If I measure the fuel pump voltage?

[Jiffy]

So - my tuner is struggling with my car, 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

 

[Steve Cea]

So - my tuner is struggling with my car, 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

If whoever installed that KB BAP wound up using the HOBBS switch get rid of it ! That switch gave me all kinds of issues like your explaining. Disconnect the Hobbs switch and put a jumper wire between the,2 wires that we're connected to the Hobbs switch ! If everything else is good with the way it was installed this is your problem hands down !!! My car ran so perfect after deleting that switch it was a miracle !!!! If you read around the net you will find many talking about this problem, very easy to do , give it a try !!

Sent from my SM-G955U using the svtperformance.com mobile app

 

[Jiffy]

Thanks but the Hobbs switch has been removed and shorted, the knob is turned to full, but I need to be able to verify it's working by measuring voltages. Voltage out of the BAP - what should that be?
Voltage out of the FPDM going to drive the pumps - what should that be at idle, part, mid and full throttle. This is the most critical question if anyone has the answer....

 

[Black02GT]

Don't have all your answers but...

FPDM has one output that runs both pumps.

The positive lead is constant, the FPDM pulses the ground to vary duty cycle.

The voltage question is tricky, the voltages are more or less what you set them to in the voltage table in the tune. I believe it's based on load.

Is your tuner comfortable with this EEC? You have to scale a bunch of stuff from stock when you change injectors, or more importantly the MAF.

 

[Jiffy]

So - what's an EEC? Same thing as the ECU with a different name?
Are you certain the FPDM pulses the GROUND wire to the pumps? That's not what I thought/expected - here's the wiring diagram that I was given to use, and I think it shows the BAP on the power wire in series with the inertia switch, and I think that has the power from the battery? Or do I have it wrong?
the diagram clearly shows the ground wire as being over in the rhs bottom corner, and there is a '+' and '-' wire going to the pumps. It's my understanding that the wire from the inertia switch is the high-current 12v from the battery and the FPDM allows more voltage through when commanded by the ECU.
Or do I have it completely bass ackwards?

 

[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....

 

[01yellercobra]

Congrats. I think that's the first time I've heard about a clogged PPRV.

 

[Black02GT]

That is a new one, crazy stuff right there glad you solved it. Thanks for coming back in and posting the problem/solution. Too many threads you see and say "that's my exact problem" read 3 pages and it dead ends.