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Thread: overboost, overboost not enabled

  1. #1
    Supporting Member II Turbo Mopar Contributor jeff1234's Avatar
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    overboost, overboost not enabled

    Im getting a backfire at 5100 rpm's. it is actually 4800 but the tachometer is high. It always happens at the same point. I thought it was the coil and replaced that. It ran perfectly once then started doing it again. I also changed initial timing, it was too high. Fuel is in mid 11's. this has been happening for awhile. Has anyone else had this experience. I cant find anything telling me overboost is on. Boost is controlled by mechanical boost controller. (commercial) ECM is 87 T2 LM
    The only substitute for cubic inches is cubic dollars, how fast can you afford to go?

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    Supporting Member Turbo Mopar Contributor
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    Re: overboost, overboost not enabled

    After the "event" do you have any codes? Do you observe the event at partial throttle? or just WOT?
    Regards,
    Miles

    DD '87 Sundance T1, SLH with rear disks
    '87 CSX #432 2.5 CB TII, SLH

  3. #3
    Supporting Member II Turbo Mopar Contributor jeff1234's Avatar
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    Re: overboost, overboost not enabled

    Miles, only at full throttle at 5100 on the tach. Since I posted I am trying to isolate the proble primarily because I don't really know what is happening beyond hearing the backfire. I switched back to 33lb. Injectors and my "85" LM to see what would happen, same result. So its not the logic module. I have been suspecting the power module so I'm getting a different one. I will then test with that. If the problem is still there then????? Tommorow I'm going to put a vacuum on the waste gate solenoid to see if it not holding and im going to pressurize it to watch the stroke for jamming or leaking down under pressure. This has been going on for a long time and I have been trying to fix it with fuel and timing changes which have accomplished nothing.
    The only substitute for cubic inches is cubic dollars, how fast can you afford to go?

  4. #4
    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
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    Re: overboost, overboost not enabled

    What boost is this at? I highly doubt the issue is caused by the wastegate flowing too much.

  5. #5
    Super Moderator Turbo Mopar Staff contraption22's Avatar
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    Re: overboost, overboost not enabled

    I would get a scanner before changing out parts.
    Mike Marra
    1986 Plymouth Horizon GLMF "The Contraption" < entertaining sponsorship offers
    Project Log:
    http://www.turbo-mopar.com/forums/showthread.php?69708-The-Contraption-2013-14&highlight=

  6. #6
    Supporting Member II Turbo Mopar Contributor jeff1234's Avatar
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    Re: overboost, overboost not enabled

    10-13 psi. I dont have a scanner so changing out components will eliminate bad ones and possibly solve the problem. I dont think the wastegate is flowing to much, im trying to determine if there is a temporary interuption in the activation of the waste gate. In other words I wonder if as fuel and spark increase but boost hesitates could this cause the problem. The ecm is monitoring boost fuel and spark, if one of these isnt in sync with the others can this cause the problem.
    So I just tested the wastegate operation visually, it is normal.
    Last edited by jeff1234; 08-18-2020 at 09:50 AM.
    The only substitute for cubic inches is cubic dollars, how fast can you afford to go?

  7. #7
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    Re: overboost, overboost not enabled

    Quote Originally Posted by jeff1234 View Post
    Miles, only at full throttle at 5100 on the tach. Since I posted I am trying to isolate the proble primarily because I don't really know what is happening beyond hearing the backfire. I switched back to 33lb. Injectors and my "85" LM to see what would happen, same result. So its not the logic module. I have been suspecting the power module so I'm getting a different one. I will then test with that. If the problem is still there then????? Tommorow I'm going to put a vacuum on the waste gate solenoid to see if it not holding and im going to pressurize it to watch the stroke for jamming or leaking down under pressure. This has been going on for a long time and I have been trying to fix it with fuel and timing changes which have accomplished nothing.
    Since it is only at WOT at approx 5000, I can't see it being the PM but if you have one to try why not as they say. I am with Brian about the boost pressure. Could we have a rip in a vacuum line that the wrong pressure is feeding the MAP that is only opening up under higher boost. Ok what is your WB reading at the event? What happens if your are above 5100 at part throttle, say 5400 and then go WOT??
    How healthy is your fuel pump and filters?
    Regards,
    Miles

    DD '87 Sundance T1, SLH with rear disks
    '87 CSX #432 2.5 CB TII, SLH

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    Supporting Member II Turbo Mopar Contributor jeff1234's Avatar
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    Re: overboost, overboost not enabled

    A/F @ 11: 11:5 to one. Lines are in top condition. I was recording rpms for a chart for Morris. At steady stare throttle I had one very brief pop at 5500 (approx) but it had never done that before. What happened in the past is at times it will rev past 5100 after the event but not always. I have had accelerations through 5100 where it didn't happen at all but this is very rare. To expand a bit more it has done this regardless of plug brand or gap and there is a new hall effect unit in the dist. New charge air sensor, new water box sensor and i changed out the tops. There is also a new O2 sensor.
    The only substitute for cubic inches is cubic dollars, how fast can you afford to go?

