P0304 misfire - cylinder 4, and it's not plugs/wires/bad injector

[ez@2gnt]

Got a weird one for you guys, b/c I've done all the basics and there's nothing like this in the archives (I searched!)

Engine throws a code P0304 -cylinder 4 misfire. Idles horrible, but engine smooths out in higher rpms. Sounds like a classic spark plugs/plug wires problem, right?

And a new plug looks like this after 50 miles (see the plug 4 on the very right of picture)
http://img53.imageshack.us/img53/8906/dsc019305np.jpg
the plugs on the left were the originals.

New wires, new plugs, same problem. By the look of the plug, thought it might be a stuck open / leaking / failed injector. Replaced the injector. no change.

Checked ignition coils. Secondary coils are within reference range of 11.3-15.3 kOhm. However, primary is slightly out of range (ref range is 0.7-0.86 kOhm)
- 2&3 terminals 1.2 Ohms
- 1&3 terminals 1.2 Ohms

However, I don't think these numbers are so out of range that the coil is suspect - And I don't see how that could cause just cylinder 4 to misfire. I would think two cylinders would drop out if a primary coil went bad.

Are there any sensors that will cause just a single cylinder to misfire? I read in the archives that someone had a CAS problem before and had idle issues, but the the thread left out some details.

any ideas?

 

[ISUJakey]

What brand of wires?

 

[ez@2gnt]

They were from a local autozone, whatever it is that they carry... Is there an issue here with different brands? I didn't bother to check the resistance of the new wires, as I thought they'd be fine right out of the box.

 

[ISUJakey]

Swap a plug wire from a different cylinder on to cylinder 4 and see if that makes any difference.

 

[gsxclusive]

Are there any sensors that will cause just a single cylinder to misfire?

I had a p0303 (cylinder 3 misfire) code. Swapped around the plugs, wires and even injectors to see if the problem would follow. None of this changed anything. Finally I had a "fuel trim malfunction" code. I tested the front O2 sensor. It was bad. I replaced the O2 sensor and the misfire and the fuel trim problem went away.

I would atleast test the front 02 sensor, but be carefull or have someone who knows what they're doing do it as you can actually kill it if you connect the jumper wire to the wrong sensor terminal.

 

[ez@2gnt]

Very interesting, gsxclusive. I need to research on how to check this sensor... I've had an aching feeling it was a sensor of some kind.

ISUjakey, I swithed wires all around. No difference.

Here's something else I just noticed. When you first turn on the engine, it idles FINE for 5-15 seconds. Then it starts to idle like crap. If you turn off the car, and then turn it on again a short time later, it will idle bad from the start. so it only happens if the engine is a little warm. hmmm...

 

[ROOKIE1]

Are you sure the connectors are on the injectors properly ? I had that code on my 90 . Turns out the clip on the connector was broken . It was not seating tightly . You know loose connection .

 

[ez@2gnt]

I've put the connectors on and off so many times, you'd think they connect right at least once. double checked that, they seem okay.

you know, these guys had problems almost exactly the same, with that stupid arcing sound around the injectors
http://www.dsmtuners.com/forums/showthread.php?t=119764&highlight=test+o2+sensor
http://www.dsmtuners.com/forums/showthread.php?t=109925&page=2

looks like vaccum leaks for some, CAS or ignition coil for others. damn 4g63

 

[bfdahl]

Do you have a A420 engine? your Avatar says non turbo. If so they are notorious for cracking intake manifold gaskests right on the corners of #4 cylinder.

 

[ez@2gnt]

This is regarding a 4g63 - my dad's GST that I'm working on. I drive a 420a.

I haven't been able to find any obvious boost leaks/manifold leaks. I still need to check the o2 sensor - haven't found the info easily but I'm still looking.

do these cars run in limp mode, even after the battery has been disconnected and the CEL disappears? maybe I should get that reset at a local shop