355 'limp mode' musings

I've had an issue with my '95 2.7 car for the past couple of weeks where I'll lose all power and the car runs very rough. Happened on startup the first time, happened yesterday as I was trundling along at 50mph after driving the car for 2-3hrs without issue.

Most of the information I can find from some Googling and searching this forum relates to 5.2 cars, hence this post.

I have no warning lights on the dash when this happens. Both banks' CEL and SDL lights illuminate and extinguish during the ignition process as expected so the bulbs are good at least.

I thought the problem was a coil pack so I changed both packs for new items last week and all was well for a few days, until last night when it went limp again.

I now guess that in leaving the battery disconnected for a couple of days before I changed the coils has probably cleared some error in the ECU, which has now manifested itself again.

Reading the workshop manual for the 2.7 system I see a nice list of possible self-diagnosable fault codes (helpfully included as an image below). I'll have a go at reading any errors off my car when I get home later but for now perhaps someone can confirm my thought process here.

The table below has a 'lamp ignition' column which doesn't seem to be described anywhere in the manual. I'm assuming that the 'S' and 'N' stand for 'Si' and 'Non' and therefore this column indicates whether the corresponding error will trigger a warning light (SDL or CEL) on the dash during normal running? Does anyone know for sure?

You may see what I'm getting at here (you may not, I may be totally wrong here); the two catalyst warning codes listed below are flagged as 'N', as opposed to the 5.2 cars where the cat warning system throws lights at the dashboard willy nilly. My car seems to have a faulty thermostat (see http://www.ferrarichat.com/forum/348-355-sponsored-bradan/456602-my-355-running-too-cold.html) which I assume isn't helping although when the issue occurred yesterday, water and oil temperatures were in what I'd consider the optimal range.

My current plan of attack is to try to read the error codes. If I can't do that then replace the thermostat, reset the ECU again and wait...
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Thanks. That's that theory out the window then...

 

Thanks Bob. I'll try that.

Do you have a picture showing the location of the plug(s) to remove? I know where the thermocouples plug into the cats but was unsuccessful in finding where the leads went when I stuck my head in the engine bay in the garage this morning.

 

Thanks, I'll have a look.

Yes, pretty much. The first time it happened was when I had left the car parked for ~30mins after driving for a while, turning the engine back on it was idling around 800 rpm and clearly not running properly, eg no power or throttle response. Restarting it did not cure it.

Yesterday I was motoring along at around 50mph and, as I brought the clutch up after changing down from 6th to 5th as I approached some traffic, I noticed I had no power again. The car had run flawlessly for ~2.5hrs before this and there was no indication it wasn't happy. As before, stopping and turning the engine off, waiting a few minutes and restarting it didn't help.

 

Thanks Pete, I'm going to try to get it into my mechanic this week, I'm not so happy pulling plugs myself.

That's exactly what I just did!

Two minute job to find and pull each thermocouple from the ECU then restart the car. Unfortunately (well, fortunately in a way) I now have two SDLs and still rough running.

Beginning to think it's more of a traditional ignition problem; leads, plugs... Will keep updating this as I go.

 

Ha! Oops.

I unplugged the small lead (on the left here edit: on the right here, somehow the photo flipped through 180 degrees...) to the thermocouple, not the power! I'll have another go by unplugging the 4 port thing.
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I tried pulling the 4 port plug too last night, that also generated some SDLs.

I left the battery off overnight to give the ECUs a proper reset but it's running the same this morning.

Plugs and leads next, I guess.

edit: Just saw the comment about the O2 sensors. Is there any easy way to check these?
edit2: The workshop manual suggests I should be seeing an SDL or CEL if the O2 sensors are on the blink?

 

Given that my problem isn't accompanied by any lights on the dash, yet I can trigger the SDLs to appear by pulling things, I'm guessing this is unlikely to be a cat ECU issue?

 

Engine sounds and feels very wrong, could be severe misfire or some cylinders down is my layman's guess. No power or throttle response. Needs ~3-3500rpm to pull away.

It happened for the first time when starting the engine after the car had sat for ~30mins after a city drive of about 40mins. Engine started rough, didn't improve after letting it run and driving for a few minutes so I parked it up, disconnected battery and swapped both the coil packs for new items a couple of days later.

Tried starting it immediately after changing the coils, it fired up as normal and drove perfectly. After this I drove it a few times, mixed driving, some city some highway, for a total of about 150 miles over the next 4-5 days. It ran beautifully throughout.

Second time it happened I was driving along at ~50mph and as I changed down from 6th to 5th and let the clutch up it lost power again, same rough idle. Limped it home and parked it and that's where this thread picks up.

As it happened again with the new coils, I thought that it may not have been the new coils that cured it at all, merely that the ECU reset effected by leaving the battery disconnected before I replaced the coils cleared some error which allowed it to run for a while until it occurred again.

With this in mind, I left the battery disconnected overnight last night and tried again this morning - still sounds rough as hell. So it's not really an intermittent issue that comes and goes based on temperature/duration of running throughout each drive as far as I can tell.

It does smell a bit petrol-y when I stick my head in the engine bay after running it for a couple of minutes.

What I'm a bit confused about is that if it was plug (eg rich running fouling things) or lead related why would changing the coil packs have made it go away for a while?