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Thread: Fuel pressure? Or possible HEP problem?

  1. #1
    Mitsu booster
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    Fuel pressure? Or possible HEP problem?

    Car is a 1987 GLHS with a MP Stage 2 computer, +20 injectors, big intercooler, walbro 190 pump, 15psi.
    I'm getting 53psi at idle and what happens is the car gets around 10psi boost and starts bucking and breaking up, boost only goes to 12psi because of the bucking and fuel pressure is reading about 73psi when this happens. Does this seem to be too high?

    Could this possibly be a failing Hall effect pickup? When cruising at a steady rpm it almost feels like the car is having an electrical issue like it's briefly cutting out for 1/10th of a second. I've checked and regapped the plugs they are champion RNY9C and look good. I've swapped ignition coils with no difference, new TPS also. The distributer cap/wires/rotor all look good and are Mopar brand with under 2,500 miles on them. I can't seem to figure this out. No codes stored in the computer either. Last year I had power module issues, found another power module which worked fine and then this began happening not too long after that.

    edit: I've also checked the timing repeatedly, everything lines up perfectly and ignition timing is 12 degrees with the CTS unplugged

  2. #2
    Supporting Member II Turbo Mopar Contributor
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    Re: Fuel pressure? Or possible HEP problem?

    Pressure at 12psi should be 12+55 or 67psi.
    our cars are very sensitive to vacuum leaks, so I would check for leaks.
    Regards,
    Miles

    DD '87 Sundance T1, 12PSI, SLH with rear disks
    '87 CSX #432

  3. #3
    Supporting Member II Turbo Mopar Contributor tryingbe's Avatar
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    Re: Fuel pressure? Or possible HEP problem?

    Get a different fuel gauge.
    Tailgate at your own risk.

  4. #4
    Supporting Member Turbo Mopar Contributor GLHS60's Avatar
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    Re: Fuel pressure? Or possible HEP problem?

    Welcome!!

    With a faulty HEP I've noticed the tach drops a split second before interruption.

    It takes a fast eye but it is discernible, and they often leave no codes.

    Replacement HEP's are often troublesome so new is no guarantee.

    Many keep used ones on hand and rotate them occasionally.

    Odds are as good with junkyard Heps as with replacements.

    Best of luck.

    Thanks
    Randy


    There is no logical reason to call an Engine a motor.

    Randy Hicks
    86 GLHS60
    86 GLHS 373 : SOLD, but never forgotten
    89 Turbo Minivan
    83 Turbo Rampage : SOLD
    Edmonton,Alberta,Canada

  5. #5
    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
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    Re: Fuel pressure? Or possible HEP problem?

    I'm with Randy on the HEP. You can test the fuel pump easy enough. Jump the coil by running a wire from the +bat terminal to the + side of the coil. That will energize the fuel pump. With a gauge on it, pinch off the return line. You should get 80+PSI which is where the relief in the pump is generally set. Anything lower and the fuel pump is bad for sure.

  6. #6
    Supporting Member II Turbo Mopar Contributor
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    Re: Fuel pressure? Or possible HEP problem?

    It is easy to repair the HEP, If you are handy with a soldering iron. The two HEP lines each contain three wires, 9V(can vary from 7.5-9V depending which ECU), GND and signal to ECU. These are fine wires are break on the inside so you cannot see. Take the HEP off the car and place on a bench and test each line with your DVM on continuity mode and wiggle the cable especially at the two ends. It is common to see failure within a inch or so where the wires enter the HEP.
    If you need more details let me know
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    Last edited by chromguy; 06-08-2020 at 10:00 AM.
    Regards,
    Miles

    DD '87 Sundance T1, 12PSI, SLH with rear disks
    '87 CSX #432

  7. #7
    Mitsu booster
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    Re: Fuel pressure? Or possible HEP problem?

    Borrowed a Snap-on gauge and the fuel pressure seems to be fine. Key on/engine off is 55psi, 12psi is 67 psi. I jumped the coil to run the pump then I pinched off the return line and it goes to 100psi. I also hooked up a smoke machine to check for vacuum leaks and only found a slight leak around the TPS.

    I took the HEP off the car and tested the wires with a DVM for continuity and wiggled all the wires and everything tests fine no breaks but it looks like there was very light rubbing on the HEP where the shutter wheel goes through? On the distributor nothing seems out of place, nothing loose.

    The spark plugs look fine they are all coffee colored, I am using Champion RN9YC I'm wondering if they are an issue? Too cold of a plug for my setup? I might get stock RN12YC and see if it helps.

  8. #8
    Supporting Member Turbo Mopar Contributor GLHS60's Avatar
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    Re: Fuel pressure? Or possible HEP problem?

    9's are best, 12's are hotter, OEM's often install hotter plugs that ideal.

    Plugs are inexpensive to replace and can sometimes cause odd issues.

    Check the stutter wheel for looseness, some are held with a dab of plastic.

    Some guys rivet them securely in place, search stutter wheel for info.

