Mechanical Question--non-Porsche
 

Looking for a little assistance troubleshooting my 2003 Nissan 350Z, and I know there's some brilliant minds here within the braintrust. So, here's the deal.

About a month ago, I could feel the car kinda "missing" occasionally, and the exhaust note would lightly sputter. This happened twice, then would clear itself out and run smooth. Another day, it happened for about 5 minutes and then threw the check engine light. Code was a "random misfire." Car has approximately 120k on it, so I changed the plugs (don't know when that was done last). Went fine for a couple weeks, now it's doing the occasional sputter again.

So, what I'm looking for is the likely culprits. I do most of my own wrenching, but I'm still not great at diagnosing. My thought process currently is replacing O2 sensors, and possibly replacing the coils. Does this sound right, or should I be looking elsewhere?

Thanks in advance.

coil packs

...btw, that's an electrical problem ;)

Coil on plug or a remote 6-pack 'all in one' unit?

When were ignition wires last changed?

What was the weather like when these events happened?

Moist, humid , damp, rainy days will help old wires arc easier.

Most likely coil packs, or plug boots. Would be nice if you could get it to missfire enough to set a specific cylinder missfire, and then you could nail it down better. I'd lightly mist the coil area with water, and drive it hard under load to try to make it missfire and set a hard code for a specific cylinder .
Also, check around the maf sensor, and air intake boots for anything loose, cracked, missing etc... You could spray a little ether to help pinpoint a vacum leak.
When you changed the plugs, was there any signs of spark leakage to ground? Usually a whitish looking powder right at the bottom of the plug/coil boot. Did you grease up the boots with dielectric grease when you put them back on? All this stuff can help to cause intermittent missfires under different humidity and load concitions...
Good luck!

Yep, coil packs would be my guess as well. You have no codes?

These are coil on plug. With 11 years on the road and 120,000 - could definitely be one or more intermittently flaking out. They are pretty cheap for this car - like $25 or $30 each. So replacing all wouldn't break the bank.

A clear diagnosis "smoking gun" would be nice. But lacking that, no thrown codes to indicate anything but a random misfire, and given that you've already swapped plugs, I'd be inclined to go for the coils. edit - see FASTFRED's post for add'l troubleshooting - good ideas!

angela

Thanks, guys. As Angela stated, they are individual coils over the plugs...and that was the next thing I figured I'd be throwing money at. If I remember right, I can get all 6 for $50 at Autozone, so no, not expensive at all.

As for the code, I don't remember the numbers off the top of my head, but they translated to "random misfire."

I did put a little grease on the plugs when putting them in. Humidity is typically non-existent here in the desert, but we have had a crap ton of rain this summer, which is very unusual.

Non technical but worth the try...
Injectors are sticky.
Add some injector cleaner in with 1/2 tank of gas.
The Chervron stuff. A little expensive ($10.00). Can't hurt.

Did that already ;)