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Thread: Puzzling fuel rail problem

  1. #1
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    Puzzling fuel rail problem

    We've been replacing the blown engine in SuperdadSC's car. With everything installed and connected we tried to start it up. It cranks but no start. So, I first checked the shrader valve on the fuel rail and there was nothing. So, I pulled the fuel lines off, stuck them in a fuel can, jumpered the fuel pump on at the EEC test plug. The pump came on and there was a nice heavy stream of fuel coming out. I connected the top fuel line to the rail and again jumpered on the fuel pump and fuel comes out of the bottom fitting Ok. I then hook up the bottom fuel hose and again jumper on the fuel pump. I let it run for several seconds then off again. I press the shrader valve again and nothing. There should have been some pressure but there was nothing not even the smell of gas or a wet spot. I am totally puzzled by this. I didn't try pressing the shrader valve while the pump was running but I'll try that tonight. The fuel rail came off of the blown motor and was working when the engine died so it should be Ok. It sat in the trunk while the engine was swapped. It has an adjustable fuel pressure regulator that wasn't touched while it was off of the engine. Short of taking everything back off of the top of the engine I'm not sure what to check next or why we're not getting any fuel pressure. Has anybody run into this before or have any ideas?
    90 5spd, best ever E.T. 12.250
    best ever 1/4mi speed 112.89 mph
    Current dyno tune 383.54 rwhp 418.88 rwt

  2. #2
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    Try jumpering the pump and start the car. Maybe the computer is turning the pump off for some reason. Or check the outlet of the pump inside the fuel tank, maybe cracked.

    Also get a FP gauge and see whats going on.
    ~Chris
    SCCoA Member #1826
    Bettie Riding jack stands
    SCARlet on drag duty now

  3. #3
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    My guess is fuel pressure regulator is stuck opened. If you disconnect the return line and jump the fuel pump relay, no fuel should come out the return line until it builds up pressure.

  4. #4
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    I'm also thinking that the pressure regulator is stuck open. Fuel does come out of the bottom fitting immediately. I'm going to jump the pump on and then press the shrader valve while the pump is running to see if anything comes out. I've never heard of one sticking open before but that doesn't mean it isn't. My only gauge is the one on my car and it's permanently mounted so I don't want to take it off. It's starting to look like I'm going to have to pull the sc and intake off again to check it out. Oh I wish I'd pressure tested it when I mounted it. This is frustrating.
    90 5spd, best ever E.T. 12.250
    best ever 1/4mi speed 112.89 mph
    Current dyno tune 383.54 rwhp 418.88 rwt

  5. #5
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    May 2011
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    825
    I would change the scrhader valve first off before yanking the blower and stuff. just cause.

  6. #6
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    OK, results of tonight. If I jumper the fuel pump on I have pressure at the shrader valve. As soon as I shut off the pump the pressure was gone. Putting some suction on the vacuum line to the fuel pressure regulator I could get a faint taste of gasoline but couldn't feel a diaphragm move if it's any indication of a pump problem. I jumpered on the pump and cranked it but still no start. Then I squirted some starting ether into a vacuum line but it still wouldn't start. If I kept on cranking with the pedal to the metal it finally almost started, sputtered and wheezed but not quite. I had to stop to recharge the battery. So, verrrrry interesting. This one is a head scratcher. There is no upshift light while cranking but this is a 5spd conversion from an AOD so should there be if the crank sensor is bad? All of the parts came off of the blown motor which cranked up and ran for 2 secs in my garage before the teardown.
    90 5spd, best ever E.T. 12.250
    best ever 1/4mi speed 112.89 mph
    Current dyno tune 383.54 rwhp 418.88 rwt

  7. #7
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    Quote Originally Posted by Mike Puckett View Post
    If I kept on cranking with the pedal to the metal it finally almost started, sputtered and wheezed but not quite.
    In normal circumstances, holding the pedal down/full throttle while cranking shuts the injectors off.

  8. #8
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    Disconnect the vacuum line from the regulator, and use a needle-nose vice-grip to pinch closed the return line, then cycle the key a few times and see if it has any fuel pressure. If it does build pressure, the regulator is no good. If it starts leaking fuel out the regulator, the regulator is no good. If it doesn't build any pressure, confirm that you still have fuel flowing out of the feed line when cycling the key on, and if you have fuel flowing through the line to the rail, but it won't build pressure even with the return line pinched off, then your fuel pump is no good.

  9. #9
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    Correct

    Quote Originally Posted by KMT View Post
    In normal circumstances, holding the pedal down/full throttle while cranking shuts the injectors off.
    You caught that before I had a chance to see this.

