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Thread: Cyl 4 running rich

  1. #1

    Cyl 4 running rich

    So the problem started with difficulty cold starting. Engine would fire and then die. If I gave it throttle I could keep it running but if I let off it would die, and wouldn't fire for a few minutes. Place reeked of gas, and would spit black stuff out of the tailpipe. Once it got up to operating temperature it was fine.

    Replaced the coolant temp sensor and its better but still having trouble.
    Pulled the plugs and number 4 was all black, rest looked fine. Cleaned out intake to turbo tube (gunk from pcv valve), air filter and reoiled, and throttle body (little bit of carbon build up. Checked distributer cap which looked fine, and replaced plugs. Test drive and 4 is black again after like 15 min of varied driving. Swapped plugs 1 and 4 and injectors from cyl 3 and 4. Test drive and and cyl 4 still black.


    One of the times I pulled the plugs it was a little bit of oil. Have not seen it again.
    Ran a compression test (operating temp and WOT) and got in order.
    120 120 130 137
    When I cold started today prior to compression test it started, and within 30 seconds died. Wideband was reading 9:1 then died. Gauge read 12.1 after dying, and wouldn't fire. Gave it two minutes, tried again and back at 9:1. After giving a blip on the throttle went up to 11:1 then slowly climbed to 14.7 as it warmed up. Left that lovely black mark on the garage floor posted earlier. Once I got it in the road no more problems. Made 4 stops, one letting engine cool for an hour and no problems.
    Afr stays at 14.7 ish while idling and 12.5 ish under boost.
    Not sure what to do next, any suggestions for what to check?

    TLDR
    Cyl 4 spark plug is black. Engine rich on cold start. Blowing black stuff out tailpipe. Not smoking. Reeks of gas on cold start
    Injectors ok
    Plugs ok
    Cap ok
    Compression higher than others
    Coolant temp sens replaced

  2. #2

    Re: Cyl 4 running rich

    So I let it cool to operating temp, over like 8 hrs, just went and fired it up, no problem. As soon as wideband started reading it showed 12.5 and started climbing. If it fires up no issue tomorrow morning Im moving on to setting up the ostrich finally.

  3. #3
    Moderator Turbo Mopar Staff Vigo's Avatar
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    Re: Cyl 4 running rich

    I would look to see if the driver circuit for that injector is intermittently shorting to ground. That would intermittently open the injector when it should be closed.

    Dont push the red button.You hear me?

  4. #4
    Hybrid booster
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    Re: Cyl 4 running rich

    What about the #4 wire? If you've swapped injectors and plugs around that's one constant. I've never had wires go bad but I would imagine it could weaken the spark enough to cause what you describe.

    Also, I have had an intermittent problem on my #4 injector plug that causes it to stop firing and run extremely bad. The wiring takes a tight bend right there and is pretty old by now. Mine got so bad I could barely risk driving the car and I never really did anything to fix it except wiggling it around but it hasn't happened in years now. Might try messing around with that next time it seems to be having trouble.
    1991 Chrysler Lebaron GTC convertible - a568 - 15psi FWD Stage 3, FMIC, TII Garrett turbo, two of the big ones

  5. #5

    Re: Cyl 4 running rich

    So I finally got around to messing with the car again. Fired up the car to warm it up, and it started no problem. AFR was about 14 flat.Let it idle for awhile to warm up and within 1 min was at 14.7. Let it idle to get up to operating temp and abouy 3 minutes in suddenly started running really rough. Ran over and checked the afr, which was now showing 9:1ish. Gave it some throttle which raised to 10 but still way too rich. Foot off throttle and it died.
    Was at operating temp at thus point so ran another compression test.
    130 125 130 135
    Not as drastic a difference as before. Added a squirt of oil and ran each cylinder again. Each cyl went up 5 for
    135 130 135 140
    Started up again no problem, afr spot on.
    Pulled injector wiring harness and all looks fine. Wires are in great shape.
    By driver do you mean the plastic piece that connects to the injector?

  6. #6
    turbo addict
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    Re: Cyl 4 running rich

    It's got to be fuel related a spark miss should show a lean condition on the wb. What ecu are you using?

  7. #7

    Re: Cyl 4 running rich

    Socketed sbec with mopar performance tune. Its not optimized for all the mods on the car but it was running fine for a long time.
    In fact the only recent change has been the addition of a catalytic converter to pass smog in CA.
    I just want to get this smoothed out before setting up the ostrich.

  8. #8
    Moderator Turbo Mopar Staff Vigo's Avatar
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    Re: Cyl 4 running rich

    Run the car until the issue begins to happen, unplug that injector, hook a test light up to voltage and see if one of the wires has constant ground. It shouldnt. It should have flashing ground.

    Dont push the red button.You hear me?

