86 2.9 Runs SUPER rich when cold/open loop, runs amazing when operating temp/closed loop

[RonD]

PCV Valve?
It is a planned vacuum leak but based on it working like it should, if the valve inside is cold and oil coated it can stick, but then is fine once it warms up

Before engine temp gets to 130-140degF the computer is in Open Loop so is using air/fuel mix tables in memory, and no O2 sensor feedback
Tables are rich, but not that rich

Could have a spark plug that's weaker or injector that's dripping, once warmed up its fine

 

[rang-a-stang]

yeah, good ideas. When I get home i will disconnect the PCV and plug the line to see if that makes a difference and will pull the plugs and get some pics of them, too.

 

[rang-a-stang]

OK, I have not tried pulling/plugging PCV yet. Here is a cold start. After I took this video and was backing it out of the driveway, a few revs blew quite a bit of black smoke.
Video of cold start

Here is the video of it warm idling. Not hot, but warm.
video of warm idle

I hope to pull/plug the PCV later today and put some miles on it.

 

[rang-a-stang]

Today is the first time I have driving it since the 8th. no real change since I plugged the PCV line other than the stone cold idle seems a little smoother but it still ran like crap as I drove away. I put a solid 100 miles on it today so I am hoping tomorrow when I drive it, it will run a little better when cold.

 

[rang-a-stang]

So after about 200 miles of driving with the PCV unhooked and the line plugged, no change in symptoms. Still runs super aweful when cold yet amazing when at operating temp. I guess this weekend, when I get home, I will warm it up and check for vacuum leaks again. Usually when I check for vacuum leaks, its when its cold. I never did pull my plugs, mostly becuase I don't want to but also becuase I know they are going to show it running rich.

 

[thorsranger91]

Is your truck an auto? If it is the dreaded t code(a4ld) then you may have a failed vacuum modulator valve. When this fails the engine sucks atf in and burns it

 

[rang-a-stang]

Nope. We have a stick. (sorry for the long delay in responding, work has been insane, I have not driven our Ranger in a month!)

 

[rang-a-stang]

I FIXED IT!!!! HOLY CATS! I got it!!!

I went back to the start and just kept thinking about each step. Any vacuum leaks? What have I messed with, etc. Then it dawned on me, every time I would check for vacuum leaks I never thought to check the EGR valve mating flange! Pulled the cover off the throttle cable and inspected. The EGR bolts were just snug (we had to remove the EGR when going through CA smog to clean the passages so we had been in there, not sure if we forgot to torque those bolts or if they came loose but they were loose). So I ordered a new EGR gasket and new plenum gaskets (not really needed but at some point my mind thought maybe the lower was heating up enough that there could be a slight vacuum leak, enough to throw off the closed loop fuel tables). I replaced the plenum and EGR gaskets. While I was doing that I left the battery unhooked thinking that would clear out the learned fuel tables but it did not. When I fired it up, it still ran really rich but the surging seemed a little less. I took it for a trip around town for about 30 mins to help the computer relearn. This morning I fired it up and it idled smoothly, no surging, no soot, no slight black smoke! WOOOO HOOOO!!!!

Bottom line: I believe air was getting in via the EGR passage. I am not sure if that air was going up into the intake and the computer was compensating or if air was getting down the EGR passgage and throwing a lean signal. Either way, it runs great again!!!

 

[gaz]

@rang-a-stang ,
Only because you brought your post back in service, I make this comment; my 2.9l's run like -RiCH when cold, so if possible, I let them warm up to normal engine operating temperature before driving the vehicle. While this isn't ALWAYS practical I am able to do it 98% of the time.

A by product of always driving with the engine up to temperature has been increased fuel economy.

 

[rang-a-stang]

Makes sense but driving it does warm the engine up quicker. If I used to let it idle until it was warm, it was a solid 15 minutes. Driving it, it take about 3 or 4 miles. (probably 5-10 mins)