Can a bad catalytic converter cause stumbling/hesitation?

[AlaskaFestivaGuy]

One of my nice LXs has, over the course of 3 years since I bought it, developed a nasty habit of stumbling/jerking/hesitating that makes it a pain to drive, and potentially dangerous.

Typically, it occurs while cruising on the flat at, say, 30mph. Most of the time when I floor it (in the proper gear), it's fine --- but not always. Sometimes, under hard acceleration, it simply stops producing power for a second or so.

Interestingly, it doesn't seem to happen as much until the car warms up (just a few minutes this time of year).

Today, I took it to a Napa-branded shop that has a mechanic who claims to know carbs. He claims that I need a new catalytic converter before he can investigate any more. The shop charged me for an hour of his time, which seems reasonable, particularly since I would never have thought the converter could be the problem.

BTW, I don't need emissions testing on my LXs in WA any longer since they're over 25 years old, so any converter failure would not be picked up by having becoming a polluter.

[WmWatt]

Replacing the catalytic converter used to be a favourite scam of muffler shops. Back when they had lifetime muffler warranties I was told more than once converter was rusted out and blowing rust back into the muffler and ruining it. Funny thing is my car has passed emissions tests all these years with the original converter. I declined the advice to replace the converter and when they eventually discontinued the lifetime warranty on all their mufflers I replaced my own and haven't had to do it again since. I'd suggest only replacing the converter if your car fails an emissions test. I'd also suggest paying the $30 or so for an emissions test to check this before paying for a new converter.

The O2 sensor and converter are emissions devices to fine tune carbon combustion, they don't have much of an effect on engine performance. If the O2 sensor fails your car will still run and until the O2 sensor warms up and starts sending a signal to the computer you car runs fine using the factory default settings.

I'd also suggest your mechanic unplug the O2 sensor and ignore the check engine light and investigate the problem that way.

[AlaskaFestivaGuy]

Here in WA, emissions testing isn't required for vehicles more than 25 years old.

But since it costs only $15, I think that might be a wise investment (assuming they'll run the test on a vehicle not requiring one). I'll be on their doorstep in 0830 Monday. Good idea!

[bravekozak]

Install a straight piece of test pipe. I passed emissions with flying colors without a cat.
It can cause all sorts of problems.
For instance, the EGR valve was stuck open for a long time on my Caravan and the cat got all plugged up with tar.
No power going up hills plus hesitation.
Blocked EGR, cleaned out intake, new low priced cat.
No more problemos.

[WmWatt]

^^ If you have a vaccum guage it can be used to diagnose a restrcted exhaust system. To see how look at the "sticky" on vacuum diagnostics at the top of this forum.

The EGR valve can be tested by gently pushing up from below to check it's not sticking, should move freely. If it's sticking it's easy to clean with solvent. Just be careful not to damage the diaphragm or drop anything into the opening where it will get sucked into the cylinders.

[AlaskaFestivaGuy]

Where is the EGR valve located? Photo would be nice!

[radi8u]

Speaking of catalytic converters, a buddy of mine broke down on I-70 and left his car on the shoulder. It took about 2 hours for the tow truck to get it back to the shop. In that time someone had attempted to cut the converter off his car! Freaking thieves!!!

[WmWatt]

The EGR valve is the cylindrical device on the passenger's side bolted on just below the carburettor. There are two bolts and a metal gasket. Mine has an orange hose and a black hose.

[TominMO]

Install a straight piece of test pipe. I passed emissions with flying colors without a cat.
It can cause all sorts of problems.
For instance, the EGR valve was stuck open for a long time on my Caravan and the cat got all plugged up with tar.
No power going up hills plus hesitation.
Blocked EGR, cleaned out intake, new low priced cat.
No more problemos.

+1 on test pipe since you don't need to do emissions. You can make one from exhaust parts at a McParts store, then take it to a muffler shop to have the parts welded together. After you test-fit it on the car, make sure you make marks on the pipe and flanges to get the orientation right, so the bolt holes will line up properly when you take it to get welded.

Another way to do it would be to unbolt the back of the cat from the midpipe, and run a hole saw drill bit on an extension through the clogged cat. Then start the car with the midpipe still disconnected to blow out the pieces of the cat. Reconnect pipe, done.

[AlaskaFestivaGuy]

My local WA emissions testing station refused to take my $15 to run a test. They kept telling me "not required for 1989" and simply couldn't understand (with their limited English capabilities) my explanation of why I would be interested in emissions testing when not legally required.

I rounded up the bolt-together parts (see photo) from O'Reilly -- Napa's closest stock was 3,000 miles away in Virginia. Not liking to go underneath cars on jacks, I will have the Napa guys put the car up on a lift and install them. I'd consider a "bypass" solution, but no shop around here would ever go along with that kind of thing for fear that I might rat on them to the government.

[bravekozak]

Testing is free in Ontario.

[AlaskaFestivaGuy]

I had the Napa-branded shop install the new (from O'Reilly) bolt-together cat, new mid-pipe, and new muffler. The old cat had indeed discombobulated itself with loose innards, but this NOT not solve the stumbling problem.

So, I (myself, since lift not needed) replaced the coil (with a $30 high-performance one). This dramatically increased power (I can go up 15-degree hills in 2nd instead of 1st), but did not fix the stumbling.

So, I replaced all five ignition wires. Problem still not solved.

So, I replaced the spark plugs. All old plugs were visibly in very good condition -- dry (no oil), light brown, clean insulator, all with gaps measuring .045".
THIS SOLVED THE PROBLEM!!! I drove it 10 miles up into the mountains at RPMs up to 4500 in 4th. Also backed off on the gas going downhill with no jerking. Previously, it stumbled at around 3700 or even as low as 3200 RPM under load and even doing, say, 30mph in 3rd or 4th with no load.

I don't recall when I replaced the plugs -- they may be what was put in the car 3 yeares ago when I bought it by the mechanic in San Diego who I had replace the cylinder head (for reasons I've forgotten).

So what makes a spark plug go bad like this? Out of curiosity, can plugs be tested? I know they clean (every 100 hours) and test airplane spark plugs, but never heard of cleaning or testeing being done on car plugs given how cheap they are (they're $20 & up on airplanes and each cylinder uses two plugs).

[WmWatt]

A spark plug has two ends and a middle. Looking at the firing end is what I do too but who's to say the other bits are good?

[AlaskaFestivaGuy]

Upon closer visual inspection of all four removed plugs, I can't see anything wrong.

It doesn't matter any longer -- the car no longer hesitates/stumbles.

I will nevertheless save the plugs for future testing on an appropriate machine (all four, even though I have no reason to believe that more than one is bad) somewhere.