NEED HELP!!! ENGINE BUCKS UNDER LOAD!!

[pocket-rocket]

A little something I found on cats:

The ongoing evolution of catalytic converter technology is driven by the need to maximize results with respect to vehicle acoustics, performance and emissions control. As complexity increases and warranty periods are extended, catalytic converter manufacturers face an ongoing financial risk when units fail before their life expectancy is reached. The long-term effectiveness of the catalytic converter can be impacted by factors outside of the exhaust system control, (e.g. gas quality) which augments the risk of premature catalytic failure.

Background - Automotive catalytic converters must provide a very high level of mechanical and thermal durability to maintain performance during their 100,000 to 150,000 mile life expectancy. The modern day catalytic converter consists of a coated converter substrate packaged in protective mat material and housed in a metallic can to contain the hot exhaust gasses. The mat material plays a critical role in protecting the substrate from engine and road induced vibrations and exhaust induced thermal and pressure stresses. However, little or no consideration is given to the mat material dynamic properties during the converter design effort. Nevertheless converter design acceptance is based on accelerated hot vibration aging tests where the converter is subjected to engine induced high temperature exhaust gases with a high level of shaker induced can vibration, often at 75 g's or higher. The objective of the investigation is to demonstrate that catalytic converter durability design can be accomplished in a cost effective manner using a fundamental mechanical modeling approach employing coupon level mat material fragility data.

[pbui3057]

Do you have any recommendations on cats? I read somewhere on the forums that all cats are somewhat non restrictive now. Is there a point to getting a high performance one? If so, then where could you get one and at what cost? Thanks again!

P.S. have you tried these yet?

[RednBlack]

Do you have any recommendations on cats? I read somewhere on the forums that all cats are somewhat non restrictive now. Is there a point to getting a high performance one? If so, then where could you get one and at what cost? Thanks again!

P.S. have you tried these yet?

First, before you spend money on a cat, either unbolt it and pull it loose, or, (this is an old timers trick), drill holes in the lead-in pipe that can be welded back up. Or, just replace it with a "Test" pipe. They don't make them anymore, but if you get the dimensions, any muffler shop will make you one for about 10 bucks. This is only for test purposes. If you don't have E Check, Hell, leave it on. I have seen Cats so bad that the engine literally burned itself up. Especially if you are on the Interstate. Another clue would be "Glowing Red Cat", and very little exhaust pressure. And what are those strange things at the end of your post? Looks like cartoons!

[94oldsdohc]

I disconnected the Oxygen Sensor and took the car for a ride. It still has the same symptom of cutting out and missing under load. I did not get a code on the ECM after disconnecting the wire and driving the car either. Should I get a code??

After reading the comments, I know there is sort of a metallic rattling coming from under the car, therefore, it may be a damaged cat as mentioned in the comments. So...the next thing I am planning is to have the cat replaced.

[pbui3057]

No problem. I at home bored off my ass, so I had nothing else to do, lol.

I was just seeing if pocket had tried any of those suggestions yet!

Would an exhaust shop be able to tell if the cat is bad without unbolting it?

[pocket-rocket]

No, I knew mine were bad from the rattling sound and replaced the exhaust system with one from one of our parts cars. Now that cat has gone bad, which I didn't expect to get much life out of a used one. I have heard good things about Carsound cats, and you can pick them up all day on ebay for about $50.

[94oldsdohc]

I plan to remove the cat tomorrow and clamp a test pipe. What O.D. size of tubing have you guys used for a test pipe?

Thanks!!

[RednBlack]

If I weren't so drunk, and it wasn't so late, I'd get out and measure it with Calipers. I am, so I did. It measures, Going in at 2.5" OD, Actually 2.475". . Going out is 2.25" OD, Actually 2.280" . Pipe sizes aren't that accurate. 2 1/2" in...2 1/4" out. I ain't doin' the length! Get a tape measure.

[94oldsdohc]

Go to sleep and take some aspirin for your hangover Thanks for the measurements.

[RednBlack]

I doubt if I ever have a Hag Over.

[pocket-rocket]

I don't remember the size, but some guys get a section of pipe that slides in the downpipe, and over the rear section of exhaust, instead of using those size adapters at the parts stores. I was going to use a peice of flex pipe untill I got something more perminant figured out. Even though we don't have emissions here, if you get cought running without a cat, I think they can fine you, and tow your car if they want to be a real ass.

[94oldsdohc]

Did the test pipe deal...but...the problem is still there the only items I have not changed are the crank position sensor, map sensor, oxygen sensor and timing belt. I will be cruising the freeway at 68 to 70 miles and during and then suddenly the car will saart to miss and shudder. After it starts, it will continue doing it and if I stop in traffic and step on it, it will start to miss. It will also do it under load and specially if I am going up an incline.

Never had any kind of problems with my previous 1994, 3.4, DOHC Olds Cutlass.

I am just running out of options and there are no codes either. Am I overlooking anything???? I getting close to selling the car cheap.

[RednBlack]

For some reason, this is seeming more and more to be a spark issue, since it calms down overnight. The old ignition modules used to do that when they got hot. Did you ever get all the right plug wires on? One bad wire can spoil the whole bunch. Or make it seem so.

[pocket-rocket]

Does the engine actually shudder? I know the early autos had a problem with the lockup in the torque convertor. Actually it was the solenoid for the lockup. Next time it does it, press on the brakes enough to turn on the brake lights. If the problem stops, it is your TCC solenoid. Only thing is I thought they did the shudder thing at about 55 mph, not 65-70.

[94oldsdohc]

All the plug wires are replaced. The shudder occurs and the engine seems to have some sort of backfire when it does. It also occurs while taking off form a standing start. the coil pack and ignitor came off a car that was running with no problems, nevertheless, you never know. i am just totally baffled