My fuel pressure weird behavior

[kokgo20]

Let me start off with some info
The car has 131K miles, 50K of those are supercharged
Couple of months ago i decided to add a little more boost, so that i needed a little more fuel
My fuel pump is Aremotive 340 with the injectors maxed out at 8200RPM it was still running a little lean, so i upgraded to Walbro 450 & new OEM fuel filter which got me the needed fuel at 8200RPM. Now we are good

Last week the car died as i was driving, found out a blown fuel pump fuse, replaced it, flew again within 1 min, replaced it with 25A fuse just to limp me home. As i was driving home the car would die at idle but it runs fine under load, it would hesitate sometimes but we made it home.
Replaced the Walbro with my old Aremotive, the car fires up and idles just fine. Bingo the new 6 weeks old Walbro fuel pump took a crap.

As i was waiting on a replacement pump, i decided to work on some cooling maintenance, by replacing the water pump & hoses and seals, Radiator was replaced in the past with Mishimoto new style radiator.

As the engine is idling to bleed the system, it died after 5 min, cranks back up just fine, and dies after a few minutes. WTF!!

Measured fuel pressure and we are at 65PSI, few minuted later as the car idles the pressure starts going down to about 20~30PSI and the engine struggles. I rev it and pressure goes back up, 1 min later it goes back down, if i rev it again pressure goes up again. Weird!!
Took the car for a drive around the block, it drives perfectly fine, but if i idle for a few minutes the engine starts struggling again.

Any idea what could it be?
It's a weird behavior of the fuel pressure that gets low at idle but it goes back up when revved.

Thanks in advance!

[necm3]

I had the exact same problem a few year back. It is your fpr that has gone bad. Replace it and you should be fine. Better yet get the radium engineering adjustable one if you are keeping the car, otherwise be prepared to replace it every couple of years. Throttle response during downshifts will improve also. (My car is supercharged as well). Hope that helps.

[terra]

If you're using a US tune, it could be that the aeromotive doesn't run well with the lower voltages that US cars send to the fuel pump at lower load. You could try setting all the values in KF_EKP_TV to 100% to see if that improves behavior.

[kokgo20]

If you're using a US tune, it could be that the aeromotive doesn't run well with the lower voltages that US cars send to the fuel pump at lower load. You could try setting all the values in KF_EKP_TV to 100% to see if that improves behavior.

It was good for over 5 years until last week

Where is that option located?

[terra]

Download the xdf for whatever software version you're on and look for that map in there with tunerpro

[kokgo20]

I had the exact same problem a few year back. It is your fpr that has gone bad. Replace it and you should be fine. Better yet get the radium engineering adjustable one if you are keeping the car, otherwise be prepared to replace it every couple of years. Throttle response during downshifts will improve also. (My car is supercharged as well). Hope that helps.

Are you saying that the increased pressure/ flow from the bigger fuel pump destroys the FRP?

[maw1124]

Are you saying that the increased pressure/ flow from the bigger fuel pump destroys the FRP?

Probably. This was my thought, but I’m waiting fo other FI guys to chime in. A regulator for stock and a regulator for FI would be expected to differ, but maybe I’m wrong.

maw

[necm3]

Are you saying that the increased pressure/ flow from the bigger fuel pump destroys the FRP?

Yes that is exactly what happened to mine. Just get a new fpr 3.5 bar and verify what I am saying. It is a cheap fix. The flow that these pumps provide is significantly larger at idle and low rpm conditions so the diaphragm on the fpr gives up. I believe your fpr was going south and when you increased the flow with the new pump it gave up completely.

[Good]

How did you measure fuel pressure?

[kokgo20]

How did you measure fuel pressure?

Rented fuel pressure gauge from autozone, you connect it to the Schrader valve on the fuel pressure regulator

[kokgo20]

Update,
replaced the FPC same issue.
got lucky to catch the EKP module being too hot, turns out it was bad. Replaced and back in business!!

[jbfrancis3]

Nicely done.