure enough without changing anything but the gauge my bfp jumped from 42psi to 50psi. I set my bfp back down to 42psi and applied 30psi to the regulator and guess what? I saw 72psi fp. It held the 1:1 ratio up to 35psi on the that gauge.

I guess its kinda good news the regulator and fuel pump are working right but it leaves my idc issue even more confusing now seeing i was running 50psi bfp and still seeing 90-93% idc's. They'll probly be close if not over 100% now at a true 42psi bfp.:confused:
 
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