advanced tuning issue: missing at light loads/coast

mops · Post by **mops** » Sun Jun 04, 2006 3:29 pm

Hello PPl.

i read the tuning guide many times and i'm experiencing tuning issue that's not covered in the tuning manual.

THe issue is visible at idle - it sound like a light missing (as opposed to voilent missing)... it's at random intervals but generally about once every second or so. miss is so light that it doesnt really affcet th engine operation, basically durning steady idle you can sometimes hear a subtle *prrr* or *pop*, which is out of "tune"

Again i cant stress it enough it only a slight miss, possibly incomplete burn...(if such thing happens)

cruise/high load areas have no problem - very smooth there

light load ares 50kpa and down problem appears again, being exxesive at coast (15 kpa)... I can reduce the problem by running really rich in these areas (like 13:1 or even 12:1 AFR). Coast is pariculary bumpy and the car is missing there more and it it is noticable there... I tried chaning ignition timing in problem areas, but it doesnt seem to affect it much...

some details:
high impendance injectors
it is normal dizzy with all components replaced
fewsh spark plugs - look really nice and even... possibly a touch rich, but nothing i cant tune out.
I tried changing between 1 or 2 simltaneous squirts up to 2 or even 6 alternative squirts - no change..
tried incerasing dwell up to ridicolously high values, like 8ms - no change..
when i attach back stock ECU everything is very smooth, no misses/pop's, etc...

I'm looking for some suggestinos what sould I do there/what to check /what to try.... I dont hitnk is hardware issue, I'm pretty confident that it is only the tuning issue.

Bernard Fife · Post by **Bernard Fife** » Sun Jun 04, 2006 3:37 pm

mops,

I assume you have already verified that the accel enrichment is not being triggered by a too low TPSdot/MAPdot threshold. (That is a very common cause of what you are seeing, and I mention it for anyone who stumbles onto this thread later...)

There may be very brief MAP spikes that aren't being seen in datalogs (and which the slower MS-1 or an OEM ECU might miss). If this were mine, I'd play around with the lag factors on the input variables, especially the MAP averaging factor (try 20 to 40).

There's more on this here: http://www.megamanual.com/ms2/configure.htm#lag

Lance.

mops · Post by **mops** » Sun Jun 04, 2006 3:48 pm

Lance, great thanks for quick and to-the-point input.

I'll check out those setting and post my results.

Accelenrich is hard to tune on my engine...
TPS based produces very slow/low feedback... while map based produces very high, very aggresive response.. with only quick partial throttle moves I can get over 300kpa/sec (thats full bar scale on the accell enrich window)...

djandruczyk · Post by **djandruczyk** » Sun Jun 04, 2006 3:58 pm

Lance's suggest is probably closer, but one thought that popped into my head is a poorly flowing injector (partially clogged perhaps) that is causing one cylinder to be on the verge of lean misfire at idle/light load, under heavy load the PW will be much larger and thus the chances of misfire might be a bit less.

If the accell enrich isn't being falsely triggered (I'd check that stuff first) then if possible pull the injectors and do a flow test on them and notice if one has a poor spray pattern. (lopsided/firehosed, dribble)

mops · Post by **mops** » Sun Jun 04, 2006 4:07 pm

djandruczyk wrote:Lance's suggest is probably closer, but one thought that popped into my head is a poorly flowing injector (partially clogged perhaps) that is causing one cylinder to be on the verge of lean misfire at idle/light load, under heavy load the PW will be much larger and thus the chances of misfire might be a bit less.

If the accell enrich isn't being falsely triggered (I'd check that stuff first) then if possible pull the injectors and do a flow test on them and notice if one has a poor spray pattern. (lopsided/firehosed, dribble)

I hear you man... that what i was thinking at some stage.

however stock ecu runs the car nice and smooth, and stock ecu runs it lean pretty much all over the place... WOT as lean as 13.7 and even 14 in some areas, generally in 15-15.5 range, doesnt really go into 16's much... in certain conditions MS2 will run that car on even 17:1... it doesnt miss, but feels weak and poor.... my aim is to produce a very smooth tune disregarding eceonmy - i.e. 15.5 leanest, once i'm happy with it then i'm going to lean it out. currently fuel economy is about 10-20% worse than stock ecu...

krisr · Post by **krisr** » Sun Jun 04, 2006 7:59 pm

I'm going to go out on a limb here. Have you verified your idle timing against the spark wizard and is your fuel pressure at idle stable when hooked to vacuum? Tried another oxygen sensor?

I'm not very familiar with your engine combo so i'm just throwing you some ideas which i've had to play with in my own setup.

mops · Post by **mops** » Sun Jun 04, 2006 8:10 pm

krisr wrote:I'm going to go out on a limb here. Have you verified your idle timing against the spark wizard and is your fuel pressure at idle stable when hooked to vacuum? Tried another oxygen sensor?

I'm not very familiar with your engine combo so i'm just throwing you some ideas which i've had to play with in my own setup.

suggestions/ideas is exacly what i'm asking for

well, i dont really have an equipment to exacly measure idle timing, nor fuel pressure. i dont think oxy sensor is stuffed, it reads very trustable figures when i'm using stock ECU. I just have basic timing light, so when i set timing on all 0 then timing light shows tcd mark matching up with mark on the engine block

Basically, i'm going by the fact that stock ecu runs the engine just fine, while MS has some issues...

However, since I just came back from a short trip...
my accel enrich treshold was pretty high to start with, so that wasn't the issue.

However I put more lag on all sensors, including 20 on map and 30 on rpm and it does seem much better now. I'm just going for another ride to verify, but so far more lag on input makes engine more smooth and stable, which is progress and that = GREAT !

krisr · Post by **krisr** » Sun Jun 04, 2006 8:54 pm

Reason why I say timing, is that if you advance your timing to far when coasting, it can make the car buck and hesitate because it's firing to early. At idle does the timing match the trigger wizard though? Surely you're not firing at TDC at idle?

You mentioned more lag making the engine run more smooth, have you tried a restriction & plenum in your MAP line? I ran a fuel filter off a kawasaki motorcycle on mine and it 'softened' up the signal a bit, primarily because I have a larger than life cam which gives me alot of overlap at idle. I found with the lag factors I could remove that filter.

Fuel pressure would be good to know when coasting too as it may be dropping your fuel pressure in the rail(s) to much causing a lean condition so you may have to richen up the high vacuum areas, try 3-4% perhaps or plug your regulators vacuum line and try that theory.

mops · Post by **mops** » Mon Jun 05, 2006 12:01 am

hm....
well, just got back from the ride....

at idle i found 12 deg BTDC is pretty allright.. tuning my idle should be a whole different thread... lets just ignore the idle for now :/
i run about 40 degrees at cruise areas....

it's the coast (i think sometimes called underrun) is the problem now....
no matter what i do i cant get any stable burn there... slight misses all the time... i can either run really rich or really lean there to reduce the problem... by really lean i mean so lean that there's no combustion.... oxy sensor reads full lean....

aswell transition from coast to cruise is pretty bad... i might try disabling AE and retune it again...

i'll post here if i make any progress...

krisr · Post by **krisr** » Mon Jun 05, 2006 12:36 am

Narrowband oxy sensor?

FWIW - My spark map looks like this for the engine in my sig. As I said, i've got no idea what combo you're running so I cant really give much better advice but just what I found in tuning my combo.