Slow down warning lights

Well if it did it without cats then I would say the cat ecu's are no good. They are very flakey to begin with. Notorious for being crap. O2 sensors don't run those indicators or shut down a bank. Thermocoupler is a thermometer sending temp to the cat ecu. You have two. Right side of engine bay just above the fuel accumulator if I recall correctly. If you run no cats you can remove the ecu's completely. Only other thing I can think of if you have a really really really rich condition with extra fuel flooding the cats.

R

 

Those lights (and the "electronics" surrounding them) are crap. Their purpose was to detect excessive heat in the cats due to pressure backup (and subsequent risk of fire) at high RPMs.

My cats are hollow so I just disconnected the sensors. They're on the passenger side fender, below the ECUs. Look for a removeable panel in the engine compartment about 8 inches across. They're behind that.

Do the slow down lights turn on immediately and then FADE out when you first start your car? If so (I learned this from the great Steve M), then the sensors are passing their self check. If the lights just turn off then the sensors don't work.

 

They are beyond crap. If you buy new ECUs....there is a strong chance they will be faulty out of the box. High fail rate on the ECU from factory. Disconnect and live life.

 

Testarossa or 512TR ?

 

I wouldn't recommend disconnecting/ignoring if you are running pre- or main-cats with the matrix still in-tact. If you are tuned on the rich side and generating more heat than designed you risk a fire.

If you have eliminated or gutted your cats then yes, you can safely disconnect the ECUs.

 

Understood. Though I quoted you, I was speaking generally, not about your situation specifically--I've found that viewers sometimes don't read entire threads and act on the last advice posted.

 

The buzzer is located behind the fuse panel. Easy to get to and easy to disconnect. The lights still work but no sound.

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Probably a stupid question but here goes. I got the 1-6 slow down light and did a little research here. I switch the wiring harness and got the 7-12 light so I assume I have a bad ECU. Couple of questions. Is there a better solution to replace the ECU with? I can only find one on Ricambi for $887. If I disconnect it will the car still run? Do I just unplug them at the wiring harness or is there more to it than that?

I have the pre cats with a capristo exhaust. 1987 TR with 14,000 miles. About 1,000 miles since I had the exhaust installed.

Thanks in advance


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Which harnesses did you swap over? The thermocouple sends a signal to the respective Thermocouple ECU and the Thermocouple ECU sends a signal to the respective light. Any wiring you swap over will swap the lights.

Did you try interchanging the thermocouples or thermocouple ECUs?

 

I switched the red and green wiring harness that plugs into the ECUs. This did change the light from 1-6 to 7-12 which I believe means I have a bad ECU so I didn’t go further and change the thermocouples. I was wondering about options for a new and better ECU and/or just disconnecting them.




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You should also swap the thermocouple connections as the ECU will also turn on the warning light if it detects a break in the thermocouple connectivity (bad connection, broken wire inside thermocouple). Based on our experience here, I'd say that there's a 99% chance that your warning light ECU is bad and a 1% chance that it's something related to the thermocouple . You don't give the model year of your TR (and your Profile is inaccessible), but early years had exposed screw connections for the thermocouple to the ECU; whereas, later years have a better, more waterproof, connector on a pigtail.

Another good indicator of slowdown warning light ECU health, or sickness, is how the self-test at first key "on" is working -- it should work every time (warning lights come on for a second, or two, and then go out). If the light doesn't come on = it doesn't look objectionable to a human, but it is still a self-test failure. Are your self-tests working perfectly every time?

 

I have a 1987 TR and I will try to add that to my profile. I believe I have the older type ECU. See attached picture. I will also try switching the thermocouple wire. Do I switch it at the ECU or where it plugs into the exhaust? The self test does work (when I turn the key on both lights come on for a short time and then go off). At least until now. Now light 1-6 stays on and I am 99% sure it is shutting down that bank of cylinders. I was hoping someone had come out with a better solution to replace the ECU. Thanks for the help. Image Unavailable, Please Login Image Unavailable, Please Login


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Yes, that's the early style.

You would switch the thermocouple connections at the ECUs, but there is no intelligent connection between these warning light ECUs and the engine = it/they can't shut down a bank. If you are losing a bank, you are losing a bank for some other reason (and maybe the warning light is giving a real result -- the typical scenario is that you lose a bank of ignition, then the unburnt air-fuel charge ignites inside the pre-cat/cat and overheats it which the thermocouple and ECU detect). Are you saying:

A. the warning light just comes on solid, and stays on, when the car is cold = bad warning light ECU, or

B. you drive around for a while, lose a bank, and then the warning light comes on = it's detecting a real overheating event?

Not AFAIK -- had some discussion in the past about someone making one, but don't think it ever happened.

 

During a cold start, both lights come on for a few seconds and then the one light (1-6) remains on. So that should mean that it’s not related to an overheating situation.


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Update from this weekend. I clean all the connections to the ECUs and put a charge on the battery since the car had been sitting without being driven for a while. When I started it up the lights came on and faded out like normal. The car was running smooth so I took it out for a drive. About ten miles in the drive the slow down light for 7-12 was coming on and off. I check the engine compartment and everything seemed normal- no glowing pipes or excessive temperatures as far as I could tell. The light continued to flicker on and off as I drove it back but the car ran well and I put it away. Not sure where to go from here because now I am thinking I don’t have an ECU problem and maybe there is too much fuel going in. Taking it to the shop as soon as they can work it in.


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Since you report it running well and no obvious overheating/glowing, swap all the connectors between the two slowdown warning light ECUs:

If the 7-12 light still has the same bad behavior = that's something for the shop to look at.

If the 1-6 light now has the bad behavior = just buy a new warning light ECU.

(Mark the ECUs with something, like a piece of tape, before the swap so you can better keep track of who's who.)

 

Ok. I will do this and report back. And by new ECU warning light you mean this is what I need to buy? Image Unavailable, Please Login


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And thanks for all your help Steve. I don’t know what the TR community would do without you!


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