HELP! car starts on 4 cylinders (no slow down lights)

I have a 90 348 that would shut a bank down intermitantly.
sometimes a slowdown light would come on, sometimes just flash once, sometimes shut a bank down other times just the light would come on full.
the cats were not over heating.
you'll know if that is happening, it's obvious.

turned out to be an exhaust ECU.
Ricambi had one,
the bad one I had was black, an the epoxy was separating from the casing.
the new one was green.
I found the bad one by switching things around.

I also disconnected them one at a time when the problem was happening.

 

I hear you but I have 2 brand new Cat ECUs (green epoxy not black) so unless one them was a bad one that should not be the problem. But we are checking it out.

Thanks

 

Ernie, the cat ECUs were swapped the first time I brought the car to FOD about 3 weeks ago. When they did that they got the 5-8 slowdown light to come on, it shut down the 5-8 bank, and the cat was glowing red. They cheched the O2 sensor and MAF sensor and found the levels of CO and HC were off ( I believe both sensors checked out OK as well). They readjusted those setting and the car ran fine. What I do not know but am in the process of finding out is whether the cat ECUS were switched back to their original places or were left as is.

The problem now seems to be on the 1-4 side but when the bank shuts down the slowdown light may or may not illuminate and then the bank may or may not come back on. In either case the 1-4 cat does not get red hot. So something electical is going on that so far has been a bear to figure out. Stay tuned.

Thanks,

Steve

 

Just to say it again, on an 89 t with M2.5, the cat ECUs CAN NOT shutdown a bank. The wiring diagram supports this, as does discussion with an experienced mechanic.

The symptoms as described by Steve indicate a lack of crank angle sensor signal to the 1-4 ECU. It isn't bank 5-8 because the tacho is not affected and it ias driven by the 5-8 ECU. It will be the sensor (not likely as it's supposedly new), the connector (possible as they are not the best), or the wiring harness (possible also coz it happened on my car). If it's not any of these problems, then the next place to look is power to the 1-4ECU, and finally the ECU itself. Until all these are checked and proven, I'd put my money on this area.

Dave

 

David, I havn't reset the ECUs yet but I will. So if the cat ECU cannot shut down a bank then what can (does it pretty much have to be in the wiring since all sensors were either replaced or stabilized)?

 

Reset the ECUs, takes 10 seconds to switch off the battery and turn it back on, then 10 minutes to let the car just sit there and idle. As before, if it starts cutting out during this process, abort it. No point continuing....

I am 99% certain it is to do with the crank sensor circuit, power, or the ECU itself, and almost certainly on bank 1-4.

There are of course other possibilities such as a bad fuel pump, or fuel pump circuit. I'd also check the ignition coil and controller. Intermittent failure here would result in no spark, but fuel still being injected. If the car is stationary when this happens, you'd certainly smell gas at the exhaust pipe. If it was a few cylinders cutting out, then the cat would get real hot real quick resulting in slow down light and possibly that lovely red glow.

Give me a call if you want to talk it through. One of these days I'll sit down and attempt to create a trouble shooting flow chart. The WSM has one, but it's only for M2.7 cars, and they have far superior diagnostic capabilities to the M2.5. In other words they have SOME diagnostics built in!

 

Dave, I'll give you a call on Monday. Thanks

 

Well then I am seriously suspecting a bad cat ecu, especially since the problem jumped sides (twice?) when the ecu's got swapped.


Try this,

Disconnect BOTH cat ecu's.
Run the car, and watch the cats.
If they BOTH get hot then I'm with Dave, the cranks sensors. You can change out the crank sensors yourself. They are WAY easy to change. 1 - 10mm nut, 1- allen bolt, and disconnect the clip. It can be done in 5 minutes. But before you change out the crank sensors peal back the rubber boot over the back of the clip (on the wiring loom side, it's the female clip) and see if you have any busted wires.

 

Ernie, Lusso64 et.al.,
All circuits, wiring, sensors, etc. were either replaced and/or stabilized (no broken wires). Cat ECUs were double and triple checked as were MAFs, ignition coils, O2 sensors, thermocouples, and more. What we found though after a second very thorough look through the cats with a boroscope is that the 1-4 cat is indeed bad and the 5-8 cat is not far behind.

The previous PO refurbished both cats about 5,000 miles ago so at first look everything was thought to be OK, but either someone did a piss poor job or the refurbish/rebuild just did not last that long.

So I am replacing both cats with Hyperflows and I am going to have FOD do it so they can complete the job and make sure this is the problem (but after everything that has transpired we are about 100% sure it is).

So thank you everyone again for your input it was invaluable and a special thanks to Dave at Ricambi America and Nick Scianna at Forza Ferrari...very good people. I will let you know forsure that this has solved the problem.

Steve

 

Installed new Hyperflow cats and wow does it ever sound great and the throttle response has increased too. Drove it all around in the hot weather and it drove great so everything looks good.

So I guess we can add another thing to look at to fix a downed bank on the 348 engines besides electrical connections, O2sensors, thermocouples, MAFs, and cat ECUs; it may the the cats themseleves are tutti finuto (all done!).

Steve

 

I have a 89
Mondial T with a 1-4 bank light intermittantly coming on and off, with no decrease in performance or bank loss.
Just a drop in RPM'S. The Tach appears to have lost 1500 rpm's and reads lower than it should. Weird

Does this sound like the same problem?

I guess if it is not dropping banks now it is not if it's when?

Thanks for any help.

Mark in Danbury CT

 

A good starting point would be to pull your ecu error codes.

 

Do what No Doubt says and also check the crank sensors. Looks like one of yours is faulty.

 

Steve, great to hear everything is well again. Now, enjoy the drive!

Dave

 

Thanks Dave, these are sweet cars aren't they?

Steve