sputter after fuel pump hotwire

**twinspoolin94** · 06-04-2014, 10:37 AM

Ok, long story short I took my car to 3sx for a tune and it was determined the fuel pump was on its way out due to a loss of pressure at higher rpm's. pump was changed to a aem 340 from walbro 255 and it was also determined that it needed a hotwire due to voltage loss. so I ordered the kit and hot wired it and I am bringing the car back to for a retune friday. On a test drive right after hotwiring, on a few occassions at low load I would get a stutter, like the fuel pump was cutting off. Battery voltage would look fine but AFR's off the gauge lean. I would give it some gas and it would recover and be normal. Did this a few times during test drive sunday but cleared up and didnt do it agian until this morning and it only did it once. Any idea on what this could be? I am leaning toward a problem with the tune and the ecu trying to compensate because low's were tunned for a 255 pump non hotwired. I am also over running the FPR. Any help is much appreciated!

**sketch** · 06-04-2014, 10:44 AM

ditch the stock FPR

**twinspoolin94** · 06-04-2014, 10:56 AM

I would but its a little late for that, dyno is friday and I am out of money. Also they should be able to tune it out with the flash ecu. Do you think this issue is due to the fpr overrun and having a tune for a non hotwired 225 pump?

**GTOJOE** · 06-05-2014, 01:19 AM

when you hotwired the fuel pump did you bypass the fuel pump resistor relay? When the relay is failing it can cause a stumble at the switch over point. It's not required for a hotwired pump.

Stealth 316 - Fuel Pump Relay/Resistor Bypass

Stealth 316 - Fuel Pump Re-Wire

**twinspoolin94** · 06-05-2014, 08:08 AM

Originally Posted by GTOJOE

when you hotwired the fuel pump did you bypass the fuel pump resistor relay? When the relay is failing it can cause a stumble at the switch over point. It's not required for a hotwired pump.

Stealth 316 - Fuel Pump Relay/Resistor Bypass

Stealth 316 - Fuel Pump Re-Wire

No, i just ran a straight hotwire. Ill make sure and do this before I bring it down tommorow. Thanks!

**twinspoolin94** · 06-19-2014, 01:53 PM

Ok, I have another thread discussing this issue but since this problem developed immediatly after the hotwire I want to dedicate this thread to discussing solutions directly related to this problem. Adjustable FPR did nothing to help this issue. Resistor bypass has been done with no change. If long term fuel trims are disabled then the car runs great, just a little on the rich side and idle is not perfect. If they are enabled car cuts out under low load and idle is extremely unstable and will sometimes die. if I reset the ecu car will drive fine for several minutes then start having issues