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Thread: Stalling and misfire

  1. #1
    Mitsu booster
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    Stalling and misfire

    I've been having several issues with my 88 Lebaron that I picked up in June. I've had a few 2.5L NA cars in my life and wanted another Lebaron since I sold my 87 about 13 years ago. I've spent countless hours on the forums reading. I apologize for the long post but will try to cover everything in detail...

    Mods include: 2.5L CB, forged pistons .020 over, balance shafts removed, 3 bar map, 52mm tb, ported 2 piece intake, TU header with big turbo, 3" swing valve and exhaust, cat, FMIC, 'Chipped SMEC using a Rob cal from D-CAL' and currently a stock swirl head with PT lifters and a recent valve lap. The trans is a 568 in a 523 case with a 4 puck ceramic clutch. Walbro 255 with AFPR, TU rail and +40's (currently stock T2 injectors).

    The (current) problem is: Usually stalls immediately after start unless I keep blipping the throttle for about 30-60 seconds when the idle evens out. It will then idle with constant misfires and exhaust popping. Vacuum is 16-18Hg and will creep down to 10Hg when it's stumbling bad. When the idle is rough and the vacuum is low the open throttle body (intake pipe disconnected) sounds like a noisy vacuum cleaner. The 3-bar MAP signal reads OK. The wideband is pegged at 16 (lowest it goes).

    If I unplug the MAP before starting it will start fine and idle and rev perfectly. If I unplug it while idling the idle smooths right out. The throttle body is quiet with the MAP unplugged. The vacuum is 18Hg. The wideband reads in the 12-14 range at idle. I've bypassed the baro with no change. I've reduced the vac system to the AFPR, MAP and Auto Meter gauge. I'm confident there are no vacuum leaks. With the MAP unplugged it idles smoother than ever.

    I've verified cam timing several times and ignition timing is set to 12*. I can play with the cam timing about 5* or so either way with the adjustable cam gear without much difference at idle. If I go much beyond that it won't stay running or start at all. 12* on ignition is the sweet spot. With a timing light on the flywheel and the coolant sensor unplugged the timing stays pretty well on 12* with an occasional blip to 16* or so.

    I've swapped the whole throttle body with TBS and AIS. I read that the TPS shares a ground with the MAP but haven't verified this. I've swapped +40 injectors out for stock T2 injectors and reset FP to 55psi. Fuel pressure is good and holds for an hour+ after shutdown. I did have issues running pig rich with the +40s until I reduced the pressure down to <30psi which concerned me.

    There is no change with the o2 sensor, air charge temp sensor or AIS disconnected. I do have a new o2 and coolant temp sensor on the bench.

    I have had other problems leading up to this which shared some of the same symptoms but I have been working through them. The engine always ran strong out of idle and had lots of power right up to the MBC setting at 12psi.

    Another issue I've had leading was bucking while cruising in gear. This may have been resolved with the new injector harness but I haven't had it out of the garage since to verify. It also had an idle surge which seems to be gone except occasionally when I disconnect the CTS.

    Any insight or suggestions would be greatly appreciated. I'm hoping to get this running right before it goes away for winter.

  2. #2
    Supporting Member Turbo Mopar Contributor
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    Re: Stalling and misfire

    You certainly been busy. I have a few questions
    1)So the AFR is 16 when everything is connected? Lowest it goes? a possible typo?
    2) Any codes?
    3)Check all grounds?
    4) was this combination running great for you at some point?
    5)I assume you adjusted the base idle with the CTS disconnected
    Regards,
    Miles

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

  3. #3
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    Re: Stalling and misfire

    Quote Originally Posted by chromguy View Post
    You certainly been busy. I have a few questions
    1)So the AFR is 16 when everything is connected? Lowest it goes? a possible typo?
    2) Any codes?
    3)Check all grounds?
    4) was this combination running great for you at some point?
    5)I assume you adjusted the base idle with the CTS disconnected
    1) Yes, the the range of the NGK AFX is 9.00-16.00. I will say that from what I've read it is well overdue for a calibration but seems to make sense when cruising and reacts appropriately when I adjust the AFPR. I'll calibrate it next time I have the car in the air.
    2) No codes unless something is unplugged EXCEPT the o2 which doesn't throw a code when it's disconnected...
    3) Grounds are good and I've added some.
    4) It has never idled great, at least not to my standards. I do realize that with the balance shafts removed and the mods it may not be a smooth idler but it idles beautifully with the MAP unplugged.
    5) I have adjusted the base idle several times with the CTS unplugged.

  4. #4
    turbo addict
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    Re: Stalling and misfire

    What spark plugs were used? Gap?

  5. #5
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    Re: Stalling and misfire

    Quote Originally Posted by tryingbe View Post
    What spark plugs were used? Gap?
    I've tried both RN12YC and RN9YC with stock gap of 0.035 IIRC. When I changed them they were dry black sooty but when it was drivable they looked good. Plugs and wires are new, cap and rotor are good, no play in the distributor and I've tried swapping the HEP and coil.

  6. #6
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    Re: Stalling and misfire

    Sounds like you have a similar build to my lancer. My fuel pressure at idle is 28psi. I know you said you confirmed your timing, but I would check it again and then again, it's amazing what can happen with a modified car with a tooth off. When your block and head were done how much did they shave off? what thickness head gasket are you using? stock cam? To me it sounds like map sensor. what brand are you using? have you verified voltage?

