misfire Support

[ulllose]

This is a wierd one i think.....i'm getting about 20-40 misfires per cycle on all 8 cylinders. This is at idle,,,,when drive higher rpms no misfires. no MIL at anytime. My idle is set at 775rpm in park
my cam 222/224 566/568 112lsa. I checked for air leaks/plug wires.etc and found nothing out of place. Is this normal to have alot of misfires on a cammed car??

Thanks

[JandJsTA]

Have you set the three tables in the engine diagnostic window under TEST PARAMETERS , low rpm by cyl, idle by cyl, and low rpm, all set to 32767 and see what happens..... This is a pretty much now become the standard adjustment with a bigger cam :)

[ulllose]

No,,,but i'll give it a shot,,,wouldn't that be for throwing ses lights?
Like raising the threshold so it doesn't trigger a SES. I'm not having anything SES lights. Or am i thinking something else?

[JandJsTA]

It doesn't actually turn off the SES .. the misfires are "usually" false after the cam change and by altering the numbers it remedies the false detection.

....excerpt from the LS1edit archives:

"The problem with using a aftermarket cam shaft with larger than stock duration, is that sometimes it throws-off the crankshaft position sensor at idle, causing the misfire. If you are only getting the misfire at idle, and not while driving, then changing the misfire table will help. It will disregard the false misfires at idle using those tables, but will still be functional to detect misfires at driving and full throttle operation above idle.

:)

[ulllose]

jandjst--

i meant to tell you thanks that did the trick......
but now i have a misfire here and there while driving on all the cylinders. So i changed the plugs and my pushrods((long story behind that one) but i needed to go back to the 7.40's. I read in my helms manual that a bent pushrod would cause a misfire,,,and i had 7.35 lenght pushrods in there when i put the car back together,,so i thought maybe because the pushrod was alittle short it could be causing a misfire,,,,anyways it has been raining for the past week and i have not had a chance to log some runs to see if the misfire is gone.....i'll post later

[JandJsTA]

Originally posted by ulllose
jandjst--

i meant to tell you thanks that did the trick......
but now i have a misfire here and there while driving on all the cylinders. So i changed the plugs and my pushrods((long story behind that one) but i needed to go back to the 7.40's. I read in my helms manual that a bent pushrod would cause a misfire,,,and i had 7.35 lenght pushrods in there when i put the car back together,,so i thought maybe because the pushrod was alittle short it could be causing a misfire,,,,anyways it has been raining for the past week and i have not had a chance to log some runs to see if the misfire is gone.....i'll post later


:thumbup: Good Stuff, but that is why you don't do the whole RPM range with that tweak..... now you have probably detected a real problem and you can log/investigate and remedy :) It's great when you see a tweak that was only a suggestion 8 months ago become pretty much fact as we all learn and share info :thumbup:

[ulllose]

Well i would love to say my misfires are gone,,but damn-it there not!!! I have no misfires at idle but now after a 30 minute log i had almost 875 misfires on cylidnder5, 400 cylinder 1, etc, etc all the way down to 120 on cylinder 8. The funny thing is i don't feel anything. I'm wondering if these TR6 plugs could be the cause (too cool). The misfire happens always in fuel cell 6 or 14 while at 10-18% tps. I'm trying to narrow it down at each misfire but this will take some time. I'm also running lean, ltft are running +7% on bank 1 and +3.33% bank 2 (this is a average for fuel cells(6-14). So maybe with all this added fuel its causeing some greif. I think i have some problems...lol

[BigKID]

If you ltft are positive you are running lean, not rich. Ltrims need to zero or slightly negative. ;)

[ulllose]

big kid-----

my bad,,thats what i meant,,thanks.
I better edit my post so i don't screw someone else up;)

[Black02SS]

I have been running TR-6's now for about 14k miles and not one problem on misfires. FYI