lakeffect2

During my personal journey in learning how to tune a '7730 ECM with a 58mm throttle body, SLP runners, and a 230/236 cam I've got nice solid starts, a dependable, stable idle, and a beast that roars when you stomp om the pedal.

The fine tuning thatI need to accomplish nextis the simple around town engine events. Specifically, I notice while cruising and letting off the fuel pedal, maybe while while coming to a light, or a approaching a lower speed zone, there is a surge while the ECM tries to balance the lower rpm with a vehicle speed that doesn't match it yet. KiInd of catches up after several surges that diminish over time (20-30econds)

Kind of RRRRRRRRUMP, RRRRRRUMP, RRRRUMP RRUMP and (wait for it)
RUMP

Previously if driving around 30-35, it just wouldn't come down in speed at all, it would just keep going like a army tank until the vehicle stopped by braking. I lowered the speed at which the TCC unlocks which seemed to help. I've also been lowering the IAC steps per a few threads around here which seemed to relate to my issues.

I'm just not sure if I'm on the right track of TCC and IAC being the true cause or if I'm just masking the real issues that I fail to grasp or are being overlooked.


As always, anyone taking the time out to offer any insight you've had to correct similar conditions will be greatly appreciated.


Dave

RBob

iTrader: (1)

Surging on decel is usually caused by being too lean. If running closed loop decel you are also fighting proportional gains. Which can also cause surging.

Try increasing the O2 window at low MAP values and add a little fuel to the VE table in that same area. that will tame the surging. As long as the INT/BLM doesn't keep pulling too much fuel.

This is also an area where the injector compensation values are critical. As the PW is typically small.

RBob.

lakeffect2

Before I saw your reply, I made several changes to the bin in question. I was also trying to get the he rpm's and vehicle speed drift down. Luckily the Prominator can quickly switch back to previous settings, as it messed the signal to the speedometer and made the engine stumble and die.

So If I'm trying to unlock the TCC CORRECTLY....in a730 ECM and $8d mask, What table sh0uld I be changing to allow the uncoupling to occur as I approach lights, speed zones . As it is, the engine RPM hangs up,the TCC does not unlock and it's like cruise control keeps it at 35mph until you fight it with the brakes.


I'm about to load a bin with the lower fuel table less lean at the near idle settings,per your suggestions,but I'm unsure of which O2 settings are in play that you refer to.

Regards, Dave

DENN_SHAH

iTrader: (1)

i don't know if your having the same thing going on that i have, but going in and out of DFCO during cost down can also cause some surging.
with no fuel, you have strong engine braking.
when the fuel comes back, you have less engine braking.
my car goes in and out several times if i don't manually down shift the trans out of OD. if i down shift it right, it only does it once or twice after im in
first gear. i can hear it in the exhaust too.
its more noticeable when the TCC is locked but its still there when its unlocked.

lakeffect2

I haven't played with DFCO yet. Please correct me if I'm wrong, but I'm thinking that if DFCO is part of the issue, I may need to change parameters so that it takes less fuel away during DFCO as I may be trying to compensate my lower fuel table by richening a rpm/kpa area when DFCO is trying to lean it out. Essentially chasing my tail.

Other issue is.... I'd still like to consider unlocking the TCC as it drifts down past a certain higher mph than current (whatever that is?), but still feel daunted by the number of TCC variables that show up. I'd like to change the correct one(S) not make matters worse by chhosing the wrong one. Any insight in that area would be appreciated.

As always, my thanks to those taking time out of their busy days to answer, Dave


P.S. My son took Shammoo out to the local dragway last night for a test and tune session, and went 14.31s at 94.7 this is without a posi rear and stock 3.08:1 gears, So it was peg-leg and rowing gears. Can't wait to throw the posi and 3.73's in there. So I have a baseline to work from.

RBob

iTrader: (1)

In DFCO there isn't any fuel. The injectors are set for 0 PW.

There are two TPS% coast unlock parameters for the TCC.

L8315: FCB 0 ; COAST RELEASE, TPS SW POINT, (32 MPH)
L8316: FCB 0 ; LO MPH COAST LOAD LIMIT, 3.1% TPS
L8317: FCB 0 ; HI MPH COAST LOAD LIMIT, 3.9% TPS

There are two pair of MPH parameters for allowed to lock, and unlock. A pair for 1,2, 3, and another for high gear (4th).

lo gear:
L831F: FCB 0 ; 40 MPH, LOW MPH TEST
L8321: FCB 0 ; 38 MPH, LOW TEST

hi gear:
L833B FCB 0 ; 40 MPH, LO MPH TSET
L833D FCB 0 ; 38 MPH, LO MPH TEST

Note that the above are from a stick cal, hence no values.

For a good explanation of how the TCC logic works hit the Tuning Guide book sticky, chapter 5, '8746/'7747/'8063 ECMs, TCC Logic link.

RBob.

corvair_nut

Using the 6395/OD$ Mask. Im having surging at mid throttle and is caused by PW moving all over. How do I make the O2 sensor have less dramatic effects on my PW. MAP/SA/IAC are all steady during the test and it bounces my WBO2 from 14 - 17 back and forth.

Help...
Ted