Nissan ECU Tuning

JEDI-77 · Joined: 13 Apr 2007 Posts: 10

I have a 1990 non-turbo 300zx. A few years back I had some extractors installed and at the time of installation the EGR was removed (the extractors did not accommodate the EGR). Since then, the car has suffered some light detonation at light throttle or cruise conditions in hot ambient temperatures (more so when the aircon is on, I assume because the aircon puts an extra load on the engine). The exact same spot where the EGR is normally active. Now, I have spent the last couple of years checking everything on the car (fuel pressure, fuel flow, spark plugs, compression….. everything that can cause detonation) and everything is fine. So it seems that the detonation is caused by the high temperature of the incoming air, and since the cooling effects of the EGR are no longer present, this allows detonation to occur. I only use 98 octane fuel, but the detonation still persists. If I use a bottle of octane booster, the detonation is gone. Using Nissan Datascan I have been able to track at exactly what location in the timing and fuel map the detonation occurs. In the fuel map, it is in the closed loop section, between 2000-3000 rpm, light load, where the A/F ratio’s are quite lean. In the timing map, the detonation occurs at an area where the ignition timing is at its highest (42 degree’s). I have been able to combat this problem to a degree by reducing the ignition timing in that area to about 37 degrees (5 degree retard). However, on really hot days (35 celcius +) the pinging is still there. Very feint, but quite noticeable if driving past a wall or barrier where the engine noises are reflected back. More so if traveling up hill. And using the aircon on these days is just impossible as that makes the pinging much worse and very noticeable.

I am reluctant to take out more timing in that area as it may affect the driveability of the car. I haven’t noticed any difference between having the ignition timing at 37 degrees compared to 42 degrees, but was wondering what would be the safest and lowest that I could go with the timing in those light throttle / cruise areas?

Also, I am planning to add more fuel to the effected areas to try and cool the combustion chamber. I will need to convert those cells from closed loop to open loop, and increase the A/F ratio from 14.7:1 to maybe 13:1??? Is that too excessive?? I know this will effect my fuel economy, but I don’t mind as I have a device which enables me to alternate between 2 separate ECU tunes. So I would only use the “non-economical” tune on hot days. Once again, is there a limit as to how much fuel I should add in this area??

If anyone has any advice or suggestions to helping me tune out the detonation, or see a problem with what I have listed above, please let me know.

Thanks

nzniggles · Joined: 26 Aug 2006 Posts: 56 Location: New Zealand

Go with the fuel idea

zrated · Posted: Thu Dec 27, 2007 11:47 pm Post subject:

seconded about adding more fuel.... also with the who EGR removal causing pinging... I really don't think that would be the problem. Exhaust Gasses are a lot hotter than your intake system... EGR recirculates extremely HOT gasses back into your intake system... Not cold. Smile

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kenbam · Joined: 15 Sep 2007 Posts: 2

JEDI-77 · Joined: 13 Apr 2007 Posts: 10

nzniggles · Joined: 26 Aug 2006 Posts: 56 Location: New Zealand

What cells did you change ?

JEDI-77 · Joined: 13 Apr 2007 Posts: 10

cb_drift · Joined: 04 May 2004 Posts: 472 Location: New Zealand

Just take more timing out......

If you notice a drivability problem and you've checked the mechanical side of things and everything is ok there - the electrical side and all sensors seem to read correctly and you've tried fueling there - keep pulling out timing....

was tuning an rb30det last weekend that ran to a MAX of 13 deg timing under load and couldnt hold more than 20's deg at light loads - thats just what it wanted to be happy....
it still made 500nm torque at the wheels over 225kw (all at low revs) and had 0 drivability issues....

another engine with the same specs took an aditional 15 deg of timing all over the board (yes the crank angle was set right) to produce the same results.....
some engines just want what they want

when it comes down to it - youve got a 300z with a 3 liter engine - it'll be pretty happy no-matter what really...

try it and see what happens...

JEDI-77 · Joined: 13 Apr 2007 Posts: 10

cb_drift · Joined: 04 May 2004 Posts: 472 Location: New Zealand

nissans take an average of 4 cells around the timing area - I have hardware trace so I see exactly what 4 cells to modify - but I dont do consult trace - so I dont know what 4 cells its using to work out the timing from a single cell of consult trace...

get an egt sensor and monitor that - zeitronix make a wideband that logs o2, tps, afm (with its 5v input), egt if you get the egt sensor and vac/boost if you get the map sensor... very useful for tuning....

take a choice - do you want detonation? if the only fix is timing - are you willing to leave it detonating if your worried about egt if your only there for a moment? it wont affect things if you only pass thru there quickly - but knocking/det will eventually add up over time....

if it is a main cruising point when you spend most of your time there then yeah - monitor egt and work out what you want to do about things - drop timing and put in fuel to cool things down maybe....

experiment - on short term - you shouldnt really be able to cause damage if you pull timing and increase fuel (unless you borewash things....)

you will at least see if your car has drivability issues or not....

and pulling timing and increasing fuel - some people think that helps with turbo spoolup which will help push the tp higher and you will get past things quicker.... (Havnt tried this - cant comment if it works or not on a factory ecu... antilag also injects more air at that point as well....)

and yes - smooth timing transitions - sudden timing changes can make for sudden torque changes which can make for detonation promoting characteristics.....

Good luck with testing whatever route you take Smile

Hope you get it sorted out so your happy Smile

nzniggles · Joined: 26 Aug 2006 Posts: 56 Location: New Zealand

Have to agree with CB, timing is about all you have left (except for a bit of water injection maybe). Like you have said, it is only under light load so if you need more power, your throttle will be down a bit more and the area of map causing problems won't be used. Also the 300's kill the aircon temporarily if you accelerate in a rapid manner.