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Thread: 1987 csx stumble

  1. #1
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    1987 csx stumble

    My daily driver 87 csx. The only stuff not factory stock are MP LM, roller cam, and no cat.

    The issue is intermittent, but occurring more frequently. When accelerating, the car stumbles, barely accelerates, and pops out the exhaust. To me, it feels very ignition related, because of the exhaust popping. Yesterday, it blew out a sooty loud bang, so I'm leaning towards ignition or possibly over fueling. Under hard acceleration, it will produce boost and accelerate better, but not like it's normal potential and it's popping and miss firing the whole way. Suddenly it stops and drives normal.

    No codes have been active. Tach, vacuum gauge read normal during this (not bouncing around) No other instrumentation is present.

    So far I've tried from a known good 88 shadow a coil, pick-up coil, complete secondary ignition system. I have a drb2 and I'm seeing no values out of the ordinary, I've looked in the fuel pressure regulator hose for fuel, none found. I bypassed the baro read solenoid with no changes, double checked cam and ignition timing and they're correct.

    I don't have another LM as a tester, as most of my stockpile is smec based

    Any ideas? Other things to check or try?

  2. #2
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    Re: 1987 csx stumble

    Quote Originally Posted by shadow88 View Post
    My daily driver 87 csx. The only stuff not factory stock are MP LM, roller cam, and no cat.

    The issue is intermittent, but occurring more frequently. When accelerating, the car stumbles, barely accelerates, and pops out the exhaust. To me, it feels very ignition related, because of the exhaust popping. Yesterday, it blew out a sooty loud bang, so I'm leaning towards ignition or possibly over fueling. Under hard acceleration, it will produce boost and accelerate better, but not like it's normal potential and it's popping and miss firing the whole way. Suddenly it stops and drives normal.

    No codes have been active. Tach, vacuum gauge read normal during this (not bouncing around) No other instrumentation is present.

    So far I've tried from a known good 88 shadow a coil, pick-up coil, complete secondary ignition system. I have a drb2 and I'm seeing no values out of the ordinary, I've looked in the fuel pressure regulator hose for fuel, none found. I bypassed the baro read solenoid with no changes, double checked cam and ignition timing and they're correct.

    I don't have another LM as a tester, as most of my stockpile is smec based

    Any ideas? Other things to check or try?
    My dad just had similar issues on his GLHS caused by a bad rotor

  3. #3
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    Re: 1987 csx stumble

    That was swapped in this case to no avail.

  4. #4
    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
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    Re: 1987 csx stumble

    I had an alternator go bad very slowly on a SMEC car and it caused a similar issue which took the alternator actually dying to rectify. Pun intended. I did get a code 54 with that, but I also had the same thing happen on a 97 Neon which didn't throw the code some years later.

  5. #5
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    Re: 1987 csx stumble

    Good thought. That alternator is new as of last summer, so anything is possible. It hits the charging voltage target of 14.2V. How could I test that? I was trying to make a fuel pressure gauge, but I'm unable to replace a fuel pump even if that is the problem, so with the rain, I opted to get inside and try again after work tomorrow if it gets me to work and back.

  6. #6
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    Re: 1987 csx stumble

    I just realized that I only looked at the plugs, I didn't see an issue and didn't change them to known good units, so I just went out and did that.

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    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
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    Re: 1987 csx stumble

    I had an oscilloscope on the alt. I think it was throwing out some unrectified AC current which was freaking out the computer. Unfortunately, I either didn't have it on there when the car would cut out, or I had it testing the sensor signal rather than the power input to them or the computer. It was certainly a learning experience.

  8. #8
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    Re: 1987 csx stumble

    what about the wheel in the dist
    it it still plasti-melt/riveted nice and snug ?


    I had an ignition under accell issue that was hard to find until I noted the lose fit of the coil wire terminal in the coil tower socket
    .. long cable flops around , breaks contact

    works fine till you stomp the happy pedal and make the cable move..

    and ,
    last year I had an ABS brake light on in my f150 - most of the year and nothing wrong with the system

    last november I replace the alternator - had an intermittent charging lamp then constant

    replace the alternator and battery (was borrowed from my car) and low and behold
    no ABS lamp since
    Last edited by Dr. Johny Dodge; 05-13-2019 at 09:34 PM.

