Possible clogged Cat Converter

[78silverbird]

I would just like to run this by some people and see if I am diagnosing this right. OK I have a 1999 GA GT 3.4L with 70,000 miles on it and about 2 months ago I started to notice that the temp gauge was reading higher then it used to and when this happened the tranny would want to slip a little bit on me in Drive (but only when I would change from park to Drive or Reverse to Drive). I now am starting to notice that the engine wants to continue to heat up even after I turn the car off and acceleration seems down a little, all of this is making me think and has been suggested to me that my Cat Converter could be clogged up, not letting exhaust gasses escape as much as they need to.

Any other diagnoses would be appreciated

[BNaylor]

There are 2 tests that can be run for a possible clogged CAT convertor or excessive exhaust backpressure or restriction. A pressure test where a special adapter/fixture is connected a the front 02 sensor bung. The reading should not exceed 1.25 psi. Muffler shops or the GM dealer can perform this test.

The easier DIY test is to procure an automotive vacuum gauge (0-30hg). You tee into any vaccum line at the intake manifold. At idle with engine properly warmed up the reading on the gauge will be in a range of 15-22 in hg. The rpms are increased to 2000 rpm. The gauge will fluctutate initially but then maintain a steady reading of similar to above but possibly a little higher. If the reading is erratic or starts dropping off towards the low range 15 psi or less then there is a high probability the CAT is clogged.

Low readings at idle (less than 15) would indicate a really bad clogged CAT or other problems like intake manifold gaskets.

[grfnkl]

right now i would say that is a good possiblity that your cat conv is clogged up. the only other symptoms that you may get, is tranny slippage while driving, and the car not wanting to turn over either on cold or warm start.

[78silverbird]

Does anyone know what an average cost of replacing the Cat Converter would be?

[BNaylor]

Originally Posted by 78silverbird

Does anyone know what an average cost of replacing the Cat Converter would be?

The OEM GM one can be expensive. How many miles are on your GA?

Magnaflow makes an excellent hi-flow CAT with ID in/outlets ranging from 2.0" - 2.5". Around $55 including shipping on EBay. Ball park $40 to have it professionally installed.

[xeroinfinity]

thats a great DIY test for the Cat.

hopfully its not your LIM gasket! thats a pita!

[Northcat]

I don't think your cat converter is plugged. It's definitely possible, but everytime I've had or seen a converter plugged the engine will start pinging and your O2 sensor should fault.

Also the engine will run normal initially, but become more sluggish the longer you drive it...shut it off long enough to let the pressure desimate and the car will start and run normal for a certain time again.

Also, depending on how many miles you have driven your car since you noticed the problem 2 months ago...I think your converter would have been clogged solid by now and you wouldn't be able to drive your car 2 miles before it died.

also I would be very suprised if a converter plugged at 70K.
I have 86K on my 3.4 L and I buy the cheapest gasoline...but perhaps blowing coolant out an exhaust valve helped clean it out in my case.

Is everything else normal in with your car? Not losing coolant? No coolant in the crankcase?

It almost sounds like your car is running lean, like the fuel pressure regulator is going bad. Higher temps, acceleration down...don't know about the transmission slipping though...


and if it does happen to be a LIM gasket, I'm your guy, tore mine all the way down to heads off 3 times earlier this spring, I can walk you through that process bolt by bolt including the tools needed list. It's really not as bad as everyone says but does take some time.

[BNaylor]

Originally Posted by xeroinfinity

thats a great DIY test for the Cat.

hopfully its not your LIM gasket! thats a pita!

Yeah Xero, it sure beats speculating as to whether the CAT is good or bad.

BTW - My brother's '01 GA GT CAT failed at 58K miles. It was replaced by the dealer under GMs CAT convertor emissions warranty for free. The CAT warranty is 8 years or 80K miles, whichever comes first.

[78silverbird]

Well I have lost some coolant but I didn't see where it could be going, no puddles on the ground, no coolant in the oil or anywhere in the engine. I'm not sure b/c I haven't checked it in a couple of weeks (been out of town) but I think it was being lost through a loss hose on the reservoir seemed to bubble out when I pressed on it. So I loosened the clamp and moved the hose up and tightened down again hoping that fixed the problem, going to check this afternoon.

[BNaylor]

Originally Posted by 78silverbird

Well I have lost some coolant but I didn't see where it could be going, no puddles on the ground, no coolant in the oil or anywhere in the engine. I'm not sure b/c I haven't checked it in a couple of weeks (been out of town) but I think it was being lost through a loss hose on the reservoir seemed to bubble out when I pressed on it. So I loosened the clamp and moved the hose up and tightened down again hoping that fixed the problem, going to check this afternoon.

One sign of an LIM intake gasket problem is unexplained usage of coolant. What occurs is it is being consumed in combustion. It does not have to show up as a leak or in the oil. Further, flaky intake gaskets could lead to CAT convertor damage or failure by causing the CAT to operate higher than 1200 degrees F internally. Here is the applicable GM TSB on the issue and the gaskets were revised.

