'97 Honda Civic misfiring, no Honda mech can fix it! Help!

[jkarolyi]

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.

[Laneco]

You've hit all the likely things that I would have checked first. Would be interested in visually seeing the spray pattern out of #4 injector though.

angela

[sewell94]

The first thing i would check in is your headgasket, those engines are known for it, i had one customer drive on a leaky one for almost a year. He had the exact same symptoms that your gf has been having. I would also check the ignitor. I would change the plugs one more time just to be safe. But my money is on the headgasket. I specialize in hondas. When the local dealership has problems they give me a call

[VincentVega]

No engine codes?

[Moneyguy1]

Pre-ignition due to carbon buildup?

Just trying to think outside the box...

[jkarolyi]

Headgasket, eh? Is compression lower with a bad headgasket? I imagine it would be...I'll check compression tonight. I never suspected that as the car only has 125,000 miles and all Hondas I know of have gone to 200K+ without touching the engine.

What is an "ingnitor?" Looked in the Haynes manual and didn't find a reference to it.

The only engine codes from the OBDII reader is Cyl 4 misfire. The injectors were tested at a FI specialty shop and spray pattern is good.

Because the car runs so good when cold, I still think it has something to do with the computerized fuel system...ie when cold the cold start system compensates for the problem.

[klaucke]

Maybe the temp sensor for the ECU is faulty, causing it to run incorrectly as the engine temp changes. I'm not sure about Honda's, but the temp sensor/sender for the ECU and for the dash gauge are not always the same (so the ECU temp sensor could go bad but your guage would still work properly).

[Victor]

It needs a bigger muffler and a subwoofer.......just kidding. Good luck diagnosing your prob.

[BlueSideUp]

Have you tried cleaning the grounds? I had a car in college that would do all kinds of weird things due to unseen corrosion on the battery terminals.

Did whoever checked the fuel system check out the fuel pressure regulator? If the fuel pressure at idle is wrong it will cause some problems.