If you come down to Chicago land for your dyno give me a call. I'd like to go with ya.

Have you pulled/changed the plugs lately?

I'd inspect them just for kicks. Honestly, there are sooOOOO many things it could be. I'd even add ignition misfire to the list. I know Nissan is known for good high powered ignition systems, but with 140K miles and exceeding the factory REV limiter, it may be possible.

Is there ANY circumstances that are common when this occurs? Do you have OBD-II? I'm sure you do, but do you have someone in your area with an Alex Pepper OBD scanner? Probably a long shot, but if so, get some scans and I'll take a look.

You got a point, just bustin you ***** dude. We shall see what happens my next monday, hopefully after the DYNO!

How does a dyno show valve float?

The plugs have less than 5000 miles on them.

I can ask around about the scanner, I don't know of any around.

Supposedly, the hp curve drops off FAST as RPMs increase.

Honestly, I don't know until I compare curves. However, I think the dyno will show more is going on here than the suspected valve float.

I'm thinking ignition or fuel delivery.

Yes, the hp/torque curves will be choppy. But how is the dyno going to reveal what the cause is? If he already knows there's a power drop off, the dyno is telling him something he already knows.

If it's fuel, I suppose the wideband option would reveal if the a/f are leaning out. But I suppose a simple fp at idle and wot would be able to handle that.

Butt dynos don't count, so at least on the dyno he'll know WHERE the problem is occuring, ie RPM range, and whether it is only occuring over a certain RPM range. He may have FP issues or IG issues that show dips elsewhere, but he's only noticing the largest dips at XXXX RPMs. That's IF he can repeat it, while on the dyno.

Pulling the heads or replacing the motor may fix the problem, but it's going to be costly. The dyno will at least eliminate SOME possibilities before he resorts to drastic measures.

He already basicly knows where the problem is occuring(high rpm). Even if it showed a problem at 2000 rpm, how is that going to reveal what the problem is?

I suggest getting on a handheld Nissan Consult and have them drive the car up though the rpm/load range and then see what the 02/ign timing and coil ohms/ign timing are all doing. If there is a problem, the Consult would probably show it(if he can get a Nissan tech that gives a rat's butt and knows what he's doing etc)

A dyno will just show where the problem is. Won't really show what the problem is. The wideband might show a a/f problem though.

That sounds like a better solution, however good luck getting a Nissan Consult.

Also, you can hear preignition or valve float, and even monitor FP on a dyno, which is not easy to do while flogging it out on the hwy. Just having it stationary has its benefits, but the graph can help point to problems also.

The more I think about it, the more I'm convinced he has a misfire. I think he needs to reduce the gap on the plugs and/or switch to fine wire electrode plugs to aid his stock ignition system at those high RPMs. The higher the RPMs, the less time the system has to charge/discharge its spark. His claim that its occurence is random makes me think it's not fuel pressure related, but the A/F graph will eliminate that concern IF he can duplicate it on the dyno.

When you dyno just bring a floppy disk to save the runs on. Then you can view them with dynojet viewer and do the old print screen .

I have 264k and can take mine to the 7k mark with no problems

Wow, it must be because you have a VE!

Don't worry...all the bandwagoneers will calm down soon.

It's probably something simple that can be figured out with some investigating.

I would say look into the SR20 valve springs, Nismo87 says they can go up to 7700rpm.

this is very interesting, I hope its not valve float, I have almost 70k and I want to do the VI/JWT

keep us updated

I've never experienced any valve float with my JWT/VI combo (7000rpm cut). I do know what it sounds like because my 94 Z28 use to do it if I held 2nd too long. I think Neal's problem sounds like an ignition/fuel related.


Dave