Allow me to preface this by saying that I have had my Z for quite some time (more than two years) and have become very accustomed to the intricacies of the car: noises it makes, vibrations, etc.

My problem began a couple of months ago (february/march) after I installed a Nismo exhaust -- I slowly began to notice a problem with the motor at or near top end. I am not very familiar with how motors act when they run too rich or lean, but I suspect very seriously that this is my problem.

The long and the short of the issue is that whenever I run the car hard above 5000RPM (under load) the motor has an odd hesitation and sort of "studders" for lack of a better term, or fires "off beat". I desperately want to say it is "pinging", but as I have never been around a car that "pings" noticeably I do not know if that is the problem or not. At any rate, I suspect highly that the car, which has a decent amount of all motor bolt-on work done to it, needs to have the ECU tuned.

Currently, the car has an Injen CAI, Kinetix plenum, kinetix cat pipes, and Nismo exhaust. These are the "breathing" mods I have done which I suspect are having some effect on the motor.

So....any voices of experience here? I am beginning to think that the next thing I should do is have an ECU reflash, but I'm not entirely sure...although I have read volumes here over the past two-something years about NA modifications and lean conditions. To be honest I'm a little bit freaked out as I have no idea what effects this is having on my engine in terms of reliability in the near or long term. I have certainly been driving with mild manners since the problem started, rarely even revving to 4000 during my daily routine.

I would greatly appreciate any sage advice from people who have experience with motors and AF issues. I tried to search for information, but it was a dizzying experience -- I came away from threads full of young, inexperienced kids bickering about Technosquare reflashes wanting to tear my hair out! That is absolutely the last thing I need right now -- I'm looking for a mature attitude and senior advice from someone who has the authority/experience to back it up.

Thanks in advance,
Richard

 

Richard,
If I were you, I would get a baseline dyno with af readings. That will tell you if you are running lean, which is most likely. Then, if you are, get the technosquare reflash. give them your mod list and they will tune for it. Redyno, and if its still not where you want it, send your computer back along with the dyno sheets and have them adjust.

 

Mike,
I appreciate the advice. I am planning on doing that, my problem is that there aren't any dyno's around here and I do not have time to run to ATL anytime soon (within the next month) before I make the trip back to Louisiana. I think I will have to find a dyno somewhere in Louisiana to pull that off!

 

Faulty injector? Have you checked w/ your dealer?

 

Something I believe it would be pertinent for me to mention is that this problem ONLY occurs under load. If I put the car in neutral and rev the motor it never happens, even if I sustain the rev above 5000RPM.

 

Have you tried removing some of your mods to see if the problem will go away?

 

change your plugs, problem solved.

 

Care to elaborate?

 

I have been looking around. I am going to try this redline water wetter and possibly a few other things -- different thermostat and colder plugs if I have to! I will be running the car fairly hard this summer on the track in extreme heat and humidity, so this is probably a good time to get the issue worked out..!

 

Ok...
The hesitation your experiencing is due to high cylinder pressures, aka load, "blowing" the spark plug out. The gap on the plug has grown due to wear over time. I'm going to take a wild guess and say the stock plugs are still in the car. The gap has become so large @ this point that @ heavy load the spark potential energy has a difficult time jumping from the electrode to the ground lead. Hence the misfire under acceleration but no miss under free reving conditions.

tada...

 

Good guess I just got off the phone with someone who said the same thing and I am headed out to the garage right now to have a look

 

Also,
If you go with iridium plugs you should pick up about 4 to 6 hp(RWHP). I did.
I haven't tried "direct hits" yet, but turbo mag and others also say they are good for 10+hp on hondas, probably as much as 14 on our z's. I plan to try some of them as soon as I install my turbo (APS single).
When I turbocharged my Miata, I had to go to platinum (all that was out then to get it firing correct at high boost and loads...
Tommy

 

Just go copper, 1 heat range colder. Change the plugs every 2 oil changes. The "special" plugs may work better for the first 1,000 miles but afterwards are no better. Changing plugs will help the motor keep it's "crisp" feeling. Response, economy, resistance to bad fuels, etc..

The 4-6 hp you picked up from the iridiums is the same amount you would have picked up just be replaceing the plugs w/ new oem plugs.

 

when i did my dyno, at the higher rpm's, my A/F sometimes jumped to 19.5 which caused the ECU to retard, thus making less power or "studdering" as you say. might be your problem as well. car is breathing too well i guess....

 

I will not be able to change the plugs until next weekend as I will be out of town until then. I ordered some "special" plugs after hearing from several people that although they are no more condusive than coppers, they do last longer without needing a change...and I hate tedious tasks like changing plugs! If they turn out to last about as long as my current set then I will definitely not be buying them again. At any rate, the price was good since I ordered them online so I didn't get gouged.

I will post after I have had the chance to change them! Thanks for the advice

 

welcome

 

Well, I have finally have some updates...two weeks after I ordered them, my new spark plugs form ClubPlug.net finally showed up!

