I recently put a fresher Engine and transmission from a 89 bII into my 89 Ranger, the engine was completely re-gasketed and all new seals and runs perfectly other than the code 41 it is now throwing.
With the swap I fixed all the exhaust leaks and vacuum leaks that it had before and was reawarded with a code 41 lol, the first thing I tried was the o2sensor with no success and then the fuel pump died and thought that had to be it so new pump and filter and it's still throwing a code 41.
As I said before it runs absolutely perfect otherwise, impressive power compared to the old engine (will pull 5th like never before) and idles smooth as glass at at the correct 850rpm, I'm stumped.

 

I was messing with the timing and discovered that the distributor wire post that I marked as #1 was not #1, redid every thing to Chilton specs other than setting the timing advanced to 12 degrees with the sprout disconnected, I'm still not sure how that happened, maybe it's always been that way I had never realy checked but man does it run now! It will easily spin the 30x9.50r15's in 1st but still getting the check engine light for the code 41.

 

111 reads & no replies, so i'll see if I can get things started.
Are the O2 sensors switching & if so, the code is saying a cyl bank is lean, so it would be helpful to know which cyl bank the O2 sensor is monitoring that's lean, then go there & have a listen to each fuel injector to determine if one sounds different. How did the old plugs read, any clues from a roasted plug that would indicate one cyl may be running lean????

 

Thanks pawpaw, the 2.9 only has one O2 sensor so I can't narrow it down that way and I only have 700miles on the engine/spark plugs since the swap but I might pull them and see what I can find.
I'm not sure if the code 41 is for running lean or it seams that it can be for "o2 sensor fault, switching not detected". It's been a very long time I've had to count the blinks to read a code and I'm a bit rusty on how to decipher which one it is?

 

I should probably describe the conditions that it sets off the check engine light. Under a load it will run literally all day without the check engine light coming on, but stop and let it idle for ten seconds or so and and the check engine light will come on every time.
I looked over the vacuum lines and wiring last night and couldn't find anything wrong but I did find that the Engine wiring harness for the fuel injectors/o2sensor and some other sensors that I used from the 89 bII didn't have a ground strap that the old engine had from the passenger-side injector area to the back of the motor?

 

CEL coming on at idle is a good clue, but it's not solidly clicking with me right now.
How is your B+ voltage when the engine is at idle????

 

What is B+ Voltage? I probably know what it is but its not clicking at the moment.

 

Battery/Alternator voltage output when its at idle.

 

Good idea to have looked over the vacuum lines, their connections, wiring & posting the CEL coming on at idle clue.


The only thing I could think of at the time is low battery/alternator output at idle, as that could affect fuel pressure & injector operation.
Come to think of it, if the idle engine vacuum is low, on that model I believe the fuel pressure regulator on the fuel rail is vacuum controlled, so low engine vacuum could cause the pressure regulator to act out. If its diaphragm is dry rotted & leaking, wimpy, ect, it could affect idle fuel pressure & if low, could cause both cyl banks to go lean, so post some fuel pressure test numbers, along with the B+ voltage.
Some wags that have come to mind, let us know what you find.

 

Checked the B+ voltage AKA battery/alternator voltage lol and my new alternator and newish battery is good. I will check the fuel pressure next, it's been something that I intended to check but hadn't put the parts together yet to do it yet.

 

I looked up this code and associated causes,
"HEGO (HO2S) Sensor signal out of range / always lean".
"No HO2S Switching Detected".

Is what I came up with, I had a similar code happen to me on a 3.0 I recently rebuilt. There was a lose exhaust manifold bolt that was causing a subtle leak, It wasn't enough to even notice but it caused the o2 sensor to freak out because it was getting too much oxygen. Check your exhaust system for leaks, check your manifold bolts (sometimes they crack or break AFTER you put them on especially if they are old) Check your gaskets make sure none of them smushed out. Last but not least I would try replacing the 02 sensor.

Hope this helps!

 

OK, good feedback on the new battery & alternator output check. Good idea to perform an idle fuel pressure check. Be sure to disconnect the pressure regulator vacuum line to check its soundness & tight fit & be sure to look inside to see if its wet with fuel, if so the regulator diaphragm is leaking, so replace the fpr. If fuel pressure checks ok, have a look at the PCV valve & its rubber fittings & hoses. As its a calculated for vacuum leak & downstream of & not monitored by the MAF sensor, any vacuum leaks in its connections hoses, or abnormal operation, like if its sticking open or not seating fully internally, it'll cause a non calculated for vacuum leak that can lean out the air fuel mixture.


^+1 on checking the exhaust manifold, gaskets, bolts, down pipe ect, since its recently been messed with on the engine swap. As Askye has posted, any leak up stream of, or close to the O2 sensor can corrupt its PID output to the computer about true exhaust O2 content.
Keep checking things & you'll likely find the culprit. Think back to the last thing that happened, or you changed just before the CEL began to turn on & double check those things. Keep us posted on how your trouble shoot goes.

 

After checking the battery and alternator voltage last night i went out this morning to a dead battery, it was almost funny. Chased the 1.4 amp short to the headlight switch, the dash light dimmer control had poped out of place and caused the short, it was almost like someone pulled my dash apart last night just to play a bad joke on me LoL.
After fixing the electrical problem I checked the fuel pressure but don't trust the readings I got. 2 with cheap generic "certified" 0-150 psi gauges, 32psi Engine Key on and 22psi Engine running at an idol and then I put a good Digital tire gauge of all things on the test port and got 39psi with the Engine off and powering the fuel pump. I need to find a real fuel pressure gauge to be satisfied on the fuel psi.
As far as exhaust and vacuum leaks go I'm almost positive there aren't any but I'm going to crawl all over and under this truck untill I figure this out.

 

Fuel pressure @ KOEO & KOER with the fuel pressure regulator vacuum hose Disconnected, should be 35-45 psi.
At idle with the fuel pressure regulator vacuum line Attached, 25-35 psi.
Low fuel pressure can cause a wimpy fuel injector squirt & a lean mixture. So again, how did the old spark plugs internal ceramic insulator look, did they seem to have been running lean????

 

Got a new a new fuel pressure tester today and with the Engine running it has 31-32psi with vacuum to the regulator and 41-42psi with the vacuum disconnected. And I pulled all the spark plugs and all six looked almost identical.



They were in the old Engine for about 7000 miles and looked the same when I installed them in the new engine.
While checking the plugs I managed to break the vacuum line going to the air filter right where the rubber boot on the end of the line connects and while fixing this I tried putting suction on the line and it won't vac down. I temporarily plugged the port, maybe I found something?