S.Trim goes crazy at light throttle?

DYE · Post by **DYE** » Tue Jun 20, 2006 11:03 pm

I noticed at light throttle, between about 2 to 8 percent my S.Trim fluctuates up and down from +27 to -7 about once a second. I've searched and searched for the cause but can't come up with any concrete answers. Anyone else have this problem or know how to cure it?

I'm using a Walbro fuel pump with 750cc RC 12-Ohm injectors, turbo with full 3-inch exhaust, no catalytic. Using the Cybernation 650cc map, updated to 750 injectors. STrim under all other conditions seem fairly normal.

Post by **Spunkster** » Wed Jun 21, 2006 9:39 am

More than likely you need to tune the areas this is happneening in a little more. Since you have not posted your calibration it is really hard to comment on where changes need to be made.

DYE · Post by **DYE** » Wed Jun 21, 2006 9:21 pm

Spunkster wrote:More than likely you need to tune the areas this is happneening in a little more. Since you have not posted your calibration it is really hard to comment on where changes need to be made.

Thanks for the response. I didn't upload the calibration because I'm just using the Cybernation calibration that comes with KPro, only difference is I've changed the value from 650 to 750 for injector sizing.

I've been cruising in the range where the problem occurs but at 10% TPS and the A/F ratio is steady at 14.7 with no fuel trimming. I've also been in those cells while cruising with closed loop disabled, TPS at 10% and the A/F ratio is steady at 14.7. Again, only at very light throttle I get this flucutation in the A/F ratio.

I'm fairly confident it's not the fuel tuning. Could it be anything else?

Post by **Spunkster** » Thu Jun 22, 2006 9:44 am

You need to get the car tuned. Until then it all speculation. All engines are different and you must get it tuned...and add to that the fact that you have larger injectors...without tuning you have a recipe for disaster.

DYE · Post by **DYE** » Fri Jun 23, 2006 7:33 am

Maybe I wasn't very clear in my last post but the cells affected run perfectly with a bit more throttle opening. I have the same cells being referenced when going 3000 rpm with 10% TPS as I do with 3000 rpm with 6% TPS with a difference of MAYBE 20 to 30 mbar.

At 10% TPS, the values in those cells produce the following results:

In Closed Loop - 0% STrim 0% LTrim, 14.7AFR
In Open Loop - 14.7AFR

But, following your suggestion, I've tried to tune it some more and I've added more fuel, taken it away and there's just no change at the very slight throttle. I was as thorough as I could possibly be, making very minor changes, testing them and then making more minor changes. All the way up to 30% more and 30% less in those areas affected, yet still get the wild fluctuations in short term fuel.

Could it possibly be that the injectors are just too large for fine fuel delivery in that range?