Question on my 86.

[limomanb]

Forgive my ignorance...but I have 2 more questions:

1. Does the Cat(s) throw a code of their own ..or do they just screw other things up and then codes are thrown? In other words...if my mechanic goes to read the code...does he see a catalytic converter code specifically?


2. Does the Cat affect the idling at all? My idles have been all ver the board....from 500 to 1600...they are fine when very cold...only after warm-up does this happen.

 

[G Winter]

A partly plugged cat will get worse as it warms up. I don't know if there is a code for the cat but it could cause all kinds of things not to be right so I am sure it would make it throw other codes . After you drive for awhile you may notice the engine begins to run warm . As for the idle speed if exhaust is restriced mixture would go rich, computer could go nuts trying to correct it.

 

[vader86]

The cats will not throw a code, they can however affect other things.

If a cat is plugged, which is really the only problem you'll have with them, then they'll get really hot and you'll definitely notice the extra heat around your footwell. You'll also notice a big power loss and generally poor running.

That itself could trigger the O2 to read improperly, but it doesnt mean the O2 has gone bad. The car only reads the O2 sensor after it has warmed up to temperature and the ECM's timers have expired.

What you can do is take a temperature gun and read the temp of the precats and main cat to see how hot they are getting. If theyre too hot, one is plugged up.

 

[limomanb]

OK...I'm fairly sure that the cat (s) is the problem. Would "bad gas mileage" be another side effect due to the mixture being too rich? I'm getting horrible mileage lately.

 

[redc4corvette]

Engine would run hot or over heat, put your hand at the rear of the exaust and have someone rev up the engine.See if the exaust blows your hand out of the way.If you have a heat gun normal engine temp at max should be around 900 to 1200 degrees at the exaust.

 

[vader86]

If the O2 sensor has failed or is reading wrong, it will definitely kill gas mileage.

 

[RonJ]

Engine would run hot or over heat, put your hand at the rear of the exaust and have someone rev up the engine.See if the exaust blows your hand out of the way.If you have a heat gun normal engine temp at max should be around 900 to 1200 degrees at the exaust.

If you suspect that your "cats" are plugged, connect an ordinary vacuum gauge to anything on the intake manifold that has vacuum when the engine is running.

With the engine running, raise the rpm to around 1500 rpm and hold it there for 20-30 seconds, if the vacuum gauge reading becomes lower and lower, a plugged exhaust is indicated.

It's simple, fast and accurate!!

Ron ...

 

[WhalePirot]

Is the engine stock?

You have one CAT, which can get plugged up if the car is running rich.

I would ensure that the tune-up items are proper before pointing at the CAT. I would pull, number and inspect each spark plug to see how each cylinder is firing. Search other threads for what to look for in a proper plug color.

A non-stock cam can cause the hunting idle, but so can other things.

When my CAT clogged due to rich mixture (a somewhat aggressive cam on a slightly modded L83), I lost power slowly. Eventually, the engine would hardly reach high RPM.

 

[vader86]

He has 3 cats.

One large main cat, and 2 precats on the Y-pipe.

 

[limomanb]

UPDATE: Turns out that I had codes 21,22 and 33. Replaced the TPS and the two relays for the MAF sensor. Took it to a Corvette Specialty Shop. Car runs better than ever!! My mechanic ruled out the cats immediately ....ran the codes and had the car back 5 hours later! Wahhoooooooo!!!