Big problem with my 86'.

[limomanb]

I have an 86 with 86K miles on it.It is strictly a weekend car. It's pretty much stock except for the Borla exhaust.
The problem is: I always warm up the car for a while....after accelerating I'll have my foot steady...then the car starts bucking and spitting violently. The spitting is coming from underneath the engine...I'll then put the pedal to the floor and go almost nowhere!! The car continues spitting and bucking. Then the SES light comes on. I'll pull over, sit for 5 minutes or so. I re-start the car and all is well...eventually this sequence repeats..this is happening all too frequently. also, my idles have been all over the board..from 500 to 1600. Waddya you guys think? Fuel pump going? MAF sensor? Something else?
Are the bucking/spitting and idle problem two separate things? Any help would be appreciated.
BTW- The last time it was in the shop...they installed a "prom".

 

[Ken]

Cats. I'll bet it's the catalytic converter(s) going bad; when they plug up and are quiet, the car won't get out of its own way - it's not able to breath (exhale). When they cool off and loosen up, making noise (mine sounded like a bad rod) the car runs great.

Sound right, is that what your's is doing, or am I coming from out in left field?

 

[limomanb]

Could be...but I've only pulled over for a few minutes...I don't know how much the cats will cool after only 5 minutes or so. Will the cats throw a code....or maybe screw something else up..that then throws the code?

 

[Ken]

In my situation, all three (the two pup cats, or "pre-cats", as well as the main converter) were all bad, and it would resume mormal operation after only ten-fifteen minutes. That's a long time when you're sittng by the side of the road though. :L

 

[Rowdy1]

Talking Left Field....

I don't know codes but a defective coil will also cause a similar reaction, or the engine will die completely and only restart after it cools down, been there, done that. It does sound like a cat symptom.

 

[limomanb]

What can I expect for a ballpark price to replace the cats? If that is the problem. I will have it done at my local Vette shop.

 

[G Winter]

Find a place to hook a vacume guage on. Have it warmed up and hold the throttle a about 2000 rpm and don't move it . If vacume starts to drop I would bet it is the cats plugged. Sure sounds like heat is the issue here,and I agree with the coil idea too. Could even be the modual in the dist, a weak one could react to heat. I wouldn't think a feul pump would react quite that much. good luck .


modual,,, now everyone knows I can't spell.

 

[Edmond]

Plugged up cats would affect the O2 sensor because the O2 sensor comes after the cats, right? I just replaced my O2 sensor a month ago and I can't remember if the pup cats came before the O2 sensor.

And if the cats are plugged, the O2 sensor isn't getting the correct amount of air to work properly. Am I thinking right here?

 

[rrubel]

What can I expect for a ballpark price to replace the cats? If that is the problem. I will have it done at my local Vette shop.

Ecklers will sell you a main cat for about $150. I've got one on my 86 and it installed painlessly.

If you have front cats (my 86 did NOT), you could probably get away with a cat-less front Y-pipe. I've got one lying around here, and I'm sure others do, so you could get one cheap. I didn't think they were even used on many 86's.
[RICHR]

 

[RonJ]

I think the O2 sensor is before the cats, they like heat, and it's module .... <G>

Easiest way to check for a plugged exhaust is to use a vacuum gauge, just like described. You don't even have to get under the car!!

Ron ...

 

[G Winter]

Thanks for the correction, Ron. My wife wasn't handy for spell check.:L

 

[Vettefan87]

Plugged up cats would affect the O2 sensor because the O2 sensor comes after the cats, right? I just replaced my O2 sensor a month ago and I can't remember if the pup cats came before the O2 sensor.

And if the cats are plugged, the O2 sensor isn't getting the correct amount of air to work properly. Am I thinking right here?

I know that on my car the O2 sensor is before the main cat, and I am pretty sure that it is before the precats.


Justin

 

[jsinga]

O2 sensor is before the pre-cat.
If cats are plugged when you run the engine at 2000 for a minute the exhaust manifold will glow a dull red and the vaccuum will also drop.
If you install a new cat it will pass a smog test without pre-cats. You can deal with the pre-cat situation in a couple different ways: get a new pre-cat pipe, get a pipe without pre-cats, punch out the pre-cats and put the pipe back on.

JS

 

[WhalePirot]

I think the O2 sensor is before the cats.

This depends on the model year, as some have 4 oxygen sensors, two each side, with one before and one after, to monitor the 'pup CATs' operation. Most though, have the sensor before the CAT. There was a fair bit on discussion about this in an old thread.

I found my CAT was badly plugged (after running rather rich, for a long time) when the engine would no longer rev past 3500 RPM.

I don't know the exact wording of the EPA law concerning legally eliminating or disabling any part of the emissions gear, for a street driven car (see above thread on 'Emissions Tampering').

I am neither advocating nor judging those who do; just stating a potential problem (large fine) that someone might wish to be aware of.

 

[limomanb]

I'm not sure if I have the pre-cats or not. It's a Borla Exhaust system. If I have the pre-cats and then opt to go with just the Y pipe and a main CAT....will I pass smog inspection....FWIW...It's CALIFORNIA smog.

 

[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.