engine miss

[werewolf]

On my 1987 4x4 ranger manual 5 speed, 2.9 v6 has a miss. it is werse when engine is cold. Runs better after engine is warm. Hooked up obd and got a 10 & 31. Would it be the Egr valve senser or would it be the EVAP control sys.below voltage. How can i test them.

 

[RonD]

Code 31 is usually a bad EGR sensor, usually.

To test if it is the EGR valve or the sensor get a length of vacuum hose that will fit the EGR valve's vacuum port.
EGR valve should only open when engine is under a load, i.e. driving up a hill or accelerating hard, so when engine is idling there should be no vacuum on it's hose.
Start engine and let it idle
Remove EGR valve vacuum hose and feel the end of the hose for vacuum there should be no sucking(vacuum) on that hose.
Now put your vacuum hose on the EGR valve and suck on it, no you won't get exhaust smoke in your mouth.
Engine should start to stumble and if you hold the vacuum long enough it may even die.
Release the vacuum, stop sucking, and idle should return to normal.
If this happens then EGR valve is good and sensor is bad, replace it.
If this doesn't happen remove EGR Valve and clean it, retest, if same results replace EGR Valve.

There is no "10" code, generally "0's" were skipped on OBDI because how do you code "0" with flashes?
So 10, 20, 30, 40, ect..........are either not used at all or are specific to an engine and model, none of which are Rangers

 

[werewolf]

ok,be having a problem.

I have a 87 2.9 v6 with standard five speed. with rough idle.and i have a code 31. ever one is talking about egr valve and egr sensor.I have pulled up pictures of these and my 2.9 v6 does not have these so how is this working. don't under stand. I can't do your test cause i don't have these parts like you say i have. thanks

 

[RonD]

EGR system was removed in '88 on the 2.9l, but different software was run on the computer so a code like 31 shouldn't come up.

What is the history of this truck?
Could previous owner have removed EGR system or swapped engine using '88-'92 2.9l model that didn't have EGR system?

Maybe Ford removed EGR system in late '87?? not sure, but computer shouldn't show 31 if that was the case

If your engine has a miss(and no EGR system) and the only code is 31 then I would disregard that code and look for bad spark, TFI systems are known failure points as they get older.
Good article here: http://www.therangerstation.com/tech_library/TFI_Diagnostic.shtml

 

[enjr44]

Or swapped the computer to one that was for egr equipped engine??