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Thread: Running rough

  1. #1
    Senior Member captdigi's Avatar
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    Default Running rough

    I need a little advice…
    I brought my car out for an event yesterday and had a real hard time starting it in the cold morning. My dash also said, “Battery Low Voltage”. The car battery was off, and the external starter battery is brand new (800 CCA). The car eventually started, and ran well, warming up to 180 h2o temp before I shut it off. When I tried to start the car again, it wouldn’t start. Even after obtaining another starter battery. About and hour later, I started the car with the car’s battery, drove out to the grid where the car was idling fine, but then started running very rough, and would only run if I heald the accelerator down. Back to the paddock… I pulled the plugs and noticed that they were pretty wet. I cleaned them, and the car started with the car’s battery, and idled fine. I shut it off, then tried to start it again a few minutes later, and it was in that rough running mode again, and would stop unless the accelerator was heald open.
    I’m new to the rotary motor so any suggestions will be welcomed.
    Thanks Much!!!
    Last edited by captdigi; 02.04.24 at 10:14 AM.

  2. #2
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    Quote Originally Posted by captdigi View Post
    I need a little advice…
    I brought my car out for an event yesterday and had a real hard time starting it in the cold morning. My dash also said, “Battery Low Voltage”. The car battery was off, and the external starter battery is brand new (800 CCA). The car eventually started, and ran well, warming up to 180 h2o temp before I shut it off. When I tried to start the car again, it wouldn’t start. Even after obtaining another starter battery. About and hour later, I started the car with the car’s battery, drove out to the grid where the car was idling fine, but then started running very rough, and would only run if I heald the accelerator down. Back to the paddock… I pulled the plugs and noticed that they were pretty wet. I cleaned them, and the car started with the car’s battery, and idled fine. I shut it off, then tried to start it again a few minutes later, and it was in that rough running mode again, and would stop unless the accelerator was heald open.
    I’m new to the rotary motor so any suggestions will be welcomed.
    Thanks Much!!!
    Don't know ANYTHING about rotaries, but just throwing out some ideas... What was the temperature and humidity?? If it were CARBURETED, I'd say carb icing.. maybe something similar for FI's? Did you take it out on track.. and did it clear up after the engine was completely warm? Also - not sure how the plugs are fired. Probably direct fire, but if you have a dist cap it could get moisture in it from condensation.
    Steve, FV80
    Steve, FV80
    Racing since '73 - FV since '77

  3. #3
    Contributing Member Lotus7's Avatar
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    Any chance you have the leading and trailing plug leads crossed?
    Ian Macpherson
    Savannah, GA
    Race prep, support, and engineering.

  4. #4
    Senior Member David Ferguson's Avatar
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    Default

    I would start with the troubleshooting process (about page 31) found in the Renesis Turtorial 2012 found on this page:

    https://starracecars.com/resources/
    David Ferguson
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    Possibly a bad ground for the hard start or just the low voltage.
    Oil temp too low can send the engine into limp mode

  6. #6
    Contributing Member TimH's Avatar
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    Street 12A and 13B motors flood VERY easily, cold shutdown being the most common cause (the ECU apparently gets confused on the 13B) Once flooded, you lose function of the apex seals so the fuel just sits there in the bottom of the chamber and can't get swept out as it would in a pisston motor. Sometimes the only solution is to pull the plugs and squirt some ATF in the holes to retore the seals. Then fresh plugs, start, and scare the neighbors with the amount of smoke.

    I don't know that PFM motors are any better in that respect.
    Caldwell D9B - Sold
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    As was said, these engines can foul plugs pretty easily. My FM (carbureted) was terrible until I leaned out the idle mixture and ran some hotter (lower heat range) spark plugs. The engine also had several race seasons and was just getting worn out. My PFM (fuel injected) is much better and I've learned it's 'quirks' and doesn't give me many problems. I say all this because I've also found that if I do test runs on colder spark plugs (NGK 10 heat range or higher), the PFM will run rough. The plugs just don't get hot enough to self clean unless I'm out driving it hard around the track. For me, heat range 9s seem to be a good balance between not fouling and being able to handle hard driving. My PFM even had the Mazda stock combination of 7s and 9s for a while, but the 7s couldn't handle the heat.

  8. #8
    Senior Member captdigi's Avatar
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    Good morning
    Would you happen to have a part number for the 9s plugs?
    Thanks!

    Quote Originally Posted by CSasfai View Post
    As was said, these engines can foul plugs pretty easily. My FM (carbureted) was terrible until I leaned out the idle mixture and ran some hotter (lower heat range) spark plugs. The engine also had several race seasons and was just getting worn out. My PFM (fuel injected) is much better and I've learned it's 'quirks' and doesn't give me many problems. I say all this because I've also found that if I do test runs on colder spark plugs (NGK 10 heat range or higher), the PFM will run rough. The plugs just don't get hot enough to self clean unless I'm out driving it hard around the track. For me, heat range 9s seem to be a good balance between not fouling and being able to handle hard driving. My PFM even had the Mazda stock combination of 7s and 9s for a while, but the 7s couldn't handle the heat.

  9. #9
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    I use either BUR9EQ or BUR9EQP. The only difference is that the Ps are platinum. I believe - but am not certain - the NGK stock numbers are 5777 and 5255.

  10. #10
    Senior Member captdigi's Avatar
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    Great! Thank you!!

    QUOTE=CSasfai;661591]I use either BUR9EQ or BUR9EQP. The only difference is that the Ps are platinum. I believe - but am not certain - the NGK stock numbers are 5777 and 5255.[/QUOTE]

  11. #11
    Senior Member captdigi's Avatar
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    Have you had any negative issues with the hotter #9 plugs? Engine wear, seal damage, etc.?


    Quote Originally Posted by CSasfai View Post
    As was said, these engines can foul plugs pretty easily. My FM (carbureted) was terrible until I leaned out the idle mixture and ran some hotter (lower heat range) spark plugs. The engine also had several race seasons and was just getting worn out. My PFM (fuel injected) is much better and I've learned it's 'quirks' and doesn't give me many problems. I say all this because I've also found that if I do test runs on colder spark plugs (NGK 10 heat range or higher), the PFM will run rough. The plugs just don't get hot enough to self clean unless I'm out driving it hard around the track. For me, heat range 9s seem to be a good balance between not fouling and being able to handle hard driving. My PFM even had the Mazda stock combination of 7s and 9s for a while, but the 7s couldn't handle the heat.

  12. #12
    Senior Member captdigi's Avatar
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    Finally got the car running after a change out of spark plugs, although will ONLY start on the car’s lithium battery. This after I hooked up a brand new, fully charged, big 800CCA mega battery. When plugged in, the dash says ”Battery voltage low”. Volt meter shows full charge when tested. When the car runs, it sounds like it’s “missing”during idle, although seems to rev ok.
    On the Motec data when running, I’m getting a Lab1 reading that flashes between “Warmup C-1”, and “Error C-5”, Also a “ Error sync Runt Error”. Also a “Low Bat Error” which I assume is from using the car battery for starting.
    Any suggestions???
    Last edited by captdigi; 02.18.24 at 6:13 PM.

  13. #13
    Senior Member David Ferguson's Avatar
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    If monitoring the MoTeC ECU with the ECU Manager, be sure to reset the errors after starting. There can be transient errors like low voltage and runt-signals while cranking. Any errors that come back are real and should be investigated.

    The Lambda warmup can take a few minutes, especially (if just idling), if it's not online after running at 2000+ RPM for 60 seconds, I would either check the wiring, or replace the sensor.
    David Ferguson
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