Engine misfiring @ 1/4 throttle, pls help
 

I have a 2003 VIII that has a mostly stock engine, with the exception of an APEXi boost controller and a fuel controller. Occasionally when driving at 4000 rpm and at partial throttle, (25%), the engine begins to shudder and seems to be only firing on two cylinders. The service engine light immidiately comes on. If I back offon the throttle, it seems to come back to life and goes away for a while. By the way, the boost curve has only been altered slightly and the fuel curve leaned 5% max. I have checked the code and it is a P-300, multi engine mis-fire.

I have changed the sparkplugs and wires, checked the gas cap, and changed the fuel filter. The wires from the APEXi controllersto the ECUare soldered and shrinkwrapped and are all tight.

ANY IDEAS ?

RE: Engine misfiring @ 1/4 throttle, pls help
 

what BOV are you runing?? and ow much boost is that 5%. If your running more than 23 that is your problem do you have a boost gauge? Is your BOV vented (I assume it not)

RE: Engine misfiring @ 1/4 throttle, pls help
 

Could be so many things. Bad sensor, bad ECU, bad coil pack...

RE: Engine misfiring @ 1/4 throttle, pls help
 

its not a bad ECU Iate when people say that its friggen retarded. an ECU just doesnt go bad out of no where

RE: Engine misfiring @ 1/4 throttle, pls help
 

The motor and BOV are stock. I'm not over-boosting the motor, just keeping it at a fixed value through the entire rev range. The 5% I was refering to is the slight leaning of the fuel curve with the SAFC II . The anomaly happens at very slight throttle opening. I have a boost guage and never boost it above 1.3 bar.

I have ordered some oem coil packs and will give that a try.

RE: Engine misfiring @ 1/4 throttle, pls help
 

Ok your tune do you have a wideband? Who tuned the SAFCII for you? your sure the lo throttle corrections are 0% and the hi throttle corrections are the ones your -5% on? what RPM increments are you useing? Try zeroing out the SAFCII and try it.


Have you done anything in the engine bay prior to the problem? maybe you have a boost leak and WOT the tirbo flows enough to not have it mis

RE: Engine misfiring @ 1/4 throttle, pls help
 

My EVO 8 will cut out if the plugs aren't properly gapped. Usually on the top end tho. Just a thought...I figured I'd throw it up here. Start with the simpleist and work toward the most difficult !!!!

RE: Engine misfiring @ 1/4 throttle, pls help
 

I read somewhere that some plugs gaps will get screwed up like yours do if the temp ratings are not right...Found it somwhere on EVOm

RE: Engine misfiring @ 1/4 throttle, pls help
 

Yea with higher boost you want to be running a colder plug. Especially with FOG's setup he would want an "8". But yours should be like a7. What kinda plugs do you have? and whats the gap?