After doing some research on the benefits of copper vs. platinum vs. iridium, I decided on iridium mostly based on what I had heard about durability and longevity. I hate rooting around to change spark plugs, so hopefully these will last longer. If not...oh well. $50 dollars every 40,000-50,000 miles doesn't really bother me anyhow

Anyhow, I finally got everything I needed out of the way in order to change the plugs (what a b!tch to gain access to them!) and started removing them...I was pleasnatly surprised to find that I am not running lean as I had feared, but am instead running on the rich side of things! Here is a photo of the used spark plugs set up in the order of the cylinders they were pulled from. Driver's side is left, passenger is right:



You can see that there is some variance in the blackness. Up close and personal you can see that the front-most plug on the passenger's side was the leanest or "least rich" of the six. It appeared to me as though the driver's side center plug was the richest. Most notably (and probably not super visible in the pic), there was a decent amount of corrosion on the electrode and grounding bit.

Well, out with the old...in with the new! Shot of stock NGK Copper vs new NGK Iridium IX:



When I started up the car, I immediately noticed how much smoother it was. I went for a short test drive with a friend of mine and ran the car up to redline after it was warmed up. I began to wince around 4500RPM, expecting the hesitation I described earlier (which started this whole thread)...but it never showed up! On the contrary, the car pulled more smoothly to redline than it has in the last 3 or 4 months! As for claims about these plugs making "more power" because they're some fancy material, I was very dubious when I bought them and I remain so now -- I bought them for the claimed longevity, not any increase in power or whatever. I did not feel any noticeable boost in power anyway, even though my car apparently needed new plugs pretty badly. What I did notice was a more smooth and responsive engine, and that's exactly what I was hoping for.

I am confused about one little thing, though: everyone talks about NA mods leaning out the AF ratio. Everyone talks about the ECU leaning out the AF ratio if you do this or that. On paper, I would be a perfect candidate for an extremely lean fuel mixture due to the NA mods I have done (intake, intake manifold, cat pipes, exhaust) since I do not have any sort of computer work done. And yet...I'm running fairly rich. What gives? Is this all circumstantial? I guess I need to do some form of tuning either way. I'm glad I'm running rich not lean, but I'd rather have a better balance so I don't foul plugs as often...

Anyway, thanks everyone for your help -- especially UnderPressure for being the first person to suggest simply changing the plugs, something which had totally slipped my mind since...well, since I've never done it before.

Cheers!

 

I'm going to make a few assumptions and try to cover all the bases of this problem. Please correct me if I'm wrong.

It sounds like if you're running too rich / lean there is almost certainly a problem with some part of the fuel system, like your O2 / MAF / ECU or fuel injectors.

If your fuel injectors aren't clean, it could cause problems, like bad atomization of the fuel. This could lead to incomplete combustion (and the soot on your spark plugs).

but,

Assuming the O2 & MAF sensors, as well as the fuel injectors, are working as intended, the MAF may not give a linear response due to your CAI (I have not verified this, it's just a guess!). In other words, let's say your stock intake can yield a particular range of air flow, say range A to B. Your MAF sensor can probably handle a range of air flow that is similar to the A to B range. Above that range, the air flow "reported" to the ECU may not be as accurate. So, if your CAI yields an air flow range of B to C, (higher flow than stock) your sensor might max out at B and this results in sending garbage data to the ECU. So, I would assume that the ECU would tend to run an engine slightly leaner if you have "too much" air flow (more air is entering than the ECU thinks is entering)

Running *way too* lean means combustion will be cold (you will waste energy heating up excess air), and you won't be burning fuel efficiently, you will see unburned hydrocarbons in the exhaust. (Slightly lean would probably be ok.) Too rich means you will have excess fuel, which obviously wastes fuel, and you will also see unburned hydrocarbons, as well as CO. In either case your O2 sensor should be saying "WTF" if you are running too rich or lean, and the ECU should correct the imbalance. If it's not, like I said, it could be one of the problems I stated above.

(edit): OK this thread explains the whole system a lot better than me, lol!
https://my350z.com/forum/engine-and-drivetrain/122214-how-the-ecu-works-and-what-needs-to-be-overcome-for-na-gains.html

 

Your welcome, glad to be of service.

 

The week before I put the new plugs in, I ran a bottle of the redline fuel injector/fuel system cleaner through the engine. I heard good recommendations about it (did not want to use seafoam because I've heard it fouls plugs) and I know it did something because my exhaust pipes turned black and sooty much, much faster than they normally do. The car seemed to be a little bit more lively especially around idle. Based on that I figured it blew a bunch of carbon buildup out of the motor. It seems like the fuel system cleaner is something I need to use more often, and at $5/bottle it doesn't bother me too much every few thousand miles.

After that I replaced the plugs, and now everything is peachy keen again -- car is smooth as glass and pulls stronger, especially above 4500RPM where I was experiencing hesitation. I'll post again when the problem reoccurs, but I doubt it will be an issue for a good long while.