Misfire plugs coil packs and valve covers

P

Party Cat

Member
Car
2003 fx35
Name
Party
Hey all! Sharing my recent experience to help others and to get some input from those with more experience.

I just got a 2003 fx35 with 125,000 miles here in Hawaii. Previous owner had taken no care of the car and said she had it a year and a half and been driving half that time with the CEL on. I have a good amount of experience with cars but never worked on a vq. Car seemed ok but had a misfire and rough idle. Took it straight to the mechanic for CEL scan and fluid check oil and new filter $92 all up. Results were 2 quart low oil, misfire on cyl 4, recommended plugs, coil packs, and valve cover gaskets ~$1200
I ordered parts as follows:
Plugs NGK iridium $30 shipped for all 6
6pcs Laser Iridium Spark Plugs PLFR5A11 22401-5M015 for Infiniti FX35 G35 Nissan | eBay

Isumo coil packs $60 delivered for all 6
6 Kits Ignition Coil Fits:Infiniti FX35 G35 M35 Nissan 350Z V6 3.5L 601871672015 | eBay

Valve covers and gaskets $113 delivered for kit
For 2003-2008 Infiniti FX35 G35 M35 Nissan 350Z 3.5L Valve Cover & Gaskets | eBay

I installed everything and found the old plugs in shocking condition. Coil packs didn’t look swollen or damaged but lotta oil on 5 and 6. Cover gaskets were toast. Put everything back together and result is running poorly and CEL still on.

I’ve read a lot and gone over a lot now. I plugged and unplugged all the coils to check for change in running. All made a difference except cyl 2. That one never changes even with different coil and plug. Runs the same plugged or unplugged.

I drive to auto zone to test drive and scan. Was getting a popping sound under light acceleration coming from under the car possibly combusting fuel in cats or exhaust? Code scan was P0300 and suggested vvt solenoid according to auto zone. I bought some MAF cleaner and cleaned both solenoids to be safe. No change.

I bought a full set of new plugs ngk platinum for $14 each from auto zone suspecting that my cheap plugs might be knock offs and no good. New plugs look good and I swapped cyl 2/4/6 first. Car sounded better but not great. Swapped all plugs and got stuck with the bolts holding the coils in place not backing out. Seems like the new valve covers have fittings that are not secure and the whole fitting turns.. it suuuucks.. anyhow I broke one coil in this removal process and now have one of the originals back on cyl 5. Still have CEL and running rough but engine sounds strong. Booked to go back to the mechanic Friday for help on the codes as I’m at my wits end with the coil/plug issues. Feels like I’ll regret getting cheap parts but hard to tell so far. Any help before then would be appreciated and I’ll keep everything posted. Mahalo!
 
Hitachi is original equipment regarding coil packs. Put your originals back on & see if u still get a mis. :cautious:
 
Thanks for the info and sorry to hear of your experience. When I changed out my valve covers, gaskets, and spark plugs I looked for good deals as well. The ebay spark plug prices seemed too good to true so after some research, I found that there were counterfeits all over ebay and amazon. I didn't want to chance it so I paid a little bit more and bought them from a reputable source. As for the valve covers, I also went with the cheaper aftermarket set. I torqued all bolts to spec so hope they hold up ok. I didn't end up using the gaskets that came with them as I heard they can leak prematurely. I ended up using the Victor Reinz/Mahle gaskets because I read good things about them. I would hate to do this job all over again because of leaking gaskets. It does sound like it can be inferior plugs or coils.

Were all the plenum bolts torqued to spec in the specified order?

Hope you figure out what the issue is.
 
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Appreciate the feedback! I also am wary of the coil packs but have swapped them around with no noticeable changes in running.

Regarding the plenum, I did not bolt it as per suggested...could that cause this much of an issue?
 
Party Cat said:
Appreciate the feedback! I also am wary of the coil packs but have swapped them around with no noticeable changes in running.

Regarding the plenum, I did not bolt it as per suggested...could that cause this much of an issue?
Click to expand...

Not sure if it can cause the issues, but I would just redo them because it's easy and you can rule it out as a possibility.
 
Party Cat said:
Regarding the plenum, I did not bolt it as per suggested...could that cause this much of an issue?
Click to expand...

It could if its leaking. Pulling unmetered air would cause symptoms like you describe.

Also, just in general, I would slow down a little bit. You've kind of shotgunned the problem so even if it had worked, you're not going to know what fixed it. Like, I think I would have just replaced the #4 coil with a O.E. one first, instead of replacing them all with a sketchy brand.
 
