I’ve replaced the coils spark plugs o2 sensor map sensor and the catalytic converter. And still no luck it will run and idle fine but will got reach above 50mph but will rev to 4 grand or more and not move. When I unhook the catalytic converter straight from the head of the motor the car runs and does good it’s just loud. When I hook it back up it messes up again. If I unhook from the bottom of the new catalytic converter it has no effect and will still not run good any help
If my engine was revving to 4k, but the vehicle was not moving, my prime suspect would be a slipping transmission (or a bad clutch if it has a manual trans)
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What were the codes you were getting before and after replacing all those parts.
And for the rest of the story:
Model and trim of your Hyundai
Year
Engine
Transmission and frequency of transmission service.
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Car runs with no cat
Car does not run with new cat
I see a link here
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Welcome to the forum…
Well, so far it seems that just throwing parts at it has not worked, how about we try to properly diagnose the issue(s) now…
1st thing is we need year, make, model, engine (if options) and transmission… Next we need to know all the codes…
Now, please go into more detail about this, you said…
and then how it coincides with this?
Does the engine still rev to 4000 in gear but not move???
My guess is that @Cavell has got it right. OP got some bad luck is all. The replacement cat is probably faulty. I don’t recall of ever hearing of a way to test a cat’s flow rate. But if there is a way, that’s the test to do. Either that or replace the cat again. If the next cat solves the issue, return the first replacement cat for a refund.
Before jumping to the conclusion of a bad Cat, the information noted by Purebred is absolutly essential, especially any codes…
A simple failing injector can allow the engine to rev while parked but fail to rev under load (highway speeds) but if so should also be throwing a misfire code.
Car runs ok with no cat.
Should run ok with gutted cat.
Will be quiet at least.
But, you might get a code now.
I wonder if a portable hair dryer could be used to test if the cat flow is partially blocked? Or a shop vac that has the “blower” function. Cat bench- tested of course, not installed on car.
What should the pressure drop be at what airflow and at what temperature?
Tester