    Try and locate a known good HEP if possible.

    They can be problematic!!

    Thanks
    Randy


    There is no logical reason to call an Engine a motor.

    Randy Hicks
    86 GLHS60
    86 GLHS 373 : SOLD, but never forgotten
    89 Turbo Minivan
    83 Turbo Rampage : SOLD
    Edmonton,Alberta,Canada

  9. #9
    Mitsu booster
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    Re: Fuel pressure? Or possible HEP problem?

    I picked up the spark tester tool and the vacuum parts. First used the spark tester and both cylinders 1 and 4 have the same misfire or "break" where it is not jumping the contacts with it set on 25KV. Cylinders 2 and 3 are perfect with no interruptions. Looks like this is the main issue. Distributor problem or could it still be a HEP issue? The cap/rotor/wires are all OEM mopar with about 2500 miles on them. I did install new spark plugs and it helped a lot but the issue is still there although not nearly as severe it will pull to redline now but when cruising at steady rpm it still misfires.

    Thanks for the help so far by the way!

  10. #10
    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
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    Re: Fuel pressure? Or possible HEP problem?

    I would definitely think HEP from everything you've described. Any way you slice it, you should have a spare to try. It's one of the very few parts that will put you out for the count when on the road if it fails.

  11. #11
    Hybrid booster
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    Re: Fuel pressure? Or possible HEP problem?

    Quote Originally Posted by cordes View Post
    I would definitely think HEP from everything you've described. Any way you slice it, you should have a spare to try. It's one of the very few parts that will put you out for the count when on the road if it fails.
    Regardless of the root cause of the issue, when all is said and done I'd keep a spare HEP (and a Phillips screwdriver) in the glove box.

    My 2 cents to the mix is I'd check the continuity from ground (at the battery) to your injector harness ground. And then check all the grounds as a project

    Any possibility of getting a video with audio of the misfire while cruising? Is your redline pull with the pedal truly to the floor or 80%?

  12. #12
    Mitsu booster
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    Re: Fuel pressure? Or possible HEP problem?

    I did find the distributor has play in it. Uploading a video hope this works. Should this have any play at all?

    https://streamable.com/55hdw3

  13. #13
    Supporting Member Turbo Mopar Contributor GLHS60's Avatar
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    Re: Fuel pressure? Or possible HEP problem?

    That's normal play between the distributor and the oil pump.

    The distributor has drive tangs that fit into the oil pump.

    The oil pump is driven by the intermediate shaft.

    Timing belt turns the intermediate shaft.

    Thanks
    Randy


    There is no logical reason to call an Engine a motor.

    Randy Hicks
    86 GLHS60
    86 GLHS 373 : SOLD, but never forgotten
    89 Turbo Minivan
    83 Turbo Rampage : SOLD
    Edmonton,Alberta,Canada

  14. #14
    Mitsu booster
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    Re: Fuel pressure? Or possible HEP problem?

    Quote Originally Posted by GLHS60 View Post
    That's normal play between the distributor and the oil pump.

    The distributor has drive tangs that fit into the oil pump.

    The oil pump is driven by the intermediate shaft.

    Timing belt turns the intermediate shaft.

    Thanks
    Randy
    That's good to hear. Here's a video of what the spark is doing. This is at 25KV. If I try it at 30KV it sparks maybe once in 30 seconds.

    https://streamable.com/ry9bt3

  15. #15
    Supporting Member II Turbo Mopar Contributor jeff1234's Avatar
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    Re: Fuel pressure? Or possible HEP problem?

    My distributor pick up from an 89 caravan has two pick up heads in it. I notice the one above has just one. When I bought replacements it was always for an 89 Caravan T1 2.5. When I check continuity there is none on one that was working when I took it off. Apparently I am not using the correct procedure by checking every possible connection possibility. What am I doing wrong?
    The only substitute for cubic inches is cubic dollars, how fast can you afford to go?

  16. #16
    Mitsu booster
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    Re: Fuel pressure? Or possible HEP problem?

    New Hall Effect sensor fixed everything. No more cutting out at any time.

  17. #17
    Supporting Member Turbo Mopar Contributor GLHS60's Avatar
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    Re: Fuel pressure? Or possible HEP problem?

    Welcome to the oddball HEP problem club!!

    Thanks
    Randy


    There is no logical reason to call an Engine a motor.

    Randy Hicks
    86 GLHS60
    86 GLHS 373 : SOLD, but never forgotten
    89 Turbo Minivan
    83 Turbo Rampage : SOLD
    Edmonton,Alberta,Canada

  18. #18
    Supporting Member II Turbo Mopar Contributor
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    Re: Fuel pressure? Or possible HEP problem?

    Quote Originally Posted by reliant K View Post
    New Hall Effect sensor fixed everything. No more cutting out at any time.
    Excellent news
    Regards,
    Miles

    DD '87 Sundance T1, 12PSI, SLH with rear disks
    '87 CSX #432

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