: Catalytic Converter Questions.......

DopeStar 156
04-14-07, 03:56 AM
While driving home tonight on Interstate 80 I noticed the car was loosing speed uphills excessively, dropping from 65 right down to 40 and looked like it would keep dropping. The car wouldn't downshift to second gear even with my foot pretty much to the floor. With all my effort I forced the pedal as far down as possible and when the car dropped to second, there was a bad rumbling with smoke coming from the underside of the car with no change in acceleration. I took my foot off the gas and it stopped, when I put it back down I had my original problem. I pulled over and stopped, then took off again. The car successfully shifted from first all the way to fourth but when I hit an incline the car wouldn't downshift. Is this problem TCC related or do I need a rebuilt transmission? My car uses the THM 200-4R.......

04-14-07, 11:18 AM
It almost strikes me as fuel related being down on power. Does it idle ok? Does it run like it is running out of gas?

Can you rev it up ok in Park or N?

Old Fleetwood
04-14-07, 04:00 PM
Yeah, but the smoke from under the car sounds BAD, like a boiled transmission.
The last time I saw that, it was some years ago on an Interstate when I passed a big Mercury wagon towing a horse trailer and I CB'd him.
He said he knew about the smoke but didn't dare stop until he got home since he knew the transmission was already cooked ( ! ).:bigroll:
I hope that's not the case with D-Star, but it doesn't sound too promising.

04-14-07, 04:08 PM
Tranny or cat converter. If converter, engine temp would have gone up a bunch.


04-14-07, 05:11 PM
Hows tranny fluid smell?

I would change it immediately, run it for a short time, and change it again. Get as much of the cooked fluid out of it if it is.

But agreed, doesn't sound good. I missed the smoke part before....

Try manual shifting, it does things differently in the trans, might be safer on it.

DopeStar 156
04-15-07, 12:36 AM
Someone at work suggested a clogged catalytic converter. Since that would've affected the idle speed it would have in turn affected shifting. The car has been running like shit lately regardless wether it's in park, neutral, or drive. He suggested I wack the cat a few times with a rubber mallet and do some high RPM revs to blow out anything in there, after all the car has been sitting most of the winter.....

My second theory is the TCC acting up again and denying the transmission the shift when it needed it.

My third theory is my transmission is on it's way out and needs to be rebuilt, but at 137k it doesn't seem too likely.

I think the problem lies with the engine idle speed and in that sence, the cat might be clogged. I do see black soot eject from the tail pipe on cold starts and the oil leak into the valves must have sent some less than pleasant shit into the exhaust system. Tomorrow I'm gonna beat the cat and see what happens.......

In the mean time, keep the info coming.....

04-15-07, 11:02 AM
Isn't this the second major issue you've had with that '89 recently? Bad timing dude! Not to mention the loss of your Malibu! Oh well, better luck is on it's way! Plus.....you're engaged!

DopeStar 156
04-16-07, 12:14 AM
I can't remember the first major issue with the Fleetwood actually. I never got around to smacking the cat around, the Garden State has been very over watered for the last 24 hours. Hopefully I'll find the time tomorrow.....

04-16-07, 11:22 AM
Sounds like a bad plugged cat to me. I have seen people change transmissions, carburetors, and many other parts only to find the exhaust had no where to go. The only sure way to tell is to loosen the bolts where the exhaust hooks to the manifolds and run it to see if it is plugged or take it to an exhaust shop and they will diagnose it for you. Try running it up in park and when you get to high rpm it should smother the engine down and run bad and the exhaust will usually have a hissing sound if it is plugged. The convertor will get hot and smoke when it is plugged causing your smoke.

04-16-07, 11:32 AM
I am not sure with computer controls how much it will "fix" it, but often plugs get black like rich mix with a plugged cat.

You should get a check engine light, do you?

You might get some idea if you directly connected a wire to the O2 line to a DVM and measure it, or data logger like FreeScan and a cheap cable like http://www.aldlcable.com/ and you can see what is going on.

DopeStar 156
04-17-07, 12:35 AM
I agree, this also would tie into my sputtering and stalling problem I mentioned in another thread. I gave it a few high revs in park in an attempt to blow out some kind of clog today. Strangely enough I saw a little bit of smoke like a lit cigarette creeping out of the tailpipe a few seconds after the engine was shut off. Perhaps now's the time for that performance cat I've been wanting.....

Blessing in disguise?

