December 10, 2019, 07:41:32 PM

Author Topic: Car keeps starting then immediately losing fuel pressure  (Read 195 times)

Offline need_a_username

Car keeps starting then immediately losing fuel pressure
« on: August 02, 2019, 12:51:22 PM »
Hi all,

As the title states I have an FD with an LS3 swap that won't run. The story behind it is very complicated-

The shop doing the swap got the car mostly running, then ran into this issue. The car will start (fuel pump primes fine) but immediately loses fuel pressure and dies. They had a fuel pressure gauge hooked up and could verify it was loss of fuel pressure killing the engine.

They disconnected the fuel pump, attached an externally-powered pump, and got the car to run. They then reconnected the original fuel pump in the exact same condition and the car ran.

I was able to drive the car for about two weeks. After parking it in my garage one night, the issue started again the next morning. Once again I can turn the key and hear the pump prime, then start the car. It will immediately die after this.

Major things I've checked:
Fuel pump - fairly new, was working fine for the 2 weeks the car drove, unlikely to be the problem
Fuel pump relay - tried it with both the original and a new one, no change
Error codes / security system - car is listing no fault codes
Other readings: MAP sensor is reading strangely high (23.8 PSI when I'm at about sea level) and temperature is off. All other readings look normal.

This car is on the stock LS3 tune and ran rough even when it was drive-able. It would constantly try to stall (needed lots of throttle) between gear shifts and when going from any gear to neutral.

I've messed with it to about the end of my limited abilities, the only guess I have is that there is some issue with the ECU shutting off fuel due to a bad crank sensor, security override, or something similar. However, it had no fuel problems for about 2 weeks which makes no sense to me. I can take it to a tuning shop, but that's about a $100 tow, $650 to tune, and $200 an hour for every hour they have to mess with it off of the dyno. Obviously I'd like to avoid that expense if at all possible and just drive it there myself to pay the flat $650.

Offline Venom13132

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Re: Car keeps starting then immediately losing fuel pressure
« Reply #1 on: August 02, 2019, 01:47:55 PM »
would help to know how they wired the fuel pump.   The best way would be to get your own fuel pump relay.   You would connect the output to the white with red stripe wire going to the fuel pump.  The ground to Ground.  The +12 to the battery (fused).  And then the input signal from the ecu.
1995 RX-7 - LS1, T56: LS6 Intake, Feed wide body, Feed CF Side skirts, Ray's Gram Lights, K-Sport coilovers, 99 spec\ tails and spoiler, SpeedHut Gauges, Aeromotive fuel pump, TwinZ Rear Diffuser
2000 Ford Excursion - V10 Tow monster
2006 BMW 650i - 4.8l V8 6-Speed Manual - Daily Driver