Intermittent cylinder misfire
 

I've visited this forum a few times over the years but this is my first post. I'm out of options. Hopefully someone here has an answer.This will be kind of long so apologies for that.

I own a 2003 touring 350z with just over 78000 miles on it. About six months ago, my check engine light began flashing at completely random intervals with a noticeable rumble and decrease in power. I took it to the nissan dealership I used to get service at and all they could tell me was it's a random cylinder misfire. In the beginning it happened pretty rarely. But in the last few months, it's been happening much more often.

Since the nissan dealership couldn't pinpoint the problem, I took it to a Midas where a coworker of mine is the manager. They found the stored codes for the cylinder misfire, but since it's random they couldn't pinpoint which cylinder it is. There are no other codes. I've had the spark plugs replaced since this problem started but that hasn't fixed it.

I used to get gas at the same BP station every time. I thought perhaps I was getting bad gas, selling regular as premium, so I started going to a different gas station. After the second fillup, the problem went away for five days until it returned. I say it's random because it really does happen at completely random times.

In the 10 minutes it takes me to get to work, the engine will sometimes rumble and lose power a dozen times or more. It doesn't matter the gear I'm in or if I'm pressing the gas pedal or not. Even while I'm accelerating, I can feel the power go down and then back to normal. And yet, there are days where it doesn't happen at all. I've tried making notes on when it happens but it really is completely random.

When I took it Midas, they suggested perhaps the car's computer needs an update. I took it to a different nissan dealership but they said the computer is up to date. In an hour and a half, they couldn't pinpoint the problem either other than the random cylinder misfire. They said it could basically be anything and they wanted to charge me $110 an hour to diagnose the problem but I wasn't willing to do that so I left. And here I am.

I'm planning on trading in the car but it will be obviously be difficult with this happening. I'm not that knowledgeable about cars so any help pinpointing this problem would be greatly appreciated. I'd also accept any temporary fix so I can least trade it in with no problems. I'm still leaning towards a fuel problem. Perhaps the fuel lines are clogged or pinched and there's not enough gas getting to the engine but that's just my personal guess. If anybody has any questions, I'll answer them the best I can. Thank you

Midas is never the answer....And if a coworker of yours is the manager, doesn't that imply that you are a worker there too?

I would have guessed plugs, coils, ecu. But you need to have a competent tech troubleshoot this issue.

I had an interesting issue when my CPS sensor was going out...trouble starting, and and I would lose power when driving (like a big power zap), but there were lights (ABS/VDC/CES) and codes associated with the issue.

I suppose I should have been more clear, even though it's the least relevant part of the post. We work together at a different job. He has two jobs.

As I said before, I have no other codes in the car except the random cylinder misfire. The car starts fine and the loss of power isn't really a big power zap. But it is definitely noticeable when one of the cylinders stops working. While pressing the gas pedal, the cylinder will give out, then go back on, sometimes multiple times. And sometimes it doesn't happen at all and the car runs fine. I'm trying to describe the issue as best as I can. I can try to post a video of the noise and rumble of the shift knob if that would help.

my guess is a bad coil pack somewhere

If its random misfire I would check fuel pump. Does it run worse with the fuel level low?

Coil pack going bad is very very common. It is not a fuel issue.

If you really want to trade it in quick then just but a set of 6 used packs off eBay and replace them all (very affordable, usually off wrecked Zs), with the intermittent code youll have to take time to trace down the bad pack.

Ive actually never had a used one go bad on me yet (replaced 3 between two VQs).

"When I took it Midas, they suggested perhaps the car's computer needs an update." -rofl must be a Ford guy.

I appreciate all the responses so far, thank you.

