Running issues - exasperated - advice much needed ! | FerrariChat

Running issues - exasperated - advice much needed !

Discussion in '348/355' started by Gottaloveit, Oct 2, 2017.

This site may earn a commission from merchant affiliate links, including eBay, Amazon, Skimlinks, and others.

  1. Gottaloveit

    Gottaloveit Karting

    Jul 12, 2012
    52
    Hey folks - am wondering if anyone else has had the problem I've got so am appealing to you guys for a "steer" on where to go with a really, REALLY irritating running problem which affects my 355. I've had the car 4 years and every time I think I've got it beaten - its back !

    I have a very early (94) 2.7 motronic with test pipes, standard headers, and high flow air filters - the exhaust valve was wired open in circa 2000 looking at the history, and the car has 56000 on the clock. I haven't thrown parts at the car just for the sake of it, but I have changed a few wear and tear bits - plugs, both lambda sensors, thermostat, fuel filters, carbon canister, and temperature sensors.

    She starts first time every time - hot or cold - , idles strongly and evenly at 1k RPM, the engine pulls strongly and healthily right the way through the rev range and we ALL know the addictive joy this gives !.However ! - she has a really annoying habit of developing a "light" misfire at 2500 on a steady, light throttle. It only happens on longer runs, so if I'm cruising at 3000 rpm - car is fine and thrumming along beautifully. If I then have to come off the throttle to reduce speed etc (not changing down necessarily), its at this point that this misfire might crop up - and it doesn't do it all the time !.

    By light I mean the sort of misfire you can hear (burbly exhaust not unlike a machine gun burst I guess) - and you can feel (slight kick or jerk). One cylinder I'm thinking. This is accompanied by a bout of rich running. If you squeeze the throttle - misfire goes away straight away - normal service is resumed !. .

    Its driving me nuts and spoiling what is a really enjoyable and super car to drive, and a car I am very proud to own frankly.

    Anyone got any ideas ????.

    Best regards,

    Laurence
     
    Skippr1999 likes this.
  2. yelcab

    yelcab F1 World Champ
    Consultant

    Nov 29, 2001
    12,661
    San Carlos, CA
    Full Name:
    Mitchell Le
    Try putting some cats back, and un-wire the bypass valve. See if that problem goes away.
     
    taz355 likes this.
  3. INTMD8

    INTMD8 F1 Veteran
    Owner

    Jun 10, 2007
    6,488
    Lake Villa IL
    Misfire is usually ignition but if it runs good at wide open throttle I find that to be an unlikely cause.

    Based on what you are describing, I would check throttle position/throttle balance between banks. With separate ECU's is it possible at light throttle for one bank to be reading zero throttle and going into deceleration fuel cutoff?

    Not sure, just an idea.
     
    taz355 likes this.
  4. zstyle

    zstyle Formula Junior

    Jun 28, 2007
    531
    Fountain Hills
    Full Name:
    Jon
    You may want to pull injectors and test them for equal spray patterns and quantity of fuel. I've seen this cause problems on 348/355.

    Above suggestions are also viable to cause problems.
     
  5. taz355

    taz355 F1 Veteran
    Owner Silver Subscribed

    Feb 18, 2008
    5,942
    Indio Ca/ Alberta
    Full Name:
    Grant
    It is very difficult for me to give advice when the basic system is not being used. I agree totally with mitchell that the bypass should be left to operate the way it is designed. I feel leaving it wide open will cause issues like you are describing.
     
  6. taz355

    taz355 F1 Veteran
    Owner Silver Subscribed

    Feb 18, 2008
    5,942
    Indio Ca/ Alberta
    Full Name:
    Grant
    You are likely getting more power on the top end. Likely not enough to notice but it is causing problems in the midrange on steady throttle.
    Good setup for the track but likely not the best on the street. For me these ferrari engines remind me a lot of my old superbike days and it is allways a trade off. My experience showed me that a bike setup for the track did not like anything below half of redline.

    Small high reving engines, when I was tuning, did not like no back pressure on the intakes at lower rpms and especially steady throttle. Sometimes you would even feel them surge.
    This is what I love about the bypass because it does both, free flowing when wide open and some back pressure when steady lower rpm, old yamaha OWO1 had a bypass for this exact reason, more midrange without hurting the top end.
     
    Qavion likes this.
  7. Gottaloveit

    Gottaloveit Karting

    Jul 12, 2012
    52
    Thanks to all Gents - opened my eyes to a couple of new paths of enquiry !. Your knowledge is much appreciated.

    Bests

    Laurence
     
  8. FCOnyx

    FCOnyx Formula Junior
    Owner Silver Subscribed

    May 28, 2012
    413
    Round Rock, TX
    Full Name:
    Jeff
    I might be way off... but does this stumble happen at a certain RPM no matter what gear you are in or does it happen at roughly the same throttle location? I ask because my car recently developed a "dead spot" around 1/3 of the throttle range. As I pressed the accelerator, at a certain point the engine power would stumble and drop out completely. As I continued pushing the throttle deeper the power came on again. It was as if there was a zone where the throttle simply wasn't being acknowledged by the car. My first guess was correct... Throttle Position Sensor. An easy, cheap fix (around $200). Once the new one was in we checked it via the SDX and sure enough, that was the problem. You might want to see if your TPS is dying like mine did.
     
