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.
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.
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
What seal? The oring on the plenum to pipe connection? Last time i looked i couldn't find them. Are they in stock?
You need to reroute your spark plug wires. Rather than me trying to explain it have a read of Goth’s thread on the topic. https://www.ferrarichat.com/forum/threads/355-misfire-when-engine-is-hot-ignition-wire-reroute-shows-some-relief.425737/#post-142671039
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.
Thanks, but I have sanity checked these, I see no sparking in the dark and all the leads, plugs and caps are new.
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.
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.
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.
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.
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.
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.
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.
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.
Thank you! They are definitely marmite. I love them but lots moan at me and ask if have the original wheels! Haha
