# SDS Tuning: VR6 Turbo



## leebro61 (Nov 7, 2001)

So I'm finally to the point with my Corrado that enough of the issues are worked out such that I can actually start to drive the car regularly...

I've been out driving with the turbo setup for the past few days and doing some datalogging in an effort to clean up the tune. I could use some tips/pointers/feedback to help me get going in the right direction.

*The setup:*
2.8 12v vr6 
268 cams/ported head
custom intake manifold
twin scroll gt35r
PLX R500 wideband
SDS em4f - v17 - 3 bar MAP
630cc injectors @ 4 bar - 93 octane

Right now I am running ~5 psi off the wastegate springs.

*The first issue I have is that at very light throttle the car bucks and trailer hitches like crazy. * If I watch the wideband, the car is lean when this is happening. The part I'm struggling with is determining the best way to add fuel in at these locations.

SDS (to my understanding) has several ways to modifying fueling. The first (and primary) means is the RPM FUEL values. Second, there is pressure based MAP FUEL values. Past that, there are also corrections for engine temperature and for the "accelerator pump." Since the bucking is still present once the car is up to temperature and the temperature related fuel modifiers are zero, I believe the issue is related to my accelerator pump settings and/or my MAP FUEL values.

My MAP FUEL values are the SDS default values, and per their instruction these values should not need much tweaking once the RPM FUEL values are tuned. I did spend some time on the RPM FUEL values before the car was turbocharged but it hardly ran consistent enough to get a good tune on the car.

My Accelerator pump sense settings are as follows:
- ACC Sense: 5
- ACC Hi RPM: 5
- ACC Lo RPM: 13

Can anyone help me get the trailer hitching cleaned up so I can move on to tuning the rest of the map? I've got datalogs I can share if it would help!

Thanks in advance, and please let me know if I've left out any important details.

Lee


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## need_a_VR6 (May 19, 1999)

No lost sync errors right?


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## leebro61 (Nov 7, 2001)

need_a_VR6 said:


> No lost sync errors right?


No sir. I played with the ACC Pump settings today and it got a bit better. It seemed to like a lower ACC sensitivity with increased ACC low rpm and high rpm settings. This seemed to work great but eventually after driving for ~15 miles I had some more light throttle hesitation. It's by far the most noticeable in the lower gears.

On a positive note, I adjusted my RPM fueling values based on last nights datalog and in boost the fueling is much better :thumbup:


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## need_a_VR6 (May 19, 1999)

So unless your tb is stupid large you should be able to put around with accel totally off. Just make sure your accel tweaks arent masking the rom fuel or map fuel being off in thkse regions.


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## leebro61 (Nov 7, 2001)

need_a_VR6 said:


> So unless your tb is stupid large you should be able to put around with accel totally off. Just make sure your accel tweaks arent masking the rom fuel or map fuel being off in thkse regions.


Yeah, I had thought about that. It's a stock obd2 vr6 throttle body, so I don't think it's a size issue. I guess what I don't know is what my afr targets should be in these high vac/low throttle regions.

I will go into these high vac regions and try adding some more fuel. Luckily I've got some decent logs that should help me get started.


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## sp_golf (Nov 28, 2007)

Just add fuel at the high vacuum range is bucks at, the accel enrichment settings shouldn't affect the AFRs when you're cruising steady. You should be tuning for high 14 AFRs but if it still hesitates you can go richer, some cars with big peak and hold injectors need to be as rich as 12 for decent driveability at high vacuum


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## leebro61 (Nov 7, 2001)

sp_golf said:


> Just add fuel at the high vacuum range is bucks at, the accel enrichment settings shouldn't affect the AFRs when you're cruising steady. You should be tuning for high 14 AFRs but if it still hesitates you can go richer, some cars with big peak and hold injectors need to be as rich as 12 for decent driveability at high vacuum


I added some fuel at all map values lower than -5 in Hg. The car drives a bit better but I still bucks a bit. I'll put up a screen shot of a map vs. rpm vs. afr datalog... (please let me know if you would like to see any other plots, ex: vs. TPS, etc.)










What I see in the above is that I'm still too lean at high vac ranges and low rpm ( 5 Volt = 29 psi (gauge)
(B) 0 Volt = -14.7 psi (gauge) -> 5 Volt = 28.8 psi (gauge)

Obviously (A) is -1 bar from sea level ambient whereas (B) is literally zero pressure, absolute. This isn't really a big deal, but would be nice to resolve the slight offset.


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## sp_golf (Nov 28, 2007)

Don't want to be rude but I think you're better off getting a tuner if you haven't figured it out already..


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## leebro61 (Nov 7, 2001)

sp_golf said:


> Don't want to be rude but I think you're better off getting a tuner if you haven't figured it out already..


I would happily pay someone to tune the car if I thought there was someone decent in the area. It's not a pride thing.

However, with that said, the car is at the bottom of my priority list and I haven't touched it since my original post. I'm not retarded, I'm sure I could figure it out... but with limited time available I thought it might be best to get some general guidance from those that have been there before. Thanks though


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## need_a_VR6 (May 19, 1999)

Sds works better without a wbo2, you just tune it to feel good and dyno tune wot. I am sure there will be spots that are hard to nail with just the rpm fuel and map fuel overlay as its not really 3d.


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## leebro61 (Nov 7, 2001)

need_a_VR6 said:


> Sds works better without a wbo2, you just tune it to feel good and dyno tune wot. I am sure there will be spots that are hard to nail with just the rpm fuel and map fuel overlay as its not really 3d.


Thanks Paul. I think I've got an idea for how I might clean up the map a bit. I'll report back what I did and how it worked out when I find some time to finish it up.


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## jaystone (Jun 12, 2004)

Hate to bump a two year old thread, but my VR turbo experiences similar symptoms with my SDS. I have played with the ACC pump lo hi settings as well with limited success. Need to look at high vacuum fuel values I guess. What was your final verdict?


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## leebro61 (Nov 7, 2001)

I had better success/consistency with part throttle once I turned SDS' closed loop cruise OFF. My guess is that I probably had poor choices of the closed loop set points. I would try turning closed loop off (if you haven't already) and then try to tune the high vac ranges.


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## jaystone (Jun 12, 2004)

running closed loop off, messed with the high vacuum fuel values a bit (seemed low). Thanks for the surprisingly quick response!


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