    Qavion likes this.
  9. taz355

    taz355 F1 Veteran
    Owner Silver Subscribed

    Feb 18, 2008
    5,942
    Indio Ca/ Alberta
    Full Name:
    Grant
    Someone smarter than me can comment but i dont think on the obd2 cars the throttle possition sensor has much to do with ignition below about 5000 rpm. My inderstanding was when the car is in closed loop it did not do much.
    Mostly used only if other issues and computer is having problems sampling. Then goes open loop and used throttle possition as a backup and should throw a light.

    I am not possitive on this I just read it i think in the wsm
     
  10. Robbe

    Robbe Formula Junior

    Aug 22, 2013
    609
    The Netherlands
    Isn't that the rpm range in which the motronic chooses another set of data?
     
  11. taz355

    taz355 F1 Veteran
    Owner Silver Subscribed

    Feb 18, 2008
    5,942
    Indio Ca/ Alberta
    Full Name:
    Grant
    I just re read it.
    In normal mode the ecu only recognizes 2 positions
    Idle and
    Wide open.

    In emegency operation it is used only because a fault is sensed for the MAF.
     
  12. taz355

    taz355 F1 Veteran
    Owner Silver Subscribed

    Feb 18, 2008
    5,942
    Indio Ca/ Alberta
    Full Name:
    Grant
    I just read the section and on the 2.7 it uses 3 positions, idle, intermediate, and wide open.

    My 5.2 is different then.

    The OP has the 2.7 so it does read intermediate.
     
  13. FCOnyx

    FCOnyx Formula Junior
    Owner Silver Subscribed

    May 28, 2012
    413
    Round Rock, TX
    Full Name:
    Jeff
    Mine wasn't an issue with the ECU interpreting data from the TPS, it was a problem with the potentiometer in the TPS itself going bad.

    It suddenly developed a "dead zone" in the middle of the sweep. Maybe dirty/corroded contacts on the track inside. We had it on the SDX and you could see values climb as I pressed the throttle (from 0 to around 28) then it dropped to null... then as I pressed farther it suddenly started reading above 50 and continued to climb to around 100 normally.
    So there was a "dead zone" in the pot where it wasn't sending a value at all. It made the car think I had very suddenly stepped off the throttle mid-way, then had just as suddenly slammed it on again a bit farther up the pedal sweep. It led to some very sketchy driving when pulling away from a light with people behind me as suddenly as I was accelerating to around 20-30mph I would slow massively (without any brake lights to warn people behind). Swapping the TPS resolved the issue immediately, so it was definitely a hardware failure on the part of the TPS pot.
     
  14. taz355

    taz355 F1 Veteran
    Owner Silver Subscribed

    Feb 18, 2008
    5,942
    Indio Ca/ Alberta
    Full Name:
    Grant
    Interesting and this was on your 5.2
     
  15. FCOnyx

    FCOnyx Formula Junior
    Owner Silver Subscribed

    May 28, 2012
    413
    Round Rock, TX
    Full Name:
    Jeff
    Yes. '98 5.2. Happened just about 6 months ago. Been running fine ever since.
     
  16. thibaut

    thibaut Formula Junior

    Feb 28, 2004
    528
    London, UK
    Full Name:
    Thibaut A.
    one thing you may want to try is to unplug the motronic computers n each side, clean the contact pins with a toothbrush and copious amount of WD40 or equivalent and plug it back all in.
    I had a sort f hesitation like that and it went away after this clean up.
     
  17. fatbillybob

    fatbillybob Two Time F1 World Champ
    Consultant Owner

    Aug 10, 2002
    26,292
    socal
    When chasing ghosts....what about connectors?
     
  18. ernie

    ernie Two Time F1 World Champ
    Lifetime Rossa Owner

    Nov 19, 2001
    22,574
    The Brickyard
    Full Name:
    The Bad Guy
    With the car being over 20 years old, and a 2.7 Motronic, you may want to start with a fresh set of eproms in the ECUs.
     
  19. johnk...

    johnk... F1 World Champ
    Owner

    Jun 11, 2004
    10,629
    CT
    Full Name:
    John Kreskovsky
    Oh no. I'm going to agree with FBB, sort of. :)Yes, you are chasing ghosts. But my suggestion is ignore it. At light throttle a lot of things can effect how each cylinder is charged. Even if everything is perfectly adjusted. With a 2.7 you basically have two separate 4 cylinders. You can never get them perfectly balanced and any almost insignificant imbalance can cause what you are experiencing. Not to mention that at light throttle it will be running pretty lean. It's not unusual for there to be a little burble. Mt 355 does it. My 308 does it. I've never given it a second thought. Crack the throttle and it screams.

    Or you can replace the O2 sensors, plugs, plug wire, coils, ignition module, cam position sensors, crank sensors, MAFs, TP sensors, wiring harnesses, ECUs, drop engine and check cam timing, have the throttles balanced, check compression and ,leak down, .......
     

Share This Page