Bucking and surging just off idle. Log and Tune.

[Emily]

Need some help!!!

The car is an Australian Commodore with 6 speed, 3.9 gears, and the usual bolt ons.... It's running MAFless 1bar SD enhanced.

I've just installed a Texas speed torquer V2 on 112 (232/234, .595/.598 on 112 LSA installed on 110 ICL). At the same time I milled the heads .030 for some extra compression.

In a nutshell, the thing drives bloody great! It has excellent throttle response and midrange torque thanks to the extra compression, (still a little weak right down low but still better than stock).

The bucking/surging/roojumping problem occurs when going really slow with just very light throttle openings. It's easy enough to "drive around" but I'd really like to get it perfect.

I've attached the tune and a short log file from today, if someone would like to have a look at it. The log will tell the story.....

Thanks in advance.

[NOS500]

Check your scan, and look at the VE AFR error, it's way out, it's lean, get the figures between 0 and -7 and your fuel trims will be spot on, make sure when you tune this you turn off LTFT and o2 sensors only when tuning with a wide band. you may need to do more throttle transitions and get up some more speed to cover more cells and more driving conditions.
Check your pe eq ratio, seems a bit lean

Also - is it a ute or sedan, if it's a sedan set torque management Max torque to 640, ute 150.

[SSpdDmon]

Need some help!!!

The car is an Australian Commodore with 6 speed, 3.9 gears, and the usual bolt ons.... It's running MAFless 1bar SD enhanced.

I've just installed a Texas speed torquer V2 on 112 (232/234, .595/.598 on 112 LSA installed on 110 ICL). At the same time I milled the heads .030 for some extra compression.

In a nutshell, the thing drives bloody great! It has excellent throttle response and midrange torque thanks to the extra compression, (still a little weak right down low but still better than stock).

The bucking/surging/roojumping problem occurs when going really slow with just very light throttle openings. It's easy enough to "drive around" but I'd really like to get it perfect.

I've attached the tune and a short log file from today, if someone would like to have a look at it. The log will tell the story.....

Thanks in advance.

I'll give you the same advice...

http://forum.efilive.com/showthread.php?t=4661

I know it's "the dark side" for some of you folks...but, see if you can find these tables in HPT.



You issue may be timing related too. If your timing is bouncing around during decel and light throttle application, it may be perpetuating the problem.

[Emily]

Also - is it a ute or sedan, if it's a sedan set torque management Max torque to 640, ute 150.

Thanks for the reply NOS500,

What does the "max torque setting" do in sedans??? I thought it somehow controlled the fuel pump in Utes but did nothing in sedans. BTW, mine is a sedan.

I will post up a new scan soon, as I was using the wideband with a tailpipe sniffer. I have now repositioned it where the narrowbands go.

[Emily]

Ok. I have installed the WB sensor in place of one of the NB sensors (it was previously in the tail pipe).

I have changed the tune to run only in open loop and have worked the VE a bit. It certainly drives better than it did before, but still bucks pretty bad under the right circumstance.

Note: I did notice today that when you let completely off the gas and let it idle along that's probably the worst of the bucking....

Here is the log file from today.

[WS6FirebirdTA00]

Fix your fueling, you are very lean, most likely one of the top issues.

Your timing is also off quite a bit. With the screwy tables you have in there, it is most likely helping to induce surge. You will want it smoother, and some more timing with that cam.

Also, do not try to run below your desired idle RPM, the car will just not want to do that.