355 - Slightly erratic idle | FerrariChat

355 Slightly erratic idle

Discussion in '348/355' started by alexanderfitu, Jan 26, 2022.

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  1. alexanderfitu

    alexanderfitu Rookie

    May 23, 2020
    40
    Full Name:
    Alexander
    Hi All

    I have just completed a major belt service on my 355.

    At the same time. I installed a Remus style exhaust (and decat pipes which were on already) which is approximately 40% louder at idle.

    I have a small problem, when cold the idle is fine. When the engine is warm, the idle is very stable around 1000 rpm, but has the occasional slight miss every 20 seconds or so. It is not a hard misfire, but you can hear it in the exhaust note, but cannot feel it. If you raise the rpm by even 20 or 30rpm, it goes away. Its smooth as silk when driving and does not stumble or hesitate from idle upwards at all.

    I did have a Mass or Circuit Airflow (MAF) Circuit Low Voltage Input engine fault code, but I attributed this to me starting the engine one time without the MAF plugged in, and it has returned since.

    The plugs were changed during the major service, and the leads+caps on both banks are approximately 2 years old, with 600 miles on them..

    I will try and obtain a video of this and the fuel trim values in the next few days.

    Somebody has suggested it has done this the whole time, but was not audible over the factory exhaust, especially as it cannot be felt.

    I am fairly confident the cam timing is correct as well, as I did degree the cams and check them using the HE TDC gauge to determine TDC on no 1. There was evidence that the cams had been adjusted in the past, and I found that the existing spec was dead on and there was no need to change it. The records I have indicate that this was done approx 6 years ago/3000 miles.

    Any input would be much appreciated.
     
  2. alexanderfitu

    alexanderfitu Rookie

    May 23, 2020
    40
    Full Name:
    Alexander
    That should read "has not returned since" RE the code
     
  3. alexanderfitu

    alexanderfitu Rookie

    May 23, 2020
    40
    Full Name:
    Alexander
    Update for today. Smoke tested intake system, found small leaks between MAF housing and pipe, and also drivers side bank (RHD) pipe to intake plenum. New seals on order.

    Smoke tested exhaust, found slight leak between "cat pipe" and manifold both sides (Frustrating as new seals here) on both sides, and fairly large leak on other end of cat pipe to exhaust clamp passenger side. Sorting all those out and will read LT and ST fuel trims and take it from there.
     
    Julia and Qavion like this.
  4. 26street

    26street Formula Junior

    Jan 30, 2021
    343
    Westchester New York
    Full Name:
    Mark k
    Air leaks behind the MAF sensor will cause problems at idle because the ecm doesn’t know the extra air in the intake system the exhaust O2 sensors will start reading lean and fatten up the mixture but once off idle the fuel fuel mixture will balance out a little better but still be on the lean side it’s just at a higher rpm the more fuel is needed

    Exhaust leaks will pretty much the same thing if the leak is before the O2 sensors small amounts of clean air will be pulled into the exhaust flow as be pick up as a lean signal on the O2 again making the car go rich

    You will see that in the short and long fuel term trims once you get the leaks straightened out still check the trims as close to 0+- but no more then 4-5+- on short and about the same on long term if your scan tool gives a total trim no more then +-13 “add short and long together “


    Sent from my iPhone using FerrariChat.com mobile app
     
  5. Zamboniman308

    Zamboniman308 Formula Junior

    Feb 2, 2020
    471
    Chicago IL
    What seal? The oring on the plenum to pipe connection? Last time i looked i couldn't find them. Are they in stock?
     
  6. ernie

    ernie Two Time F1 World Champ
    Lifetime Rossa Owner

    Nov 19, 2001
    22,576
    The Brickyard
    Full Name:
    The Bad Guy
  7. Zamboniman308

    Zamboniman308 Formula Junior

    Feb 2, 2020
    471
    Chicago IL
    Does the slight misfire begin right when it goes into closed loop during warmup?
     
  8. alexanderfitu

    alexanderfitu Rookie

    May 23, 2020
    40
    Full Name:
    Alexander
    Yes Eurospares in the UK has an alternative at £8 or so.

    I had a really difficult time sealing the "Cat" tubes at the manifold side, despite using new gaskets etc. I managed to reduce the leakage 80% with the smoke tester but not completely. Also had a fairly big leak at the "cat" tube to exhaust muffler side which I sorted by rotating the exhaust slightly on its mounts.

