Hi guys, just a quick hello from Australia..:) I lurk around here from time to time but my home forum is http://www.aus300zx.com...

Anyway, I'm after some peoples views on a problem I am having, one that I think is linked to the EGR. Having read a few 300zx forums over the years, it seems quite common to remove the EGR when the engine is out. It cleans up the engine bay and avoids some nasty problems if its not working properley. However, this recommendation seems to always be for TT's, but being an NA owner myself I'm starting to believe that the EGR removal is not a wise move for the NA. I want some of you tech guys to tell me if i'm wrong or right.

 

Now, my car suffers from light / part throttle detonation on hot days and having the aircon on. I can easily accelerate through it, and there is no detonation at WOT, even on a 40 degree day as proved on a dyno. It has already cost me one motor a few years back (cylinder 6 dropped down to 100psi and was burning oil) and unfortuneatly the nasty ping gremlin has also carried over onto my 2nd motor. The only link between the 2 motors is that in both occasions, the motors have run without an EGR as it was removed many years ago. Over the years, I have replaced all (and I mean all) my engine sensors, fuel pump, injectors, fuel regulator, dampner, checked fuel pressure, CAS, MAF, played with timing, ran with colder plugs.... etc etc.... everything you could possibly do to counter act pinging.... but on really hot days, the pinging remains... The only way I have been able to deal with it is to retard the timing a little, and also have an aftermarket piggy back computer installed (UniChip) with which I can take out some timing in the light throttle area's...

 

So after all this, I regret having removed my EGR which was removed when I had my Headers / Exractors installed which did not have a fitting for the EGR plumbing. And since then, all the plumbing and solenoids have been removed so trying to put the system back in would be a nightmare. My theory is that since the NA runs a higher compression ratio under cruise conditions (10:1 compared to 8:1 on a TT off boost), the high ambient temps make the NA more prone to detonation under these light throttle conditions where the timing is quite advanced (around 35-40 degree's on my manual NA), and the A/F ratio is lean as the O2 sensors try to maintain a 14:1 A/F ratio... Its at these light throttle conditions where the EGR is active and uses inert exhaust gases to cool down the cumbustion chambers..

 

So is my theory totally incorrect, or just so plain obvious that this post is a waste of time?? If so, then perhaps we should be careful with advice such as removing the EGR as although it may be fine for the TT, it may be detrimental for the NA.

 

Cheers

I had a very similar problem with my turboed NA and it only happened on really hot days and only between 1000-2500 RPM

long story, but it's related to EGT levels and the only thing that really helped (for me) was adding fuel to the low/mid load areas of the fuelmaps (in the chip)...downside is the slightly higher fuel consumption.

 

Do not retard timing in those areas...it will make things worse ! (EGT levels will get even higher...although you might not hear the pinging anymore)

 

-Eric

What grade fuel are you using ?

I use 98 RON fuel which here in australia is our high octane fuel. We also have 100 Ron fuel but it contains ethanol so us zedders avoid using it...

 

But yes, my car will still ping on hot days with 98 RON fuel. Whats more annoying is that I am using an aus-spec ecu which is designed to run with 91 RON fuel. However, I still have to retard the timing a little to eliminate the pinging. This makes the car fine to drive with the aircon on, except for very hot days (33 degree's +). Funny thing is, with the aircon off, I can drive around in extreme heat no problems.

 

Cheers

 

What grade fuel are you using ?

I wasnt aware that retarding the timing increased the EGT. Still, it does remove my pinging by retarding the timing a few degree's in hot weather.

 

In regards to adding more fuel in those low area's, wont the O2 sensors compensate for the extra fuel by leaning out the mix even more?

 

Cheers

 

I had a very similar problem with my turboed NA and it only happened on really hot days and only between 1000-2500 RPM

long story, but it's related to EGT levels and the only thing that really helped (for me) was adding fuel to the low/mid load areas of the fuelmaps (in the chip)...downside is the slightly higher fuel consumption.

 

Do not retard timing in those areas...it will make things worse ! (EGT levels will get even higher...although you might not hear the pinging anymore)

 

-Eric

In regards to adding more fuel in those low area's, wont the O2 sensors compensate for the extra fuel by leaning out the mix even more?

 

Not if you put the ECU into an open loop mode at those points too.