Go4DaMo Posted June 15, 2015 Report Share Posted June 15, 2015 Hey, W family. 1st & foremost...can't wait for the W-Body Nationals this year! 2ndly, my 92 3.1 is sputtering, sometimes to the point of stalling abruptly and spontaneously when hot. Some days it's perfect. Some days, it'll want to leave you stranded. My 1st thought was the new pos Airtex fuel pump is failing, because it has been whining loudly like a vacuum cleaner when hot. Now, I'm thinking FPR. It's showing 43 PSI w/key on, 37 at idle. When I pull the vacuum line to the FPR, 43 PSI again. Am I on the right track here to replace the FPR? Thanks! Quote Link to comment Share on other sites More sharing options...
pitzel Posted June 15, 2015 Report Share Posted June 15, 2015 Doesn't sound like FPR to me. FPR is characterized more by internal rubber seal failure inside the FPR itself, which allows petrol into the vacuum circuit. That amount of fuel pressure variance is perfectly normal. I'm thinking more along the lines of coils and/or ICM and/or ECU. Any codes or SES light? Quote Link to comment Share on other sites More sharing options...
Go4DaMo Posted June 15, 2015 Author Report Share Posted June 15, 2015 No SES light. Now at 10-14 psi. No signal is going to the fuel pump relay under the hood. Just the constant power supply to the single prong. Quote Link to comment Share on other sites More sharing options...
Go4DaMo Posted June 15, 2015 Author Report Share Posted June 15, 2015 It sounds like the DeLorean trying to run off low-octane fuel when it was stuck in 1885 Quote Link to comment Share on other sites More sharing options...
pitzel Posted June 16, 2015 Report Share Posted June 16, 2015 Fuel pump relay is only used for a brief few moments during startup, basically to give it a 3 second prime so there's enough pressure to actually get fuel into it for the starting process. All other times, the relay is de-energized and the fuel pump is energized through the oil pressure sensor switch. Quote Link to comment Share on other sites More sharing options...
carkhz316 Posted June 16, 2015 Report Share Posted June 16, 2015 Fuel pump relay is only used for a brief few moments during startup, basically to give it a 3 second prime so there's enough pressure to actually get fuel into it for the starting process. All other times, the relay is de-energized and the fuel pump is energized through the oil pressure sensor switch. this, and in addition, it only needs a few psi to trip the switch to power the fuel pump. So unless the oil pressure light is coming on, your fuel pump should be getting power. Agreed with pitzel that pressure sounds normal with vacuum/ no vacuum. Only time those things seem to fail is when that rubber diaphragm ruptures and then you'd see raw fuel leaking out and getting sucked into that vacuum line. Quote Link to comment Share on other sites More sharing options...
Go4DaMo Posted June 16, 2015 Author Report Share Posted June 16, 2015 What could be causing the relay to not be primed? That is my current, tho possibly not only problem. Thank you, both! Quote Link to comment Share on other sites More sharing options...
Schurkey Posted June 17, 2015 Report Share Posted June 17, 2015 (edited) Fuel pump relay is only used for a brief few moments during startup, basically to give it a 3 second prime so there's enough pressure to actually get fuel into it for the starting process. All other times, the relay is de-energized and the fuel pump is energized through the oil pressure sensor switch. Are you sure? Far as I know, the relay works during key-on prime, AND any time the engine supplies a crank signal to the ECM, the oil pump switch is the failsafe backup system. I'd have said the fuel pressure is low, especially if it's now 14 psi. This could be a failing pump, a ruptured pulse damper, a restricted fuel filter, or poor voltage to the pump, or poor ground circuit for the pump. The fuel pump wiring is notoriously under-size. Both my '92 and my '93 have excess voltage drop everywhere I tested--totaling more than one volt of drop on the + side of the circuit, and about 1 volt of drop on the ground side. Have you verified that the fuel pump circuit fuse is still good? Edited June 17, 2015 by Schurkey Quote Link to comment Share on other sites More sharing options...
Go4DaMo Posted June 17, 2015 Author Report Share Posted June 17, 2015 (edited) The fuse** is good, yes...likely easier to test voltage and ground before taking a look at the pulse dampener or replacing the pump, ay? Much appreciated! Edited June 19, 2015 by Go4DaMo Quote Link to comment Share on other sites More sharing options...
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