MS3 Random misfire

[kizzoalfa]

Hi,

I have random misfire sometimes while cruising sometimes while accelerating. Not really load of RPM dependent. (Never happen at idle.)

I attached a picture where I marked one of them. I used a full throttle right after the misfire as a marker in the log.

I have replaced ignition coils, sparkplugs and leads as well. I am running MS3x full sequential ignition and injection.

Firmware is alpha18.

What do you think, is my misfire related to any of the fuel settings or it is something else?

I attached msq and SD_log.

Please if any of you have some time please take a look. My VE table is not blended yet it is just after some VE analyzer tuning.

Thank you very much.

[protomor]

I haven't had time to look at the datalog yet but it could be wiring or it could be throttle accel related. At least those are my only two thoughts. Doesn't seem like you're getting resets.

[kizzoalfa]

Hi,

Wiring is new and I doublechecked it. I had some misfire also when I was running MS3 injection and Ms3x Tacho out ignition as batch injection. I was thinking if I change to sequential it will dissapear since it is some fueling issue due to the big 440cc injectors but looks not.

Since running sequential I have a full new harness for the sequential system. New connectors for injectors, new for coils etc.

Do you think it can be some AE related?

[protomor]

It could be AE. could be a dead spot in the TPS or the calibration is off.

[billr]

Looking a the .msl I have two questions: I see the TP "marker" spike at about 5.5 seconds, but nothing just preceding that which would indicate a misfire. The posted screen-shot looks (to me) like it is the TP and PW right at the time the marker is made, but doesn't really relate to the misfire event. Is there some logged parameter that clearly indicates misfire? I'm guessing only a knock sensor could do that, but don't see how to display that signal. The other question relates to spark advance. I see several points (74,85,101,103,107,110, and 116 seconds) where the advance makes a "step change" when things like rpm, MAP, PW, and TP are all relatively constant. What could make advance do that? I admit, these questions are as much about helping me as the OP, but maybe they will help...

[kizzoalfa]

It could be AE. could be a dead spot in the TPS or the calibration is off.

If it is TPS issue I should see it in the log. I will check my AE settings.

Thanks

[kizzoalfa]

Looking a the .msl I have two questions: I see the TP "marker" spike at about 5.5 seconds, but nothing just preceding that which would indicate a misfire. The posted screen-shot looks (to me) like it is the TP and PW right at the time the marker is made, but doesn't really relate to the misfire event. Is there some logged parameter that clearly indicates misfire? I'm guessing only a knock sensor could do that, but don't see how to display that signal. The other question relates to spark advance. I see several points (74,85,101,103,107,110, and 116 seconds) where the advance makes a "step change" when things like rpm, MAP, PW, and TP are all relatively constant. What could make advance do that? I admit, these questions are as much about helping me as the OP, but maybe they will help...

The advance does the downsteps because IDLEADVANCE became activated (2s after TP below 1.3%) at those points.

The real "misfire" happen in the log at 4.405s as it can be seen in the AFR change as well. At that point with constant TP I have noticed a hesitation from the engine and right after the event I made the mark by 100% TP to find the event easier in the log.
(Is there any other way to create markers in the log while logging- I mean any button etc.?)

[stevemgbgt]

pressing space bar makes a line on the log I believe.Steve..

[kizzoalfa]

I turned off AE today by setting the treshold high enough to avoid AE. The misfire is still there.

Does any of you have any idea based on my MSQ?

Thanks,

Zoltan

[kizzoalfa]

Hi,

I do not have too much experience in log analysis but does any of you think based on the log and the mark where I noticed the "misfire" that it could be caused by some lean / rich condition?

Thanks,

Zoltan

[kizzoalfa]

Today morning I changed my sequential settings from Full Sequential to simultaneous, 1 squirts / engine cycle. The situation with the "misfire" issue looks better. However at 14.7 AFR while cruising sometimes I feel engine not running as smooth as should be. (It was worst in full seq.).

Is there any explanation behind that the engine is running better in non simultaneous mode? Does it possible that I use injecion timing incorrectly? I tried it all the times end of squirt, 360 deg and changed up to 450 deg while did some experiment.

Does it possible that my engine with the 8.0:1 NA compression ratio is not happy around 14.7:1 AFR's?

Does any of you have some lessons learned about required AFR value for such a low comression engine like mine?

Thanks,

Zoltan

[muythaibxr]

Did you check for sync loss?

Ken

[kizzoalfa]

Ken,

in the attached log the lost sync counter is always zero, so there should be no sync loss. The log was done by SD log. As I marked the missfire the AFR became richer after the event means unburnt fuel. (I tried new coil, wires, plugs, not ignition related. Also tried to change ignition advance but no change so far.).

The misfire I notice is more or less a small backfire when going not sequential. The symptom is that I press throttle to accelerate - not hardly just normal acceleration - and as RPM start to increase (car pulls very nicely) I have like in one cylce a kind of misfire where engine power is less than should be but engine will accelerate just after the event.

I tried to go add more fuel today but look like did not help.

[jsmcortina]

As I marked the missfire the AFR became richer after the event means unburnt fuel.

Unburned fuel shows as LEAN not rich. (The oxygen sensor sees more oxygen.)

James

[kizzoalfa]

Thanks James.

AFR goes from 13 to 13.5 at the time when misfire occurs. This means we have more oxygen, so unburnt fuel present. Question is why the misfire happen. Missing ignition? Not properly burnt prior cycle? Do you have any idea based on the log and msq?

Thanks.

Zoltan

[kizzoalfa]

Does anybody has any idea based on my log? I am stucked now. Any idea is appreciated.

Zoltan

[gslender]

You don't have AE decel set to 0% do you? Set it to 100% and that might be the issue (100% means no fuel cut, 0% means cut it all!!).

g

[kizzoalfa]

Hi,

the decel fuel amount was set to 95 while I had the misfire. I can try and set is to 100%. You think that after accel I go back to 95% fuel amount and this causing some lean issue?

I also tried the new accel pump AE but the misfire is still there. As far as I know if I go with the new accel pump settings there is no effect of the decel fuel amount setting (after accel the fueling goes to 100 so no portion is removed.).

Thanks,

Zoltan

[kizzoalfa]

Hi,

today I changed the decel fuel amount to 100, same misfire. I also turned off AE later, did not help. I also noticed that around 14.4 - 14.7 AFR while cruising my engine somtimes have a small surge.

Does it possible that what I think misfire is a lean surge caused by that my engine need to run richer ?

(Engine has 7.8:1 CR, 9mm lift 272 deg exhaust and intake cams, IO 22deg BTDC, EO 63 BBDC.)

Any ideas?

Thanks,

Zoltan

[Dookie454]

Hi,

today I changed the decel fuel amount to 100, same misfire. I also turned off AE later, did not help. I also noticed that around 14.4 - 14.7 AFR while cruising my engine somtimes have a small surge.

Does it possible that what I think misfire is a lean surge caused by that my engine need to run richer ?

(Engine has 7.8:1 CR, 9mm lift 272 deg exhaust and intake cams, IO 22deg BTDC, EO 63 BBDC.)

Any ideas?

Thanks,

Zoltan

My engine 383ci v8 had 8.9:1 compression and larger cam and had surge/bucking at cruise more when ARF was at 14.7:1 than it did when at 13.7:1... but then I read some widebands arent 100% correct all the time due to whatever reasons... so.. tune it till it runs good.. then see where the settings are at and try to improve from there.

I also picked up what I think was a lean misfire around 1800 rpm free revving when running in batch fire mode.. switching to sequential mode made this go away but it was a v8 so it was probably worse case.