Slow Down light on Mondial t not typical

I have an 89 t. The 5/8 slow down light comes on at about 3800 rpm at differnt times. I have had the O2 sensors changed and checked the cats. Only one side comes on so I switched the ECUs and the problem switched sides to where the 1/4 light would come on. Figured it was a bad ECU so I replaced it. Now the new ECU is doing the same thing except that if I drive faster or in a lower gear to get the rpms to 4200+ the light will sometimes go off.

Switched the new ECU, side to side again, and the problem follows the new ECU.

Any recommendations for what else to check? There is no loss of power, the car runs great, just passed California's new Smog Check 2 with flying colors. No smell of gas or indication of anything else being wrong.

Thanks, I know there have been a lot of questions regarding the ECU's slow down light. I have tried to check past posts but none seem to fit my problem.<font color="000000"><font face="courier new,courier"></font></font>}

I can't think of anything that would cause the problem to move with a new ECU from one side to the other. Try adding additional external grounds to both ECU's.

Which wire is the ground wire that I would tap into?

don't tap into anything. find a good chassi ground near the ECU's and run a 12ga. wire from the chassi/frame/body to a mounting stud of the ECU housings. Someone just posted that Ferrari of Denver adds a ground to problematic 348 ECU's.

Wait a minute...which ECU's? The Motronics or the Cat Temp ECU's?

The Cat Temp ECU. It mounts on the inside wall of the trunk. The ECU looks like it is encased in a plastic compound and that it is not grounded by the mounting bolts.

http://www.ferrari-talk.com/discus/m...tml?1091716388

That was taken care of when we changed the 02 sensors.

However, if there was a ground problem, why does it follow the ECU?

I am going to try re-setting the ECU this weekend.

Thanks for the input.

Re-set the computer by pulling the ground cable off the battery the letting the car idle for 15 minutes.

Took a 200+ trip on sunday in about 95+ heat, no problems.

However, at about dusk driving on the freeway home, the light started to come on again. This time it was when I slowed up and let off the gas a little. If I gave it more gas and increased my rpms the light went off. Light came on and stayed on for about 30 seconds when I got in the slow lane for my exit off the freeway.

Is there some reason the ECU might be too sensitive? Am I running rich?

Driving at below 3500 rpms or over 3800 rmps seems to keep the light from coming on. It only comes on at that small range between 3500 and 3800 rpm.

No loss of power, no change in sound, smell or visuals (no red cat).

Did I just get a bad ECU, even though it was brand new?

If your car is like my older Mondial, there are three flywheel electro-magnetic sensors - one for each ECU &amp; one for the tach. If those sensors go bad, then the ECU does not get a good signal &amp; that may tripping the 5-8 light. Just a thought, as my 5-8 sensor went bad &amp; damaged the exhaust header when a fuel charge ignited in the header.

Have you checked Alternator output under load ( lights, AC on) ?