I understand that above 5000rpm the vtc solenoids switch off slightly adjusting the timing. Will it be ok for me to disconnect the VTC solenoid connectors so see if it's the root of my Z related evil?

 

My problem arises at about 5000rpm & above where it just quickly runs out of steam perhaps nackered VTC springs or solenoids or something?

 

I don't know much about this topic:confused:

Just found this on TT.net and tought it was quite interesting;-

 

http://www.twinturbo.net/net/viewmsg.aspx?forum=technical&msg_id=780753

I'm not sure that the VTC is activated at a specific speed, there will be a number of factors involved that affect it's operation - I expect there is an entire map in the ECU. However, the manual section describing it starts here, if that's any use :- http://www.300zx.co.uk/tech/manual/manual/efec/029.gif

There is one byte in the ECU that controls the VTC. From my understanding, it's the point where the ECU stops the advancement of the timing on the inlet cam. On stock this is 5500rpm.

Not that that's any help with the problem!

Rob are you sure the cams are correctly timed? That sounds like possibly the cambelt has slipped a tooth or two. Are you sure the fuel pump is ok? Is the fuel pump controller ok?

 

Just a few thoughts...

 

CheerZ,

 

Andy

 

Oh, is the car decatted or not?

I wondered if the cam timing was correct so i changed the belt a couple of months ago, the old one was actually lining up fine though and thus made no difference. I also changed fuel pumps around the same time and i also tried running a direct 12v feed to the pump to eliminate the controller.

The car still has cats and occaisionally (doesnt seem to be doing it now) has the rotten egg smell. Perhaps a collapsed cat?

 

Tonight im going to try different coil packs to make sure one of them isnt breaking down at high revs but im doubtful its this.

 

Cheers

Could well be collapsed cats - what is the exhaust flow like from the tail pipes???

Originally posted by John Dixon

There is one byte in the ECU that controls the VTC. From my understanding, it's the point where the ECU stops the advancement of the timing on the inlet cam. On stock this is 5500rpm.

Not that that's any help with the problem!

 

John,

I have been thinking about this and in the manual it is unclear at exactly which point the VTC is triggered and lists a number of inputs that at first appear to affect the enabling of the function. After further thought I and having read the following by Devin (ZfromJapan@tt.net) :-

 

79F6 - VTC Release

This is the Valve Timing Control Release. One of the nice features of our engine is the VTC which advances the timing on the intake cam. One of the down sides to stand alone ECU's is that this great feature is lost. Only a hand full of stand alone ECU's have the ability to use the VTC, one of which is the $2500+ Electromotive Tec 3.

The stock value for 79F6 is 76hex. 76hex is 118dec, times 50, equals 5900rpms. This is the point where the ECU ends the advancement of the intake cam and the valve overlap. The advanced tuning of this one little value is almost an art. The very high end tuners are very secretive about what value they use here, and what I know about it, I promised not to talk about. I suppose there are a few cam experts floating around tt.net that may be able to take this info and run with it.

On the 300Z.bin code I lowered the VTC Release to 62hex which equals 4900rpms.

 

... I am convinced that you are correct in what you said, (give or take a few hundred rpm, but that will probably vary from model to model) but in my opinion there are a number of factors that have to be taken into consideration and these are that signals from the following sensors must be within a predefined range, and they are :- MAS, TPS, RPM, Temp, and Neutral position sensor.

 

The last is the most interesting of all for me, because since my auto/manual conversion I know that my neutral switch has been Donald Ducked and the ECU thinks the car is permanently in neutral. Therefore, this explains where my top end torque/power has disappeared to on my last dyno run. EUREKA !!!!!

 

Now I am certain that getting the netutral switch fixed will get me back the 30bhp I've lost and make my cruise control work again - hurrah ! :D

This thread has started me thinking! I have a top end power loss too. Power went from 314@wheels to 285@wheels on the same RR when i thought it'd lost some punch. Curve is totally flat from 5500rpm up.