04-17-07, 01:28 AM
Bad float causes all kinds of headaches too. But usually accompanied by lots of black tailpipe smoke....

04-17-07, 07:43 PM
If the cat is bolted in, maybe you could unbolt it and see if that changes anything?

DopeStar 156
04-18-07, 01:50 AM
As far as I know it is bolted in. My shop manual refers to a test at the A.I.R. Pipe with the hose and nipple from a propane enrichment device and fuel pump pressure gage. Where would I get those things?

How hard is it to replace a cat? Maybe I could do it myself.......

04-18-07, 08:14 AM
It's quite easy, provided you have the tools or access to the tools that'll help you get it out. The original cat is gonna be rusted into place pretty strongly.

DopeStar 156
04-20-07, 02:32 AM
What tools are you referring to? I don't think it'll be too hard, the pipes under there are all silver, no rust on them.

04-20-07, 07:04 AM
GM's test procedure for the cat is to remove the O2 sensor and install a fitting and a pressure gauge, then in gear rev the car up to a certain rpm and measure backpressure.

A local Snap-on, Mac or tool dealer like that probably has the O2 adapter.

Pull the plugs too, see if they are black like they are running rich. The PCM might be pulling fuel back like crazy, so it is hard to say for sure. Also a plugged cat can also backfire through carb at higher throttle. It won't matter if engine is cold or warm, it will run bad all the time. Note that, if it runs good cold and bad hot, that is a sign the cat is ok.

Look for signs of excessive heat on the cat, like blueing of the metal.

If you end up replacing the cat, see if you can get a 87 Monte Carlo SS cat. It is a "wide mouth" cat with less backpressure. You will need an exhaust shop to do custom flanges at the front and back. Hooker has the flange with a cat back exhaust. You might be able to contact them and get just the flange. It wouldn't be too hard to make one. It is about the size of a 3x5 card. Any good exhaust shop worth their salt should have no issues making it work.

04-20-07, 08:24 PM
Random Technologys(sp?) have great cats!

DopeStar 156
04-20-07, 08:43 PM
It's definately something heat related. After driving around all day it started driving shitty again. Something is getting hot and screwing with the way the car drives.....

DopeStar 156
04-22-07, 08:36 PM
Someone else suggested today that I hollow out the cat and drive with it like that. I have over a year until I'm up for inspection so I have that long to replace the thing if I do that. Opinions?

04-22-07, 09:28 PM
You can (obvious legal issues still), but be cautious, that stuff is a health hazard, so don't breath any of the dust or touch the material. It is loaded with Palladium and other chemicals. Use gloves and dust mask.

Expect some louder exhaust, but not objectionable, but louder.

DopeStar 156
04-23-07, 12:21 AM
I picked up a pressure/vacuum tester kit at work today so I'll do that test the shop manual calls for before breaking my cat. I'll have to go from the A.I.R. pipe instead of the O2 sensor since I don't have the fitting for that.......

DopeStar 156
04-23-07, 12:41 PM
New question, I found a Magnaflow cat for my car on ebay for like $73. Should I just grab it and switch it out? Sounds like the cheapest cat replacement I've ever heard of if I do it myself.......

UPDATE: The price just dropped to $70 with free shipping.....

04-23-07, 01:18 PM
May as well go for it, if it wasn't the problem it was probably getting old anyways.

DopeStar 156
04-23-07, 06:38 PM
I bought it, A Magnaflow cat for $70 is too good to pass up......

DopeStar 156
05-02-07, 12:10 AM
Just came in today, on Friday I install it. My car's gonna run so well, this thing is great. Lotsa passage through here.....


Cadillac Giovanni
05-03-07, 05:45 PM
Let me know how that works out. I had an incident with my catalytic converter a while back, and for about 10 months i ran it with the old cat hollowed out because it was the simplest solution at the time.

The only downside is that it made the exhaust very loud INSIDE the catalytic converter. With a hollow space like that it just echoes and can get quite high in volume. I purchased a replacement (I forget the brand) and it also seemed quite scarce inside compared to my original, i could actually see through it from one end to another when held up to my eye. Unfortunately, it still allows some reverberation, and the exhaust is nowhere near as quiet as it was with the stock cat.

long story short, screw catalytic converters. Next time i get under that car I'm cutting a straight hunk of pipe and put the cat out of commission.

DopeStar 156
05-04-07, 02:38 PM
There's definately a noticable difference, the car has more pick up which is what I was looking for.