PO304 misfire on cylinder #4 help
 

Hello 350Z community!

This is my first post! I just bought a previously enjoyed 2004 base 350Z and the service engine soon light came up.

The error code was PO304 which is a misfire on cylineder 04.

I've done the following:
* Changed all the spark plugs.
* Change the ignition coil on #4 which is the middle one one the left side if you are looking forward from the driver's seart.
* Erased the code and drove it for a couple of days. Then the code came back on.

Now the car was sitting for a while so it might be a plugged up fuel injector. Is it possible to add fuel injector cleaner additive in the gas tank, drive it around for a while and see if that solves the problem?

After that, I'm thinking of changing the injectors after getting a mechanic to check for intake/exhaust leaks?

I really doubt if it's sticky values or loss of compression as it really doesn't loose power and the misfire seems really rare for it to take two days for the code to show up again.

Any advise on what I should do now is greatly appreciated.

Thanks in advance.:D

You could have saved some serious coin by just having the problem diagnosed at a shop instead of simply throwing parts at the problem. A can of Techron is cheap. Try that.

If the code doesn't clear after that, then have a qualified mechanic do a diagnostic on the misfire code. If the job's easy enough for you to do yourself (having no idea what your skill set is) then go for it. Otherwise, let them perform the fix.

And finally, don't assume anything about loss of compression or whatever. Get a gauge and check it. Assumptions will get you nowhere.

How many miles are on the car? How long has it been since it was fully serviced? How soon after you purchased the car did the CEL come on?

Thanks fro the response...

The car had regular service with a Nissan dealer afaik but it sat for a while and didn't get driven often. The miles are 107k.

You're right about assumptions as I worry too much. I'm going to drive with a bottle of injection cleaner and if the check engine light comes on after that, I'll have an expert look at it.

I should be more specific in the sense that has anyone actually clean a fuel injector with a fuel additive to the point that a misfire went away?

Yes, I have. I was getting a general misfire code on a POS Saturn I used to own. I used a bottle of Techron and the problem went away (I then switched to Chevron gas and have only been using that ever since).

Nothing beats a good purpose-made injector cleaning tool like the one OTC makes though.

I'll try that kit. Thanks so much for the advise! :)

Not a prob. You're going to need a compressor and a fuel injector pulse tester to make it work properly. Unless you're cleaning injectors regularly, it's a bit spendy. Still, if you have a set of working (but clogged) injectors, it can pay for itself after a couple uses.