Had thought plugs initially, but now wondering if it's VTC related. I think I'll try connecting a meter across them when driving, and see if it changes at the expected point. I'll let you know what I find out. Do manuals have a neutral switch BTW?

Yes they do, from memory it's towards the back of the box on the drivers side. And it sounds like your symptoms are similar to mine.

Dont mean to put a damper on the hope of getting back your lost 30bhp, but wouldnt no neutralswitch mean the car fails to advance the timing between approx. 2000 and 5000? Meaning get it sorted and you'll have more power in this range, but your timing ok above 5000.

Wording it another way;- Doesn't 5000+ have same cam timing as tickover or being in neutral. With it thinking ur in neutral, above 5000 ur fine but below ur lossing some precious torque.

 

?

Or have i got the wrong end of the stick? I really don't know to much about vtc.

 

Andy McD, how do i know what the exhaust flow is like? sorry to sound stupidbut air's flowing out, what's considered alot?

Shall i get a bin bag and time how long it takes to fill?:D

LOL! Erm, just a healthy amount of gas - like the mornin after a vindaloo :D

 

You sure you reconnected your neutral switch when you put your 'box back on? ;)

 

CheerZ,

 

Andy

As you know I didn't do it, but when we looked under the car recently the wires have been bridged and the switch is not connected.

 

Originally posted by andyduff

You sure you reconnected your neutral switch when you put your 'box back on? ;)

Well i know i put mine back on!

 

Also t'was happening long before changing my clutch just it was hard to rev that high without slipping.

 

I'm gunna time my bin bag filling. Anyone give me a time to compare to? :D Might get some decat pipes which will tell me if its a/the cats, just worried bout my tubby seals.

That would depend on whether the solenoid operates in the normally ON, or normally OFF mode - it's not clear from the manual, but my symptoms would indicate normally ON. Time and experimentation may tell ...

 

Originally posted by Robtor

Dont mean to put a damper on the hope of getting back your lost 30bhp, but wouldnt no neutralswitch mean the car fails to advance the timing between approx. 2000 and 5000? Meaning get it sorted and you'll have more power in this range, but your timing ok above 5000.

Wording it another way;- Doesn't 5000+ have same cam timing as tickover or being in neutral. With it thinking ur in neutral, above 5000 ur fine but below ur lossing some precious torque.

 

?

Or have i got the wrong end of the stick? I really don't know to much about vtc.

RTFM FFS some people are sooooo lazy :D

 

http://www.300zx.co.uk/cgi-bin/manual.cgi?list=efec&dir=&config=&refresh=&direction=forward&scale=0&cycle=off&slide=30&design=default&total=190

 

HTH

 

CheerZ,

 

Andy

And obviously I read that, but it does not 100% clarify whether it fails open or closed. But I will find out ....

 

Originally posted by andyduff

RTFM FFS some people are sooooo lazy :D

 

http://www.300zx.co.uk/cgi-bin/manual.cgi?list=efec&dir=&config=&refresh=&direction=forward&scale=0&cycle=off&slide=30&design=default&total=190

 

HTH

 

CheerZ,

 

Andy

Originally posted by AndyP

And obviously I read that, but it does not 100% clarify whether it fails open or closed. But I will find out ....

 

Andy that wasn't aimed at you lol

 

When you remove them they are open - this doesn't mean they can't fail closed, but if there was a bad connection then they would stay open...

 

HTH

 

CheerZ,

 

Andy

That's when the ignition is off, but they could be automatically energised when the ignition is turned on. May do a bit of research at the weekend ...

 

 

Originally posted by andyduff

Andy that wasn't aimed at you lol

 

When you remove them they are open - this doesn't mean they can't fail closed, but if there was a bad connection then they would stay open...

 

HTH

 

CheerZ,

 

Andy

Just went for a quick drive with the solenoids disconnected and it really does make a difference.

 

It's a case of slowly..slowly.. 4700rpm fast!! 5300rpm (my prob kicks in) slowly.. slowly..

Im glad the Z has this VTC system, without it id be slow as mr.slow.