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VP 5L auto GasResearch LPG with $12P always feels flat momentarily when you poke the throttle. In fact, once I was going 80k's and floored it and it backfired and blew a piece out of the air box. Just been reading about RDSC and TIBS.

To disable RDSC retard do I just set "spark RDSC negative change limit" to Zero? Currently it is default 9.84 deg.

What about disabling TIBS? Set "Minimum speed to enable bump spark" to say 255 kph? Currently it is default 19 kph.

Anyway, I've made these changes.

Burst Knock Retard - If coolant < This then skip Burst Knock Retard changed from -40.00 DegC (0x00) to 151.25 DegC (0xFF).
Tip-In Bump - Tip-In Bump spark Vs TPS & RPM (Subtract Table Bias) changed. (table is now all zeros)
Tip-In Bump - Upper Bump Spark Limit (Subtract Table Bias) changed from 45.00 Deg (0xD5) to 0.00 Deg (0x55).
RDSC - Minimum Coolant Temp To Enable RDSC changed from 5.00 DegC (0x3C) to 151.25 DegC (0xFF).
RDSC - RDSC Tip-Out - Spark RDSC negative change limit changed from 9.84 Deg (0x1C) to 0.00 Deg (0x00).
RDSC - RDSC Tip-Out - Spark RDSC positive change limit changed from 9.84 Deg (0x1C) to 0.00 Deg (0x00).
Idle Drive - Idle RDSC Enable RPM threshold changed from 1150.00 RPM (0x2E) to 0.00 RPM (0x00).
Idle Drive - Idle drive Negative change limit (Tip-In) changed from 9.84 Deg (0x1C) to 2.46 Deg (0x07).
Idle Drive - Idle drive Positive change limit (Tip-In) changed from 9.84 Deg (0x1C) to 2.46 Deg (0x07).

The Idle Drive changes are an attempt to sus out some cold idle issues. Changing several things at once to "save time"... LOL

BKRTD is normally disabled in stock manual bins "Burst Knock Retard - If RPM > then Zero Burst Knock Retard" - set to 0RPM.

For RDSC, the flag "RPM derivative spark control option" turns it all on and off (disables RDSC, idle drive and tip in bump).

Excellent. Thanks for that VL400. I'll undo my changes and do the above, then try it out tonight. Haven't actually got this tune in the car yet.
On the way to work this afternoon I pumped the throttle at about 60kph and it backfired and the piece that blew out of the air box last time now is completely lost. Duct tape to the rescue. Dunno how I would have fared if I had an LS motor with a plastic inlet manifold.

Does that gas system drop in fuel enrichment when you hit the throttle? I suspect less retard when the power comes on might increase the problem. But I have no experience with this and nothing to go on. It will be interesting to hear your results.

If the airbox is exploding I guess that means its detonating real early. Or miss firing completely hence the backfire and explosin getting back to the intake. Maybe you need to try and give it less timing with hot MAT? Just a thought to get the discussion rolling.

Gas carb has separate idle, transition and WOT mixture settings. I think it does go a bit lean just off idle but I think the problem is that much worse if it retards at the same time, so it seems to me. One theory I have as regards popping back when retarded and/or lean is that if the mixture burns so slow (lean) or starts so late it doesn't get sped up sufficiently by the squish event at TDC and consequently burns way slow, then if there is still the remnants of a flame present in the cylinder when the inlet valve opens and exposes a bundle of air+gas, then hey presto, external combustion.

VL400 wrote:Or the flag "Map A: set=RPM derivative spark control option"

http://pcmhacking.net/forums/viewtopic.php?f=28&t=3499
Got told this 12 months ago and didn't try it and forgot.
Sorry about that.

Took it for a run just now and no real difference. Maybe just a whisker but nothing to get excited about.
Next step is to have a look at the off-idle transition mixture. Brass jet in rubber hose setup.

Yep, it was leaning out above idle.

Now gotta get the idle mixture right somehow.
With the idle mixture screw full in (rich) it still idles rotten when cold. After about 20 mins it finally idles nice but just this morning I discovered that the reason for the 20 minute delay is that the under bonnet temperature finally makes the plastic PCV hose go soft and the vacuum sucks it flat and cuts the flow down to almost zero. Hence the idle richens up just enough to come good. (talking LPG here not EFI) Only just rich enough because when you pump the brakes when idling it stumbles a bit. I pulled the hose off and blocked it and went for a drive when it was cold and for the first time in what seems like forever it idled okay.

Anyhoo, got to thinking maybe put a solenoid valve thingy in the pcv line and when the brakes are on i.e. car stationary the valve blocks the PCV flow so it will idle. If that's a success then I might make something that uses vehicle speed, has time delays, also brake input and whatever else I can think of.

Now I have to find an electric valve that will fit the PCV hoses. First thing that comes to mind is an old LPG lockoff. Anybody got any other suggestions?