Results 1 to 9 of 9

Thread: Fouled plugs and misfiring

  1. #1
    New Member Not Verified Feedback Score 0 VR4Play's Avatar
    Join Date
    Sep 2010
    Owner Since
    1996

    Location
    Philly area
    Posts
    19
    Thanks
    1
    Thanked 0 Times in 0 Posts

    Fouled plugs and misfiring -- EDIT

    Hi All,

    I have a dilemma related to the state of my '97 VR4 engine that "seems" to defy logic. The engine has 150K miles with no issues other than jumped timing once.

    I've recently did performance upgrades that may very well surfaced a problem I've had for a long time of which I wasn't fully aware. By attempting high teens boost the issue became apparent. The car is at a local shop with a 4wheel dyno that specializes in WRX's, STI's and the like. They are well known in the area and always have a full lot of cars up for builds or tuning.
    First, the symptom:
    The engine is fouling all the plugs with just a few miles of driving. Pulling them out they look like they were spray painted black. At atmosphere while the plugs will foul the engine runs fine but will misfire at high revs under load. The engine idles fine with no hint of roughness, no valvetrain noise. Boost is out of the question as the misfire becomes a big issue.
    The parts upgrade & maintenance parts:
    • Injector Dynamics ID1050X Injectors 11mm (Blue)
    • Adaptor Tops Denso Lower Cushions (Set of 6)
    • BKR7E NGK Spark Plug
    • AEM 91-97 3000GT / 92-97 Stealth R/T Turbo Series 2 EMS
    • Delete MAF
    • Mitsubishi 3000gt coil packs
    • Plug wires
    • Install EBCS - HKS boost controller is routed to turbos.
    • Turbosmart BOV Plumb Back Uni 38mm-Black
    • Gates Racing timing belt
    • Inspected and cleaned throttle body and IAC
    • Smoke tested - leaks eliminated

    Examined for possible cause of the symptom:

    • Replaced plugs multiple times
    • Eliminated EGR
    • Compression test - OK
    • Leak down on front cylinders - OK (within 5% of each other)
    • Multiple maps tried including back to stock AEM map
    • Replaced coil packs
    • Checked fuel pressure - OK
    • Checked F:A ratio with 3 different gauges - all agree

    They see nothing usual on the AEM side. All parameters align with what should be a proper tune.

    I would really like one of the experts here to give some guidance about what to check/look at. If they have experienced this exact problem. Any suggestion is very welcomed!

    Thanks in advance ............ Dennis

    EDIT: Sorry for the delay getting this for you guys. Spending most time on my '70 Firebird RestoMod project. Attached is the AEM-EMS data file some of you requested. The only way I could attach it was to change the extension to'PDF'. After downloading, please change the extension back to 'CAL'. Hope this helps.

    EDIT #2: here are additional comments
    Yes both temp sensors are working and reading correctly on the aem. i thought we already tried a different ecu as well but i will check my notes and or try another just to rule out.


    Yes every cylinder [is involved]. It doesn’t want to tip in. Just hesitated then revs up. Unless we put a lot of fuel in it, but then it will just foul plugs.

    Hopefully, ths gives you more info to chew on.
    Attached Files Attached Files
    Last edited by VR4Play; 03-25-2021 at 06:14 AM. Reason: Further Comments From Tuner

  2. #2
    The one. The only. verified Feedback Score 14 (100%) stealthee's Avatar
    Join Date
    Sep 2010
    Owner Since
    August 28, 2002

    Location
    SWPA
    Posts
    4,086
    Thanks
    182
    Thanked 700 Times in 530 Posts
    A bad coolant temp sensor will cause fuel to dump.

    [06-05, 19:29] OhioSpyderman: Brian, finding a woman is NOT the answer, you need to shop for a good VACUUM

  3. #3
    Forum User Feedback Score 0 box's Avatar
    Join Date
    Jan 2011
    Owner Since

    Posts
    206
    Thanks
    3
    Thanked 31 Times in 22 Posts
    If the parameters and the tune are actually OK, I'd be trying another AEM ECU.

    Upload a datalog while it's playing up. Does the AEM have an internal or external MAP sensor? I've had GM style MAP sensors play up before, you wouldn't know it's faulty going off the computer screen.

    It hasn't got a blocked cat or something has it? I can't see anything about an upgraded exhaust so assume it's standard.
    Last edited by box; 01-23-2021 at 04:39 PM.

