348 Engine Misfire / Rough Running ??

You have a solid connection with the plugs and wires? Have you tried contact cleaner on the wire ends...Mine was running a tad rough and this helped me.

The lambda sensor is the same thing as an o2 sensor....From what I have heard, if an o2 sensor is going bad, you will for sure get a check engine 1-4 or 5-8...not sure again though....

I would touch up a lot of your electrical connections with Stabiliant 22 or some kind of contact cleaner as a starter...

 

Justin, your Slow Down Lights aren't really going to be triggered on your car because you don't have cats.

http://webpages.charter.net/aircover/348/1994Ferrari348Spider.html#SlowDownLights

Those warning lights are heat-triggered, and your test pipes are not going to get hot enough to trigger them.

Unfortunately, that hurts the diagnostic process a bit for your car...because you don't know if you've got a fouled spark plug, or on which side, or a bad spark plug wire, or which side it might be, or if either coil pack is bad (or MAF).

Also, keep in mind that your O2 sensors are *ignored* when you are at full throttle...so if you are seeing different behavior when your accelerator is to the floor than when you are at partial throttle, it may warrant checking O2 sensors.

The good news is that you aren't seeing white or grey or black exhaust smoke at idle. That rules out some fair amount of really nasty possibilities.

My **guess** would be that you are running too lean (that's the typical backfire problem)...except the black soot exhaust seems like the other way around...such as you've got a bad spark plug wire or fouled spark plug. A bad plug wire on the 348 can manifest itself under inconsistent circumstances (e.g. between 5,000 and 7,000 rpms only).

But the cheap test would be to simply replace all 8 spark plugs. For a **test**, the $2 Champion OEM spark plugs would do fine to tell you if your problem was from fouled plugs or not. Since you ran at peak speed prior to encountering your issue, this would be a good test.

Other possibilities would include a fuel pump going bad, or a bad fuel pressure regulator, or simply a clogged/bad fuel filter. These items, if malfunctioning, could cause a lean condition.

You'll want to get an air/fuel mixture sniffer (e.g. wideband lambda) to test to see if you are venting fuel or running way, way lean (which the pros could probably tell you just from your description of the exhaust soot color that you gave).

 

Try re-setting the ECU's first - it's free to try. Most Euro cars do not put a check engine light on even if there are stored codes.

Disconnect the battery for a few mins, reconnect and start the car without touching the accelerator pedal. Leave ticking over for 10 minutes before driving.

 

Chris is right to tell you to reset the ECU's (after all, that's a free thing to check/try)...BUT...pull your trouble codes first! Resetting your ECU's will erase your trouble codes, and you may need that information if this is a sporadic, tough to duplicate problem.

 

It's common to get a backfire when you are running too lean.

O2 sensors are ignored when your engine is cold, and are ignored when you are at full throttle.

So if you get a backfire at idle when the engine is cold, then it isn't from the O2 sensors ('cause they're ignored!).

 

Here is what I would check for starters:

1) MAFS connections, and inside the sensor. Make sure it isn't dirty inside. If you are using a K&N filter (or any filter that needs to be oiled) you may have gotten some of the oil on the air temp wire. Non-residue electrical contact cleaner can be used to clean off the inside of the MAFS.

2) The connection on the back of the intake cam sensor. Looking at the engine from the back it's on the right hand side of the engine, just behind the air box and under the MAFS.

3) The connections for the O2 sensors. They are located between the oil filter and under the air box. You may even want to pull the O2 sensors and check the condition of them. Since your car is chipped you may have fouled them by running a bit rich.

4) Spark plugs. Pull those to see if they are also fouled by having the mixture rich.

5) Check your vacume tubes. Make sure you didn't have any come loose.

6) Crank position sensors. You'll have to get under the car for this one. They are on the bottom and to the side of the crank pully.

7) Water temp sending unit connection. It's located under the intake plenum. Remove the air box to get at it better.

 

Sorry to hijack....but.....

What does white smoke at idle look like? My car puts out a lot of exhaust at start up, I am either just recently noticing it or my car has just started doing it because the weather is colder... It seems like a lot, but to me, I figured it was normal because my car doesn't have cats. The exhaust tends to settle down a lot after the car has been running for a while (either that or I stop paying attention to it)...

Do you notice a lot more exhaust smoke in colder weather?

Car runs fine except for this exhaust whine which I have had forever....I'm thinking it could be a leak in the muffler gasket or exhaust manifold gasket.

Another Fchat rode in it about 5 months ago (he has a 348 also) and said that his car def. doesn't whine like mine....maybe someone this weekend will be able to troubleshoot it.

 

I'll get a small amount of white smoke on startup on a cold day if I haven't driven my 348 within the past day.

Right or wrong, I chalk it up to "oil settling" and don't pay it much attention.

 

I would definitely do a compression and leakdown test on this car. Burnt valves will do all sorts of funny things to mixtures as fire and pressure is going to places it shouldn't. Is the popping from the exhaust or intake? By the way, cooking valves is a manly thing to do!

 

As well as the oxygen sensor it could also be a small crack / leak in the exhaust manifold's (which could also account for the TVR'esque noise)

 

Could be burnt exh valve. Easy cheap check if you don't have a compression tester (around $20 or so at parts store) is to disconnect plug wires one by one, til you find the one that stops the popping when disconnected. BE SURE TO USE INSULATED PLIERS AND GLOVES OR YOU'LL GET A SURPRISE! Alternatively, disconnect the wires to each injector one by one. A good time to check your injectors anyway-a bad injector will cause a lean condition in that cylinder, thus extra heat= burnt valves. Unburnt fuel getting by exh valve at compression may burn in the exhaust (pop), ugly black soot in exhaust pipe. Hope it's just an electronic problem.
If it's an exhaust valve, pm me for a good source.