Umm... no one seems to know how to fix this...

[240zDailyDriver]

wow sounds like I have some work to do then, . Thanks guys for your comments! I actually didn't know what a colortune was... but now I do! That little thing will definitely come in handy (thanks Jim!). Alright well, again I am going to try and fix this thing once and for all! Wish me luck! (I will keep you posted on whats going on!) Thanks again!

[240zDailyDriver]

Alright guys... I have replaced all of the electrical... and have come to the conclusion that it is not an electrical problem. So I am going towards the fuel... I know it is not the carbs because I have an extra pair that I switched out temp. and I am still experiencing the same problem. I have started at the fuel tank... cleaned it out noticed that it is in relatively good condition. Some of the hoses on the other hand were falling apart. I replaced those hoses... I was curious though... would anyone happen to know what the correct diameter of the outlet hole for the fuel rail is? I was thinking maybe it might be too big not allowing the proper pressure when I need it... Thanks again!

[rdefabri]

Not sure if you mentioned this - but IIRC, you need to eyebrow the cylinders on a 240Z block if you put on the N42 head (larger valves).

I don't know if NOT eyebrowing it will cause catastrophic damage, but you were asking about valve clearance - could that be a possible cause? Did you eyebrow the cylinders?

[madkaw]

Good point about the eyebrowing of the block. I would check cylinder compression before you do anything else. You might have tweeked all of your exhaust valves and now you can't hold compression enough for the car to run properly. What do your plugs look like?

[JimmyZ]

One of those pressure gauges used as a combination fuel pressure/vacuum gauges would show any valve issues. It might also point towards other things as well.

Here's a link to one... http://images.google.com/imgres?imgurl=http://ecx.images-amazon.com/images/I/31Y6DP8778L._SL500_AA280_.jpg&imgrefurl=http://www.amazon.com/Fuel-Pump-Vacuum-Gauge-TU1/dp/B000RT9BY0&usg=__UcZvlG60aQx_fzJCxkTHyvM-qgQ=&h=280&w=280&sz=10&hl=en&start=2&um=1&tbnid=cNrcexDkmA0lSM:&tbnh=114&tbnw=114&prev=/images%3Fq%3Dfuel%2Bpressure%2Bvacuum%2B%2Bgauge%26um%3D1%26hl%3Den%26rlz%3D1T4GGLD_enUS307US307

Pretty nice to have.

2c

[240zDailyDriver]

Well, I have actually never heard of eyebrowing cylinders... sorry, could you explain a little on that one? (I just put an N42 on because my mechanic told me it would raise compression)... I did check the compression within the cylinders and I am getting 185 psi in each cylinder... with the exception of cylinders 2 and 6 which are at 180... umm and the plugs look fine... if there are any other questions... due ask!

[rdefabri]

Search the forum for eyebrowing - I actually thought of doing the same as you, which is how I came across it.

Basically, the N42 has larger valves than the E31/E88 of the 240Z. Since the N42 was introduced on the larger bore 2.8L of the 280Z, there's no interference with the block when the valves open for the exhaust stroke.

If you are running a smaller bore 2.4L (which sounds like you are), the valve will make contact with the block on the exhaust stroke of the cycle, which can cause damage.

Can't say this is the primary cause of your problem, but I'll bet it's contributing to it.

[madkaw]

PICS,

It sounds like what JimmyZ said in the first post, you are running out of gas. Check your fuel pump output and your filter. Does it act perfectly normal under 4000rpm even under hard acceleration?

[rdefabri]

Look very closely at madkaw's pics and you can see the "eyebrow". It the chamfered edge of the piston bores to allow valve clearance.

Since he mentioned the sputtering starts at around 4,000 rpm, I wonder if the valves are closing prematurely given the higher rpms (assuming they aren't already damaged)?