  9. #9
    Supporting Member Turbo Mopar Contributor 2.216VTurbo's Avatar
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    Re: Cyl 4 running rich

    I am suspicious of the cat, I've had them overheat causing the honeycomb core to turn into a molten wall of restriction that wouldn't allow any exhaust thru. Stranded late one night years ago in GLHS #991, I used a cold chisel from my boneyard bag to window the thin sheetmetal of the inlet side of the cat so I could limp it home breathing thru the 1" square cut out. This doesn't explain why just one cylinder gets unhappy but make sure you have good vacuum at idle just the same.

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  10. #10

    Re: Cyl 4 running rich

    So I finally had some time today and tried to replicate my issue of intermittent periods of running rich. I picked up a set of noid lights to see if the injector was firing properly, and also to quick put it on when it started running rich.
    Well I couldn't replicate the problem! Injector appears to be getting proper electricity (flashing light) and never ran rich. I only let it sit and idle to warm up, occassionally giving it a little throttle to see if that would trigger it and all was fine.
    I did however start hearing a slight poping noise once it got warm. I gave it some throttle and exhaust gas started coming from the engine bay consistently. I couldn't see exactly where from but it was behind the engine and not from the valve cover, so I'm guessing the header. It came out in a long line, almost like the gasket was leaking. The turbo is relocated by header and it was definitely not coming from it. Also as I let off the throttle and the rpms decelerated, it would start to making a harsh metal on metal rubbing sound which got me nervous and I shut it off. The sound would subside as the rpms reached idle and did not occur when the throttle was open (only did partial, no WOT).
    I am really suspicious of the cat. According to Chuck it ran fine. The ONLY change has been the addition of the cat to pass smog, and the problems started shortly after. It actually only started showing problems after a few passes at the dragstrip...I am hoping that if that is the root problem it hasn't caused too much damage.
    Thoughts?

  11. #11
    Buy my stuff!!!!!!!!!!! :O) Turbo Mopar Vendor turbovanmanČ's Avatar
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    Re: Cyl 4 running rich

    Where is the wideband located? All the grounds intact? Sounds like a cal issue. Simply unbolt the DP and see if the problem happens again.
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  12. #12
    turbo addict
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    Re: Cyl 4 running rich

    Cracked header causing computer to pick up knock on one cylinder and retard timing.
    Ian Adams Function>Form 1990 shadow scrapped, too rusty:( 1991 Spirit R/T Scrapped, parts sold:( 1989 Turbo Caravan Daily beater with built-[I]ish [/I]​engine slowly evolving into weekend turbo beater.

  13. #13
    Moderator Turbo Mopar Staff Vigo's Avatar
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    Re: Cyl 4 running rich

    The computer could pull all 16* of timing and the cylinder would still burn enough of the fuel that it wouldnt spew black smoke/liquid fuel out the tailpipe.

    Dont push the red button.You hear me?

  14. #14

    Re: Cyl 4 running rich

    Prerty sure whats coming out the tailpipe is a mixture if water and soot.
    Running with the DP disconnected sounds like it will be loud. I will havevto wait a week for vacation. I can do it on a weekday. Will have to let the engine warm to operating temp to replicate the problem.

  15. #15
    Moderator Turbo Mopar Staff Vigo's Avatar
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    Re: Cyl 4 running rich

    Soot is unburned fuel from running exceedingly rich or having a lot of misfires.

    Dont push the red button.You hear me?

  16. #16

    Re: Cyl 4 running rich

    Double checked, wideband is after the cat. Not the the sensor connected to the computer though. Was low on oil, so topped it off and the sound no longer happening, but still got some smoke from the back of the engine. Only happens when at operating temp though. While cool is fine.
    Still not running rich though. Seems like that problem has disappeared???

  17. #17

    Re: Cyl 4 running rich

    Any thoughts? Im thinking the rich cyl is a result of the harness itself. Would I be better off building a new one from scratch or sourcing one from one of you guys?
    Going to fire it up tonight and see if it still puts out some smoke from behind the engine.

  18. #18
    boostaholic
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    Re: Cyl 4 running rich

    it is possible to have a pin hole leak in a power steering hose that can spray on the exhaust manifold. Happened on my GLHS before I pulled it apart. Flammable stuff!

  19. #19

    Re: Cyl 4 running rich

    Finally got myself motivated to work on the car. Tried starting it up and it cranked but didn't fire. Pulled the number 4 plug to see if I was getting spark. Car instantly fired up but no spark on number 4. Plug is all black already, and has less than 50 miles on it.
    Any thoughts?

  20. #20
    Hybrid booster
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    Re: Cyl 4 running rich

    Did you ever try swapping spark plug wires or a new set? Last set I purchased was less than $20.
    1991 Chrysler Lebaron GTC convertible - a568 - 15psi FWD Stage 3, FMIC, TII Garrett turbo, two of the big ones

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