    I had to prove this to a guy in a Mustang once. He didn't believe that his car wouldn't start if he held it to the floor. He was wrong!!
    Venetian Blue 1995 5 Spd...............No ET
    Orange Crush Pearl 1995 Auto SC........11.175 @ 121.85 MPH
    462.54 rwhp, 461.42 tq
    Garage:http://www.sccoa.com/forums/garage_v..._vehicle&id=13

  10. #10
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    Quote Originally Posted by Mike Puckett View Post
    OK, results of tonight. If I jumper the fuel pump on I have pressure at the shrader valve. As soon as I shut off the pump the pressure was gone. Putting some suction on the vacuum line to the fuel pressure regulator I could get a faint taste of gasoline but couldn't feel a diaphragm move if it's any indication of a pump problem. I jumpered on the pump and cranked it but still no start. Then I squirted some starting ether into a vacuum line but it still wouldn't start. If I kept on cranking with the pedal to the metal it finally almost started, sputtered and wheezed but not quite. I had to stop to recharge the battery. So, verrrrry interesting. This one is a head scratcher. There is no upshift light while cranking but this is a 5spd conversion from an AOD so should there be if the crank sensor is bad? All of the parts came off of the blown motor which cranked up and ran for 2 secs in my garage before the teardown.
    Mike,

    If you are losing pressure as soon as the pump shuts off and there are no visible leaks, the most likely cause is an injector stuck open or a leaking fuel pressure regulator diaphragm. The diaphragm is easy to check, just disconnect vacuum hose and see if fuel is coming out of the regulator vacuum port when pump is running. To test for a leaking injector you will need to pull the rail off of the heads with the fuel lines and injectors in place, and turn the pump on without cranking the motor.

    David
    1991 SC AOD 4.2..2.3 Whipple..........10.910 @ 125.61
    2016 SRT Challenger Hellcat...............707HP/650TQ

    My Garage

  11. #11
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    The reason I held the pedal down was to see if maybe I had flooded the cylinders with gas. The fact that it tried to catch made me think of a stuck injector. I did get a taste of gas when I put suction on the vacuum line so I'm wondering about the regulator. A friend is coming over tonight with a fuel pressure gauge so we can check the pressure. Only problem if it is the regulator or an injector is that I've got to take all the stuff off of the top of the motor. Another thing I've wondered about. It has a Quarterhorse tuner with a Dave Dalke program in it for the 50# injectors. If the car battery is disconnected for several weeks could the Quarterhorse tuner lose its program? We have a no spark condition as well it appears. It could be that there is a no spark condition due to either a problem or the EEC is shutting it off due to the lack of fuel or maybe visa versa. I'm speculating here. Remember, all of this was working when the motor died.
    90 5spd, best ever E.T. 12.250
    best ever 1/4mi speed 112.89 mph
    Current dyno tune 383.54 rwhp 418.88 rwt

  12. #12
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    If a stuck injector (or two) is causing it to 'flood'....did you look at the O2 sensors and plugs yet? They might tell you something, and is a bit easier than yanking the injectors themselves, which may be necessary yet...

  13. #13
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    EEC won't shut off spark because there is no fuel pressure and battery being disconnected will have no impact on QH battery drain. It uses/drains QH battery anytime car isn't running. It could have a bad battery and lost the tune, but you will need to hook it up to your laptop with BE and the correct strategy file to determine that.

    Starting to sound like you have a harness unplugged somewhere. Double check the area by the EEC test port where there is a bunch of them.

    David
    1991 SC AOD 4.2..2.3 Whipple..........10.910 @ 125.61
    2016 SRT Challenger Hellcat...............707HP/650TQ

    My Garage

  14. #14
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    Made some progress. A friend brought over a fuel pressure gauge and got that hooked up. After trying to start it multiple times it is now holding fuel pressure. It falls off gradually and appears to be back to normal after reading as high as 70 the first time we checked it. It is getting fire also. I can pull a plug wire off of the coil pack and see the spark. And, it almost starts up and actually ran for a second. We redid the plug wires several times to no avail. All of the electrical plugs are seated in their sockets and no loose ends. We were wondering about the crank and cam sensors. I guess even the DIS module could have died. I'm thinking that even if the cam sensor was bad it would still start up after 3 tries or no. If the crank sensor was bad would it completely prevent starting or would it allow the engine to catch occasionally while trying to start like it's doing? I'm again charging the battery back up so it's possible the battery is too low. It read as low as 10.6 volts during cranking. I also found 2 loose hose clamps on the IC tubing which tightening didn't help.
    90 5spd, best ever E.T. 12.250
    best ever 1/4mi speed 112.89 mph
    Current dyno tune 383.54 rwhp 418.88 rwt

  15. #15
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    Woodstock Ga
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    I appreciate all of the help from Mike and the forum. It has been almost three months without a car(2 sc's) and the strain of everything has hit us hard. My wife doesn't like sharing her Jeep!!

    We are close and I am hoping the SC gods will be kinder to us!

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