F355 Head Scratcher | Page 2 | FerrariChat

F355 Head Scratcher

Discussion in '348/355' started by yelcab, Aug 6, 2020.

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  1. yelcab

    yelcab F1 World Champ
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    I don't think a bad fuel pump can cause one bank to go lean while causing the other bank to go rich.
    Same with a bad or dirt MAF.
    But, if I can rig up a fuel pressure gauge at the rails, it would be a good idea. My 95 used to have schreider valves at the end of he rails for checking pressure. I do not know why that was removed on the later cars.
     
  2. yelcab

    yelcab F1 World Champ
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    On a 355, disconnecting the 3 pin connector on the TCU would cause the output to go to 5V and cause the SDL to come on. Driving it for half an hour would cause it to shut the bank off. Is that not the case in your car?
     
  3. Ferrarium

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    Do you have 1 or 2 MAFs?
     
  4. F355Bob

    F355Bob Formula 3

    I had a 95 2.7. I disconnected both ECU and drove without them for 5 years. No problem on a 95. My car would randomly shut down a bank and car would just fall on its face. It had no acceleration especially under load. If I shut the car off and restarted, it ran perfectly until it happened again in 10 miles or500miles. Totally random. I always thought it was fuel pump or relays. It really is a stupid system put in because if you loose a plug on this wasted spark ignition, you loose two cylinders and you've got raw fuel igniting in the cats. I could not drive the car in the rain, because it would misfire. Never realized it was a bad cat ECU that was getting moisture in it when it rained or was really damp. Barely made it back home several times and down right dangerous when you are in highway traffic at 70mph and all of a sudden car won't accelerate and speed just drops off.
     
  5. Ferrarium

    Ferrarium F1 Veteran
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    All part of the 355 charm I suppose.
     
  6. yelcab

    yelcab F1 World Champ
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    5.2 F355 has only one MAF.
     
  7. Ferrarium

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    Ahh yep that different MAF would not affect banks differently then as you stated. Sort of feels like a combination of issues.
     
  8. Badabing!

    Badabing! Formula Junior

    Mar 30, 2014
    731
    NYC
    Just some random thoughts/guesses;

    I assume you verified that the CEL (bulb) works?

    Maybe the O2 sensors are faulty? Try replacing or swapping with known good ones from another car?

    Try removing cats and running with straight pipes for testing/comparison purposes?

    Visually inspect inside of cats?

    Measure exhaust temps on each bank ?




    Sent from my iPhone using FerrariChat
     
  9. yelcab

    yelcab F1 World Champ
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    Yes, CEL bulb is there. No CEL codes verified with a scanner.
    O2 sensor may be responsible for being too slow. I have some new ones but I have not tried it yet.
    Cats were removed, swapped with another set of Hyperflows. Same issues. Visually confirmed no melted or broken cats on both sets.
    Not yet measured exhaust temp of each bank.
     
  10. taz355

    taz355 F1 Veteran
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    Bruce had some problems with fuel pressure at the track and I would think he could tell you the symptoms of high or low but
    I think you all ready know these things and that’s why you suspected it.
    This is one of the reasons I will be setting up my car with 2 fpr with gauges.
     
  11. taz355

    taz355 F1 Veteran
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    Good luck and keep me posted.
    You have mentioned all the things I would be checking.
    Fuel tank being dirty may be an option but if you had the fuel pump out you saw how clean it probably was so that rules that out
     
  12. yelcab

    yelcab F1 World Champ
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    Correct. The fuel tank was clean as a whistle.
     
  13. johnk...

    johnk... F1 World Champ
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    Have you check the rubber tubes connecting the air inlet to the air boxes? If one is cracked that side could be getting much more air than what the MAF says and the other bank could be getting less. Thus one side rich the other side lean.
     
  14. yelcab

    yelcab F1 World Champ
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    So I am thinking through this scenario ... since I can overcome the hesitation by smashing the gas pedal and force the ECU into a enhanced mixture condition, it probably means the underlying hesitation is caused by running too lean on one bank due to some kind of fuel starvation. The header temps at the exhaust ports should indicate which side is lean. All I have to do is figure out why.
     
  15. Ferrarium

    Ferrarium F1 Veteran
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    I thought you mentioned 1 bank was lean and 1 bank was rich.
     
  16. yelcab

    yelcab F1 World Champ
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    Yes, and it's the lean bank that is probably hesitating ...
     
  17. Ferrarium

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    Since there is no code saying "the left bank dilythiym crystal is cracked" I'd send out the injectors for cleaning and replace the FPR's first up, cheaper and easier than buying and hooking up pressure testers etc it needs to be done anyhow and if they are not a problem now they will be.

    If it is fuel air, with 1 MAF its clearly not that, the components list is really small assuming the 02 and thermocouples are working correctly and there is no vacuum/air leak post MAF. The stuff is 25 years old, replace them all, refurbish the car, how can that be a bad thing. What $300 to do it, no brainier to me at least.
    • FPR
    • Injectors
    • Fuel pumps
     
  18. yelcab

    yelcab F1 World Champ
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    Eric, read the first post.

    Left and Right fuel pressure regulators have been replaced.
    All eight injectors have been sent out for cleaning.
    Fuel pump (single) has been inspected, rubber bits changed, and fuel pressure confirmed at 55 psi at the end of the fuel filter. It's good. I have yet to flush the return fuel lines. I can do that when the engine is out.
    I have new o2 sensors but have not installed them yet, waiting to do more diagnosis
     
  19. spaghetti_jet

    spaghetti_jet Formula Junior

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    dumb question: are the O2 sensors plugged into the right plugs? i.e. front o2 sensor is not plugged into the rear o2 wire?
     
  20. yelcab

    yelcab F1 World Champ
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    No it's not a dumb question. I have never made that mistake.

    I have made other dumb mistakes like plugging the center SDL connector to the right side SDL TCU which caused a CEL in no time at all. Come to think of it, the list of dumb mistakes is pretty long, but it does not include swapping the O2 sensors front to back.

    It does include having four O2 sensors in my hand OUT of the boxes and not be able to figure out which two are front and which are back sensors. Since then, I have bought some blue heat shrink material to install on the front sensors as soon as I get them.
     
    Qavion and spaghetti_jet like this.
  21. taz355

    taz355 F1 Veteran
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    Just my personal opinion no mistakes made 1 time are dumb
    Otherwise the list is quite long as well, but I thought that was called learning without the aid of others
     
  22. bcar1

    bcar1 Karting
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    did you put these on? I thought they were oem
    Image Unavailable, Please Login
     
  23. kenneyd

    kenneyd Formula 3
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    For testing purposes, could you unplug all the O2 sensors for a test drive?
    I believe that will force it to stay in closed loop. If the studder under load goes away, that should point to something in the O2 department (either wiring or sensors)

    My other hunch would be ignition coils(I see you said they were new), wires or plugs. Coils can be fine when cold, and break up when hot.
     
  24. Ferrarium

    Ferrarium F1 Veteran
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    If you unplug the 02 sensors it should force into open loop not closed loop generally as closed loop takes feedback from the O2 which would then be non functional unplugged rendering closed loop broken, it should then default to open loop.
     
  25. kenneyd

    kenneyd Formula 3
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    Oops, your are correct, I meant open loop.
     

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