Catalytic Converter?


#1

About 5 weeks ago my 2008 Hyundai accent’s check engine light came on. It came on right after I filled up a tank of gas and started running a bit rough. About a year ago the same thing happened, and it turned out to have been because of some bad gas (I ran the tank down, refilled and everything went back to normal). I assumed that was the same thing this time because the gas was from the same location and the problems started right after the fill-up.

I drove it for about a week and then it stalled out completely. Rpm wouldn’t go over about 2,000 and if I tried to drive I wouldn’t go over about 10mph. I took it into the local shop. Replaced all kinds of fuel sensors, spark plug coils, and the main computer, and I think the fuel pump (all of which got fried). The error codes are all fixed and the car idles just fine. Only problem, when you put it in gear to drive it almost immediately bogs down, rpm stays below 2k (still) and eventually it will totally stall out.

The shop is now saying they think it’s the catalytic converter - but they aren’t sure. They have had my car for over 3 weeks now and I’m losing (have lost) faith. Plus it’s already cost me $1500 and I’m not wanting to spend more on their hunch that it’s the catalytic converter.

Any ideas?

The car idles smoothly now, no error codes. But as soon as you try to drive it barely moves. It feels like there’s a governor on the engine or like there’s not enough fuel getting through.

Thanks for any advise on what to try next.


#2

for one thing, try another shop. some of the experts here may have more insight tho


#3

Something in the exhaust system may be clogged, and if so, it could be the cat, or it could be something else. Its an easy enough test though. The shop should remove the front O2 sensor and put a pressure gauge in its place. Then start the engine and rev it up, if the pressure goes over 100 psi, then chances are that something in the exhaust system is clogged up. Check the tailpipe for a potato or banana, particularly if you have teenagers living around you.

Doing a pressure test is a lot cheaper that replacing a cat just on a guess.


#4

How many miles on it? The cat is warrantied for 8 yrs/80k miles.

If the car’s sitting in park can you rev the engine? Or does it seem restricted?

It could be the cat, but then the question is what caused to cat to fail. Often there’s something else wrong that causes the cat failure, and if you don’t get that fixed, the new cat will also fail.


#5

Like the previous comments…I’m going to suggest getting a second opinion and finding the real problem. Most of the time, in my opinion, the catalytic converter is not the problem.


#6

whatever the cause I would not keep paying a shop to take guesses


#7

The sympoms suggest an exhaust restiction, probably the catalytic converter. The computer and fuel pump were foolish guesses. How were they “fried”? Hit by lightning?


#8

I doubt that it has anything to do with the exhaust system, since the exhaust system works just fine when the car is in park then theres no reason it shouldnt continue to work just fine when the car is in gear.
Putting the car in gear does nothing to alter the way the exhaust system operates.


#9

A partly plugged cat will let a car idle, but interfere with driving it because of much higher throughput.


#10

but there`s no added throughput the engine is bogging and dieing at idle in gear.

“when you put it in gear to drive it almost immediately bogs down, rpm stays below 2k (still) and eventually it will totally stall out.”


#11

“…if the pressure goes over 100 psi…”

I think you mean 10 psi.


#12

No, I meant 100 psi, but if you have a reference that says 10 psi, I am open to accepting that. I forgot where I got the 100 psi figure, with 60 as normal.


#13

We’re both too high:


#14

Wouldn’t it be easier to use a vacuum gauge on the intake manifold to check for a clog somewhere in the exhaust system?


#15

When my cat went bad, I had a code for it. It took the GM dealer about 10 minutes to diagnose it and replace it under warranty. I’d get it to the dealer for a second opinion of what’s going on.


#16

re 10psi vs 100psi:
If the gauge is capturing and holding the peak psi then 100 psi makes sense.
I don’t think a steady 100 psi is possible.
The average pressure in the cylinder during the power stroke (BMEP) only reaches 150 psi or so, at full load.