intermittent missfire?

[Joeman]

My #4 cyl has been misfiring lately when I start the car. It has magnecors/ denso Iridiums and a fairly new cap/rotor... all of that probably 8 months ago and problem free until now. I've already checked the cap/rotor/ wires for looseness, checked for condensation anywhere or water in the plugs and the plugs look clean as well.

Once the car has been running for 5 minutes it starts running smoothly...or if I shut it off and on maybe 1 out of 7 tries it will start out smooth and be fine through my drive until I shut it off and restart, then the miss comes back.

[cencal180]

you check the destributor? make sure the wires are in wright order.

[Joeman]

Nothing is in the wrong order. It's been running fine for 8 months, then it just started missing all of a sudden. Nobody has been under the hood to be switching wires around.

What else would I check with the distributor? Nothing is loose, the cap and rotor looks good.

[Joeman]

suggestions please? cmon somebody has to know this.

[idlafie]

S13?? S14??

How many miles on the motor?

Original owner or 2nd / 3rd owner?

Could be anything from leaky injector, stuck, burnt or leaky valve, but since you mentioned that the plugs are coming back clean, then that pretty much rules that out. Other option would be to run both a compression & leakdown test & see what the results reveal.

Anyhow, hope this helps.

ID

[johngriff]

when it is "running roughly"

Systematically pull each individual spark wire (do not ground to chasis while doing this) and each injector signal lead. You will figure out pretty quickly which device is not activating and where. From there, it is a matter of tracking down, device signal, trigger etc.

[Joeman]

s13, 200k miles. 3rd owner but I've had the car for almost 3 years. I already pulled each wire the problem is with #4 cylinder not firing. plugs look good.

I assumed it was a spark problem. I've never experienced a leaky injector or burnt valves... Do they show similar symptoms as a dead plug? What's the quickest SAFE way to rule out injectors as the problem?

[johngriff]

start it up with an extra spark plug in wire no4, if the plug fires, then it is the injector lead/injector.

Clean plug no4 off. If it is totally clean and sparks, then inj is not firing. Check injector lead w/led or test light.

[Joeman]

cool thanks...why didnt I think of that. :bigok:

If I do need new injectors... what's the biggest/best I can upgrade to with everything else still being stock?

[johngriff]

Just throwing this out there,

I am 99% sure it is not the Fuel Injector Itself or the Spark Plug Itself. It is more than likely it is going to be the wiring, plug wire, cap and rotor.

[240LE]

s13, 200k miles. 3rd owner but I've had the car for almost 3 years. I already pulled each wire the problem is with #4 cylinder not firing. plugs look good.

I assumed it was a spark problem. I've never experienced a leaky injector or burnt valves... Do they show similar symptoms as a dead plug? What's the quickest SAFE way to rule out injectors as the problem?

get an inline spark tester, much easier than adding an extra plug, and get yourself a compression tester to check the valves nd piston rings. Do you have any white smoke?

[punxva]

try unplugging the injector harness while the motor is running on number 4 and if nothing happens, put a diode on the connector in the wiring harness and see if it lights up, if it does then its teh injector, if not you've got bigger problems

[snappy]

^^^ Im having a similar problem in my DOHC, I found oil on the combustion chamber side on the #4 cylinder spark plug and on the plug wire in the VC cylinder. I think it's misfiring and people I've showed it to say the same. I installed a remanufactured head, valves- the works, along with all new gaskets a year ago. I just changed all the spark plugs and am still having problems.

I haven't checked my compression yet. Could it be a piston ring?

PS. My car still runs like a champ when I am driving, but when I'm at idle it shakes.