Too true...retrospectively that’s totally true. I went off the recommendations for the shop I went to and with how poorly uplept the car was I thought it was certainly due for some new parts. I did need the covers and seals. Did need plugs badly. Still left thinking shotty coil packs could be suspect. Cars back into the shop this morning to scan codes and check for changes with reconfiguration. Fingers crossed for a good solution.
 
Updates:

Got the car back from the mechanic today. They did a lot of diagnosis and only ended up spending $130 all up which I’m cool with. They tacked it down to misfire on cyl 2 and 5 which are the same two I was having doubts about. They believe it’s faulty injectors causing the problem. I’ve heard a injector suspect type of ticking under the plenum as well. Also pulled a fresh plug right after install and start up on cyl 2 and it looked like it hadn’t met any fuel to me. Photo attached.

I’m planning to get some refurb injectors and install 6 unless anyone has any input to steer me another direction to test first...
 
Party Cat said:
Rebuilt injectors ordered. Will post results after install.
Click to expand...
Just a couple days late... but you ordered rebuilt, a second set to replace what you have?

RC Engineering in CA will rebuild & blueprint your existing injectors, but it takes sending them to the mainland and back again. Just another option, but you're already moving forward.
 
Ah thanks for the tip! Injectors were only $60 delivered with lifetime warranty.

Installed and still have the CEL on...I’ll have to go get the codes read again and see if any change. Car seemed to run the same as previously but didn’t test drive only started and revved it.
 
It’s been a minute so back to update.

No noticeable change with the new injectors. Still have CEL and P0300 code. I drive around a bit more than usual and the car had a nasty smell and smoke came off the headers (seemed like header area) after parking. Getting a crazy popping sound from under the car still. Sounds like mini detonations.

I suspect the cats are totally wrecked. They look bad from the outside and the popping sounds like in that area. Also the previous owner was driving with misfire code and bad plugs for possibly 9+ months.

Not getting a cat code only random misfire.

Mechanic wanted to compression test before any more parts order. I tested myself and got 160-165 psi across the board.

Any input on if the cats could cause all this trouble if they’re very seriously blocked or deteriorated?

One other area of suspicion was that on cyl 5 and 2 when the injectors are shit off or coil packs pulled, engine seems to run the same. That’s why I comp tested first to see if the engine is ok. It’s still possible it’s an issue with those particular coil packs but I have tried multiple to see if I could get a variation.

Any help appreciated!
 
I suspect your cats could be toast as a symptom of the misfire and are probably not the cause of the issue.

You can check to see if the cat is bad by checking the voltage on the 2nd (downstream) o2 sensor.

Voltage should fluctuate between .1 and .9 I believe but dont quote me on that

If your cats are shot, you can buy one used on ebay for waaay cheaper.

Look for G35 ones as well since not all sellers list them for the fx even though they are the same.

I bought a low mileage one for around 100-150 shipped during my misfire issue last year.
 
Indeed you are correct. I checked in with a local exhaust specialist and did a test drive. He thought exhaust flow seemed sufficient. The popping is likely unburnt fuel detonation in the exhaust. Also suggested it’s a possible wire issue from moving the harness around while changing the rocker cover.

I think next logical step is to check cylinder 2 coil pack/ plug for spark...then eliminate factors plug, coil pack etc...
 
Also check for vacuum leaks on the rubber part of the intake, I have seen those crack and cause similar issues. Easy to diagnose and replace.
 
Have you looked at your fuel trims with an obd scanner?

Thats how I discovered that it wasnt a coilpack/spark issue but a vacuum leak somewhere causing the misfires from the ECM trying to overcompensate with fuel for the added air entering.
 
The shop I took it to did scan that and found its was making out rich trying to compensate for missing fuel so he suspected the injectors. That’s how we ended up down that road.

Still seems that cylinder 2 and 5 are specifically not having any solid functionality. With the coil pack plugged or unplugged engine runs the same on both those two specific locations.
 
That ticking sound you specified earlier is normal on fuel injected cars. My fx ticks when warmed up and idling, totally normal.

My Lexus GS350 had a super loud tick since new but never skipped a beat or broke down.

The misfire/intake manifold gasket issue I had happened with only 60k miles on the FX....and it was a California car so it wasn't in an extremely harsh environment.

Iits an older car and these are just wear and tear items...
 
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