Warning Light!!! Help Please!!!!

either a faulty cat or more likely a faulty thermocouple on that bank.

dont worry!

 

The same problem just happened to me this a.m. My 355 had been running
"rich" for a couple of days, so I put some Techron in the car
yesterday hoping that would help. Today, the SLOW DOWN light
came on when I was over 6k RPMs for an extended period of time,
and went off when I lowered the RPMs. When I parked in my garage, the
area was redolent with an unusual odor. I have a set a test pipes, and
have already called my mechanic to schedule an appt for Monday to
check out the problem. Is there any chance that this could be just a
thermocouple issue, and not damaged cats?

Regards,
Gregg

 

Although 355's have their fair share of cat problems, if the cat is not the issue it is more likely an exhaust temperature ECU problem.
My car's slow down light would come on as soon as the car was started (cold) making it a dead giveaway that it wasn't the converter.
I would predict it is either the ECU or the thermocouple first (especially if you have test pipes).

Let us know how both of you make out.

Pino

 

Turned out to be oil fouled spark plugs. Car is running great now.
I'm no mechanic, however, the rich mixture travelling toward the
cats probably caused them to heat up. They were not damaged,
however, I've left them off for the time being, and had the
test pipes reinstalled.

Gregg

 

Thanks for posting the results!
I would not have thought that would cause a problem. Something else to keep in mind when the light comes on.

 

Gumball: Quick test for you, when the 'slow down' light illuminates, pull over and look to see if your catalytic converter(s) are glowing red. If so, real problem, either wait to cool and drive slow home or flatbed.

If not glowing, most likely electrical gremlin, less cause for concern, but must be resolved nevertheless.

Search old and new archives for "thermocouple, ecu, slow down". Lot's of pertinent information that will assist you in resolving the problem with your chosen technician.


Greg: You did have a misfire, are injecting fuel without igniting it, and it's burning in the exhaust, not the cylinder. The tip-off is high rpm driving and the smell. If your catalysts were installed at the time, look at the honeycomb-like matrix to see if it's "coned" shaped. That's an indication of overly high temperatures and the matrix breaking down.

Oil fouled? Hmmm. Old plugs or what? Lack of miles, garage queen? Leaking valve seals/guides, rings? Did you do a leakdown test?



A false positive 'slow down' may or may not be accompanied by loss of power, but will never dump unburned fuel into the exhaust. Loss of power in this situation is caused by injectors not firing, so no fuel. Typically only on one bank at a time, too, which is why an easy test here is swapping thermocouple ecu's.


Best regards,

Rob Schermerhorn

 

Rob, thanks for your input. 10k on the plugs and about 14k in the last year and 1/2, including 2500 mile trek from Houston to Cocoa Beach.
Drive for fun about 4-5 days a week, sometimes pretty short trips in pretty bad traffic. I did not do a leakdown test. I have the results
of the last one, what is an acceptable delta, if any.

Regards,
Gregg

 

Glad to see you're driving

For a street-driven car (not race), at 12% I'd say "hmmm", at 15% I'd want to know if it's guides/valve seals or rings and start saving up for repair. At 20% I'd consider scheduling the repair or at least keeping an eye on plugs and oil consumption more often, power and efficiency is being lost, though still not keeping anyone from having fun driving. At 20% leak there may also be other issues such as idle stability, off-idle throttle response, plug fouling, misfire, exhaust emisions. I'd also double check results and verify test equipment.

For a serious race car, I'd reseal the top end at the end of a season if leaking greater than 5%, depending on owner's budget and desire to win. Definately at 10%.

Best regards,

Rob Schermerhorn