    Hopefully they should make a difference, will test it when the intake side seals arrive.
     
  9. alexanderfitu

    alexanderfitu Rookie

    May 23, 2020
    40
    Full Name:
    Alexander
    Yes exactly.
     
  10. alexanderfitu

    alexanderfitu Rookie

    May 23, 2020
    40
    Full Name:
    Alexander
  11. ernie

    ernie Two Time F1 World Champ
    Lifetime Rossa Owner

    Nov 19, 2001
    22,576
    The Brickyard
    Full Name:
    The Bad Guy
    Did you read the thread?

    The wires need to be moved up higher, and away from the headers/catalytic converters. Even a heat shield under them.
     
  12. Zamboniman308

    Zamboniman308 Formula Junior

    Feb 2, 2020
    471
    Chicago IL
    I'm chasing this on mine. I think its happening on his before the engine compartment gets hot enough to matter. I doubt its wire related. It's got to be part of the engine management. As soon as it flips out of the preprogrammed values and into closed loop you'll notice it. Like within a min or 2 after a cold start. Smooth as a silk while in open loop.. then will exhibit a slight occasional burble stumble you can notice in the exhaust. Most wouldn't even notice it.
     
  13. alexanderfitu

    alexanderfitu Rookie

    May 23, 2020
    40
    Full Name:
    Alexander
    I did yes, sorry I have probably not explained my issue correctly, as zamboniman308 it's not actually heated related, it's as soon as "warms up" and goes into closed loop.

    It did not do this before the major, and the plug wires are in exactly the same place. Will try and post a video up shortly.
     
  14. alexanderfitu

    alexanderfitu Rookie

    May 23, 2020
    40
    Full Name:
    Alexander
    Yes that is exactly my behaviour. As soon as the intake o-rings get replaced and I have no more intake leaks I will test again, and try and get a video of the idle.
     
  15. alexanderfitu

    alexanderfitu Rookie

    May 23, 2020
    40
    Full Name:
    Alexander
    New intake side o rings installed today. Smoke tested and confirmed no leaks. Ran until cooling fans kicked in. Initially seemed the same but its definitely smoothing out and getting better. I suspect driving it will help.

    Have not checked fuel trims yet, but will do.
     
  16. Zamboniman308

    Zamboniman308 Formula Junior

    Feb 2, 2020
    471
    Chicago IL
    When i smoked mine, the throttle bodies had a little leakage. Haven't had time to pull the plenum and go further. Looks like a headache to refit with the engine in.
     
  17. alexanderfitu

    alexanderfitu Rookie

    May 23, 2020
    40
    Full Name:
    Alexander


    Here is a video from full cold start, you can hear closed loop around 4 minutes I think. It is not nearly as bad after I did all the smoke testing, but you can hear still small occurrences of it. I will report back on idle stability after I drive the car properly in the next few weeks.
     
  18. Zamboniman308

    Zamboniman308 Formula Junior

    Feb 2, 2020
    471
    Chicago IL
    Any progress is good progress. I think I'm going to try and pickup some of those orings myself.
     
  19. Drock28

    Drock28 Formula 3

    Jan 13, 2013
    1,430
    Montreal
    Full Name:
    Tony
    just listened to a good amount of that vid.. and the idle seems completely normal to me..
     
    swoshsteffo likes this.
  20. alexanderfitu

    alexanderfitu Rookie

    May 23, 2020
    40
    Full Name:
    Alexander
    It's quite hard to hear on the video, but it's audible around 7 minutes.

    I drove it today some more. It definitely has a rough idle, seems about the same. Not sure I am going to spend any more effort trying to ge tit any better as it drives absolutely fine above idle.
     
  21. Zamboniman308

    Zamboniman308 Formula Junior

    Feb 2, 2020
    471
    Chicago IL
    I have a couple 02 sensors on the shelf. I may see if they help when the weather gets better.
     
  22. radlu

    radlu Formula Junior

    Jun 6, 2005
    416
    Nice wheels.
     
  23. alexanderfitu

    alexanderfitu Rookie

    May 23, 2020
    40
    Full Name:
    Alexander
    Thank you! They are definitely marmite. I love them but lots moan at me and ask if have the original wheels! Haha
     

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