Hello all! I have a 95 Civic VX. I got it used. The o2 sensor was bad from day one. I just replaced it... so, I have never witnessed Lean burn before today. When the lean burn kicks in, it runs rough. It's almost like a skip. AS SOON as lean burn kicks out, it runs great. the plugs are new, fuel filter is new, and of course O2 is new. Any help or advice is much appreciated. Thanks
Ok, no one has a clue I guess. Just an update. I installed new wires, dis cap, fuel filter, rotor button. Seafoamed the intake. The plugs are fairly new splitfire plugs. I'm thinking of switching out to platinum... maybe a little hotter plug will help the stumble in lean burn.... just thinking if my spark is not strong, it won't burn a lean mixture. Thanks, Ken
I would change the plugs to exactly what OEM specification is...that lean burn design could be pretty sensitive to plugs. If you wanted you could try platinums after you confirm that it's working again.
Dirty EGR ports are a known cause of rough running/stumble especially during lean burn.
There's a nice writeup about how to do it to a crx, which is almost identical in terms of the intake manifold. Here's the link: http://www.gassavers.org/showthread.php?t=8721
That guy hacked the ports before jb welding them. I preferred to drill and tap with SAE threads on mine. That way in 25k I can do it again without grinding. I used teflon tape and lock washers/short bolts to put it back together.
It's not the EGR valve that usually ends up being the problem. It's almost always the ports. These are small passageways in the IM that allow exhaust gases to evenly reach all four cylinder ducts.
I've cleaned two vx's so far. Both went into lean burn pretty well, and weren't very dirty when cleaning. However, the one crx I've cleaned (no lean burn) was AWFUL. It took a length of wire and a lot of solvent to get them clean. It ran pretty well during normal operation before cleaning too.
Spend the time, it's a pain but you can't rule it out until you do it. Spraying/seafoam will NEVER get them even close to clean.
Disconnecting the EGR does the same thing as clogged injectors would; that is, no exhaust gases get through and thus, the a/f ratio is wrong. Stumbling/rough running is the result. This would be exacerbated by(or shown only during, as is your case) lean burn. Lean burn is really sensitive to everything being just right.
As for dirty injectors, it could help. Although, dirty injectors would likely show in "normal" mode as well as lean burn mode. A good way to know if injectors are dirty is to check the color of the plugs. If one or two are very white or there colors are inconsistent, you can assume injectors need to be cleaned. The reason for that is of course that you have only one 02 sensor and that 02 bases a/f on sum of four cylinders. If one is flowing poorly, the ecu will enrich all cylinders to compensate. Thus, 3 out of 4 are rich looking plugs, one is very white. That could happen with 1,2,or 3 injectors.
I'm going to repeat what the others have stated because it's so important:
1. Check compression. You will have to check with the repair manual for the specs.
2. Clean the EGR ports. Take the intake manifold off and do it all correctly. Seafoam won't do it.
3. Get the right plugs. Don't settle for equivalent at the auto parts store. They have to be the exact plug as specified by Honda. There is a label under the hood of my VX with the plug info on it.
4. Check the ign timing. It's OK to advance it by a bit if it makes lean burn work better. But listen for pinging and back it off if you ever hear any pinging under hard acceleration.
I think I need to clean the intake. everything else seems to be in check, compression, timing, plugs, etc. The only reason I was thinking Fuel injectors is because I thought one may be leaking... but from what ive seen and read, the intake and egr ports would need to be cleaned... I hope I can do this properly. thanks for all the advice!
Well it's not the Intake. Cleaned EGR ports, they looked fairly clean... but I cleaned them out anyway. Still no lean burn... it's funny, after doing all of this, my Fuel Economy is actually down a little 1-2 MPG... could be cold weather... it runs perfect though... just no lean burn!!!!! don't know where else to go... except fuel injectors