  4. #4
    I don't bite Feedback Score 0 familyMAN's Avatar
    Join Date
    Sep 2010
    Owner Since
    2001

    Location
    Southern IN
    Posts
    2,047
    Thanks
    59
    Thanked 100 Times in 82 Posts
    post a datalog file of start up, cruise and boost. As well as your calibration file.
    1992 Kilder Green VR4 - First 4G swap in a 3S. 2.0, auto, awd. 9.65 at 143mph. Now LS swapped. 8.52 at 162.

  5. The Following User Says Thank You to familyMAN For This Useful Post:


  6. #5
    New Member Not Verified Feedback Score 0 VR4Play's Avatar
    Join Date
    Sep 2010
    Owner Since
    1996

    Location
    Philly area
    Posts
    19
    Thanks
    1
    Thanked 0 Times in 0 Posts
    Quote Originally Posted by familyMAN View Post
    post a datalog file of start up, cruise and boost. As well as your calibration file.
    Thanks for the suggestion. They said they would be happy to send along. Get back to all of you with it.

  7. #6
    New Member Not Verified Feedback Score 0 VR4Play's Avatar
    Join Date
    Sep 2010
    Owner Since
    1996

    Location
    Philly area
    Posts
    19
    Thanks
    1
    Thanked 0 Times in 0 Posts
    Quote Originally Posted by box View Post
    If the parameters and the tune are actually OK, I'd be trying another AEM ECU.

    Upload a datalog while it's playing up. Does the AEM have an internal or external MAP sensor? I've had GM style MAP sensors play up before, you wouldn't know it's faulty going off the computer screen.

    It hasn't got a blocked cat or something has it? I can't see anything about an upgraded exhaust so assume it's standard.
    Will definitely pass this along. The sensor issue I hadn’t thought of. Regarding the exhaust: some years ago I put on a Tanabe Medalion cat back with a 3SX downpipe and high flow cat.

  8. #7
    New Member Not Verified Feedback Score 0 VR4Play's Avatar
    Join Date
    Sep 2010
    Owner Since
    1996

    Location
    Philly area
    Posts
    19
    Thanks
    1
    Thanked 0 Times in 0 Posts
    Quote Originally Posted by stealthee View Post
    A bad coolant temp sensor will cause fuel to dump.
    I had no idea. With the bad coolant sensor, besides the fuel dump, what would happen with the coolant? I assume overheating?

  9. #8
    New Member Not Verified Feedback Score 0 VR4Play's Avatar
    Join Date
    Sep 2010
    Owner Since
    1996

    Location
    Philly area
    Posts
    19
    Thanks
    1
    Thanked 0 Times in 0 Posts

    Addendum to Original Post

    In the original post I forgot to list upgrades I did ~10 years ago. After those upgrades and a great tune by Ray the car performed completely differently. Came off the dyno at 410AWHP with same torque (~408). Not a monster by any means, but respectable for an old fart like me. Upgrades ~10yrs ago:

    3Sxecutioner gen 1 turbos
    550 injectors
    Larger SMIC
    Dejon hard piping
    Supra pump (not hot wired)
    Tanabe Medalion cat back
    3SX downpipe with high flow cat

    The reason for the upgrades this time was I had begun to get stumbling when in boost under load. Thought that its been 10 years since the last tune, even though I put on only ~15K miles on it, so it was past time to look into everything. And if there was any significant tech improvements I would make those changes. Hence, the new injectors and the AEM II.

    That's it for all the engine upgrades past and present. I realize not all I listed may have contributed to this problem. Listed only for the sake of completeness.

    Dennis

  10. #9
    Forum User Feedback Score 11 (100%)
    Join Date
    Sep 2010
    Owner Since

    Posts
    787
    Thanks
    0
    Thanked 156 Times in 107 Posts
    Quote Originally Posted by VR4Play View Post
    I had no idea. With the bad coolant sensor, besides the fuel dump, what would happen with the coolant? I assume overheating?
    I've had a bad coolant sensor before, the sensor will sometimes report a very low coolant temperature causing the engine ECU to respond with excess amount of fuel.

  11. The Following User Says Thank You to BlackStealth For This Useful Post:


Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
The 3000GT/Stealth/GTO Web History Project
3000gt.com
3000GT / Stealth International WWWboard Archive
Jim's (RED3KGT) Reststop
3000GT/Stealth/GTO Information and Resources
Team 3S
3000GT / Stealth / GTO Information
daveblack.net
3000GT/Stealth/GTO Clubs and Groups
Michigan 3S
MInnesota 3S
Wisconsin 3S
Iowa, Nebraska, Kansas 3S
North California 3000GT/Stealth
United Society of 3S Owners
3000GT/Stealth/GTO Forums
3000GT/Stealth International
3000GT/Stealth/GTO Event Pages
3S National Gathering
East Coast Gathering
Upper Mid-West Gathering
Blue Ridge Gathering