Fuel pump voltage and effect on ECM fueling
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Car: 1986 IROC-Z
Fuel pump voltage and effect on ECM fueling
I'm chasing a possible charging issue on my $6E car and I noticed that the fuel pump voltage is about 0.5 V lower than the battery (charging) voltage. Is this normal? I'm curious if the ECM uses this voltage reference for the injector pulse width correction tables, because I also seem to have a rich condition that I'm having trouble eliminating. I found the following post from 2001, but it wasn't clear which voltage is used for the PW correction: https://www.thirdgen.org/forums/diy-...orrection.html
I've measured the voltage drop at both the ECM and the fuel pump relay, which leads me to believe there might be a problem with splice S163, shown here. The voltage at Fuse No. 2 is good and the drop only happens when there's a load on the circuit (car running). Charging voltage is 14 V on the nose.
I've measured the voltage drop at both the ECM and the fuel pump relay, which leads me to believe there might be a problem with splice S163, shown here. The voltage at Fuse No. 2 is good and the drop only happens when there's a load on the circuit (car running). Charging voltage is 14 V on the nose.
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Re: Fuel pump voltage and effect on ECM fueling
I have noticed slightly lower voltage at the pump vs battery on my car when it was using stock fuel system. I upgraded to the racetronix walbro kit with hotwire and it made a big difference in voltage at pump. I saw closer to 13.5 volts after i did the hotwire swap. It just plugs fuel relay power source into the alternator output so you see closer to charge voltage than battery voltage. Helps gain more output from the pump but only really needed if you are on the verge of maxing out a single pump which is closer to 550 whp, depending on setup.
I dont think fuel pump voltage itself will cause fueling issues at the ecm. Less volts may hurt pump flow output but as long as its still delivering more than the engine can use, it will maintain fuel pressure. Check to see if the pressure drops at all.
Battery voltage will however change injector output due to the offset tables. They should be calibrated so voltage drop still delivers enough fuel to maintain air fuel ratio, unless you have non stock injectors and dont have injector offset data, then perhaps a charge issue will change fueling. Could go lean could go rich depending on offset table values
I dont think fuel pump voltage itself will cause fueling issues at the ecm. Less volts may hurt pump flow output but as long as its still delivering more than the engine can use, it will maintain fuel pressure. Check to see if the pressure drops at all.
Battery voltage will however change injector output due to the offset tables. They should be calibrated so voltage drop still delivers enough fuel to maintain air fuel ratio, unless you have non stock injectors and dont have injector offset data, then perhaps a charge issue will change fueling. Could go lean could go rich depending on offset table values
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Car: 1988 IROC-Z Convertable
Engine: 350 Cam, Heads, Heders...etc.
Transmission: 700-r4 "Raptor"
Re: Fuel pump voltage and effect on ECM fueling
I'm chasing a possible charging issue on my $6E car and I noticed that the fuel pump voltage is about 0.5 V lower than the battery (charging) voltage. Is this normal? I'm curious if the ECM uses this voltage reference for the injector pulse width correction tables, because I also seem to have a rich condition that I'm having trouble eliminating. I found the following post from 2001, but it wasn't clear which voltage is used for the PW correction: https://www.thirdgen.org/forums/diy-...orrection.html
I've measured the voltage drop at both the ECM and the fuel pump relay, which leads me to believe there might be a problem with splice S163, shown here. The voltage at Fuse No. 2 is good and the drop only happens when there's a load on the circuit (car running). Charging voltage is 14 V on the nose.
I've measured the voltage drop at both the ECM and the fuel pump relay, which leads me to believe there might be a problem with splice S163, shown here. The voltage at Fuse No. 2 is good and the drop only happens when there's a load on the circuit (car running). Charging voltage is 14 V on the nose.
Last edited by bphage; 06-19-2013 at 02:02 PM.
#4
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Re: Fuel pump voltage and effect on ECM fueling
I'm chasing a possible charging issue on my $6E car and I noticed that the fuel pump voltage is about 0.5 V lower than the battery (charging) voltage. Is this normal? I'm curious if the ECM uses this voltage reference for the injector pulse width correction tables, because I also seem to have a rich condition that I'm having trouble eliminating.
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Re: Fuel pump voltage and effect on ECM fueling
I appreciate the comments, guys. I'm glad to know that the voltage drop I'm seeing is normal, so to speak. I probed the orange supply wire and found that most of the voltage drop occurs between the fender fuse and the splice I mentioned in my first post. If I clip a test lead between the battery and the splice, the fuel pump voltage goes up by about 0.3 V. At this point, I don't think a separate feed line is necessary because I'm not maxing out the pump.
Also, thanks for confirming that the injector pulse width correction table uses the fuel pump voltage.
Also, thanks for confirming that the injector pulse width correction table uses the fuel pump voltage.
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