Some sort of jerkyness...Help :)

[CDE]

Hello...I searched for something like this but didn't turn up anything...

car: 89 24sx coupe (KA24E)

I'm having a problem that is driving me nuts.

When I'm cruising along at speeds 70-100+KMPH the car jerks ever so slightly every few seconds...sort of has good days and bad days.

-I had 2 injectors replaced recently, and then other 2 seem fine-Could this be from an exhaust flow issue? It sounds like crap and I think it could possibly have a plugged cat that would cause this?-Could it be an O2 sensor?-could it just be crappy belts? They are in need of replacement, but would a potential slipping belt cause that?-Or a fuel delivery problem?-ALso, It seems to be worse in over drive. If it really starts to bother me I usually take it out of OD and then I don't really notice it...-I had it checked out by a transmission pro. and he didn't think it was the transmission because it shifts fine, and the oil is good...

Sort of a 240 n00b...It just helps to narrow this down before I do something on it because I'm at university all week, and then work all weekend...ergo I have not much time to fiddle.

Any help or thoughts would be appreciated
Modified by CDE at 12:06 AM 3/23/2005

[CDE]

Forgot one thing...

There also seems to be a loss of power...When I boot it to pass someone or to make a light, the engine works real hard but it doesn't seem to have the pull it should.

(it's an auto...sadly).

[benemorius]

It could indeed be anything you just mentioned, with the exception of belts. (at least it doesn't sound so very likely to me)

The cat can be checked by bypassing it, or by checking engine vacuum. (vacuum that starts out good and slowly drops can indicate a clogged cat)

The O2 sensor is best tested with a multimeter. Normal reading is between .1v and 1v, with a higher reading indicating a richer mixture.

Fuel system can be checked with a fuel pressure gauge.
Modified by benemorius at 10:25 AM 3/27/2005

[CDE]

Thanks for the tips benemoruis.

I think the shudder is being caused by the TPS (throttle position sensor). I ran a few tests on it and they were a little wacky. I'm going to replace it when a parts store is open after easter...

Thanks for the tip on the cat. How exactly do I test that though? Just by the sound of the exhaust to me it sounds like something it plugged or constipated. In a few months I think I'm just going to get a better system anyways. something that flows and sounds a little nicer

appreciate the feedback.

[benemorius]

In your case the best way to test the cat is probably by getting a vacuum gauge for $14-$20 and monitoring your engine vacuum. It should include basic instructions on how to connect it. A pretty good indication of a clogged cat is vacuum that starts out decent when you first start the engine, then steadily drops.

Alternately, you could get a test pipe and replace the cat with it and see whether it makes a difference. In my opinion, checking vacuum is easier and cheaper.

[CDE]

Alternately, you could get a test pipe and replace the cat with it and see whether it makes a difference. In my opinion, checking vacuum is easier and cheaper.

Yeah...especially when the cat is welded to the pipe, lol.

I found a cracked hose upon an inspection tonight. It is the hose that goes to the top of the valve cover on the side opposite to the oil cap. I will be replacing this after the holiday once stores are open again...

Could this cause these symptoms? I'm also going to check all the other hoses the best I can later tomorrow. do I just spray carb cleaner on the hoses and look for bubbles for cracks?

[benemorius]

You can't really rule much out when you're having drivability problems, but having said that I doubt it's that particular hose.

If you're checking for vacuum leaks, start the engine and spray carb cleaner in an area you suspect may be leaking and listen to the engine for changes in rpm. When carb cleaner finds a leak and makes it's way into the intake through vacuum hoses, it alters the engine rpm.