zsmizzy

i have a 93 s13 hatch with a stock ka24de motor. for some reason it seems to drop cylinder 2 after it warms up to operating temps and only runs on three cylinders. ive changed the plugs, wires, cap and rotor, and the injector on that cylinder. nothing changed. so today i picked up an ecu and tried that, did the same thing. it seems to dump way to much gas into that cylinder and nothing happens, just smells like gas and gas vapor ends up coming out of the exhaust. after i run it for a bit i can pull the plug out and see gas sitting on top of the piston and if i pull the injector gas sprays out a little bit and is sitting where the injector plugs in. no smoke and compression is good as far as i know. keep in mind it only does it after it warms up to normal operating temps.
any ideas? need to figure this out asap.
thanks

The Guy

Hmmm.... Check MAF. Is it a completely stock motor?

Hijacker

MAF wouldn't cause an issue in only one cylinder like that.

It could be a loss of compression in that cylinder doing it to you since you already swapped out the components that I would have targeted first (ignition system)

murphy660

thought you wanted a reliable car?

i'd say the the injector o-ring is shot. dumping too much into one and leaning out the others

is it only one cylinder? ya sure?

The Guy

Compression was my first thought, but he said it was good, so.... is it stock? Boosted? Tuned?

Hijacker

He says "as far as he knows". So I don't know if that's a "best guess" or he put a gauge on it and tested that cylinder. But since he's swapped for an injector, and he's still getting unburnt fuel, compression would be my guess. Over-pressure would cause all 4 to dump fuel, MAF would cause issues not related to a single cylinder not firing, so I can only imagine it's a compression issue.

actionpaintball

1. Check fuel pressure
2. Check o2 readings (assuming running rich)
3. Check injector resistance and injector wiring resistance. Check injector pulse with a NOID light. Swap injectors around and see if the problem stays at that cylinder or follows the injector. Visibly check spark on that cylinder.

The Guy

Wouldnt fuel pressure cause a problem among all four cylinders since there is only one fuel pressure regulator for the system and not one for each individual cylinder? Same thing with o2 sensor?

actionpaintball

Fuel pressure is one of the easiest things to check. If you have a spike in fuel pressure and a single weak injector, it can be leaking while the others are still holding back for a while (until they fail). A potential increase in pressure beyond what the system was designed for may be the actual cause of the initial failure to begin with. Almost every trouble tree you follow for a cylinder misfire/fuel system check, will have you check the pressure of your system before getting any further.

You are assuming the overfueling is all in one cylinder. The 02 sensors ultimately feed the information back to the computer to tell if the system is running rich or lean, and compensates by altering the injector pulse.

The basic breakdown of the problem is this: You need to find out if that cylinder (and all cylinders) are getting over fueled or simply not igniting the air/fuel mix...or possibly both.

actionpaintball

As long as it's not some ridiculous motor (like the FORD triton 5.4L where spark plug access is difficult) I always start out with a good compression check, wet and dry, then check fuel pressure at start and when running. Then do a basic ignition system check and monitor the 02 sensors on an OBDi or OBDii scanner as well as all other available sensors to make sure they are in the expected range. This will shake alot of small issues out (like ground wires, burned wires, bad vacuum leaks ect..)