EXHAUST TEMP warning light....

[Lazzman]

I was SO proud of my wiring job. Every light and switch seemed to be working perfectly. Then, I had an extended session charging the battery with the engine running.

I found something very curious about the EXH TEMP ligth from the CATALYTIC CONVERTER sensor; the light came on with ignition, timed off (even before the seat belt light) and interestingly, comes on when you gun the engine- I started wondering what is wrong with my wiring when the thought occured; is it working correclty and warning me of a burned out catalytic converter? Any opinions? Ger

[Roadtrip]

My understanding of the EXH TEMP warning light is that an overheat condition is signaled to the driver by first flashing, meaning slow engine speed to reduce heat buildup, and then finally comes on steady which means immediate shutdown.

Could it be that you have bare wire somewhere, that when you rev the engine, the wire shorts out, thus illuminating the caution light?

[Lazzman]

No- the wires are all still exposed pending dash replacement. The wiring is pretty solid at this stage. Another member sent me an EMAIL suggesting that the mixture was too rich and that this could do it. Will look into it... Ger

[desert spider]

The light will come on for two reasons:
1, The O2 sensor has been in place for a 30,000 mile interval and the mileage counter which is programmed to turn the light on is working. It doesn't mean that anything is wrong with the O2 sensor, and this doesn't mean that your sensor necessarily needs replacing, but it is a good idea.
2, The mileage counter has not clocked a 30,000 mile interval and you actually have a bad sensor. This can be caused by (a) the sensor is overdue and is worn out, or (2) you have been running over rich and the sensor is coked up. Pull it out (it's a simple job) and see if it is coked up. If it is, clean it off and re-install it and look for the source of the rich fuel mixture. If not, it's probably o.k., so re-set the sensor clock if your car has gone a 30,000 mile interval. (another simple job).
If, after all this it still lights up, replace the sensor and re-set the clock.
Jim Evidon,
Desert Spider '84

[papajam]

Jim gives a great description of the exhaust warning light as fitted to the closed loop, O2 sensored S3 Spiders with L-Jet. Correct me if I'm wrong but I think that Ger's '78 S2 SPICA Spider has neither an O2 sensor or a mileage counter and the light indicates high exhaust temp only.
I take it Ger that the light didn't come on prior to the rewire? Is it possible that the thermocouple may have been damaged during the rewire? Is it even the same thermocouple? I've never had the cat overtemp device apart but maybe there's an adjustment?
I'm shying away from an actual overtemp condition because the sensor would be cool during idle and thermocouples, at least the ones I'm familar with, are quite slow to respond to temperature changes so having the light come on by simply blipping the throttle would seem unlikely.

I think.

[Roadtrip]

I think Jim E is thinking L-Jet instead of SPICA. The 78 SPICAs had an cat overheat warning only. Of course, the SPICA has a mechanical mixture computer with no O2 feedback loop like an EFI system.

It was there just to prevent damage to the cat. If prior to the rewire, the exh temp light circuitry was operative, but not indicating overheats, I highly doubt that simple rev'ing of the engine (even if grossly rich) would cause an immediate overheat light. And why would the engine be rich, all of a sudden, yet run the same? Still think it's a bare wire somewhere that grounds as the engine moves slightly in it's mounts.

[desert spider]

Yes, indeed. I was speaking of L-jet and not Spica. Sorry.
Jim

[bbalanoff]

Does anyone know if a catalytic convertor sensor for a 78 spider can be bought?
Brian

[Roadtrip]

Try DiFatta Bros for a new one or APE for a used one.

[81alfa]

Gerry,
If you can remove the sensor be sure it is not bent and touching anything inside the Cat. Con. I had mine replaced and the sensor had bent touching the metal which caused it to read overheated, sending the light on. Also it must be tight in the unit. As for replacements I found one at Mieneke(spelling?) and the guy even drilled a hole for the sensor and spot welded it in. $147.00 after market Cat. doesn't vibrate like the orig. ones do. Metal heat def. always hums after a few hundred miles on the orig.
Good Luck.