Engine Oil or Coolant Leak (Install New Intake
Manifold Gasket) # 03-06-01-010B - (10/24/2003)


Engine Oil or Coolant Leak (Install New Intake Manifold Gasket)

2000-2003 Buick Century

2002-2003 Buick Rendezvous

1996 Chevrolet Lumina APV

1997-2003 Chevrolet Venture

1999-2001 Chevrolet Lumina

1999-2003 Chevrolet Malibu, Monte Carlo

2000-2003 Chevrolet Impala

1996-2003 Oldsmobile Silhouette

1999 Oldsmobile Cutlass

1999-2003 Oldsmobile Alero

1996-1999 Pontiac Trans Sport

1999-2003 Pontiac Grand Am, Montana

2000-2003 Pontiac Grand Prix

2001-2003 Pontiac Aztek

with 3.1L or 3.4L V-6 Engine (VINs J, E - RPOs LG8, LA1)

This bulletin is being revised to change the model Information. Please discard Corporate Bulletin Number 03-06-01-O10A (Section 06 - Engine).


Condition

Some owners may comment on an apparent oil or coolant leak. Additionally, the comments may range from spots on the driveway to having to add fluids.

Cause

Intake manifold may be leaking allowing coolant, oil or both to leak from the engine.

Correction

Install a new design intake manifold gasket. The material used in the gasket has been changed in order to improve the sealing qualities of the gasket. When replacing the gasket, the intake manifold bolts must also be replaced and torqued to a revised specification. The new bolts will come with a pre-applied threadlocker on them.

Notice

An oil leak may result if the vertical bolts are not tightened before the diagonal bolts.


Diagonal bolts may require a crows foot to tighten.

Tighten

1. Tighten the vertical lower intake manifold bolts (1) to 7 N.m (62 lb in).

2. Tighten the diagonal lower intake manifold bolts (2) to 7 N.m (62 lb in).

3. Tighten the vertical lower intake manifold bolts (1) to 13 N.m (115 lb in).

4. Tighten the diagonal lower intake manifold bolts (2) to 25 N.m (18 lb ft).

Parts Information

Parts are currently available from GMSPO.

[xeroinfinity]

another test that can be done for the cat is to use a pyrometer which is a high temperature thermometer by placing the probe on the inlet of the converter, about 50 mm in front of the unit and read the temperature.
Then place the probe on the outlet side of the converter, about 50 mm to the rear of the converter, and again read the temperature.

The outlet should be at least 40 degrees Celsius hotter than the inlet. If there is no difference, the converter is faulty and should be replaced.

Next you can use an emissions analyser to check that the carbon monoxide and hydrocarbon readings are close to normal. Enrich the mixture with the addition of propane to the inlet air. The converter should hold the CO and the HC readings down to normal. If not, then the catalytic converter may be faulty.

Lean conditions arent the cause of cat failure.
Rich fuel setings build up and plug converters.

I too just replaced my LIM this past weekend on my GT. It was leaking oil and coolant out the back of the motor(under TB) and oil into the coolant... what a mess

The new gaskets(with metal rings) are the shit! Dont know why it wasnt done sooner :

[78silverbird]

Well if that is my problem how much did it cost and how long did it take you to do?

[78silverbird]

Well this afternoon I went by the Muffler shop to see if they could run a pressure test to check Cat Converter. They didn't have any of the equipment needed to do that so they checked it by checking the flow out of the tail pipes... hardly any the Cat had to be clogged went ahead had it replaced checked again much better flow. Assumed that was the problem and went on my way. Well it must not have been the problem b/c I am having all the same problems a little more so then before (except the acceleration that seems to be better) I have also been getting really bad MPG hoping that was b/c of the clogged Cat. Please help what else could be causing all of this.

Again symptoms experiencing:
Elevated heat levels
Continuing to heat up after car is off
Slipping tanny when engine heat is up, otherwise the tranny's fine

[xeroinfinity]

Originally Posted by 78silverbird

Well this afternoon I went by the Muffler shop to see if they could run a pressure test to check Cat Converter. They didn't have any of the equipment needed to do that so they checked it by checking the flow out of the tail pipes... hardly any the Cat had to be clogged went ahead had it replaced checked again much better flow. Assumed that was the problem and went on my way. Well it must not have been the problem b/c I am having all the same problems a little more so then before (except the acceleration that seems to be better) I have also been getting really bad MPG hoping that was b/c of the clogged Cat. Please help what else could be causing all of this.

Again symptoms experiencing:
Elevated heat levels
Continuing to heat up after car is off
Slipping tanny when engine heat is up, otherwise the tranny's fine

Well since they couldnt perform the right tests on the Cat, I'd hav found somewhere else to check it. Converters these days really do last a long long time.

The heating up could be a gasket leak, not sure of which, either your head or Lower intake
The head gaskets can be checked with a compression test, though it doesnt always catch it. Last year My SE was all good on the compression test, but when I torn it down, it was indeed blown out, letting coolant Pour into the oil.
Got damn lucky it didnt screw up the bearings.

As far as the LIM, are you still loosing coolant mysteriously??

And the excessive heat will make the trans act a bit rough, with poor power.

Been racing on it hard??

I would bet it is the head gasket though.....

[78silverbird]

Well seeing as I had hardly any exhaust coming out the tailpipe before I changed the Cat and quite a bit after words I would guess that the Cat was clogged. Also I do trust the muffler shop I went to, it's the best one around here. As far as I've heard they are always able to diagnose the problems pretty accurately. If it was the head gasket would the coolant always leak into the oil b/c I have checked the oil several times since this problem and changed it once and the oil had no coolant in it. As far as me loosing coolant mysteriously, it seems to be a little low since last I checked. However the engine is still hot so it could rise a little when it cools.

No, I try not to race it hard probably baby it more then I have to. I have raced it before but just a couple of time from red-light to red-light with friends I try not to push it.