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Fuel related problem....NEED HELP!!

Discussion in 'Engine/Tuning' started by turbov6joe, Oct 29, 2015.

  1. turbov6joe

    turbov6joe Defensor Fortis Established Member

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    Ok, I'll try to simplify this issue the best can so hopefully I get some good advice. Here lately I've been having a hesitation/popping issue when going to full boost/WOT when I stab the gas to the floor...if I roll into it she doesn't usually act up. I replaced the spark plugs...didn't help. I swapped out the fuel rail pressure sensor with two others that I know are good....didn't help. I checked all vacuum lines for leaks....nothing. I dropped the fuel tank and verified that there were no lose hoses, connections, or issues with the fuel socks....all good there. I replaced the fuel filter with a new one...no help there either. Today I put the car on the dyno to tune for e85, and had my tuner data log all the fuel related parameters...he noticed that the fuel pressure at idle was 66 psi. He also noticed that while going to almost WOT the fuel pressure would quickly drop off to ~33 psi around 5000 rpm, then jump right back up. We took the Kenny Bell BAP out of the loop and that made no difference with the idle fuel pressure. I unplugged the FRPS when idling and the fuel pressure jumped up to default 77 psi like it should....so that told us it was working like it should. The last obvious things to check were the FPDM's. Tonight when I got home I removed and replaced both FPDM's with two known good ones and started the car....the fuel pressure was still around 66 psi at idle. I swapped out the FRPS with known good ones, and still had the high idle pressure. At this point I'm sorta at a dead end with ideas of what to check next. The car runs like a top when just driving around, and pulls like a beast until it hits that fuel pressure drop off point. Anyone else have ANY ideas at all...even ones you think are crazy??? All help will be greatly appreciated!
     
  2. cj428mach

    cj428mach Well-Known Member Established Member

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    I would think the problem is in the tune.

    In a returnless system the ecm looks at the frps and uses it to determine how much it needs to drive the fuel pumps. Since you're over 60+psi and I assume base pressure is set to stock, the ecm should be sending a signal for the pumps to slow down/stop.
     
  3. turbov6joe

    turbov6joe Defensor Fortis Established Member

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    The car already had a tune on it when the issue started. It was back in for an e85 tune when the tuner noticed that the fuel pressure was sitting at 66 psi at idle. He then data logged an easy pull to redline and noticed that the pressure dropped off into the 30's around 5k rpm, and that's right when it popped and sputtered before it came back to life.
     
  4. cobraetti

    cobraetti part of the zombie squad Established Member

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    huh im having a similar situation
     
  5. turbov6joe

    turbov6joe Defensor Fortis Established Member

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    UPDATE
    I data logged the fuel pressure at idle and it was reading 60 psi with the line on. I removed the line and it dropped to 40 psi. I put a vacuum gauge on the FRPS line and it read 20" of vacuum, so I know that was right. Here is where is gets weird. I ran the same procedure a few more times and the drop was only 10 psi, even though the vacuum was verified at 20". Why would it drop 20 psi one time, then only 10 psi the next few??? I replaced both FPDM's with 4 different ones and that didn't help either. My main issue is that my FP is too high at idle, falls off during a pull for a second, then jumps back up. I'm going to check the voltage at the pumps to see what that is at idle. Anyone know what that should be at idle?
     
  6. turbov6joe

    turbov6joe Defensor Fortis Established Member

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    Got it figured out...the 2 ground wires to the fuel pumps were grounding out on the body. Turns out the insulation on the solder connections had rubbed off and the wires were touching the body.
     
  7. Brutal Metal

    Brutal Metal Well-Known Member Established Member

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    Damm dude nice find, congrats..
     

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