New 2002 QX4 owner

[jaworski88]

Hi All -
I just picked up a 2002 QX4, but has some issues that the PO didn't want to deal with. The issue is: Engine runs rough, the CEL is on with code P0304, which is misfire on cyl 4. Owner said that he replaced the spark plug and ignition coil on cyl 4 with non genuine infiniti parts, but with no effect, i.e., the problem is still there.

I was planning on replacing the cyl 4 ignition coil with a genuine part from the dealer, and all new spark plugs, and also the condenser ignition coil. Also I will clean the MAF and throttle body as well.

Is there anything else I should try? Has anyone here had this problem?

I appreciate your assistance.

[04pathse]

the #4 fuel injector could be dirty or faulty, maybe try swapping #4 fuel injector with one from a different cylinder to see if the code follows.

[jaworski88]

Thanks for your input...yes, that's a possibility I hadn't thought of. I'll keep you posted on my progress/outcome.

[macgiver]

mac , definately swap whatever you can swap - BEFORE you buy, like especially a coil pack , they're "easy",even though doin' the right thin' like ALL NEW PLUGS, COILS ,( wires? ) Ya gotta get the skinney on the REAL problem first ,unless you burn doubled up Ben Franklins for a hobby For a "High Dollar" part & labormay show to be the "Full Fix" , that put's you over $$ wise . Respectfully G 2/27/2018

[macgiver]

Fuel injector w/multimeter tests approx. 12 - 14 Ohms (see FSM for spec.) , the "Transistor-Pak" or aka Igniter may have the cyl. # 4 transistor failure , a reeeemote next =bad wiring / poor connector somewhere"over the rainbow" Seriously , an LED indicator such as a "Logic Probe" can be used
for seeing if the JUICE is getting to the "Low voltage" ckts feeding Coil-pak & / or injectors. Being a visual indication , and logic probes usually "Buzz" upon indicating in addition . G T 2/27/2018

[macgiver]

If you give the #4 injector a couple of raps with the plastic handle end of screwdriver sometimes "shows it up"
like you will momentarily get rpm's up 'n runnin smoother - then you've pretty positively identified.Work's then cut out for you.It may stay good ,for a while? - serious cloggage usually won't permanently correct .

[jaworski88]

Thanks, guys, for your help. I am making notes for when I tackle this problem hopefully this weekend. This is my first Inifniti, let alone first luxury car, so this engine system is new to me. Your suggestion begs one question: are all the ignition coils interchangeable? I didn't think they were for fitment purposes, i.e., some have slightly different shape in order to fit in that particular cyl. I just thought I read that somewhere...

The Field Service Manual I got from this forum is the most comprehensive manuals I've seen. I found the whole procedure for diagnosing misfires. Between that and the help from you users, this forum is Awesome! I can't wait to start wrenching on my QX4!

Thanks again for all your help!

[barnaclebob]

5 out of 6 ignition packs are interchangeable. One of the back ones is unique. Too bad we lost all of the pictures for how to replace spark plugs otherwise you could see it in that thread.

[jaworski88]

Update: I think I got a little lucky. The sales guy at the Infiniti dealership gave me a good discount on parts. So this weekend I replaced the ignition condenser coil (old one had gooey stuff on it), replaced the ignition coil and spark plugs. That fixed the misfires, but now I think the misfiring damaged my catalytic converter because it is kinda loud now. Has anyone heard of that, misfiring damaging a catalytic converter? It almost sounds like a motorcycle now, and it's clearly coming from the converter. I am just glad that it doesn't misfire anymore and the CEL went off on its own.

I'm thinking that the PO replaced the coil with a bad one (non-genuine brand). It had a much higher resistance than the new I got. Hope this helps someone...

[04pathse]

I think the misfiring damaged my catalytic converter because it is kinda loud now. Has anyone heard of that, misfiring damaging a catalytic converter?

Yes it does happen, a vehicle should not be driven in a misfire condition as it dumps a cylinder’s worth of raw, unburned fuel into the catalytic converters and quickly overheats them and leads to their destruction.

When a misfire is detected it causes the CEL/SES light to blink which is supposed to get your attention because it can cause serious damage to the cats and also o2 sensors...

Usually when the cat is damaged you will get a CEL/SES light and code for that but not always.

[jaworski88]

Thank you for your quick reply. I believe the PO was driving it for several weeks while it was misfiring before she decided to get rid of it. So far, I have no cel on, and no other DTCs, thank goodness. The engine seems to run pretty smooth in the engine bay (no more misfires!), but underneath at the left Cat, it's significantly loud. My neighbor asked me if I had a Hemi in there, lol. Thanks again!

[yeldogt]

FYI -- the two oval shaped cans that sit about under the front seats are not CATS .. they are resonators. The OE ones crack at the seams and leak ... the dealer fix was to put some goop on the joint and use two SS bands to hold them together. This fails ... if they are leaking and not "fixed" you can have the sides welded together.

Because of the OE cost ---- most use aftermarket assemblies when the OE's rust. The original system used a combination of SS main parts and cheaper steel pipes. Unfortunately -- the pipes fail way before the assemblies. It may seem better to just get the aftermarket parts -- about $500 ... but it's actually better to try and fix the OE. I have owned three 02's and never had any rust through on the oval resonators after the. Each required at least two pipe fixes before it was determined that I should replace them .... the aftermarket stuff is not SS and only holds up for a couple of years .. sound is also different.

[jaworski88]

Thanks, yeldogt, for enlightening me of that! That's good to know, and probably better that they're not Cats like I thought. I've been driving it around, and still no CEL, and engine runs smooth. When I tap on the gas while it's idling, almost sounds like there is something rattling in the area of the left resonator. I might take it to a muffler shop and see if they can tell me what's going on exactly under there. I'll keep y'all posted, and thanks!