1988 Ranger 2.9L emissions fail, low idle miss

[88rangr]

Hello fellow Ranger owners,

I failed emissions.

I have replaces and corrected.

Plugs
Wires
Cap
Rotor
Set timing

I pass the 30 mph test, but fail the idle test, hydrocarbons are elevated, obvious miss in cylinder.

What else would you check or replace, all new sensors but the TPS.

Thanks for the help in figuring thos out.

 

[RonD]

At idle the computer doesn't use the O2 sensors, and it does run engine rich, best guess would be you are burning some oil via rings or Valve guide seal leaks.

High vacuum at idle sucks oil thru valve guide seals faster.
Make sure PCV system is working well, that reduces the amount of oil that can be sucked in by leaking seals and rings.

Pull out spark plugs and see if you can detect which cylinder is misfiring, and why.
Look at the tips, for oil or Rich burn.

I assume you have timed the spark, if at 12deg BTDC try 10deg BTDC

Check for vacuum leak
After engine is warmed up and idling, unplug the IAC Valve's 2 wires
Idle should drop down to 500RPM or engine may even stall, either is good it means no vacuum leaks
If idle stays high then you do have a vacuum leak

Vacuum leak can cause computer to run engine Richer than needed and can also cause Lean misfire depending on where the leak is.

 

[88rangr]

At idle the computer doesn't use the O2 sensors, and it does run engine rich, best guess would be you are burning some oil via rings or Valve guide seal leaks.

High vacuum at idle sucks oil thru valve guide seals faster.
Make sure PCV system is working well, that reduces the amount of oil that can be sucked in by leaking seals and rings.

Pull out spark plugs and see if you can detect which cylinder is misfiring, and why.
Look at the tips, for oil or Rich burn.

I assume you have timed the spark, if at 12deg BTDC try 10deg BTDC

Check for vacuum leak
After engine is warmed up and idling, unplug the IAC Valve's 2 wires
Idle should drop down to 500RPM or engine may even stall, either is good it means no vacuum leaks
If idle stays high then you do have a vacuum leak

Vacuum leak can cause computer to run engine Richer than needed and can also cause Lean misfire depending on where the leak is.

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Thank you, I will do that to double check, it has 240,000 miles on her.

Burns some oil, but not horrible, may try some engine honey. Will look into O2, there are two of them I think.