I am having a problem with fuel pressure. I have a AEM FPR and AEM rail with a walbro 255, and precision 880cc injectors with a resistor box. I had it tuned a couple months ago, but noticed that it's been running really rich at idle and lean when cruising.

very strange, I thought it had something to do with my battery so I changed it and still the same. I also tried a new fuel filter. at idle the needle on my FP gauge mounted on the rail bounces around 30-35psi. the screw on the top is tight and I have never touched it.

I adjusted the FP to 40-45PSi and that brought my A/F to 12.8-13.2 @ idle instead of the 11.2-11.6 I have been seeing. is it normal for the FP gauge to bounce around between 40-45psi at idle w/ vacuum line hooked up? I've never seen that before. what to do from here? I don't have a clue.

 

help!!!!!

 

i haves seen that before..i think it also depends on the gauge you are using..if its liquid filled or not i mean..

 

it's liquid filled. been using it for less than 2 years.

 

its either your fuel pump or fuel regulator

 

just went to mess with it again, and the gauge struggles to hold 40PSi of fuel pressure. adjusting my FPR all the way up and could not get it to budge. I am clueless. I'm starting to think my pump, but wouldn't a pump not run at all if it were bad? I have a walbro 255. it's about 4 years old. would a bad resistor box cause what I am seeing? rich at idle lean up top?

 

i had the exact same setup, aem rail, aem fpr, pte 880s, 255lph pump. i also had the same problem. i just couldnt get the setup to hold a steady fuel pressure and since it isnt neccesary for my setup i ditched it.

i ditched the aem rail and reg and the problem stopped.

 

wow. thanks for the info. It used to work, but now I have no clue what is going on.

 

I Would think its the regulator.

Get a pliers and pinch the return line, and tell me what the gauge does.

 

just tried this and the gauge did nothing. pressure stayed bouncing around 40psi. vaccum was hooked up, just pinched it

 

I think its your fuel pump
Can you just try out your stock pump?
If its not that, your regulator is faulty

 

I don't have one right now, but in any case, I would have to drop my tank(DA) to change it. would running race gas(leaded 116 octane) on any of these products I have cause an issue? besides O2 sensor...obviously..

 

no its a pressure issue.

maybe you can try a stock regulator and see if you get consistent pressure

 

with a stock regulator, my gauge stayed around 30-35psi. I don't know. this has thrown my tune way off. it sucks

 

with the stock reg, was it consistent and not bouncing?
Therefore you found your problem.

Just get a Aeromotive FPR

 

whenever my pressure was low with the AEM in there aroun 30-35psi, it would not bounce. it would hold that pressure solid. so the OEM held it solid at 30-35 psi also. it's low with both regulators. it held about 25psi overnight with the AEM back on there. I'm starting to think my pump, but when they go bad, I thought they just quit?

 

regulator for sure

 

They could get weak.
I had a dirty gas tank, and my oem fuel pump was weak.
Also didn't hold the fuel pressure.

 

Nope, they can fail slowly. The motor will die fast, but the pump portion slowly. They can wear around the pump fins (or gear, idk pump type), possibly from grit or a bad bearing/bushing. Running leaded gas could be an issue if it doesn't have the required amount of lubricants in it. I wouldn't guess "off-road" racing gas is as regulated as street gas, so it might have much less. The pump would wear significantly faster in that case.

The other thing is the regulator may be bad, but if pressure doesn't skyrocket when you pinch the return hose, nor does it get super rich, it's most likely the pump.

 

thanks all who have gave input, I got a new Walbro 255 to replace my old one so I'll throw that in and I am going to be looking into a better regulator down the road even if it isn't the regulator. I will also update and let everyone know if the pump was the issue

 

Update, the pump wasnt the issue. I'm still in search of the problem. I installed the new fuel pump and pressure is still low with AEM fpr and stock FPR. pressure wants to stay at 35psi, doesn't jump around though(looking at my pressure gauge mounted to the AEM Rail). tried to pinch off return line and nothing happened with OEM FPR and AEM.

I am clueless. what else can I check? changed my fuel filter but on my new fuel filter the inlet and outlet were on opposite sides from the original one I had in there. I hooked it up the way it says on the arrows located on the top but I dunno if this would cause my problem. would injector seals cause this? I see no fuel anywhere, so I am clueless what to look for.

 

Have you checked the fuel pump wiring?

 

thanks for reminding me, I got around to checking the voltage yesturday and to my surprise, even with another main relay in I only get 5.2VDC to my pump. this is the cause, now I need to find the root so I can fix it. so Im in my car right now in the process of finding the problem.

 

I don't get this, with the car running and I disconnect the fuel pump under the rear seat, I get 12VDC+ until the car dies. I am clueless as to what else controls the voltage. in all my diagrams, it has a solid 12VDC and ground to the pump. why am I seeing 5VDC and unplug it and I see 12+?

also my battery light is on unless I rev it a little at idle to get it to go away, but sa soon as I disconnected that plug to my fuel pump, even that went away. this **** is kicking my *** and I'm starting to get a little frustrated.

I am not sure what role the fuel sender unit plays in all this, the plug is a 4 wire plug and in my diagram it only shows the fuel pump and then I have to find the fuel sender seperate and look at that as a seperate circuit.

 

help....anyone