Misfire/Stutter at 2000rpms with my 2bar tune

[Brett SS]

Hey guys,

As the title says I get a Misfire/Stutter at 2000rpms with my Maggie 122 at part throttle/light load. It has always been there with my 2bar tune and doesn't seem to matter what the conditions are but sometimes it's worse than others (maybe when it's hotter). The overall combo is a stock LS1 bottom end, 224/232 blower cam, Patriot Performance LQ9 heads, Maggie 122 running 11psi, 4500rpm hi-stall, 4.11 gears etc.

I've tried tuning it out but so far haven't been able to do so even with smoothing everything out as these engines are sensitive to changes in spark etc between cells. Has anyone else come across this issue and know where to point me?

I believe that it has to be somewhere in the 2 bar tune as last year I needed to rebuild the blower and went back to an LS6 intake with a 1 bar tune and the issue went away. This to me would remove the fuel system (minus injectors as they didn't get used in the 1 bar) and all plugs/leads etc.

It also seems to be intake independent as I've had a few different intakes on as at one point I thought it could be turbulence in the intake tract etc. It also seems to be there whether the blower is spinning or not as it still happens when I had to bypass the blower and open the bypass valve.

Any help is appreciated as it can get frustrating at times and is also stopping me from swapping diff ratio's as it would bring that rev range into a main cruising speed where now I can just go past it. I've attached a copy of one of my recent tunes and a log file/config file if anyone wants to have a look. There isn't really anything you can see in the log file at 2000rpms as the AFR's and spark are pretty constant but I still get the stutter.

[Brett SS]

Anyone? Surely there is someone who has solved a similar issue or can help point me in the right direction.

[Google]

Your config "Mafless 2bar Full SD Mode.cfg" would suggest your not using a maf. If the maf is off of the car then follow the steps in this link and try to tune it.

http://www.hptuners.com/forum/showpo...35&postcount=2


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[SSUte01]

Brett,

Check out this link, it certainly sounds like your issue assuming everything else is in line, fuelling, spark etc.

http://www.hptuners.com/forum/showth...00+maggie+miss

Hope that is of some help

Cheers

[Brett SS]

Your config "Mafless 2bar Full SD Mode.cfg" would suggest your not using a maf. If the maf is off of the car then follow the steps in this link and try to tune it.

http://www.hptuners.com/forum/showpo...35&postcount=2

..

Thanks for that, but even with those suggested changes there are no changes to the issue. I've been running SD tunes for 4 years atleast now and have only come across this issue with my maggie.

Brett,

Check out this link, it certainly sounds like your issue assuming everything else is in line, fuelling, spark etc.

http://www.hptuners.com/forum/showth...00+maggie+miss

Hope that is of some help

Cheers

Thanks heaps for that mate, it sounds exactly like my issue. Seeing I'm running in SD mode all the time I'm thinking I might have to buy a second wideband to install in the second bank as it will be the only way to see what is happening between banks. Another option will be to drive around and log it with the wideband in bank one and then swap it over and log it again in the second bank.

Now if that is my issue and one bank is running leaner than the other (makes sense as issue seems to be worse when it warms up and lean cruise is enabled etc) how do I tune around it?

[SSUte01]

Have you still got O2s in there. Even in Open Loop I find the O2s are very, very useful tools in determining certain issues, you may not always be able to determine quantitative date, but certainly qualitative when you can't. Having not experienced what you described and just 'guessing' over the internet, I would say, find the lean bank and tune to that if staying permanent Open Loop (which I probably would) or alter the O2 switchpoints so that the lean bank isn't so lean and fattens up a bit. Alternatively, if you are in OL, don't run stoich at the problem area, try to see if a little richer at that load/rpm point reduces or removes the issue, kinda like tuning large cams.