Hi SVTP,
It’s been a while but I am back seeking some input on a fuel delivery issue. I have owned my ‘04 Cobra since 2012 and have done minimal modifications of my own since buying it. The car came with a build sheet that was partial/not 100% correct, so as I’ve owned the car, I’ve jotted down part numbers and done research to build out a truly accurate list of the things I have verified or seen myself.
Without getting too deep, here’s what I’m running: Kenne Bell 2.2L, Siemens 60lb/hr injectors, Zone 5 Performance MDM Jr. fuel pump driver (I’ve seen less than favorable opinions about Z5 - wired in post-FPDM), Precision Fuel Pump Hanger Assembly, and Walbro 10000128 (GT40?) pumps.
A couple of weeks ago I drove the car to work. My first couple of stops before getting onto the interstate, the car was sagging at idle a little bit (down to 600-650rpm) which is not normal. On the interstate I’d notice a very slight surge while at cruise/unaccelerated (not at all abrupt or strong, just barely noticeable). About 20 minutes into my 25 minute commute, the car suddenly quit and I got over to the side of the road. No re-start other than a cough and die. I plugged up my tuner (old DiabloSport Predator) and noticed no FRP (<8psi). No pump noise either (I know they’re nearly silent but I can usually hear them).
We got the car home, direct-wired the pumps to 12v, and both would run (7-7.5a current draw each - seems in line with what newer 255lph pumps mention) but made no fuel pressure (verified by disconnecting the fuel filter inlet - no gas moving with the pumps running). Dropped the tank, found a split/blown out line. Replaced the lines, reinstalled the pumps, then reinstalled the tank. No joy - the car still won’t start (pumps not running). We verified the pumps make pressure by direct-wiring them again to the battery and sure enough they move fuel - the car starts and I can see pressure (high/unregulated) at the FRPS.
With the key on, pumps not running, I can unplug the lead between my FPDM and the Z5 MDM Jr., plug it back in, and most of time the pumps will run but they run non-stop, assuming 100%, even though the car isn’t started. I see 11.9v-ish from my FPDM (RD/BK and BN/PK wires) into the Z5 MDM Jr (whether the pumps are running or not). This voltage number should lower (shut off pumps) once the pumps make pressure to the FRPS and are ready to start, correct? If anybody has easy access to their FPDM, I’d be curious to know what the output is from the FPDM once the pumps are primed and the car is ready to start.
If I saw a voltage change from the FPDM yet my pumps kept running, I would throw in the towel and say my MDM Jr. has bitten the dust and replace it but I’m just not seeing where it’s failed - the MDM Jr. seems to be doing what it’s told (give me fuel, the car says).
Anybody got another idea or area I should be digging into?
Thanks in advance!
Josh
It’s been a while but I am back seeking some input on a fuel delivery issue. I have owned my ‘04 Cobra since 2012 and have done minimal modifications of my own since buying it. The car came with a build sheet that was partial/not 100% correct, so as I’ve owned the car, I’ve jotted down part numbers and done research to build out a truly accurate list of the things I have verified or seen myself.
Without getting too deep, here’s what I’m running: Kenne Bell 2.2L, Siemens 60lb/hr injectors, Zone 5 Performance MDM Jr. fuel pump driver (I’ve seen less than favorable opinions about Z5 - wired in post-FPDM), Precision Fuel Pump Hanger Assembly, and Walbro 10000128 (GT40?) pumps.
A couple of weeks ago I drove the car to work. My first couple of stops before getting onto the interstate, the car was sagging at idle a little bit (down to 600-650rpm) which is not normal. On the interstate I’d notice a very slight surge while at cruise/unaccelerated (not at all abrupt or strong, just barely noticeable). About 20 minutes into my 25 minute commute, the car suddenly quit and I got over to the side of the road. No re-start other than a cough and die. I plugged up my tuner (old DiabloSport Predator) and noticed no FRP (<8psi). No pump noise either (I know they’re nearly silent but I can usually hear them).
We got the car home, direct-wired the pumps to 12v, and both would run (7-7.5a current draw each - seems in line with what newer 255lph pumps mention) but made no fuel pressure (verified by disconnecting the fuel filter inlet - no gas moving with the pumps running). Dropped the tank, found a split/blown out line. Replaced the lines, reinstalled the pumps, then reinstalled the tank. No joy - the car still won’t start (pumps not running). We verified the pumps make pressure by direct-wiring them again to the battery and sure enough they move fuel - the car starts and I can see pressure (high/unregulated) at the FRPS.
With the key on, pumps not running, I can unplug the lead between my FPDM and the Z5 MDM Jr., plug it back in, and most of time the pumps will run but they run non-stop, assuming 100%, even though the car isn’t started. I see 11.9v-ish from my FPDM (RD/BK and BN/PK wires) into the Z5 MDM Jr (whether the pumps are running or not). This voltage number should lower (shut off pumps) once the pumps make pressure to the FRPS and are ready to start, correct? If anybody has easy access to their FPDM, I’d be curious to know what the output is from the FPDM once the pumps are primed and the car is ready to start.
If I saw a voltage change from the FPDM yet my pumps kept running, I would throw in the towel and say my MDM Jr. has bitten the dust and replace it but I’m just not seeing where it’s failed - the MDM Jr. seems to be doing what it’s told (give me fuel, the car says).
Anybody got another idea or area I should be digging into?
Thanks in advance!
Josh
). On the FPDM input to my Z5 MDM Jr, there is a 5W/100ohm resistor that had failed (wide open). So I soldered in a new one for $.60 and we're back to running.
