I appreciate anyone´s opinion on this subject. My 95 F355 Spider has 18K miles. The car runs great for about a couple of hours. After that, the engine sounds like one side (1-4) is "off tune" compared to the other side (5-8) and small explosions occur right after shift acceleration. What exactly happens after those couple of hours is that I accelarte, lets say, to fist gear, and regardless of the RPM, just when I´m about to shift to second, the explosion occurs when the RPM is going down. At first I thought it may be a valve problem, but discarded it since the car does not do anything bad for hours. The "check engine" light comes on even later after the explsions start. I had the inyectors cleaned to make sure gas is sprayed evenly and no "liquid" fuel is being left to cause the explosions, but it didn´t fix the problem. I live in Monterrey Mexico and the ferrari dealership does not have a full set up shop with computers. Cars are sent to Puebla, a day away. Could the thermocouple sensors be the problem?
The exhaust thermocouples are not your problem...they just tell your ECUs that you have either OK or "too hot" exhaust. Most backfires are just due to lean fuel/air mixture (lots of potential causes)...but your F355 has an exhaust bypass valve that I'm unfamiliar with. Backfires when the revs are coming down might even be related to timing-belt slap.
It could also be an air leak into the the exhaust manifold, has the tone of the cars exhaust changed since this started?
I changed the timing belts at 15K miles (3K miles ago). I´m not so sure if the problem started when new belts were placed, but it may be that. Correct me if I am wrong but I guessed the timing belts were not the problem becasue the explosions appear after I have been driving the car for at least an hour. My guess was that if it was an engine related problem it had to appear as soon as the car reached normal driving temperatures. I have even driven the car up to 7,5 rpm and have driven it quite fast and at high rpms and no problems. The backfires appear suddenly for no aparent reason, but they always occur when rpms go down. Once the first explosion apperas, the following become louder. About the possibility that it may be an air leak into the exhasut manifold, Yes, once the car starts bacKfiring, the tone of the engine sounds "uneven", like one side is not as smooth as the other. In case that may be it, is such leaking supposed to appear right after it reaches normal temperature? I guess my question is why the car waits for so long to do that? Thanks for the feedback
LOL. I wasn't even going to ask but.... I need some entertainment so I just gotta know what the hell timing belt slap is?? Oh.. and pleeease tell me what the exhaust bypass valve would have to do with a lean mixture. Sorry Feliciano as soon as I find out the above answers I'll come back and give some suggestions
Timing belt slap is when your engine is turning faster than your cam belt (say, due to taking your foot off of the throttle at high speed). To prevent timing belt slap, Ferrari installs timing belt guides on the 348 model (I have no idea if they do this for the F355). By having this guide just above the timing belt, Ferrari can minimize the "wave" height that moves through the timing belt whenever you back off of the throttle. A big wave in the belt makes a big SLAP! The smaller the wave, the less timing belt snap occurs. Here is an actual picture of a cam belt guide from my 348, as well as a close-up and overall 348 engine diagram from Ferrari that shows two cam belt guides schematically: Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login
My 355 makes a crack sound when hard in acceleration and backing off between gear changes. I have heard similar with others particularly if fitted with tubi. Try resetting your ecu overnight by turning off isolation switch and in mornind with all air and accessories off simply turn on key and let idle for 5-10 mins until idle is steady and maybe this will help as the ecu does a diagnostic. Did this with mine 98 355 when it started running a little roughly (recommended by ferrari mech) and it solved problem.
A slightly burnt exhaust valve will also allow a little fuel/air to escape when it shouldn't (i.e. during the compression cycle) under some conditions...when that fuel/air hits the cats, it's going to POP!
After reading more responses to my inquiry, I typed "manifold" in the search button and was ammazed at how many f355 owners have had related problems with manifolds. Definitely I will have my mechanic check the tension on timing belts since like I said, they are barely 3K old. But I will have both the by-pass valve and the manifold checked. From what I have read, it seems like Ferrari wasn´t that eager to build manifolds from the higest quality material (too thin) and that may be a problem, for it has been for many F355 owners it seems. Some say they´ve decided to "coat" their manifolds with ceramic, but don´t know if that is possible in my town. So my question is this, Can I get rid of all problems by simply installing a complete TUBI system on my car?. Has anyone done the same? and if so, Has that fixed the "explosions" problem? I know the sound of a TUBI system can be good to the ear, but can it also be effective in getting rid of backfire or exhaust overheating problems? Thanks again
Those little feet on the 348 timing belt system were only there as a pre-cautionary measure and are suppose to be a mm or 2 above the belt. If you look at your picture you will see the water pump holds the belt down on the intake pulleys. There is no "Belt Slap". In all the years I owned a 348 and the 3 belt changes that I did I monitored the bottom of those feet I never showed ANY evidence of the belt touching the bottom of the feet. I know this because I painted the feet to see if the paint would wear off because of the belt touching them, it never wore off. Anyway there is no way that even if there was a small amount of upward movement it would be very minor and would definitely is going to cause a back fire. There are no feet on the 355 engine there are two timing belts instaed on one. Feliciano. I would first check to see what codes are coming up on the ECUs (I think you said the CELs were coming on) It could be one(there are 2 one for each bank) of your water temp sensors is not supplying the proper signal to the computer. The temp sensor is used to adjust timing and mixture when the engine is cold. But I would start first with ECUs codes. That will tell you which sensor is bad, there are several.
Tony, That little "crack"/pop you here is probably unburned fuel from the combustion cycle that enters the hot exhaust pipe/header tube on the exhaust stroke its normal, you don't necesssary have a burnt exhaust valve. This will generally happen on an up shift. It will be more pronounced with the tubi because it is less of a silencer than a stock muffler. You should here it on a 355C with the factory Challenge race exhaust and no cats. Sounds like an F1 car "pop", a little blast of fire even comes out of the exhaust pipe. Also you don't have to let the ECU reset overnight a few minutes will do. Regards, Vern
Your headers are probably cracked a common problem with 355s, when lifting on the throttle the cracks allow cold air into the cylinders causing popping or backfiring from too lean a mixture.
i heard some on saying that headers are different from manifolds, but I always thaught they were the same... Are headers something else?
Thanks Vern It is when on an upshift and it sounds great as does the Mille miglia exhaust that I have installed. I didn't note that the enquiry was for a 95 355 which may operate a little differently in the ecu switch off mode, am not sure.
Exhaust Manifolds = Headers. It is a Glitch with 355s. The OEM Headers are Garbage & will require replacement @ some point. Make sure your replacements are 1.5mm & 304 Stainless Alloy. DO NOT Purchase Ferrari Headers !!! There are many Superior Aftermarket Manifolds. I went with QV (London).
