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Thread: Suddenly Rich on Decel

  1. #1
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    Question Suddenly Rich on Decel

    The car

    89 daytona
    Intercooled 2.5 w/a555
    Stock computer controlling boost
    3 inch cat back exhaust

    The problem

    Started my car after work yesterday and took off for home. Slowing down for my first corner I noticed that my exhaust was not popping on deceleration as usual. Looking at my afr it was reading 10s to 12s when it is usually high 13s and 14s. Coming to a stop it stayed rich for a bit then levelled out. It seems to be acting normally under acceleration and boost. I reset my computer but it made no difference. If I put the car in neutral and roll up to a stop my afrs are normal, but if I engine brake it runs pig rich again. Any ideas what I should be looking at? My AFR is taking a lot longer to calibrate on startup now and I am afraid of ruining the sensor.

  2. #2
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    Re: Suddenly Rich on Decel

    O2 sensor?
    TPS?
    coolant temp sensor?
    MAP?

  3. #3
    turbo addict Murphy's Avatar
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    Re: Suddenly Rich on Decel

    any codes?

    I would lean toward it being the TPS
    95 spirit 3.0/543 15.0@91 N/A, 14.5@96 on a 50 shot RIP 87 shelby Z - project car, maybe I can drive it this year 91 spirit - roll it, chop the top, do some burnouts! RIP

  4. #4
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    Re: Suddenly Rich on Decel

    No codes thrown.

  5. #5
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    Re: Suddenly Rich on Decel

    Finally got some time to look at the car. Changed out tps and reset the computer. No change. Pulled a plug and the center looked a nice chocolate brown but the outside ring was wet. But after starting it up and letting it run a bit a new symptom developed. The rad fan started kicking in, running for a second or two, and kicking out again and repeating. Checked at my in car gauge and it wasnt even halfway up the gauge. Now suspecting coolant temp sensor.

  6. #6
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    Re: Suddenly Rich on Decel

    Anyone else have some input???

  7. #7
    Mitsu booster
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    Re: Suddenly Rich on Decel

    I'm having the same problem. I get a loud popping sound when I decel. The popping is at regular intervals, spaced about 3/4 second between pops.

    Radiator fan was kicking in and out, but I believe that was fixed when I replaced the coolant sensor.

    Idle is inconsistent (varies by 50-100 rpm); could it be the HEP?

    Checked MAP and voltage is within expected range at idle and with ignition off.

    Checked TPS voltage and it's 0.9V at idle and 3.9V at WOT. Bought a 560 ohm resistor to see if I can bring the TPS voltage down to within the expected range.

    I still need to check O2 sensor and S/D sensor.

  8. #8
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    Re: Suddenly Rich on Decel

    The popping is normal (from what I hear) and I want mine back! Mine goes full rich on decel and makes a buuaaaaaaaahhh sound, instead of its normal happy burble. I swapped in a different computer and it seems happier. Time will tell I guess. My car did, however, make very loud popping noises when my speed sensor went out. Something to check on yours cout.

  9. #9
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    Re: Suddenly Rich on Decel

    All seems well with the "new" computer. It burbles nicely on decel and is in the 12s instead of the 10s.

  10. #10
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    Re: Suddenly Rich on Decel

    For those who care the computer must have been the problem. Put a couple hundred kms on and all is well. Keeping an eye on my oil though as it was fuel contaminated at last oil change. Hoping that the rich on decel was the cause.

  11. #11
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    Re: Suddenly Rich on Decel

    Back from the dead. Started driving the dogtona again this spring, I have been driving it for about three weeks and all has been well until today. Hopped in for lunch and took off. The darn thing never seemed to get off of the "cold start" circuit running 10s on decel and as low as 9 while idling! Reset the computer and it seems to be running better but possibly still a bit rich. Why is my computer learning to run rich????

  12. #12
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    Re: Suddenly Rich on Decel

    Bump for the night crew. Hooked a volt meter up to the o2 sensor (bosch) and it seems to be reading normal, ranging from .2 to .8 volts at idle.

  13. #13
    turbo addict
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    Re: Suddenly Rich on Decel

    Its probably running rich because the O2 is bad. Usually when the sensor goes bad it will cause the computer to dump fuel. Id say im 95% on that being your problem. Swap that sensor out to an NTK one from a parts store and im sure you wont have any problems anymore.

    Also, codes, im curious.

  14. #14
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    Re: Suddenly Rich on Decel

    It hasnt thrown any codes until tonight. Got a code 13 for map vacuum but i had been messing with the baro solenoid. Replaced the map with another and it runs the same. Tested the map and fpr and their lines for vac leaks and all seem ok.

  15. #15
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    Re: Suddenly Rich on Decel

    replace baro and map with known good i had a leaking baro do this stuff to me before.
    then replace o2 w known good not bosch. is the o2 sensor in stock location?
    then replace big temp sensor w third one that is known good.
    If ecu thinks its warming up too long that sensor is most likely the culprit. plug for that is a piece of crap too...
    If you changed the ecu w other stock known good one and you still get the extended/constant open loop, your harness may be compromised.
    Now is a good time to redo all your grounds/electrical connections underhood with copper cote or the like.

  16. #16
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    Re: Suddenly Rich on Decel

    That's what my car was doing but it was to do with timing

  17. #17
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    Re: Suddenly Rich on Decel

    -bypassed baro, same result
    -switched map, same result
    I ordered a mopar o2 sensor this morning.

  18. #18
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    Re: Suddenly Rich on Decel

    Quote Originally Posted by Dony409 View Post
    That's what my car was doing but it was to do with timing
    Yeah but if your timing is off, its always off.

  19. #19
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    Re: Suddenly Rich on Decel

    I know it has been months but I figured I should post up my progress to help others who may come across the same issue. I replaced my Bosch O2 sensor with a Mopar unit and the car ran fine. This lasted a couple weeks and then the same rich condition came back. I started wondering if my fuel pressure was through the roof, so I asked a friend of mine to borrow his fuel gauge. He asked what my vacuum to the fpr was. I didnt know but my in-car gauge read 18 in/hg which is lots. He unplugged the line to the fpr and felt barely any vacuum at all! Turns out that when I built my vac lines out of spare parts I used a "T" that looks big from the outside, but it has a restrictor on the inside, limiting vac signal to both my map and fpr. Put a new unrestricted T in and all seems to be well again.

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