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Hello, I have a situation that I just can't solve. So here goes and maybe someone here can provide a different perspective. I have a 64LeMans with a v8 326. I installed MSD ignition and MSD Atomic fuel injection with return. Replaced also the fuel sending unit in the gas tank. The fuel pump is MSD installed on the frame below the gas tank. The filters before and after the pump are correctly installed. After the issue to be described below, Working with MSD I replaced the fuel pump and the regulator. This all was installed by a hot rod shop in Tampa in November of 2017 and has run fine until about a month ago. It will start but after starting the fuel pressure falls off and stalls. The hand held display shows plenty of RPMs. I clamp off the return line, set the fuel pump setting to be PWM (Pulse with modulation) without regulation. Start the car and it idles and revs up to 3k plus RPMs just fine. I turn off the engine. Unclamp the return line, change the fuel pump type to PWM with regulator or No PWM with regulator. Start the car up and it works fine. Idles and revs up just fine. I turn off the car. Try to restart it. It starts and idles at 850 to 950 RPMs. Then immediately the fuel pressure falls off and the engine stalls. I have also updated all the firmware / software from MSD to be current. Any ideas on trouble shooting?
 

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I'm not familiar with the MSD pump, nor the Atomic EFI hardware and software - so keep that in mind.

Sounds like you have a hardware/software issue, or possibly a wiring issue. Is the fuel pump being powered via a solid state relay or a standard relay? Using a voltmeter monitor voltage at the pump when the issue occurs in PWM mode, then recheck at the ECM pin that supplies the pump relay and see if they are the same - they should be. Also confirm the pump ground has the same amount of resistance to the battery that the ECM ground point has to the battery. Or you could load test the pump wiring with something like a halogen headlight bulb.

Personally, I don't see the need for running the pump via PWM. That is something that is done for street driven cars in the 800-1500 HP area that run a single pump. Magnafuel makes pumps designed to operate in such a manner. But on a stockish 326 Pontiac I can't see any reason for it. A regular old Walbro 255 should more pump without an issue (and it's cheap). I'd run it in on PWM mode and see if the problem is gone. It might require re-tuning.
 
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