My girlfriend's '97 Honda Civic DX (non-vtech) is misfiring, and while I thought I was an OK mechanic and pretty good at diagnosing, this one has me stumped. It's been misfiring for over a year now, so if I can fix it, the rewards will be *very* sweet.
Car starts fine (a bit long to start sometimes, hot or cold makes no difference). For the first two minutes the car runs perfect, no misfiring at all. As soon as the needle moves away from cold range the problems starts. Cruising is OK, but whenever you push the accelerator more than a little, it misfires on cylinder number four. OBDII indicates this code as well. Used to be a random misfire, but is now steady. Still a random misfire at idle when warm. Plugs indicate lean conditions on all plugs, but especially number four. Done so far to fix:
New plugs, plug wires, coil pack, distributor cap. New fuel filter, fuel injectors tested (fine). Hooked up my timing light to each cylinder...each cyl fires steady when the the misfires occur, but no idea if enough voltage is getting to the plugs. Listened to the injectors with a stethescope, all click fine even when misfiring. Tested O2 sensors, they work as they're supposed to.
Ideas:
1. Find some way to measure the spark voltage and see if it's up to par.
2. Swap fuel pumps with her sister's '97 Civic EX (identical part number).
3. Swap the MAP sensor with the EX (identical part number)
4. Get a used ECU on ebay ($50) and see if that fixes it. Re-sell on ebay if not.
What would you guys do next? The shop she usually uses is a Honda/Acura specialist (that's ALL they do) and they are stumped too! Any ideas are much appreciated.