misfire problem

[mops]

Hello.

I hate to post yet another 'help me' thread, but i'm not sure what to do.

I noticed just today, faint misfires that make tuning impossible. They all all over the rev range. They are most common in the low kpa area, but are present as well on higher load conditions (less noticable though).

I mentioned they are 'faint', as in they dont make the engine 'buck', but rather for example while idling i hear engine miss a beat, and then i see afr spike. on idel they occur maybe 1-2 times/sec, on coasting every other ignition event seems like misfire, while on high lod it's hard to tell because you can't hear it, yet the afr gauge is very unstable.

I run direct coil control with stock dizzy. I have replaced plugs and rotor arm. today i hooked up stock ecu to the car to try it out and it was smooth as a table top. hooked up MegaSquirt again and misfiring....

I tried adjusting ignition advance across broad range - 10 to 36*, at various bing - doesnt seem to make any differencce.. i tried dwell from 2.8 to 4 ms.

It's really bad with ego control. Once ego control sees too many misfires it richens up then once 'missfire flood' stops then it leans out to the other extreme of the range (i use 10%) and it mekes car co very unstable...

what else might be causing this ? which setting should i play with ?

[Jackal]

If its a boosted engine it could be spark plug gap, well it coould be gap anyways..... You could dry gapping plugs @ .028, see if that helps then move your way up.

[mops]

thanks for input.

i do not think gap is the problem. Stock ECU runs this engine GREAT ! I mean no misfires, AFR's very stable... migth I add accel enrich is near perfect... i.e. engine is running 15 afr then i stab the throttle and momentairly afr's go to 11....

what i did so far:


1.today i made extensive grounding unpgades, so ms is grounded at the battery now.

2. i logged afr's via lc-1 comms interface, to confirm it's not just ms thats getting the noise... sadly (for me) LC-1 logworks report same as MS, so all good there.

3. i played with the settings... just changing stuff there and there, revving the engine observing the differences, and i noticed following things:

a) the misfires are less common on low timing advance. i lowered idle to 6* and misfires still occur but once every few seconds, still better than that it was, but still not perfect. I do not understand this behavior, and appreciate explanation.

b) engine runs much differently when I set it to burst injectino mode instead of alternating. i can lower my idle ve bins quite significantly with burst mode (2 injections per cycle), while maintaining same afr's. I do not understand this behavior, and appreciate explanation (missfires still there)

Comments anyone ?

[mops]

update.
After installing ignitor, the car runs much better. AFR's are very stable, and at certain conditions it runs as lean as 17.9:1 AFR without misfireing.... I tuned the lower portiong or map table last night with autotune then mstweak...

i think the other thing that helped it is the removeal os the MS2 faceplate from the db37 side. with the faceplate limiting it, the connector couldnt go all the way in, and now it does.

another thing i noticed that i need on average 5-10% less in every ve bin that I needed previously.

I still have some minor issues with starting and idle, but now engine responds to tuning as described in tuning manuals therefore I can actually do something.

as I get it all tuned, I'll post a success story.

Thanks guys and gals !

[bleoh]

Did you try adjusting your dwell? I added a few tenths to my start value and the small misfires went away.

[mops]

yes, i tried adjusting dwell to ridicolously lo9ng values like 8ms, and that made no difference.

problem is that vb921 coil driver does not provide enough current to drive my 1.1 ohm coil.