ben73

I just got home from my first session at the strip with my WB in the car. I ran close to my previous best of 12.81 into a 20+mph headwind.

I notice that it goes lean (13.7-14.0) on the gearshifts and takes almost a second to recover. Anyone have any idea why this might be happening??

'7747, Crossfire with 700r4, TPS at 100% for the entire run... I shift at aroun 5800, which drops the rpms to about 3800 in the next gear, so its still in the same cell in the PE AFR table (3200rpm table)....
The MAP stays maxed out also....

Ken73

Ben, is this with the X-ram or the SY-1?

ben73

G'day Ken,
X-Ram this week ;-)

ben73

Well I did some more tuning on this today and make some improvement by fattening up the VE2 table around 4000-4400.. This is where the engine speed begins 2nd and 3rd gear after a ~5800-6000 shift...
Any comments?

ben73

I'll post a WB log, that may help explain the situation.....
This shows a WOT run thru 1st and 2nd.
The pink line in the lower 1/3 is Throttle position. In the top 2/3 there is rpm in blue and AFR in green. The white vertical line is showing the AFR peak at 13.4:1 just as it begins to pull in 2nd gear @ 4114rpm.
The blue line in 1st gear is non-linear due to a bit of wheelspin, ignore that..

ECM is a 7747. The AFR spike is obviously triggered by the sudden decrease in rpm, even tho the TPS remains at 100.. What causes this?? I have tried tweaking the VE2 table around this area, but to no avail. The PE AFR table is currently set to all 12.2's for safety while i tune this bug out.. Are there any gain parameters in the 7747 that might allow me to slow down the rate at which it makes changes to AFR while in PE??

Any suggestions gurus?? ;-)

Pablo

iTrader: (1)

I dont think I can help you with this one (obviously im no guru), if you were letting off the throttle (like a stick car with a weak tranny) I would have said pump shot. Im assuming of course that youve done WOT runs that sweep from well under 4000 to 6 and you dont have leanness at 4 when you do that. I wonder if the big manifold allows alot of fuel to condense onto the walls when the rpms and vacuum drops suddenly on the shifts

Mostly im posting because im curious to know which injectors and pressure you are using to run that mph.

ben73

Hi Pablo,

My injectors are 90's at 15psi..
Yeah, I've run it thru 2nd at WOT from well below that point and the problem is not there, its only on the gearshift..
Despite this, I still tried modifying my VE tables so the peak is at the RPM's that the engine sees when it hits 2nd and 3rd, but it hasn't really changed a lot. I was hoping that this would add fuel as the rpms fall from ~6000 to the VE peak at ~4000.. Nope. ;-(

As far as I can see, the only thing that could trigger it to pull out fuel is the rapid fall in rpm's between the gears.. The TPS stays the same, as does the MAP.. I'm working thru the hack (not at all my stong point ;-) to see if I can locate anything that may be pulling the fuel out based on rapid rpm drop, maybe a bit of derivative action that may be responding to the rapid rate of change in the rpms?? Dunno, I'm clutching at straws....

In a few weeks I plan to swap out my 7747 for a '8625 PCM, hopefully that will give me the ability to tune out the problem and get the power back..

Ben.

SBNova

Ben, I read your post a few times, and I looked at the logs you sent me (to look at tps vs map), and the only thing I can offer here is maybe its a volumetric problem with the engine. Not a mechanical problem- just maybe the way the air/fuel is flowing through the intake from a high 6k to a lower 4k is doing something here. Have you tried to look at pulse width when this occurs- is it changing?