Hi,

First post! I have a 98 accord M/T, with the 4 cyl vtec engine, 91K miles and I keep getting the check engine light. OBD says fuel mixture is lean. I have replaced plugs/wires/cap/rotor/air filter. Injectors look original and don't leak. Previous owner replaced EGR valve.

My mechanic does not want to shotgun parts at it and has suggested "maybe" the fuel filter should be changed or maybe the EGR isn't working right. Other than that he is stumped.

Any ideas what else could cause this lean condition and how to test?

Thanks for any replies!

 

02 sensor would be my guess. It might be reading wrong.

 

> 02 sensor would be my guess. It might be reading wrong.

Wouldn't that show up on the error code reader? BTW, I have NO driveability problems, no missing, passes smog etc.

 

I agree, primary o2 sensor is suspect. You do have a CEL - you just told us that!

 

Thanks notoriousB - Is there a way to test the O2 sensor? Wouldn't a bad O2 sensor show up when the OBD code is read? Or is it possible for it to be a "little" bad so as to just show up as a lean mixture? I'm not very familiar with what the OBD can and cannot do!

 

OBD codes do not always tell you the exact root cause of your problem. The code you're seeing is telling you that the o2 sensor is detecting a lean condition. Unless you've dropped your fuel pressure, installed smaller injectors, or otherwise reduced the fuel input to your engine, most likely the "lean condition" is a false reading by the o2 sensor, most likely a 0 (or very close to) voltage reading from the sensor.

I'm not sure if there's an o2 sensor test process and I'm currently about 3000 miles away from my helms manual so I can't check that for you.

 

Thanks, that makes sense. I'll look into it.

 

Bump one for the 02 sensor.

NOT your fuel filter. This gen accord doesn't have a traditional in-line filter.

 

There is a service bulletin about lean running conditions... caused by a failed fule pressure regulator, and hose. I will try to post a link later....

 

Wow, thanks. I asked the mechanic if he had measured the fuel pressure and he did not. I will try to search for a service bulletin as well and will post back if I find anything.

 

How about trying this?
Disconnect the primary 02 sensor and then reset all the PCM faults.
Restart the car and let it run - take it around the block if you like.
Reread the fault codes. If you show a Primary 02 sensor and no other faults than yes, you probably have a bad 02 sensor.
I am no mechanic but I think I know how the PCM works. When you disconnect the 02 sensor the PCM relies on "pre-programmed stored parameters' to determine optimum fuel delivery. If your lean fuel problems go away then the PCM is doing it's job and the 02 sensor is faulty.

 

Sorry it's been a little bit, but here are the three pages of the bulletin that deals with this issue....

page1
http://community.webshots.com/...qnqOx

page2
http://community.webshots.com/...UlDJJ

page3
http://community.webshots.com/...seqNT

Good luck.

 

That sounds like a good strategy, but doesn't the PCM rely on the signal from the O2 sensor to trigger the lean condition fault code? If the O2 sensor is disconnected I wouldn't get a lean condition fault code but I couldn't be sure the fault did not actually exist. Or is there a second O2 sensor that would generate the lean condition fault code if the car was truly running lean?

Sorry if this is a dumb question, I seriously need to read the manual and familiarize myself with this car

It makes the twin SU carbs on my Datsun seem easy

 

HondaTechPro - Thanks! I had managed to find the title to that document but not the actual text - AWESOME!

Local Honda dealer wants $42 for the reg and $8 for the vacuum tube kit. Any reason to fork over the extra $8 for a length of vacuum tube? I have a M/T with cruise control so it looks like I simply need a length of vacuum tube with no other connections.

 

I'm pretty sure any vacuum hose of the correct length will work... the factory just has the bends molded into it.... 8 bucks is 8 bucks... its your call.

 

Well, I can report back that the problem I'm having is NOT the fuel pressure regulator

Changed it with a new Honda part, got the light reset and it is back on after <50 miles.

My next "guess" is the EGR valve. Anyone know of a good source for one that doesn't cost an arm and a leg? Is this a reasonable part to get from a junkyard? New OEM are $$$!

I HATE throwing parts at a problem.

[RANT] Why do we need all this OBD crap if it can only suggest a problem that may/may not exist but lend absolutely no help to diagnosing what is wrong? [/RANT]

Anyone have a good way to test the EGR?

Thanks

 

have you tried an o2 sensor yet?

 

and you may need the cap some of the m/t need is and some do not its only $8 plus its bent nice and will look oem!

 

hey whats up everyone!!!!! this is my first time here. Notorious i have been reading about your problem, one thing that i haved fix in a few accords already is a cracked exhaust manifold. the o2 sensor can read the extra air coming into the exhaust stream and give the computer a lean reading, this can also lead to a burn valve. hey i also agree with everyone else on the o2 sensors, but if you want to know once and for all if the o2s ar good, just hook up a scanner and read the data and the o2s they should be constanctly switching between lean and rich, and the readings from the o2 befor the cat and the one after shoud be diff. I HOPE THAT HELPS!!!!!!

 

allhonda.... first post and you can't even figure out whose problem this is..... wow

 

Hey allhonda, thanks for the ideas. I hope it's not an exhaust manifold. I don't have a scanner but I have an oscilloscope. What voltages would I expect to see at the upstream and downstream O2 sensors?

Thanks

 

notoriousB,

I haven't yet tried the O2 sensors. I priced them out at around $50 and $70 or so and was hoping to narrow it down before blowing the cobwebs out of my wallet and plunking down the dough

I'm thinking you might be onto it because the last few times I drove it I smelled a distinctive "rotten egg" smell which is unusual for this car - is that a clue??

 

Just wanted to resurrect this thread for the benefit of future searchers. It seems the cause of the problem was (drumroll please) . . . the O2 sensor

I put a new one on and after a few miles the light went off and has stayed off.

Mucho props to NotoriousB for calling it right away