KrisGXL

Hi all, I'm having some somewhat minor problems with my engine stumbling under very light loads in the mid 14 AFR range. It only happens under light load/above idle conditions, for example just cruising along at 50kmph and decellerating slightly. It feels like a lean surge with some missing/stumbling, but it is happening at around stoichiometric. The motor seems to run very smooth if I richen things up to 12.5:1 while cruising, and I get no stumbling or missing however this is not very practical . I tried changing spark plugs and wires however this had little or no effect. I tried holding my leading plug wires close to the coil's (one at a time) to check for spark, and i get a frightning spark(will jump about 2") and the spark is perfectly smooth, it does not drop out at all, or drop out in conjunction with the missing when I rev the motor a little in the driveway.

The car:
I'm using a MS 1 V3.0 with MSnS extra029j on my S4 NA GXL. I'm running fuel and spark firing leading and trailing exactly the way described in the FAQ. As for signal conditioning I built a 2nd VR conditioner in the proto area. Currently I am using an Innovate LM-1 wideband(having issues synchronizing with the MS though). Due to the fact that MS gets a jumpy signal from the wideband I am running the car in open loop 100% of the time, and it's tunned by the reading on the wideband not the one in megatune. I thought it was possible that the wideband could be out of wack but it reads exactly 20.9% O2 on decel every time. <-------(feel free to comment on this also please). Also i've slowed the update speed of the wide band down to 1/12sec, even tried 1/6 and 1/3. This is an unrelated problem that doesn't concern me so much, the NA isn't to hard to tune by hand anyway.

My only conclusion is that at the moment I may need new fuel injectors. Like I said earlier the car runs perfect under accel or cruising 60kmph where the motor is actually under load. It also pulls really strong to redline at WOT, no problems there, only under really light load. I have some new high impedance 550 cc secondary injectors that i can put in the car(their sitting beside me right now), and i may just replace the primary injectors with new ones because their 20years old anyway. I also wonder a little bit about the stock EGR valve, if this will remain open without the factory ecu in place or not(note: I do not have the factory ECU in place). If so it may cause some problems for me but i don't really know. Any thoughts on this would be greatly appreciated. Thanks

topspeed7

if u are not using an egr valve u need to disconnect the vaccum line that goes to it the egr
it may not be the problem but at least u know for sure its not that

KrisGXL

It's fixed. It was a leaky EGR valve. I'm so happy that it's smooth again.

Kris