  7. #7
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    Re: Stalling and misfire

    Quote Originally Posted by turboshelbys View Post
    Sounds like you have a similar build to my lancer. My fuel pressure at idle is 28psi. I know you said you confirmed your timing, but I would check it again and then again, it's amazing what can happen with a modified car with a tooth off. When your block and head were done how much did they shave off? what thickness head gasket are you using? stock cam? To me it sounds like map sensor. what brand are you using? have you verified voltage?
    I've checked timing several times but it's not impossible that it skipped a tooth. I figured that swinging the adjustable cam gear 12* in either direction might indicate this (one tooth is 14* or so IIRC).

    I don't know the history of the head but it was straight. It's possible it was milled before. Same goes for the block. I'm using a Felpro gasket, stock cam and a genuine GM MAP. The voltage looks good between 18Hg and 0Hg according to a chart that I can't find at the moment.

    Compression is 140 across all four cylinders. I don't have access to a leakdown tester.

    When I bought the car it had a ported big valve G head but had dropped a valve seat. The cal was originally set up for a ported swirl head with +1mm valves. I'm told that it ran great prior to the dropped seat but I don't have experience with it to compare.

  8. #8
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    Re: Stalling and misfire

    Where did you get the genuine 3 bar map at and what is voltage with just key on car not running

  9. #9
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    Re: Stalling and misfire

    Quote Originally Posted by turboshelbys View Post
    Where did you get the genuine 3 bar map at and what is voltage with just key on car not running
    It was already installed and I was told it was a genuine GM part. Looking at it, it doesn't actually say Delco or Delphi but does have the 12223861 part number. Key on voltage is 1.58V. Can you tell me how this compares to yours?

    Can someone shed some light on what the SMEC does when the MAP is unplugged?

  10. #10
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    Re: Stalling and misfire

    Another thing I'll mention is that the throttle is extremely touchy which has made learning to drive standard... interesting. Revs jump from idle to 1800rpm with the slightest touch. When the MAP is unplugged the throttle response is nice an smooth. I thought this may be due to the 52mm tb on a stock head but I'm questioning that now.

  11. #11
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    Re: Stalling and misfire

    Quote Originally Posted by RyGuy View Post
    It was already installed and I was told it was a genuine GM part. Looking at it, it doesn't actually say Delco or Delphi but does have the 12223861 part number. Key on voltage is 1.58V. Can you tell me how this compares to yours?

    Can someone shed some light on what the SMEC does when the MAP is unplugged?
    Okay your voltage seems good at the map can you post up a picture of your distributor location I'd like to see how far retarded or Advanced it is

    Sent from my SM-S903VL using Tapatalk

  12. #12
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    Re: Stalling and misfire

    Quote Originally Posted by turboshelbys View Post
    Okay your voltage seems good at the map can you post up a picture of your distributor location I'd like to see how far retarded or Advanced it is

    Sent from my SM-S903VL using Tapatalk
    Also when you are checking the timing, are you rotating the motor to TDC with the flywheel Mark at zero, pulling the entire distributor out and making sure that it is horizontal to the block, and then checking your cam timing that matches with the cam caps?

    Sent from my SM-S903VL using Tapatalk

  13. #13
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    Re: Stalling and misfire

    Quote Originally Posted by turboshelbys View Post
    Also when you are checking the timing, are you rotating the motor to TDC with the flywheel Mark at zero, pulling the entire distributor out and making sure that it is horizontal to the block, and then checking your cam timing that matches with the cam caps?

    Sent from my SM-S903VL using Tapatalk

    "Sorry, you don't have permission to upload photos." but it's not far off from parallel to the block. I followed the Donovan's timing procedure which is how you describe. I've verified it with a timing light, both ignition and cam timing (with ignition at 0).

  14. #14
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    Re: Stalling and misfire

    Quote Originally Posted by RyGuy View Post
    "Sorry, you don't have permission to upload photos." but it's not far off from parallel to the block. I followed the Donovan's timing procedure which is how you describe. I've verified it with a timing light, both ignition and cam timing (with ignition at 0).
    Check your private message

    Sent from my SM-S903VL using Tapatalk

  15. #15
    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
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    Re: Stalling and misfire

    Who burned the chip? Do you have the capability to burn another cal?

  16. #16
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    Re: Stalling and misfire

    Quote Originally Posted by cordes View Post
    Who burned the chip? Do you have the capability to burn another cal?
    All I know of it is 'Chipped SMEC using a Rob cal from D-CAL' which was in the previous-previous owner's sale thread back in 2010 or 2011. I don't have a burner, unfortunately.

  17. #17
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    Re: Stalling and misfire

    With the key on and MAP sensor unplugged, at the pigtail I measure 5V reference, 60milliohms to ground, and 4.85V signal.

    I figured the signal should only have voltage when the MAP sensor is plugged in... Or am I missing something?

    Edit...
    I found a good explanation of this here:
    https://www.2carpros.com/questions/m...not-responding
    It sounds like this is normal.

  18. #18
    The moderately moderate moderator Turbo Mopar Staff
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    Re: Stalling and misfire

    Makes me wonder about the cal. Is it a 3 bar cal? Have you tried a regular turbo map to see if it runs better?
    Bryan
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    SDAC National Member, SDAC Buckeye Chapter Member

    A man has got to know his limitations.....

  19. #19
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    Re: Stalling and misfire

    Quote Originally Posted by black86glhs View Post
    Makes me wonder about the cal. Is it a 3 bar cal? Have you tried a regular turbo map to see if it runs better?
    It's definitely a 3 bar cal. The car has a history of running properly for the previous owners and the AFR are good out of idle.

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