2011 mild cam ram with MDS off

hey all

i would usually never tune something im not familiar with and i am not a hemi guy, but a local customer approached me with what i thought was a simple issue so i figured i'd just do him a favor for cheap.

i always feel bad for guys that walk into a shop, they go hey cool lets add aftermarket stuff to your stock vehicle, then AFTER the job is done they say 'ohhhh yeah you need to get it tuned, and we don't know how, and we don't have anyone'

hoping you can help me help him

his story was he had a cam lope wipe out on his 2011 dodge ram 5.7 hemi. the shop fixing it talked him into a comp 201-300-17 and also an MDS delete kit (non-MDS lifters, from my understanding). my research shows this cam is barely bigger than stock so definitely not a very involved tune, and MDS deletes are commonplace.

his complaint was that after the cam swap, as the engine warmed up, it threw codes and the idle went to absolute hell, could barely get it home, but cold idle was great. the shop told him the MDS code needed to be tuned out and it'd probably be okay.

i disabled the MDS system and variable cam timing in the tune, and any code i could find related to cam timing or MDS, flashed it, and test ran it.

same problem.

review the log, and i find it enters closed loop, short term trims begin to drop to -20%, at which point it idles a bit rough but o2s reach target and they begin switching, then as temperature increases trims increase to -35% and o2s peg at which point it barely idles.

..... any tips ?

threw a log up if anyone interested

post the tune if you can,

check to see if the neural network is still active , I find the 10-12's run better with out it on.

Quote:

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Originally Posted by 3dodgechick

post the tune if you can,

check to see if the neural network is still active , I find the 10-12's run better with out it on.

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i did disable the neural network
one thing i realized last night is i dont know for sure if the vvt is locked or limited
but that still doesn't satisfy me as an explanation of why the idle and trims go totally south as it warms up

oh ill post the tune tonight but you won't see much
just disabled codes, vvt, mds, neural net
it acts the same as before tuning, no real difference

the journey continues.

so i went back over there and tried a few things.

i verified that the cam does move by 7 or so degrees so that means its a limiter on the VVT not a locker.

i verified the cam position target error was 0-0.5 degrees so that means the guy that installed it probably did degree it properly right?

the timing advance when it warms up is modulating from 10 to 0 degrees kinda thing. not only does that seem low but obviously the idle spark PID controller is fighting the cam.

i found the PID parameters for idle spark control and tried to dumb them down a bit to decrease that modulation and not accentuate the cam lope. it stabilized a tiny bit but on my first attempt the throttle PID was surging.

two things are confusing me

i can't figure out why the idle timing would be so low even with a stock cal. other vehicles with cams of this size i've usually targeted at least 20 degrees of timing. i cannot find a place to fix this reliably yet. just by sound/feel think it might idle better @ like 22-25 degrees of idle advance. i tried just jacking the minimum timing table up in the idle range but the damn thing would barely start so that was a bad idea.

the other thing is it is pulling a crap ton of fuel still, 35% or so, which is nuts. this cam shouldn't have such a difference in VE. so i tried for the hell of it just dropping 20% base VE in the idle range, but it still trimmed the same. again i suspect if the timing wasn't completely retarded then the trims MIGHT level out a bit but man that's a lot of trim.

i feel like there's something fundamental im missing

oh right you wanted the calibration. here's the one im mucking with right now, again, not gonna see much. this one has the VE table kinda mangled from me seeing if dropping the VE in idle range affected the stft dropping so badly, and it didn't so next time i go back i'll start with stock again.

okay i figured it out in theory
spark is referenced against both map and ve (which is itself effected my map)
cam makes less vacuum
idle spark base is pulled from part throttle table
stock spark table in that region is like 10deg atdc
spark pid controller is lowpassed by the retarded spark value
cam at that low advance barfs raw fuel
ecm reads raw fuel pulls fuel
trims go to hell and pulls idle lower
spark and fuel get into a race for the bottom

Quote:

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Originally Posted by rfesu

okay i figured it out in theory
spark is referenced against both map and ve (which is itself effected my map)
cam makes less vacuum
idle spark base is pulled from part throttle table
stock spark table in that region is like 10deg atdc
spark pid controller is lowpassed by the retarded spark value
cam at that low advance barfs raw fuel
ecm reads raw fuel pulls fuel
trims go to hell and pulls idle lower
spark and fuel get into a race for the bottom

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BINGoooooo


Remember the values in these tables are ATDC is -XX and BTDC is XX
I always start with 8-10* in the idle areas on the PT spark table, and the Minimum spark table I set to 6* in those same areas and work from there.

Then I'm free to work on the VE tables.

can you tell me why hemis seem to run such low timing at idle in general
any other motor with a cam like this, aluminum heads, and normal compression id be shooting for 20-25 degrees as a starting point

Its combination of dual plugs and the valve angle, when my uncle(purpleram) & the others involved with the "new hemi project" back in late 99 the idea for the combustion chamber and valve angle cam out of the r5&hemi99 programs, flatest valve angle possible to help cross flow with out having the high ram drawback of the g2 hemi., the r5/hemi 99 are canted , in low rpm situations canted and wedge style valve arrangements the exhaste pulls hard on the intake charge ,which at high rpm is a good thing but at low speed it pulls to hard, which not only draws out cylinder pressure but also fuel charge, the g3 doesn't have this issue like most engines, since the fuel part per million is higher , it's denser doesn't need all that lead time to ignite,the small bore 3.917 helps also(*) the plug advantage is due to the positioning of plugs , ......if you take to pin light and shine it in to a cylinder in the position of a spark plug , you'll see a bright spot on the cylinder wall, that's were flame front hits 1st, take two pin lights and position them as if they were g 3 spark plugs........... no bright spots.

(*) I'm sure some of you have noticed that oem 392s take a few more degrees at idle with the same cam that is in a 5.7

thanks for your knowledge. really appreciate it.

so i finally got to test all this and determined some things then got stuck

i made a big flat area in the min spark table of 7 degrees, set all the idle tables to a warm 800 rpm target, and started the truck. the great news is, with the spark stuck at the minimum 7 degrees, it's half way there. the idle isn't great, but it's WAY better. the trims are now coming back up too.

by my initial 'feeling' of how it runs at 7 deg, i figure it needs another 7 or 8 degrees to fully stabilize. so i run the spark up in the part throttle table to 15-16 degrees and try again, figure i can just move it back down a few degrees if it behaves. i am modifying way larger areas than required at the moment just to be sure.

now i've run into more trouble somewhere.

something is limiting my spark, or it's not pulling from the base part throttle table at all during idle conditions. it simply gets stuck at my minimum spark value (plus a few degrees here or there from the PID controller) regardless of the part throttle table commanding 16-17 degrees.

what's preventing spark from pulling up to my part throttle base values once the truck warms up?

i looked at some cold/hot iat/coolant tables but im not within the thresholds for those. all the timers for startup spark modifiers have expired.

log/calibration/preview pic attached

Attachment 145632

oh. i think it's MBT spark.

nope ! no idea where this ecm is getting its idle spark target from but im becoming convinced it's not part throttle spark table

i went back and tried a bunch more stuff. i simply can't get it to idle at my desired spark value. it's always just using the minimum spark value. completely stumped.