Okay, kind of started a thread related to upgrades to my '89 Coupe with only 90K miles on it.

The car had an over heating problem that the previous owner did a half *** job putting new head gaskets on and thus I had to rebuild the top end of the engine as he did not torque driver side head down correctly and thus blew back through the cooling system.

The heads were stamped with a very reputable head shop here in town and so I took the heads to him. They pressure tested and the heads are in great shape and was able to confirm the heads were completely rebuilt when he had them in the shop about a year ago.

Jump forward... New radiator, new aluminum water pump, hoses clamps, yada yada. Just for kicks a ZR-1 140 amp alternator and aside from the headlight bushings which are ordered the car is a awesome, however...

Compression test was AWESOME and all the cylinders are withing in 10 pounds and hold pressure. Nearly no ridge in the cylinder walls. Can even see the cross hatching still..

Rough idle and I don't mean lope. So I put premium gas and a can of Sea Foam and it appears to be doing better. Have not had a chance to run the tank out so we will see. It is starting loads better.

So was thinking injectors need a cleaning. Tomorrow a new fuel filter... the basic work up on a newly acquired 28 year old car. I think I have a handle on that part.

Here is the rub. My dad has an '89 Greenwood Edition and mine just does not have quite the same "grunt" although it has less miles. Checked timing and new cap, rotor, wires and plugs... tuned up nicely.

I am beginning to thing that perhaps the catalytic converter and/or pre-converters are bad as the converter is smoking when I shut the car off.

Yes, I want to rip all the smog control bullshit of of this car, but I am not looking for an excuse to do so at this moment. But I did experience a car previously with similar issues before and the cat was just clogged.

So, what do you guys think about my situation and the cat is just done for?

Is there anywhere you can still buy a cat "test tube" or should I just take this cat, cut the flange and weld up my own?

I know the cats run hot for a reason, but smoking when I park the car????

 

sometimes oil will drip off a valve cover or from the rear of the intake on to the cat;if youre are original Id probably just buy a new Y pipe/cat assy
if your injectors are original just replace them makes a big difference

 

There are a bunch of reasons that your car, may not feel the the same. Do you may have the same exact engine and trans combo? Auto verses manual will make a difference and if your rear end is geared different there will be a HUGE seat of the pants difference in feel.

Cats being clogged is certainly a possibility but a bit on the remote side unless your overheating head situation traveled downstream and jacked up your converters.

 

If you suspect the cats are an issue, there used to be test kits out there. You would drill a hole prior to the cats and check for back pressure. I had it done at an exhaust shop on my old truck and that was a pellet type cat and there was some strange stuff going on with it.

Any smoke coming form a cat is external fluid burning off

As for the injectors. I have cleaned them out myself before. I used B-12 fuel cleaner and forced it into the injectors while triggering it with 12v. Home brew, but I found a lame injector this way and saw the result of running the cleaner though. This was a different car that I can remove the injectors with 2 bolts. On the vette I would replace them since it takes so much work to do this.

I had the pre cats fail on my 90. No signs of them going out. They just fell apart and clogged the main cat. The restriction made it impossible to go over 2000 rpms. Painfully with the 6 speed I was able to limp it home under 2000 rpms.

 

Check your fuel pressure if you havent already

 

First of all, filling the tank up with 93 octane and a can of Sea Foam has improved idle and start up tremendously.

Not out of the woods yet, but then too I have not driven her much.

I have already scoped out a new exhaust system with headers along with a new program via a custom chip.

 

All good points, but extremely obvious. After 30 years of drag racing and engine building I would not make an apples to oranges comparison. The two cars are identical with similar mileage. That being the factor that lead me to the comparison.

I know the difference between performance and performing well and mine is not in spite of a new top end job and phenomenal compression and leak down numbers.

I now believe it is in the fuel delivery system as well as cat. Being mine is an '89 the cat is in front of the differential and that is what is smoking. NOTHING aside from a leaking tranny is getting on it back there and I know the smell of burning transmission fluid.

In addition there is not leak one on my car. I monitor the parking and have had it on the rack (my brother owns his own shop) and have nut and bolted the car from front to back.

And since I have had experience with bad cats on other cars that also overheated (why mine had a top end job) and blew a head gasket and I also determined the cat was bad by the sheer fact that it was getting extremely hot and performing badly, well... here we go again.

I am just looking to see if anyone else has had this same experience. The problem with the C4 is that is covers so many drive train combos and alterations. 1989 to 1992 seem to be the most "one off" years out of all of them all.

 

Everyone keeps saying the same thing...

1989 did NOT have cats forward. It had pre-cats and then actual cat is just ahead of the diff and there is nothing leaking on it aside from possibly the tranny and I have ruled that out.

I have rack this car from valance to valance. I have even parked it with newspaper under it to rule out leaks...

Not my first rodeo cowboy, so please offer up something that I am missing.

 

Question: How can anything on the inside of the exhaust system make the outside of the system smoke? Is your exhaust system rotted out?