Fuel pump voltages as read with volt-meter

[Jiffy]

So - my tuner is struggling with my tune, and this is what he's finding (bearing in mind he's never seen a Cobra Mustang - 2.3L Whipple, 60lb injectors etc - never tuned one before - because this is Australia and the Terminator was never released here) - but he's an experienced tuner.

When the car goes off idle the mixture goes really lean. The harder into it, the leaner it gets and the more worried he becomes. The ECU reports back via the SCT logging that the fuel pressure is dropping and so it is increasing the voltage to the pumps, but they're not increasing pressure to the fuel rail. This is either because they're NOT getting the extra voltage, or they're driving so hard they're cavitating (I don't believe this is the case). Bearing in mind there is now a 40a BAP fitted (it was used when I bought it), therefore it may be faulty OR it may be wired incorrectly. It is wired with the FPDM between it and the pumps. Adjusting the tune appears to have no affect on the fuel pressure or the mixture.

So, as the next step - I've asked him to measure the voltage at the pumps to see how it responds to the ECU. What voltage typically should he see at the pumps at idle, just off idle, mid throttle etc? 6v, 10v, 14v, 16v etc?

Finally, do BOTH pumps run off the FPDM or is one pump wired with 12v all the time and the FPDM spools the other up and down, or do both run off the FPDM?

Thanks in advance guys - Jeff

 

[decipha]

both run off the fpdm if one ran all the time the ecu wouldn't be able to reduce voltage to reduce fuel pressure

instead of measuring voltage at the pump you should prob just replace the pump, if your logging the pressure drop and tuning changes are having no affect it can only be a failed pump(s)

 

[Jiffy]

Or a BAP breaking down under load, or a faulty FPDM, or a problem with the wiring. I cannot be sure that it's wired correctly so I need something to test to prove if the problem is in the tank or out of it.

 

[Jiffy]

ok found the issue!!

It turned out to be the PPRV!! So, it was totally gummed up with crud (I have always run the car to almost empty) and the PPRV was sticking due to all the crud clogging it up. What would happen, was the car would start due to residual fuel pressure in the rail, then the fuel pressure would erode as the idling engine consumed it, and the ECU would command more voltage to the pumps to raise the fuel pressure. The valve would be stuck closed, the fuel pressure behind the PPRV would build and build until it was reaching around 130PSI and the valve would open, the pumps are running flat out and LOADS of pressure hits the fuel rail, the FRPS would say "WHOA!", the pumps would close down, the PPRV would close, the fuel pressure was trapped in the rail, and the 60lb injectors couldn't open far enough to allow the revs to build because there was too much pressure behind them, then as it reduced down as it was consumed at idle the FRPS would command 'more fuel" and off we'd go again!

Pulled the tank, checked the PPRV, found it clogged with shit, cleaned it out and VIOLA!! 575rwhp at 14lbs with a 2.3L G2 Whipple (3inch upper), JLT Ram Air, Accufab SBTB. Thank **** for that....