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CEL 99 accord (fuel trim malfunction - too lean)

3K views 3 replies 3 participants last post by  nusdogg 
#1 ·
My 99 Accord EX just got P0170 and P0171 codes. F23A1 motor. Tested primary o2 sensors and voltage fluctuates consistently between 0.180 and 0.840. could O2 sensor be bad? or do i want to look into checking fuel pressure regulator or the MAF sensor? CEL comes and goes.. mostly stays on. also light knocking / valve clatter when cold between 2500-4000 rpms. once motor is warmed and driven all motor noise goes away. unsure if its related
 
#2 ·
Take your MAF out and look at the inside see if it's got some fuzz around it, possibly from the air filter, this could cause lean codes to pop....just take a small straw from a brake cleaner bottle for example and lightly brush it off. clear the codes and see if they come back.........as for the engine noise it sounds like a matter of oil pressure building up...i could be wrong though
 
#3 ·
For the noise it looks like I'll need a valve adjustment.

Accord does not have a MAF.. has a MAP, which was clean. Cleaned gunk out of the EGR. now the code comes and goes, and it's started bogging down in the lower RPM's, and seems slower.. thinking a couple things could be wrong. Fuel pressure regulator/filter, cat converter (smells sulfur like).

will post back at a later time with update or solution.
 
#4 ·
If its a lean mixture code, check that you don't have any vacuum leak before the TB. And I doubt the 99 Accords have MAF sensors; instead, they have MAP.

Voltage should fluctuate from .1-.9 volt. So yours might be fine since .8v is closer to .9v.
 
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