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need advice on an RB26 map

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Hi, I recently had my car mapped by an "old school" Japanese tuner who is accustomed to dealing with the HKS V-Pro; mine is the first Link he has ever done.  The car made good power on the dyno and runs well, but the idle is just a little bit more lumpy than I would expect and I'm wondering if someone wouldn't mind taking a look at the map.  The tuner says the injectors are to blame but I want to make sure there isn't anything else that could be cleaned up at all.

The engine is an RB26dett running multiple throttles and stock turbos with Bosch EV14 1000cc injectors and R35 GT-R ignition coils.  It has been mapped using MGP as the main fuel table load axis with a secondary table overlay to compensate according to throttle position.  Closed loop lambda is set to on and the sensor works great but for some reason the gain is set to 0.  Increasing the gain to about 5% causes a tendency for the engine to swing lean at idle.

I would greatly appreciate any help or advice anyone can offer!

 

5-31-2017.pclr

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I suspect the issue might be using MGP as the load axis on the main fuel table.  The RB26 usually has a weak and sometimes unstable vacuum at idle so most tuners use TP as the main load axis.  They then normally use the Open loop lambda target table to enrich under boost conditions and often a 4D table is not even required.  Sometimes just a few cells in high boost areas requires 4D correction.

If you can post a log of the car idling we can take a look and see if there is any opportunity to improve what you have without a complete re-map.    

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Thanks, I'll attach a log file below.  After looking at the AFR with the car warmed up it's actually pretty close to the target but the idle still doesn't feel very smooth and if I play back this log file and look at the main fuel table it appears just as you've described, that the vacuum signal is fluctuating.  Would it have any positive effect if I even out the values in the idle area of the fuel table (4 cells between -70 to -60 MGP, 750 to 1000 RPM)?

Log 2017-06-18 2;01;17 pm.llg

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I always tune RB26's with TPS as the main fuel load table. I even use it as the main load on the ignition table with a 4d map for boost correction. I find it makes them much snappier. You are getting fairly low in the injector pulsewidth at idle. It is possible that the dynamics of your particular injectors are not consistent enough at that low of a pulsewidth. You could try to change the 1000 rpm cell at 5.8 psi in your Target AF table to 13.8 or so. If its a low pulsewidth issue this may stabilize it a bit. It seems to be maintaining idle fairly well in the log.

Blaine Carmena

Carmena Performance

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I agree with Blaine here, you log doesnt really exhibit any problems - it looks like it is idling quite nice.  I too think it is potentially the very short injector pulsewidth at idle that gives odd behaviour under some conditions and maybe giving it a slightly richer idle might help, maybe try less advance also as it has ~20deg at idle.

Also your CLL is potentially being randomly disabled due to the "MAP delta" lockout combined with the unstable MAP.  I would try increasing this from 0 up to about 3KPa.

iE59sBV.png

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Thank you both for taking a look at it.  It's a strange feeling at idle; the idle speed is completely stable but I can feel it sort of stumbling or missing a little.  It doesn't feel like a misfire, more like driving a car that has a dirty MAF sensor.  I'll try increasing the MAP lockout value.  Also, would filling in the Short Pulsewidth Adder data for the injectors help at all?  I tried doing so but since the car has already been tuned without it, the values provided with the injectors make the whole map go lean.

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The short pulsewidth adder table may not help if you are at the point of marginal misfire due to minimum pulsewith. Its more there to keep the fuel calculations consistent when using low pulsewidths. You may be beyond that. Filling that table will only effect a small part of the map. It should have no affect on higher load areas. Save your map beforehand then try it. That way you can always put the old map back in if you dont get the result you want. You will likely have to tweak the fueling a bit in the low load areas where the injectors are approaching their lowest points.

Blaine Carmena

Carmena Performance 

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Thanks Blaine, I'm finding that if I target a slightly richer AFR and try to keep the injector's actual pulse width above 1.54 it smooths out a lot.  I think I'll leave the pulse width adder alone unless it's absolutely necessary.

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