Cam surge - Pointers to tuning out.

[Terminal_Crazy]

Looking for some experienced pointers.

Running 1995 LT1 Z28 M6
383 LT1 Hi compression 11.5:1
223/231 .610/.594 112 LSA cam
AFR 210 heads. Comp Ported. 2.08i 1.6e

Car runs very well. The roads over here are just too short.
Idle is pretty sweet now.
Currently running SD Closed loop tune.

The problem is just between ... lifting off the clutch and giving it some juice, ie between 1000 - 1600 RPM
If i give it a little throttle and get up above 1500 rpm it's fine. It will just about take 6th gear at around 1500rpm.
If i'm sat in traffic and rolling about 5-10mph throttle closed, in gear, it'll start bucking slightly, increasing to violent.
If i nail it, it's fine, your above that range.

I've had the idle lowered at 850 but put it back up to 900 again which helps a little (masks the problem)
I've tried timing up & down 5-10 degrees and not seen any real difference.

I've been told to go closed loop & richen it up.

Looking for info & direction to try.


Thanks
Mitch

[1project2many]

What's the timing at when this happens? Also, is the pcm going in and out of DE while this happens?

[Terminal_Crazy]

What's the timing at when this happens? Also, is the pcm going in and out of DE while this happens?

What's DE ? Not familiar with that term. Decel Enleanment? is that the same as DFCO Decel Fuel Cut Off ?
That's what i wondered last night. Don't think so as inj. bpw. still shows in log.

The motor seems to like lots of timing. Idles at 39 Degrees

Just traced some data logs from earlier tonight.

rpm Adv mph kpa %tps Wideband Lbpw
#3730 1191 42 10 38.3 4.3 16.49 2.04
#3731 1327 42 11 38.4 5.1 16.49 2.08
#3732 1347 42 11 35.4 5.1 16.37 2.03
#3733 1178 42 10 39.1 5.1 17.32 1.89
#3734 1241 42 10 38.8 5.1 17.08 2.06
#3735 1403 42 12 35.8 5.1 16.49 2.01



#4895 983 38 9 46.5 5.1 15.08 2.5
#4896 912 38 8 49.1 5.1 15.02 2.55
#4897 984 39 8 49.1 5.5 15.14 2.72
#4898 1015 38 9 47.3 5.5 15.25 2.62


#9116 860 29 8 58.0 5.5 16.32 3.59
#9117 909 31 8 53.9 3.5 16.14 3.2
#9118 752 30 6 55.4 4.3 15.96 3.11
#9119 906 31 8 55.0 5.5 16.08 3.19
#9120 1030 33 9 49.8 4.3 16.08 3.04
#9121 829 32 7 50.2 3.1 15.73 2.69
#9122 918 33 8 50.2 3.5 15.31 2.66
#9123 1064 33 9 45.0 3.1 15.31 2.5

My VE Table slopes down below Idle map/rpm.
Just read about flatening it out below this point. Any thoughts on that.
What about Spark advance? I've got 4 degree spread between 45 & 60 map on 1000rpm row.


Thanks
Mitch

[1project2many]

Decel Enleanment? is that the same as DFCO Decel Fuel Cut Off ?

Decel Enleanment is when the intake is leaned out on slight deceleration to make sure the engine doesn't go rich. DFCO shuts fuel off completely.

I'll try and look at the data tonight.

[lionelhutz]

Have you tried cranking the stall saver coolant temp to maximum to disable it? The idle speed error timing correction could be fluctuating the timing too.

[Terminal_Crazy]

Decel Enleanment is when the intake is leaned out on slight deceleration to make sure the engine doesn't go rich. DFCO shuts fuel off completely.

I'll try and look at the data tonight.

Cheers.

This is running $EE
There's a few other things i can check later.
Toss out any suggestions please.

The Fuel trim setting i've got at 5.1% so that's something to check.

Thanks
Mitch

[Montecarlodrag]

Adjust the throttle stop and datalog the IAC position. You want it to be less than half the steps when the engine is at operating temp. If you leave the IAC steps too high at idle it won't have any room to control it.
That cam will not have much torque at idle to keep the car moving with the throttle closed. It may be the nature of the animal. The above adjustment may help.

[Terminal_Crazy]

Have you tried cranking the stall saver coolant temp to maximum to disable it? The idle speed error timing correction could be fluctuating the timing too.

Hi
Stall save was tuned out from info from Steveo.
Stall Saver Min Coolant Temp is set at 151.3.
Everything else is set/zeroed as per Steveo's info. (I'll check again later)

Idle speed error correction has been very much lowered. Timing doesn't seem to fluctuate. I might try & remove it completely.

I have a suspicion I lowered the Individual Fuel Trim Max TPS down to 5.1% where it was 7 or 9 before not too long ago.
This is around where it starts bucking. Fuel trims have been played with so i'm wondering if it's not smoothed out at such a low figure & bouncing around both sets of fueling.


Thanks
Mitch

[Terminal_Crazy]

Adjust the throttle stop and datalog the IAC position. You want it to be less than half the steps when the engine is at operating temp. If you leave the IAC steps too high at idle it won't have any room to control it.
That cam will not have much torque at idle to keep the car moving with the throttle closed. It may be the nature of the animal. The above adjustment may help.

Hi

I drilled out the IAC passage on the throttle body. Blades closed as far as they'll go. All as per the usual correct setup. TPS sensor checked voltage etc.
Engine in last log was idling with IAC around 28 steps.

Looking on a section of log, 5.5% throttle, motor starts kicking. IAC is faily stable moves from 38 down to 37 then to 36 with at least 3 logs between.
This TPS% is above the setting for the Individual Fuel trims so I have the suspicion I'm in the transition from trimmed to No trimmed Fueling.

I'll adjust & check this weekend.

Thanks
Mitch

[Terminal_Crazy]

Just upped the Individual Cylinder Fuel Trim - Max TPS% from 5.1 to 10.5%

BIG Difference. It's still there but no where near as severe.

The BLM's started started to drift apart so i'll need to play with off idle fuel trims.

I was guessing that by 5% TPS the fueling might have settled down... WRONG assumption. :-)


I'll keep playing

Thanks Guys


Mitch