Fuel Drop at higher RPMs

[azkikr10]

Okay I searched and was not able to find an answer. First off I have 660s 255 fuel pump and fpr set at 42 psi. I noticed that when I go WOT the fuel drops off at about 5.5k till I letoff. I also need to add a ton of fuel to get the thing to 10.5:1. I've so far checked out the fuel pump for a smashed O-ring and replaced the vaccume lines for the fpr. Any other ideas would be great.

 

[Wing0tj]

have you re-wired the fuel pump, I'm pretty sure the reason for doing so is that it doesn't receive adequate voltage at higher rpms. Could be wrong but worth looking into.

 

[91-gsx]

try bypassing your fuel pressure solenoid. when i have that hooked up i get knock and when i bypass it the knock goes away. its worth a try, its easy to do and easy to reverse.
later

 

[azkikr10]

sweet i'll try the silinoid when i get home. Also, no I dont think its because my pump is not rewired. I know other people and they dotn have that same problem

 

[oldman]

Which afpr do you have? My Aeromotive was leaking pressure from the adjustment screw until I sealed it with thread sealant. I would look into that and seal it if necessary to ensure that 1:1 rising rate is properly maintained, especially at high boost levels. Also check the other end of the fuel system, did you properly install the pump by applying lubricant to the o-ring prior to install? A ripped or damaged o-ring will also effect your fuel delivery as well as a clogged fuel filter.

 

[azkikr10]

I checked O-ring on pump.. All good there and i'm assuming that i check the adjustment screw on the fpr by doing another boost leak test? I have an Aeromotive but mine is the -10an one that I reduced to -6

 

[oldman]

I checked O-ring on pump.. All good there and i'm assuming that i check the adjustment screw on the fpr by doing another boost leak test? I have an Aeromotive but mine is the -10an one that I reduced to -6

Yes, pressurize the intake and spray soapy water right at it. Also watch the relations between your boost and fuel gauges during the pressure test by pressurizing the fuel system using the fuel pump check connector at the same time, especially near your max psi level.

 

[azkikr10]

Yes, pressurize the intake and spray soapy water right at it. Also watch the relations between your boost and fuel gauges during the pressure test by pressurizing the fuel system using the fuel pump check connector at the same time, especially near your max psi level.

Thats a good idea. Never thought of doing that. I also moved my fpr last night because the line looked slightly kinked and bypassed the fp silenoid. Neither one worked. I will try the adjustment screw test tonight hopefully and let you know how it works out. I have my doubts though because I hold boost and fuel pressure solid up untill 87% idc and then it drops off, usually at 5900 rpm. As you know, an Evo 16g hits 20psi way lower than that.

 

[steve]

How are you measuring the drop off in fuel pressure?

Steve

 

[azkikr10]

How are you measuring the drop off in fuel pressure?

Steve

I'm using dsmlink. IT shows my fuel drop off at 5900 but my idc is going up. Fuel goes from 20ms and just drops off untill redline.

 

[steve]

, Glad I asked. It's very likely nothing is wrong with the fuel system.

Post your log.

Steve

 

[azkikr10]

, Glad I asked. It's very likely nothing is wrong with the fuel system.

Post your log.

Steve

Well i get invalid file type when I try and upload it. Here is the dsmlink thread with the file inside or I can email it to you. http://www.dsmlink.com/forums/showthread.php?t=6817

 

[steve]

Since the DSMLink gods think you have a fuel problem I defer to them.

Steve

 

[azkikr10]

Any way to tell if my fuel pump is faulty?

 

[steve]

I don't know how accurate it would be but you can try connecting a adjustable pressure source to the AFPR so that you can set the fuel pressure to various values and put the return line into a bucket. Run the pump at a pressure for a some fixed time and measure how much you get. Repeat at a different pressure and compare the results to a typical flow sheet for your pump. That should at least give you a swag at how the pump is working.

Steve

 

[azkikr10]

Sounds like it would be a lot less trouble to just buy a new pump.

 

[steve]

What if it's not your pump?

 

[titogs95]

I sort of have the same issue...

Check this thread for the info > LINK

I rewired the fuel pump and nothing. but I am leaning toward the fuel filter (might be clog). Other than that, I am clueless.....

Off topic: Funny you have more answer than I do. I guess I don't suppost to type too much!

 

[azkikr10]

What if it's not your pump?

If it's not the pump then I got a backup . I don't think it's my fuel filter because I replaced that about a year ago. Just running out of ideas here. You think if i just bumped up the fuel pressure that would work as a bandaid till I figure this out? I'm only getting 16mpg right now so I dont think it can get much worse. I Know my valvecover slightly leaks but like I said before, my gm3bar shows boost till redline so with the exception of the adjustment screw on the fpr I should hold fuel till redline too correct?

 

[steve]

If this was my car I'd be checking to make sure the AFPR isn't leaking reference pressure under boost, and flow testing the pump.

Steve

 

[azkikr10]

you know I guess I can do that. Any idea where I can find a flow sheet for a wabrow 255 not hp?

 

[steve]

Try this to start. http://www.stealth316.com/2-fuelpumpguide.htm

Steve

 

[beat90tsi]

I'm thinking a 255 HP be a good upgrade for you. Or if you're ambitious, pick up a Supra pump and just be done with the thing.

The 255 (non high pressure) flows measurably less at higher pressures and the lower voltage from your wiring would worsen the situation. I would re-wire, buy a better pump (HP, or Supra) or do both.

 

[Turbo Talon DL]

OK, I know this is about fuel pressure during high RPM boost, but I have a question that pertains to it. When people inatall their MBCs and run them from the turbo outlet, that only allows the turbine to spin at a certain speed, not allowing the manifold boost to drop off, close the WG, and increase pressure. So, if I used the manifold as a pressure source insted of the turbo outlet, would this allow more fuel pressure because the boost pressure would not drop off as much? PM me with an answer, and I hope that this question makes sense.

 

[azkikr10]

I'm thinking a 255 HP be a good upgrade for you. Or if you're ambitious, pick up a Supra pump and just be done with the thing.

The 255 (non high pressure) flows measurably less at higher pressures and the lower voltage from your wiring would worsen the situation. I would re-wire, buy a better pump (HP, or Supra) or do both.

but I would think that the regular 255 would let me flow more than 32lbs/min