CODE 40?

  • Tiny
  • psh1
  • 1994 Ford Ranger
  • 13,100 miles

Vehicle is 1994 Ranger, 3.0L, 2wd, 49 States emission, 131,000miles.
Failed California Smog at 15MPH on all gases(HC 172: CO.73: NO 1354.)Fine at all other tested speeds.
Diag from shop indicates Code 40(; I am unable to find this code.) Repair recommended is new cats(both) and reman engine install(low compression cylinders #4-100 and #5-130.)To correct rough idle. No recommend of fuel filter, injector clean, throttle body or MAF clean. My question is: what should be the cylinder compression reading and what is code 40?
Any questions, comments, or recommendations will be appreciated.

Wednesday, September 19th, 2012 AT 5:52 PM

1 Answer

  • Tiny
  • hmac300
  • Expert
  • 42,944 posts

Cyl compression should be within 20% of each one which you are close to the 20%but not there yet. All that code 40 is is a cylinder balance code and says #4 is reading electonically off. The low cylinder can be a valve starting to burn or go bad, a vacuum leak or a larger internal problem. Check fuel pressure as that can give a rough idle as well as a vacuum leak. With the engine running it should be 28-45 psi

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Wednesday, September 19th, 2012 AT 8:00 PM

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