I have noticed it does seem to happen more often with low fuel which is why I suspected it was a fuel problem. I had a problem with the fuel gauge for a while. It would show less than was actually in the car. For example, after a fill up, the gauge would only read as half full. Then sometimes it would read as full but slowly over a half hour or so, the gauge would decrease, until settling on about half full. I'm not sure if that's relevant or not. But it wasn't a constant problem. It would happen on and off until perhaps a couple months ago when it stopped happening altogether. It's possible one of the places I took the car fixed this problem, but it was never mentioned so I'm not sure. Is there a temporary solution if it does happen to be the fuel pump? I've read before that it's an expensive part and difficult to change in a Z which I'd rather not do since I want to trade it in.

As for the coil pack being the problem, I'll definitely look into that. I'm sure not if that's the case though since they were checked for voltage problems before and I was told they are fine. I'm taking the car back to Midas on Friday and they're going to look at things more closely free of charge since I know the manager. I'll be sure to mention that. I would take it to nissan instead but I'm just not willing to spend so much on diagnosing the problem and then however much the repair will cost if they ever find it.

If anybody else has any suggestions or questions, I would appreciate it. Thanks again.

The misfire is intermittent, which is exactly why all tests on the packs came out fine. There is a lot of heat and vibration in that area, which makes it difficult to repeat an intermittently failing coil pack on the bench.

The fuel gauge issue you are having is also common and unrelated.

I did as you suggested and found a set of six new coil packs on ebay for $84.99, the first one in the list that came up. I verified the compatibility for my car. Do you recommend I just buy them now and have them installed before checking if they are indeed the culprit? It's times like this I really wish I was a mechanic.

You can get new OEM coil packs for just over $100 on ebay.

Hanshin makes the factory coils for these cars. You can buy them by name or you can pay 10x what they're worth in a cardboard Nissan box, open the box, and then realize it's a Hanshin coil.

Some places will list Hitachi as the factory OEM pack manufacturer. Hanshin is a subsidiary of Hitachi. It's now Hitachi Automotive Systems Hanshin. Hitachi and Hanshin both sell coil packs for this car and they're going to be the same thing yet the prices will be all over the place.

Hanshin also owns a coil factory with Denso. They're probably identical to stock, too.

THIS!!!!!!:eek::cool::cool::cool: Listen to him!

Thank you for the additional responses.

How long does it take to replace all six coil packs? I called a local nissan dealership and they said about 3 hours. Is that accurate? They also said I would need some gaskets replaced as well and the total cost just for the labor would be over $400. Is that true?

I notice I have a misfire when the car is warming up. After That It's All Good

Could someone tell me about how long it should take to replace all six cord packs? And if gaskets are also going to be required? Since I have no clue. Thank you.

If you're mechanically inclined. 20 minutes to pop intake up enough to zip the coil bolts out and pop coils out/in. And maybe another 10 to change coils. 20 to zip it back up. 1 hour tops. If you've never done it before....2 hours? It's not hard at all honestly. Text me if you need a hand bud. Pm for my cell :)

Thank you for the replies. I had a feeling what nissan told me was wrong. They told me three hours and that's by trained nissan technicians. I was also told I would need gaskets replaced as well. Is this true? If I'm just replacing the coil packs, is there anything else that also needs to replaced at the same time?

Spark plugs

I've already had the spark plugs replaced less than a year ago. That's what I checked first when I first started having this problem. Thanks though

Three hours????? To do coils??????? They are insane.............I will happily give you my phone number and talk you through it to save you the money from the stealership.......It might take three hours on the books to do valve covers (really only an hour in real time) but just to pop the coils out? It's a handful of bolts.....IF THAT. Yeah, coils are extremely easy to do on this car without taking a huge amount of stuff off. It isn't hard, I promise you that. And no you don't need any special tools. Couple sockets, ratchet, magnet, and a pair of vice grips/pliars. Good to go! Oh! and the beer lol.

Just re-read your post and yeah it's 3 hours to do gaskets......but unless you are leaking oil you don't need to replace them. The rule of "if it aint broke don't fix it" with VQ motors is very true. Just do the coils and don't **** with the gaskets, unless the spark plug tubes are full of oil. That's the only reason to dig deeper and pull valve covers off.