348 TS CHECK ENGINE LIGHT

It sounds bad! i will be happy to take it off your hands for 20k today.

I am sorry to hear about your couple of problems. I dont think it is shorting yet, if you are not losing power then it is proabably not. I wish i could help more. someone here can answer better than me. good luck you will get it worked out.
john

 

Hello:

I own a 95 F355 and from what I understand the emissions systems are similar. I have experienced the same problem (See General Discussion - Help sold a F355 spider with no cats).

The check engine light may be associated with the oxygen sensors and the slow down light may be associated with the thermal probes.

My mechanic switched the thermal probes from side to side and the the slow down lights switched to the other banks.

Hope this helps!

 

OK, some feedback, based on my personal experiences with my 1990 348ts. Some of this you already know.

The "Slow Down" lights are triggered by a signal from the ECU for the exhaust temperature sensors. There is a thermocouple in each catalytic converter. It reads the exhaust temperature and sends a signal to the temp ECU for that side, which reads the signal and sends the information to the main Motronic ECU for that side. If there is a high reading, the "Slow Down" light comes on. If it stays high, the Motronic starts shutting down that bank so that your car won't burn down.

You can have a correct, fully functional "Slow Down" warning if your catalyst is actually overheating. Or you can have a false signal if the temp ECU is defunct. This is very common. As you may have read elsewhere, one way to diagnose this problem is to swap the temp ECU (not the Motronic ECU) from one side of the car to the other. If you HAD the slow down light on 5/8, and you switch the ECU to the other side, and it now shows a problem on the 1/4 side, then the ECU is the problem. If you still show the light on the 5/8 side, then there is another problem. Easy to test, it only takes a few minutes to swap the temp ECU's.

That's the "Slow Down" light. The "Check Engine" light is telling you that the Motronic ECU (behind the seats) has read a problem in one of the parameters that is covered by the self-diagnosis function included in the 2.7 system. You need to learn how to download that information (it's easy, takes no special knowledge or tools), then erase the stored information and start over. The system can read and store faults that may have been instantanious (a loose connection, e.g.) or may show a failure of one of the covered components. In many cases, the "Check Engine" light is what I call a "ghost". It happens once in a while, but nothing is really wrong. Mine used to come on from time to time, but once I cleared the stored memory and reset it, I haven't seen it come on for a year, and I didn't have to fix anything.

There is a whole section in the Workshop Manual covering the self-diagnosis system on the Motronic 2.7. It may look imposing, but the procedure isn't difficult and can be done in a matter of minutes.

Hope this helps.

 

The temperature ECU's are ridiculously expensive, I think around $300 each. If you determine that the ECU is the problem (i.e. the warning light switches from side-to-side when the ECU is switched side-to-side), then you CAN simply disconnect the exhaust ECU's so that they no longer give the false signal to the Motronics, but then you no longer have the warning system in place, and if your catalysts really do overheat, you could be in deep doodoo.

If you still have the "Slow Down" light on the same side after switching the ECU to the other side, then something is making your catalyst run too hot, and you need to figure out what is wrong. Most likely something is making that bank run excessively rich, and the unburned fuel is burning inside the catalyst. You may even see it glowing red hot. This is something to take very, very seriously.

If I remember correctly, you can tell the difference between the old style temperature ECU's and the new style ECU's by digging a thumbnail into the sealing material on the back of the unit. I don't remember whether the new ones are soft or hard, it would say somewhere in the archives. I installed new ones about three years ago, and I haven't seen a "slow down" light since then.