Alright sorry to start a new thread but I can't find any info. I have an 02 Accord Coupe automatic with the F23a4 ULEV motor. The car starting losing power and acting like it was going to stall about a month ago. CEL came on code was I believe P0171 system too lean. I knew the cat was going out so I replaced it with a high flow and cleaned both o2 sensors. Checked the plugs not great but seemed ok. Also checked the injectors, MAF, and PVC. All seemed good. Now the issue is when I start the car and rev it cuts out hard from 1k through 3.5k. It clears up after 4k IN PARK. When driving it has the same issue but it will not rev past 4k. When driving if I'm very light on the pedal it will climb through the low rpms without cutting out but once you get into it it stops. Now 4k seems like limp/safe mode but wouldn't it be the same in park or nuetral? Also I cleared the code and it hasn't come back. Any ideas??

 

Check your oil.

 

System too lean is a tough one. I'm battling it myself on my 96 Accord. It's either a lack of fuel issue (fuel pressure regulator, fuel filter clogged, low fuel pressure, fuel injector), unmetered air (bad egr system, vacuum leak) or your 02 could be bad as well. Check out these and diagnose accordingly (no pun intended):

 

Thanks Ill look into those. Drove it around this weekend check engine came back. Also it will rev past 4k if its pushed hard I wasn't pushing it before so I didn't know. I'm thinking maybe o2 or the fuel filter. Like I said I cleaned the o2 didn't replace though and its got the in-tank mesh filter crap with the pump its supposed to be lifetime but you never know with the quality of gas today. Gonna get the codes checked again see if theres anything new and go from there, Ill keep the thread current.

 

Is the system too lean code the only one showing up? I ask because p0171/172 is usually the code present subsequent to a larger problem and is not normally the only code present.

 

There was an old code p0420 low catalyst effiency. I replaced the front o2 sensor and it ran good for a few day but now its doing the same thing. Hesitation bad it just really doesnt wanna go. The check engine light is back on some im gonna get it checked again but im bettin its p0171 again.

 

So I checked the codes and sure enough its throwing p0171 too lean and the p0420 catalyst effiency. I replaced the cat about 3 weeks ago with an aftermarket high flow could this be the problem? Thing is I really dont see the cat and or secondary o2 causing all the problems that Im having.

 

Check for exhaust leak using seafoam. After confirmed no leaks, replace the oxygen sensors.

You can clean an oxygen sensor. Period. These are the most sensitive sensors known to man.

I'm guessing you need to get a real cat. Never understand why anyone would want to get a "higher flowing" cat, rather than one that works the way it's supposed to.

 

The o2 sensor was replaced and the problem was there with the stock cat also. But a bad cat or a high flow cat not working within stock standards shouldnt cause a system too lean code. The problem must be between my tank and ignition. Im gonna put on some new wires and plugs simply because it needs them. Im at my wits end with this thing and ready to put it in the shop.

 

lean = too much oxygen which could be from an exhaust leak as i said...seafoam it and look for white smoke billowing out from exhaust manifold/pipe

 

Wow I cant believe I overlooked something like that. I will definitely do that Ive been only looking for a lack of fuel not the possibility of too much oxygen.

 

you sould check fuel pressure and if its above 50psi at 3000-4000rpm you sould check for dirty injector

 

this is totaly wrong IMO

 

So update today it started misfiring. Throwing codes p0303 (cylinder 3 misfire) p0304 (cylinder 4 misfire) and p0300 (random misfire detected or some ****. Smells like its running rich but still throwing p0171.

 

The car is completely inoperable now. It will start and the idle will hit 1000 and then slowly decreases to 500 with a hard misfire. As soon as its in gear it drops to 500 and as soon as I touch the pedal it dies. I literally just replaced the plugs and wires like an hour ago. Im wondering if maybe its the injectors or fuel pump/mesh filter..?

 

Did you check for an exhaust leak ? Does it do it when the car is cold as well as when the car is warm ? If it only does it when the car warms up, definitely check for an exhaust leak.

If it does it also when the car is cold I would swap out the distributor.

 

Also, you could have a clogged cat. I would remove the oxygen sensor or the downpipe with the oxygen sensor connector unplugged and see if it still does it.

 

I havnt had a chance to check it out yet today but it does seem to do it all the time. I never got a chance to do the seafoam to check for an exhaust leak but I imagine that could have caused some valve problems? And to clarify are you saying to remove the downstream o2 sensor and see if it still happens? My cat was jus replaced.

 

So crazy update on this thing for anyone who is following. Started the car after about a month of sitting dead and it ran great (well at least as great as it was before the misfire started). Havnt had a misfire problem yet but what I have had is that damn system lean code. When you are real steady on the throttle it will accelerate great but any large movement of the pedal (like flooring it) causes it to sputter and slowly climb rpms. Also it isnt wanting to start when it gets hot. Itll turn over for a while, then start to catch but wont stay running and when it finally does it idles rough at 500 rpms for about 20 seconds before it jumps back up to idle at 900. Ive got a fuel pump and strainer on the way but im jus not totally sure thats the problem. Ive heard that the fuel pump relays can have issues when they get hot but I can hear it coming on. You can even smell fuel when it isnt starting like its flooding.. distributer issue maybe..?

 

Oh yeah and since Ive got it back up and running Ive tested the injectors which are all working correctly as far as the electrical side, also took off the fuel rail and visual inspected it and the injectors. Had a friend cycle the pump with the line off the rail it seemed like it might have been a little low pressure but didnt have means to test it where I was. Removed and cleaned the throttle body also.

 

One of the first things I would look at with even your first sympton is the timing. Set the crank at TDC and pop the cam covers to verify everything is lined up right. Probably things are ok there, but that's a pretty basic check.

 

Just wanted to close this up by letting everyone know the problem turned out to be the fuel pump. It was running weak fuel pressure was low. I replaced the pump and its been running awesome for about 3 weeks now Ive put 1000 miles on it with no issues. Was pretty disappointed in myself for not figuring it out sooner haha.