OK, the motor 99 CivicSi B16A2 in a 99 Civic Si was just rebuilt because a valve seal and the rings in cylinder one needed to be replaced. So...while we were in there why not do a little mod. We added Weisco 10:75:1 Pistons, and Eagle Rods. These were the only additional mods to the existing mods that are I/H/E, Crower Stage 2 cams and complete Crower valve springs, Ti retainers, Manley (SP?) Valves, Mild PnP, ITR IM, RC 270s, AEM FPR, AEM Cam Gears. ECU is the factory ECU and a VAFC will be purchased tomorrow. The car is ***** out on the low end and vtec is engages for more pleasantries when the car is still relitively cool, but when the car is to temp, its still awesome until the vtec x-over...then it stumbles and its weak up top. We had a OBD2 Code scanner connect and pulled a random misfire. My buddy donated his Stock 99Si to help us trouble shoot it. We swapped distributors, pulled same code. Swapped Map sensor, pulled same code. Swapped ECU, pulled same code. We ran out of time to swap O2 Sensors but were thinking that could be bad/fouled and sending bad signals to the ecu? We also did volt and ohm tests to the crank sensors, vtec stuff, checked grounds, vacuum and all were good. Leak down is at 3% across the board and compression is at 230 +/-2 in all cylinders. The motor is solid, no rich backfiring or lean popping in the IM so we are pretty positive it has to be some electrical snafu. Any of you all-moter freaks had this happen and or any other clues? We won't have the luxury of swapping parts from the donor Si for another week and i'm really tired of driving a Toyota T100 4x4 (although it is interesting to tower over a slammed civic).

 

ever check those injectors? give that a whirl. could be clogged or burned up. When checking compression you pull the injector plugs? just because the injectors can handle the fuel off vtec doesn't mean their duty cycles are up to par when needed in vtec.

one other possible is bad coil wire(if external now).

 

my bad, checked injectors, even swapped them out for stock oe 240s'. All injectors were recently cleaned and were clicking away while listening w/ a stethoscope. No external coil and we confirmed they it (oe coil) was good by comparing mine to my buddies stock 99 Si along with the ignitor in the dist. We compared be checking thier volt / ohms and they were all the same. Were really leanng towards an O2 sensor. Think its possible?

 

i think injectors are too big, thats about 15% more fuel across the board, i.e. 234cc to 270cc injectors without a vtec controller ... also pull your plugs out and check the gaps, keep them between 028 and 032 ... what color are plugs after a full run shut it right down and then pull plugs and check ...

check Lip's suggestion too about injector wiring plugs.

Greg

 

Thanks guys, I'll print out your suggestions and take them with me tonight and post results.

 

Well, we got a hell of alot closer. Our thoughts about the fould O2 was on the money. With the 270 injectors, barely any stumbling at all through Vtec X-over, cold or engine up to temp, a little rich on the bottom though. We took Cheetah and Lips suggestions into consideration and having already tested the RC 270s' and found them to be working fine, we swapped in some known good 240 injectors and no stumbling. The O2 sensor was Faq-ing us up because yesterday without the new O2 sensor, it stumbled on both sets of injectors. and with the addition of a VAFC in the next day or so, the car will be on par with the 270s. Hoping for numbers in the low-mid 170's whp when tuned with VAFC and wideband O2 and I can't wait to see those tq digits with how hard it pulls on the *** dyno compared to when we started this project. I'll post results when done tuning with VAFC.