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    Re: overboost, overboost not enabled

    Does a 100% stock tune act the same???? So the WB does not notice the event?? I would have thought it would go lean as you did not mention about any black smoke during the event.
    Regards,
    Miles

    DD '87 Sundance T1, SLH with rear disks
    '87 CSX #432 2.5 CB TII, SLH

  10. #10
    Supporting Member II Turbo Mopar Contributor jeff1234's Avatar
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    Re: overboost, overboost not enabled

    Miles. Lol, I was watching the road ahead. Seriously, I went out right after last message and put star washers under a body to intake ground strap just in case. I then went out to test. Stock LM/33 lb injectors and i turned the boost control all the way down to the stop. The result was less violent back fires at 10 psi same rpm but a/f was 12.5:1. I think this is because the1985 tune won't acklcomodate 10 psi???? With 3 bar map and my tune fuel is always at mid 11.5 to 1
    The only substitute for cubic inches is cubic dollars, how fast can you afford to go?

  11. #11
    Supporting Member II Turbo Mopar Contributor jeff1234's Avatar
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    Re: overboost, overboost not enabled

    Miles. Right after this last post I changed my power module to one that didn't work with my mptune chip. It worked with the stock LM. I made four full throttle runs. #1 went right through 5100 rpm no backfire to 5700 rpm. #2 backfire at 5100 rpm but accellerated firmly to 5700. #3 same result as #3. #4 same result as #'s 2 and three. The first run was about 170° the next three were at 198°.
    Jeff
    The only substitute for cubic inches is cubic dollars, how fast can you afford to go?

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    Supporting Member Turbo Mopar Contributor
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    Re: overboost, overboost not enabled

    First run was at 170??? Coolant temp?
    So the last 3 runs backfired
    Does it act up with a stock LM? Just want to be sure.
    Regards,
    Miles

    DD '87 Sundance T1, SLH with rear disks
    '87 CSX #432 2.5 CB TII, SLH

  13. #13
    Supporting Member II Turbo Mopar Contributor jeff1234's Avatar
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    Re: overboost, overboost not enabled

    Yes, it does. Yes, those are coolant Temps. Busy all day right from the start. Sorry I didn't see you post till this afternoon.
    The only substitute for cubic inches is cubic dollars, how fast can you afford to go?

  14. #14
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    Re: overboost, overboost not enabled

    Have you tested the fuel pump? Newish filter? What fuel you running?
    Regards,
    Miles

    DD '87 Sundance T1, SLH with rear disks
    '87 CSX #432 2.5 CB TII, SLH

  15. #15
    Supporting Member II Turbo Mopar Contributor jeff1234's Avatar
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    Re: overboost, overboost not enabled

    Brand new pump from Turbosunleashed that he is replacing Walbros with. Brand new stock filter from O'Reilly, likely the last one left in the system. I am Using 93 octane pump gas.
    The only substitute for cubic inches is cubic dollars, how fast can you afford to go?

  16. #16
    Supporting Member Turbo Mopar Contributor
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    Re: overboost, overboost not enabled

    Folks say that a faulty MAP and VSS can caused weird things to happen, if you have a spare kicking around.
    Spark or fuel as they say..
    Are you always logging data??? The LM gets a bit overwhelmed at RPM around 5000 or greater
    Regards,
    Miles

    DD '87 Sundance T1, SLH with rear disks
    '87 CSX #432 2.5 CB TII, SLH

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    Supporting Member II Turbo Mopar Contributor jeff1234's Avatar
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    Re: overboost, overboost not enabled

    This problem happens when logging data or not
    It happens with two bar or three bar maps. Im not familiar with the VSS term, what does that refer to? Vehicle speed sensor? I'm not logging any codes.
    Today I increased plug gap from .020 to .025. The only change it effected was it idled better. The other problem is still there.
    The only substitute for cubic inches is cubic dollars, how fast can you afford to go?

  18. #18
    Supporting Member Turbo Mopar Contributor
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    Re: overboost, overboost not enabled

    VSS =Vehicle speed sensor
    I am now officially out of ideas.
    Regards,
    Miles

    DD '87 Sundance T1, SLH with rear disks
    '87 CSX #432 2.5 CB TII, SLH

  19. #19
    Supporting Member II Turbo Mopar Contributor jeff1234's Avatar
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    Re: overboost, overboost not enabled

    Thanks for trying to help me with this problem, I appreciate it.
    The only substitute for cubic inches is cubic dollars, how fast can you afford to go?

  20. #20
    Supporting Member II Turbo Mopar Contributor jeff1234's Avatar
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    Re: overboost, overboost not enabled

    Miles, who can explain the weirdness of these cars. On a number of occasions I have checked for codes on my 87 TII LM and found none. As long as I had the 85 stock T1 LM in the car I thought, why not check for codes. There were none on my OTC 4000 E but I couldn't get into any of the data streams either, just the check codes screen. So for the heck of it I changed the OTC back to 87 TII and looked for codes on the 85 LM. To my surprise I got two. 15 and 34. 15 is the VSS. I took a gamble and bought a new one this morning and O'Reilly had it to me by two o'clock and I had it in by 3:30 pm. I just finished testing it. The idle improved, operation between the gears had smoother throttle transitions and while the idle would return to normal most times in the past sometimes it idled 1700 rpm's and I would have to shut off the engine to get the idle back to normal. It is now returning to normal idle every time at this point but we will see if it holds. I did four each of third gear full throttle events. First one was good, no surprise there, second one backfired, third one did not backfire and the fourth one did not backfire. I'm not claiming a win just yet but things are looking up.
    jeff
    The only substitute for cubic inches is cubic dollars, how fast can you afford to go?

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