  9. #9
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    Re: 1987 csx stumble

    To test the alternator for issues, just disconnect the field coil wires. It will stop charging and run off the battery.
    Regards,
    Miles

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

  10. #10
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    Re: 1987 csx stumble

    Good excuse to go through all the engine grounds and check for a loose or corroded wire?

    Jeff

  11. #11
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    Re: 1987 csx stumble

    A little update from today. It ran poorly on the way to work, but it could maintain the proper speed, so I put little thought toward it. On the way home, it was at it's worst, barely capable of reaching 40 MPH. I pulled off the hyway and into a parking lot and disconnected the white 1 pin bullet connector that is the alternator output to the battery (just behind the battery). Wouldn't you know it, it ran just fine, so I reconnected it and it ran like crap again. Disconnected once more to be sure and it ran well, then reconnected and I arced the connector, leaving a little gob of molten copper in the female end of the connector. I turned off the car, cleaned it out with a screwdriver and left it disconnected for the drive home, or until the battery gauge read low enough to be concerned. That's about 4 off ramps. I reconnected it and MAYBE it's making better connection now due to the better fit of the pin to socket, but it ran perfectly the whole way home.

    Further road tests tonight after I spread the terminal out a little more to be sure it's making good contact.

  12. #12
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    Re: 1987 csx stumble

    Excellent news!
    Regards,
    Miles

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

  13. #13
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    Re: 1987 csx stumble

    Just when I thought I was on the right track,..... I'm stumped again.

    Yesterday, I changed the alternator with a known good unit and it seemed ok, so I parked it for the night.

    Today I made and ran new cables, 4 ga. from the head to the negative battery terminal, and a separate cable , also 4 ga. from the alternator to the positive terminal. I also cleaned the terminals, even though they weren't bad. While behind the battery, I gave all the fuse able links an aggressive tug and broke one of the little orange ones. So I repaired that too. I didn't even get out of the driveway and the stumble returned.

    I have a little more info and I don't understand why it does this. On the way to work at 5am, it runs with a slight miss, but I can maintain proper speeds. On the way home at 2pm, rain or shine, it runs terribly. Today, on the way home, it was running very poorly and I was waiting to get to a side street to pull over and try things and suddenly, it was repaired by itself and back to normal.

    After the cables today, I made an inline fuel pressure gauge, and I taped it to the windshield, and I'll see tomorrow if that has anything to do with it, but I'm doubtful.

    I have checked codes, cam timing, the shudder wheel plastic welds, and watched all sensors through a drb2 and I don't see anything out of whack.

  14. #14
    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
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    Re: 1987 csx stumble

    Have you bypassed the baro read solenoid to eliminate that as a possibility? I had one that was bad and causing a cutout due to inaccurate readings once.

  15. #15
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    Re: 1987 csx stumble

    I must have forgot to state that I had. yes, I did. Also not mentioned is coolant sensor swap with known good one.

  16. #16
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    Re: 1987 csx stumble

    Quote Originally Posted by shadow88 View Post
    I must have forgot to state that I had. yes, I did. Also not mentioned is coolant sensor swap with known good one.
    If you are still running the 87 electronics with the MAP in the logic module, rev the car and pull the MAP hose during engine decel to evacuate any moisture from the MAP hose into the car.
    These are known and prone to condensation build-up in the line which interferes with the MAP signal. It may take a few times to use the engine vacuum to vacate the line free of moisture.

  17. #17
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    Re: 1987 csx stumble

    ^ just reminded me of the map replacement in a buddy's charger
    - drove like a dog , barely when acting up

    sensor was wrecked by the moisture in the line and time

    also a problem was the road salt build up in the corner of the lm closest to the rust hole in the wheel well

    also , once with my TII set up I had an AIS issue (code)
    I replaced it and the code went away but the issue didn't and there was no other codes

    so I thought what's the closest thing to the ais"
    tps.. so I switched it for another and all was well

    swapping back either of the old parts brought the issue back

    car HAD to have both but never threw a tps code

  18. #18
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    Re: 1987 csx stumble

    It's running the map/ baro on the strut tower.. This morning, drove to work monitoring fuel pressure and that was spot on 55 at 0 vacuum. Rising and falling like it should. Swapped map sensors with known good from my shadow without improvement.

  19. #19
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    Re: 1987 csx stumble

    You switched the HEP correct??
    Regards,
    Miles

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

  20. #20
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    Re: 1987 csx stumble

    Oh yes, known good one again from the shadow, as well as the entire ignition system.

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