I was wondering if engine valves, can cause a p0171 CEL? Anyone know? Thanks 2000 accord ~70k city miles on it

 

I think it might cause a rich condition, but not sure if I'm right about that.

Around that vintage Honda uses throttle-position, manifold pressure, & RPM as the primary variables. If the valves are off, the engine is likely taking in less air than the computer calculates.

 

Dealership is saying the reason the CEL and code p0171 is on is because the valves need readjusting. I know it's not the Upstream senor, or fuel pressure since I those checked out fine before taking the car to the Dealership.

So you have doubts that could be the cause of the code

 

Most common reason for P0171 is air intake leak. If Long Term Fuel Trim (LTFT) goes down after 10-20 secs of high rpm (2500-3000) then an air intake leak ( vacuum line, PCV, intake manifold gasket, etc) is likely.

I don't think tight exhaust valves (intakes rarely go tight) could cause P0171 as this would not affect Air/Fuel mixture. If you don't have an engine miss I would discount this as reason for P0171.


good luck

 

In my mind(?) I was thinking about valve timing being off, and the volumetric efficiency lower than it should be.

Valve-clearance adjustment (that's what the dealer seems to be saying) would barely make any difference if anything.

So... search thoroughly for any vacuum leaks.

 

smoke test was done. No leaks detected. Fuel trim increases at 2500 rpm

 

When was the last time the timing belt was replaced? If it hasn't been done yet, 18 years is too long. Honda says it should be changed at 100K or 7 years, then 60K or every 6 years. At 18 years, you've got a ticking time bomb waiting to break.

 

I had a P0171 caused by a single damaged injector. Fuel is added to balance fuel trim until limit (~30% total fuel trim), and code 0171 is set. An injector leak down test is necessary to ID a failing injector unless it shows damage (resistance out of spec or physical damage). A dirty injector could also cause this code.

Given the effort to access the injectors, it might be advisable to swap out all injectors w/ rebuilt set.

good luck

 

Never been replaced. Would that cause a P0171? Thanks for the suggestion. What would happen if the belt broke? Car wouldn't start, or would that cause further damage?
That sounds rather expensive, how much did it cost you to do?

 

You should tell us whether it's a 4-cyl or a V6. Automatic trans?

The 4-cyl is an interference engine, so if the timing belt breaks the pistons would hit the valves ($$$$$). Pretty sure the V6 is also interference but not positive. The belt won't cause any problem at all until the moment it breaks.