F355 5.2 catalyst ecu diagnostics

Here are the symptons:

1997 F355 spider with recent major service. All three cat ecus are the newer, green versions, replaced four years ago. Intermittently, I will get a "slow down" light, and then the ignition will cut out one bank for a few seconds, then the light goes out, and car drives normally (light comes on, ignition cut, then restored and light out, all in about 8 seconds). Has happened a total of three times. After the second time, I cleaned and treated all connectors to cat ECUs with Stabiliant 22a. Cats are NOT overheating, and car drives perfectly otherwise. I do NOT have a "check engine" light. Will codes be stored for me to determine which of the three ECU's is bad if I use a Snap On OBDII code reader?

Would it be simplest for me to just purchase a new cat ECU, and swap it with each of the three positions until the problem no longer occurs?

 

Might be cheaper and more efficient to contract a couple of hours of diagnostic time with an SD2 machine.
Sounds exactly like my recent overheating cat due to a bad ignition wire so my ECU's were accurate. I don't recall getting a CEL at that time. Only Slow Down and subsequent bank cut off. If you don't have an overheating cat swapping the ECU's should work but expensive if the issue is elsewhere.

 

Green versions? I got one from Daniel a year ago or so and it is black like all my others---has worked perfect..

 

The ones on my 348 are also green, and look pretty new. I was also under the impression that these were better than the originals. Not sure if the cat ECUs are different for the 348 and 355.

 

The cat ecu's are different on a 355 from the 348. Green is a different epoxy, more resistant to cracking from heat, and allowing water to enter, the housings are still black plastic...but they can still fail, I would presume, just less often.

 

Gotcha----I coated all mine with black silicone chaulk to seal out any water if they do crack from the heat..

 

Note:

1) I believe the system is malfunctioning on my car, because the minimum time (according to the workshop manual) for the ignition shut down after being tripped by the cat ecu is 2 minutes, and mine is shutting down for only a few seconds (again with a steady "slow down" light).

I have searched the archives, but have found no information on how to test the thermoprobes. Does anyone know if their is a ohm spec for them?

Thanks again all.

 

Just got back from a friend's shop, we ran an OBDII scanner, no codes stored, and O2 functions are normal. Have a FCA trip to Vancouver, BC on Friday; will beg Ferrari of Seattle to run a SD1/SD2 check to see if they can find the cat ECU that is acting up.

 

Your car has 2.7 motronic, so there is no post cat O2 sensor that would catch the added richness caused by a bad ignition wire and trip the CE light.

 

I currently own a '97 355 spider 5.2. There are times I wish it was a 2.7!
Based on my experience the SD2 should isolate your problem.

 

Agreed John...just trying to beg my way into FoS right now. They are booked, and I have a trip starting Friday morning, leading a bunch of FCA members up to Vancouver, BC.

Their initial thought is a malfunction of the system, based on my description of the problem and (minimal) diagnosis thus far. They suspect either a bad cat ECU or bad connector, but want to hook up the car and do some further testing...problem is when they can try and fit me in...

 

Just got back from FoS. Mark the service manager ran extensive tests, using SD2 and checked and probed all the connectors. Testing was inconclusive, as the catalyst ECU's are responding normally. He thought the right side ECU may be suspect, but unsure. Since only the left and right catalyst ECU's can cause a "slow down" light. I am going to swap the wiring with the central cat ECU used to monitory Y-pipe temperatures. (the right cat ECU and central cat ECU are adjacent to each other, making this a simple swap) If the problem moves (the Y pipe ECU will trip a CE light instead) or goes away, then that is the bad one.

As it was explained to me by Mark, the center cat ECU is only used by the Motronic to monitor exhaust temps at the Y-pipe to confirm the exhaust valve is opening and closing when it should.

The left and right cat ECU's are monitoring more specific temperature thresholds, which can set off either flashing or steady "slow down" lights, depending on how hot an over temp it is reading.

 

Put about 350 miles on this weekend, driving up to Vancouver, BC and back. This includes some pretty "spirited" driving, including a wonderful run up to Cypress Bowl. No "slow down" light with the ECU wires swapped between the right side catalyst ECU and the center Y pipe ECU. No "CE" light either.

I will continue to monitor (since this has been an intermittent thing) but after this many miles, I think we found the culprit. According to Mark at FoS, even though the ECU may be "defective" it may work perfectly fine in the center Y pipe ECU operation, as apparently the specs for it's operation in this position is less stringent, as it is only monitoring the operation of the exhaust bypass valve (telling the Motronic computer the valve is opening and closing when it is supposed to, based on the exhaust temperature reading).

 

F355spider, great news! Will you try swapping the ECU’s back to confirm the suspected faulty unit?
On a related note. You mention the thermal-couple for the Y pipe. I recently installed a Ferrari Ansa OEM challenge exhaust in my 355. The quieter canister model, not the more aggressive challenge system. This system does not have the connection for the Y pipe thermal-couple. Is operating the 5.2 355 without the thermal-couple monitoring the bypass valve cause for concern? Does the ECU use the signal to adjust operating conditions?

 

On a 5.2 motronic you will need it, otherwise it will not get a confirming temperature signal that the valve is open/closed when it should be. The Motronic knows the valve is open by the hot temps from the thermocouple...and closed by the lower temps presented. Without it, you will likely get a "check engine" light after a few drive cycles. The exhaust ECU's are only a monitoring/protection system, not part of the operation of the engine management (to the best of my limited knowledge reading the WSM).

I don't intend to swap the wires back, I enjoy NOT seeing the "slow down" light.

 

Okay after 7+ weeks of driving, I have now gotten a "Check Engine" light and the code comes up as P1448, which is related to the exhaust bypass valve. That would now confirm that the bad Cat ECU was the right side one, because I swapped the right side cat ECU with the center ECU for the exhaust bypass valve and went from having a "slow down" light to now a "Check Engine" light for the exhaust bypass valve. So I have ordered a new cat ecu from Ricambi, and will swap it out tomorrow.

 

Good job !!!