I am having a misfiring issue under low load. My setup is s4 med street port, lt8s, 4 750cc Siemens, stock coils and igniters. The microtech was throwing rpm error codes and after cleaning up the grounds it seems to have fixed that but I am still experiencing issues when cruising under low load and taking off from a stop. When doing so it goes from running very smooth too misfiring and backfiring violently and sounds like it is running on one rotor until I step on it a little and it builds a little boost and runs like a top. When cruising at 2800-3000 rpm the issue doesn't seems to be there. If I cruise at a lower rpm it will begin to buck and misfire. Any settings that could be causing this ?

This is also in normal mode going to switch to matrix and see if I have better luck

check spark plugs, fuel filter/pressure , clogged injector or uneven flows on the injectors , big difference on compression too .

Plugs are a week old, I'll flip the injectors around and see if that helps. Filter isn't too old but ill toss in a new one anyway, compression is good

I swapped primaries with secondaries and still having the same issue. My battery is almost toast so ill be buying a new one today could low batt voltage cause injectors to misfire?

no but a bad alternator will give u issues

Today started it up seemed to run fine. Let it warm up and then if I give it a quick blip it revs pretty good, now if I just free rev it at 1800-2500 once it warms up it starts to misfire/possibly run on one rotor and stops holding idle and shows rpm error. When holding it at those revs it shows rpm crs and afrs are 13.4-14.0 before it starts to have trouble, is this too rich? Am I just fowling out the plugs and causing the misfire? Should I pull more from the rpm crs at that rev point?

is that with the wideband O2 adapter installed on the microtech or is it just a reading you grabbed? otherwise the AFR figure is useless, they don't come factory with a wideband input unless you ordered/installed it.

if so that AFR is fine and i would tend to think you may be correct that one rotor is dropping out.

put a timing light on all 4 plugs and rev it to the problem area and see if the light is becoming erratic or if the timing is bouncing all over the place indicating a CAS wiring issue.

if it is rather smooth then you probably have a faulty injector plug on one of the primaries. to figure out which rotor is dropping out you could spray carb cleaner into a front or rear intake runner port(blowoff valve service port, or ACV pressure sensor service port), if it smooths out and runs normally then you aren't getting fuel to that rotor at light loads.


screw RPM cruising maps, it is only a necessary function on the MT8 boxes carried over to the LT series where matrix mode was not part of the programming, with the LT8 in matrix mode all the cruise maps do is create problems. zero them all out and pretend it does not exist, do all tuning in matrix mode at the appropriate load/RPM level. the LT8 can be fine tuned without it.

The afr reading is from my innovate wideband. I do not have it connected to the lt. I drove this car last summer with this issue being very intermittent ad the only thing on the car that has changed is a stainless -06 fuel system with aero motive reg at 40psi and went from front mount to a v-mount setup. I'm thinking it may be the injector clips but I will also get my hands on a timing light

Close thread, figured it out

mind sharing your solution?

Plugs were a little dirty and my fuel mixture was a little rich with oil (running premix)
New leading plugs and a few liters of straight gas into the tank and it seems to have fixed the issue

wow

I still seem to have a small issue with this sometimes when I cruise at under 2500 rpm. It will misfire then I floor it and build boost and it goes back to running fine