LMM timing limiter and pilot issue

[camcojb]

This one is kicking my rear.

Works perfect on the LBZ. I can command pilot off and get the timing I desire.

At first I didn't believe it was boost related, now I'm not so sure. This is a major limiter for the LMM.

I'm not positive it is either, that was just my hunch. Especially after seeing my roll-on wot datalog where in second gear I initially got full timing with the pilot off, then as soon as it shifted gears, loaded the truck to full boost it dropped back to 22 degrees and locked, never moving from there for the rest of the run.

I'm trying a couple changes now, and I'll datalog tomorrow. If it changes things I'll let you know, but I think we need Ross to find a table we're missing.


Jody

[camcojb]

ok, went out and tried 12-15 different tune changes today. Here are the results.

The pilot off and limited timing deal doesn't appear to be boost related, at least if it is, it's at a pretty low boost (under 35 psi for sure). If you put a 1 in the fuel pressure max pulses map (B1021) the pilot is off, but timing is limited to (in my case) 22 degrees no matter what you put in the timing tables. If you put a 2 in the fuel pressure or anything larger, the timing control comes back, but the pilot is back on at 3.5 mm3 and 240 US. Also, although you get more timing, you still cannot get more than 26.3 degrees on my truck. That may be a boost related table as I could get 38-39 before with the single turbo, but that only made 35-38 psi. I tried lowering boost down to 40 psi with the same results.

I tried every combo on the pilots I could think of. If you zero out the pilot tables from 70% tp up and from 2400 rpms and up and then go into the pilot 1 B9117 table and zero out the 180 and 190 mpa rows top to bottom, the pulse drops to 150 US. This is the change I made before on the single turbo that netted me the 2-3 tenths gain. I never did get the pilot completely off before, but never knew about the fuel pressure max pulses table, not sure it was even available in January 08. A quick datalog into a 20-30 mph headwind confirmed the power difference as even with the big headwind it matched my best ever 60-80 mph runs at wot with the old combo; I'm sure it'd beat it easily without the wind. Before dropping the pulse to 150US and with no headwind I could not match my old combo. I did not do any full passes, just wot partial runs due to the wind.

So zeroing out the pilot 1 in the wot fuel pressure area does pick the truck up, yet according to the table it shouldn't do a thing as it is only listed up to 30 mm3.......... No idea why but it'll help an LMM.

So there's still two issues; one, zeroing the pilot tables does not shut them off on an LMM. Setting the fuel pressure max pulses to 1 will shut off the pilot, but then limits timing to 22 degrees total. Also, that 22 degrees locks there, even on the shift when the rpms drop to 2500 or so and you're commanding several degrees less. So more than you want at the shift, and less from there up.

The second issue is that even with the pilot on at 240 US or the new 150 US you cannot get over 26.3 degrees; I raised the tables to ramp up to 29 degrees with a 30 degree max, still the same 26.3 degrees. It ramps up nicely on the shift as it should, but stops there, won't go higher. This was not an issue with the old stock single turbo combo and 35 psi of boost, so it seems the higher boost levels of the twins are causing it.

So I think there's some table or limiter in the LMM's that when you pick 1 pulse to help fuel pressure the timing maxes and sticks to 22 degrees, at least at my boost level on my truck (I tried between 40 and 52 psi, still the same 22 degrees). Then, the second thing is the 26.3 degree limit which I think may be related to boost, as I could get almost 40 degrees before at a lower boost level.

Jody

[LBZoom]

I've got a question... what is the benefit of shutting the pilot off at higher TPS? Just curious is all

[camcojb]

I've got a question... what is the benefit of shutting the pilot off at higher TPS? Just curious is all

more power. It was worth 2 to 3 tenths in et on my old combo. That was pretty much a race tune, so it would likely affect things differently on a milder tune.

Jody

[OSUBeaver]

Nice write-up Jody. Thanks for taking the time to do that.

[camcojb]

Nice write-up Jody. Thanks for taking the time to do that.

you're welcome. Baby steps man, at least we can now improve the situation. Ideally Ross would have a ton of time on his hands and would locate these missing tables limiters.............................

Jody

[GMPX]

Next week I will look in to it, I was actually adding in some MAF tables for the Bosch ECM this week, so while I'm running hot!

Interesting it's an LMM thing only, but at least you have given me some numbers to go on.

Cheers,
Ross

[camcojb]

Next week I will look in to it, I was actually adding in some MAF tables for the Bosch ECM this week, so while I'm running hot!

Interesting it's an LMM thing only, but at least you have given me some numbers to go on.

Cheers,
Ross

I'm not positive it's LMM only, but Rob said the LBZ's do not have this issue; pilot completely off, and any timing he wants.

Jody

[IdahoRob]

Nice job Jody.

Jody, did log mm3 and make sure you are getting where you want to be in the mm3 table for timing? In the past I've seem LMM's only go to 79mm3 max even though should be in the 110mm3 range, just a thought on the timing limitation.

[camcojb]

Nice job Jody.

Jody, did log mm3 and make sure you are getting where you want to be in the mm3 table for timing? In the past I've seem LMM's only go to 79mm3 max even though should be in the 110mm3 range, just a thought on the timing limitation.

my logs have been in the 100-110 mm3 range at wot.

Jody