F355 Cylinders 5-8 cutting out

On the 348, those exhaust ECU's are just behind the spark plug connections on each side of the car (not on engine, but where the spark originates). The 355 may have to remove some side covers to reach them, I'd guess.

First, however, I'd simply look back there at the cats. Those old baffled cats glow a dimly lit red when they are overheating. If yours are red, then don't do the other tests.

 

Jeff your school of thought is right on the money.
But I don't think it's the ECU's... I think it's the cats or the thermocouple.

First of all any "white particles" on the exhaust tips? Usually a sign of cats going bad.

Get a EGA and sniff the exhaust to see if your cats are working. If they are and you still get the light, then it's probablly the thermocouple processor. Lambo and Ferrari use the same one and it will usually go bad before the ECU.

If you follow the braided steel whire from the thermocoupler, it should go the thermocoupler sending unit, a small plastic box (usually white) about the size of a cigarette pack... It's a plug and play unit. When the sending unit reads too high a temp, it sends the signal to the ECU to either display the light, or if real high temp, to shut down the offending bank. Cheap fix. Get a reading on the cats before you doing anything...

 

My F355 was doing the same thing. I just unplugged the cat temp sensors on both sides to see what would happen. I drove it awhile & the car never lost power again. So I diagnosed it as a bad CAT temp unit. I hear from other posts here that these temp units go bad. You can do the work yourself very easily. I would do it when the engine is cold, HA!

 

Exactomundo!

Just follow the braided wire to the connector for the exhaust ecu, then unplug it. Now follow that wire to the exhaust ecu box (short trip maybe 6") and then unplug the ecu from the wiring loom. You will find it on the back side of the shock tower. Swap sides, then plug them back in.

By the way good work using the "search button". Too many people just ask with out looking first.

 

Thanks for the update, and nice job.

 

can the thermocouple be out of order causing shuting down on some cylinders an havind check engine light on (not longly) and not the slow down light on.
I have some trouble like described in this post, sometime not all cylinders are runing, sometime all are ok when I drive fast. I sometime feel like having a 4 cylinder car !
I sometime have check engine on but only a few seconds..
F355 Motronic 2.7

 

Yes.

Try the above proceedure to help find the problem.

If your check engine light has been coming on you will want to pull the codes.

 

yes maybe but how can I get the code ?

 

I'm not certain if the cat ECU's are different on the 5.2 cars over the 2.7, but there IS an updated part (at least for the 5.2 cars). You can identify the newer style cat ECU's as they have a green painted dot on them. All three of mine were updated to the newer style back in 2003. Supposedly these are the same ones as used on the 360's.

 

I had the same problem on my 1995 355. Thought it was the ECU relay. Turned out to be the complete fuse box at the passenger's footwell.

 

Is this Ecu relay on any map in the owner manual or hidden ?

 

Hello Dr Ferrari !

I worked on my F355 M2.7 today here is what I checked:
Cleaned the sensor on the flywheel seam to be ok.

 

I cleaned all the sparks plugs., all the wires and plugs cleaned.tried do diconect the temp sensors of the cat and seams to be ok , it light on the indicators withh cylinder numbers, tried to drive like this and did not change the problem.
looked at the thermocouples (x2) dont seam too be damaged .I still have like ingnitions cutting under 3000 RPM and after run well...
Tried to find the obd plug and not under the dashboard, not in the fuse pannel, not in luggage compartiment, not found too near the ECU on each side of the car. ?
Nico

 

my car haventanymore cats it have tubi pipes and the Eu version doesnt have the self diagnosis button near ECU...it is only for US verSion.

 

There is a known problem with 348's and 355's in which a bad spark plug wire will cause problems at low RPM's but run fine at higher speeds. That type of problem would explain why you do not see a Slow Down light. The Slow Down light is for overheated cats, not bad spark plug wires.

Overheated cats shut down half of your engine at all speeds, fast and slow.

Bad spark plug wires first impact your engine only at low speeds/rpms.

 

As far as I know none of the M2.7 systems have OBD2 connectors, by the way.

 

So I will test all the plug wires to check the "ohm" resistor of each...
it seam to be true that Mo 2.7dont have obd plug. In the repair manual they talk about SD1 pLuged on the ECU...
I should never have sold my 348 for a 355, even if it is abetter car it is more often out of order no !

 

Spark plug wires are a small thing. I drive a 348, so I do give 355 owners a hard time, but I only say such things in good fun. The 355 is a fine car.

An issue here or an issue there is really no big deal on a finely tuned vehicle. Once in a long while a thing will go wrong with any machine. It's not something upsetting.

 

Modern Ferrari spark plug wires generally do not suffer failures that will be found with an ohm meter. The problem they suffer is a breakdown in the insulation allowing them to "Leak" or short to ground or another wire. The loss is not always even complete.

It is compounded by the fact that unlike American cars where the standard has always been to elevate, insulate and seperate the wires to prevent just that, the Europeans (as very well shown on the 355) tightly bundle them and cram them in a hot grounded metal area that requires an absolutely perfect wire to perform properly.


Standard repair method on 355, 456, 550 for rough idle not immediately attributable to any other cause:

A Throw away the Champion plugs and install NGK's.
B Install new spark plug wires.

God bless coil on plug ignition.

 

I heard that sometime on F355 there are problem with ignition coil...is it possible to check it simply looking at them (damages, crinkle) or should i test them ?
I did not found damages on the cable for spark plug ..
I have a feeling that it should be a sensor that doesnt work well because it sometime work fine...but I dont know yet my 355 as I knew my 348...

 

Post a picture of your old one. I'll be the silicone seal had failed, and moisture got into it.

 

Nicolas

Check to make sure that the Mass Air Flow Sensors are clean and connected properly. Have a look at the condition of the wires on the connectors for the MAFS. Make sure there are no broken wires. Be sure to check the wires under the rubber boot covering the back of the connector.