GreenAdam66

My daughter's 99 Accord (4 banger, auto transmission) is running really, really bad - completely undriveable. It will idle OK and seems relatively fine to about 3000 rpm, but stumbles and dies if you try to rev harder. I've limped it around the neighborhood trying to get a CEL to be thrown, but nothing at all.

A little history: I replaced the timing belt and water pump just a couple thousand miles ago and everything was fine. After reading online about this problem, I wondered if the timing belt had skipped a tooth or something, so I pulled it apart and checked everything - seemed to be right on the money. I also ran a resistant test on the crank position sensor at the same time - no problem there. Now I'm really, really stumped. Bad ECU maybe (since no CEL despite the engine missing like crazy!)?

Thanks for your help!

holmesnmanny

It might be the cat clogged up. You can try removing the oxygen sensor to open up the exhaust and see if it runs better.

Maybe cap, rotor, plugs need replacing.

user456101

Yes, probably the cat. Watch Scotty Kilmer's YouTube video "Find out if your car really needs a new catalytic converter" but it might be the fuel pump is getting weak. Watch Scotty Kilmer's YouTube video "How to tell if your fuel pump is bad"

GreenAdam66

Great ideas, guys - and thanks VERY much for the links provided! A weak fuel pump was definitely something that crossed my mind (for a second), but I didn't know how to test that. The potential of a clogged cat never even crossed my mind.

I'll do some checking and see what pans out. Thanks again!!

GreenAdam66

One other question about this... any idea why I'm not seeing the check engine light come on or any trouble codes being generated? As bad as this thing is running, I would have guessed it would trigger an "engine misfire detected" code or something like that!

holmesnmanny

it just doesnt throw a code for every issue

MAD_MIKE

On the 98-02 cars there are some codes that do no illuminate/blink the CEL or D4 lamp. Only way to verify is to use an OBDII code reader and check for any stored(no CEL/D4) codes.
One other aspect is even though the vehicle has better self diagnostics from OBDII, it is still a speed density system. It's not a 'smart' computer compared to other vehicles of the era. It's simple and robust.

GreenAdam66

UPDATE:

I finally got some time tonight to dig into this. I watched the recommended video on Youtube about how to determine if your cat is clogged and built myself a backpressure gage. I hooked it up tonight to the oxygen sensor hole located just below the exhaust manifold and started the engine - a little over 6 psi of backpressure at idle when it should be 1 psi or less! That definitely seems to be the root cause of the problem I'm dealing with. I'll do some more work tomorrow to figure out if it's the cat itself that's clogged, if it's the muffler that's clogged, or if it's BOTH. Most likely the cat, but we'll see.

THANKS so much for pointing me in that direction since it was definitely not on my list of things to check out - who knows how much time I would have spent eliminating other ideas until I came to that one! Saved me a ton of time and almost certainly some money too!

holmesnmanny

just rev the car with the oxygen sensor removed, it will go over 3k if the problem is clogged cat