engine running too lean

[mazdamama]

when i do the check engine light test i keep getting the following codes for eec IV.

172: system indicates lean bank 1
136: system indicates lean bank 2

and
411: unable to control rpm during low rpm self test.

i assume that all of these are related somehow, and if i can find why the system is lean, it will fix them.

my guess is vacuum leak, but i cant find any leaks, so any advice would be greatly appreciated.

 

[Wicked_Sludge]

sounds like a vacuum leak to me.

buy a can of brake cleaner and, with the engine running, start spraying little bursts around all the gaskets and hoses. if you find a leak, the RPM will change. pay special attention to the rear of the intake manifold gasket, 4.0's are notorious for leaking here.

 

[mazdamama]

thanks for the tip, about how many rpms will the engine rev up to if it sucks in the brake cleaner or starter fluid? what should i watch for ?, because it allready fluctuates between 7,000 to 10,000 rpms during idle.

 

[Wicked_Sludge]

im assuming you meant 700-1,000 RPM

try unplugging the IAC at idle and see if the truck idles steady with it unplugged. if not, your going to have a hard time finding the leak with brake cleaner (though its not impossible with a trained ear).

another option is to use a mechanics stethiscope to probe around possible vacuum leak areas. lacking a stethiscope, a long peice of rubber tubing held to the ear would work.

 

[mazdamama]

i also started getting rich and lean both banks, (172,173, 176, 177)

so unplugged the IAC and did the CEL test and this is what i got.

411: unable to control rpm during low rpm self test. and
412: unable to control rpm during high rpm self test

but... no lean or rich codes.
does anyone think that this probably points to IAC or is still possible that it may be a vacuum leak?

 

[Wicked_Sludge]

i wouldnt think so...any air that might be "leaking" past the IAC would have already been metered by the MAFS. lean codes come about from "extra" air getting in that the MAF cant detect, causing the mixture to lean out.

unless the action of unplugging the IAC jared a bad IAC gasket into sealing itself.

another possibility is that the lean codes are old and/or left over from a previous vacuum leak that has since been fixed (either accidentaly or deliberately).

 

[mazdamama]

well battery has been disconected and codes have been reset, but they still pop up. also , the rich and lean codes come from the o2 sensors, which have allready been replaced, so i doubt its an o2 problem.

 

[Wicked_Sludge]

i would still be on the lookout for vacuum leaks. did the engine idle steady with the IAC unplugged?

 

[shadetree]

A clogged fuel filter, or weak fuel pump will also cause lean codes.shady

 

[mazdamama]

yup, i just changed both last week, in attempt to fix the problem,hasnt made much of a difference allthough im happy that my fuel gauge is working again.

 

[94redranger]

Let me know how it goes mazdamama because I am having same problem with the same codes you are getting, I also suspect intake gasket leak. On my engine anyways because it uses a little bit of coolant and all other hoses and stuff like that are good. Does anyone know how to tell if the MAF is bad by unplugging it or something?