Topic: Engine lean code?

[Torch_Ind]

Well cleaning the map sensor and TB didn't get rid of it so I guess I'll start vacum testing lines.  Its actually running better than it has in a long time.  On a side note I finally bored my intake out to 62mm and that mod is worthless until you do this!  Much different.

Are you getting this code after your 62mm update?

[jcsanders79]

I got the code before I bored the intake out and its still here.  The TB has been on for a while though.

[Torch_Ind]

so it was there before the tb. does the engine have high miles? could be blow by going in to the intake throw the pcv system? what year is it?

[jcsanders79]

Its a 97' auto that was rebuilt around 105K (engine and trans) with another 25K on it.  I had it rebuilt and have had little issue with it since.  Didn't get to work on it like I hoped this weekend so I don't have any updates.

[sharpxmen]

did you end up replacing the O2? keep thinking about your problem and since yours is '97 seems odd that you don't get the wot code but only the closed loop one (odd in terms of not having enough fuel as if it was a fuel delivery problem should also appear at wot) - if you're OBDII (i think it is) you could monitor the fuel trim in closed loop with a usb scan tool and a laptop to see what you get, pcm should learn and the trim should decrease in time and since i think you mentioned your O2 needs to be replaced i'm thinking that might be the problem in the end. Keep us posted, really interested in hearing what the problem is when you get to the bottom of it. good luck!

[Torch_Ind]

did you check the basic's also like fuel pressure. good spark or plug gap? 

[SDWE61988]

I ironically have the same issue right now.  I have a code 51 on my 95YJ.  I just installed a 2.5l engine from a 97tj in the jeep and added a banks header.  I was wondering if my issue is not enough fuel also.  Everything seems to run very strong, however I keep getting that code 51.  I used to stock fuel injectors and rail from my old engine and they were quite dirty. So If read this thread correctly, I should be see 31 psi on the rail with the vacuum line connected and 39 psi with it disconnected?

[sharpxmen]

I ironically have the same issue right now.  I have a code 51 on my 95YJ.  I just installed a 2.5l engine from a 97tj in the jeep and added a banks header.  I was wondering if my issue is not enough fuel also.  Everything seems to run very strong, however I keep getting that code 51.  I used to stock fuel injectors and rail from my old engine and they were quite dirty. So If read this thread correctly, I should be see 31 psi on the rail with the vacuum line connected and 39 psi with it disconnected?

i'm not 100% on the 31 at idle (or throttle closed) - could be 30, but i am pretty sure on the 39 with no vac. Keep in mind that you are more likely to not have enough fuel when under load and when the injector duty cycle increases (stays opened more) and the required flow is higher - it is a good place to start, it will tell you if the fuel pressure regulator functions properly, you can then test it on the road and see if you lose pressure, but if it's too much you would actually feel the engine stumbling - if your press is lower under load at wot compared to when you unplug the vac at idle then it could be the filter or pump. You could run a test with te vac line disconnected on the road just to eliminate the possibility of not being at wot to make sure you don't get a "false positive".
did you use your old temp sensors for intake air temp and engine temp (dunno if that would make a difference for this particular code but something to consider).

EDIT: just noticed your comment on the injectors: if your injectors are plugged or don't deliver enough fuel your fuel pressure in the rail will not change or be affected in any way.

[SDWE61988]

I will have to test this out, look at the pressure.  I just installed a new stock style fuel pressure regulator a couple months ago.  (this rig is breaking the bank this year).  I replaced the filter last summer.  I will have to get apressure gauge on there and see if I can narrow the problem.  I did end up using the old sensors from the old engine to minimumize issues of incompabliity, plus all of the new sensors had different plugs on them. 

[sharpxmen]

what year is your Jeep? did you use your old throttle body (not sure if the tps is different or not)?

For a pressure gauge i used an autometer one but there are some cheap ones out there you can use (they won't be as accurate but just in case you want to go on a budget) - to connect to the fuel rail (this is for my '95 YJ so you'll have to make sure yours is the same) i used a braided stainless steel hose with AN-4 fittings at both ends and a female 1/4'' NPT to male AN-4 adapter to connect to the gauge. the hose has to be resistant to fuel. The pressure check thread on the fuel rail is AN-4 but if you use this setup you will have to remove the valve that is in the center (same as the tire valves, but don't loose this one as it is fuel resistant, the regular ones are not). There are also ready made fuel pressure gauges that have the adapter for the fuel rail so you don't have to remove the valve, i did it this way as i wanted to have the gauge permanently installed on the dash so i can monitor when driving. Double check the threads to make sure i didn't screw up on the info - did this about 3 years ago and it's a bit foggy :)

also, make sure there are no check valves on the map sensor vac line (there should be just a plastic vac line going to the intake with nothing on it) - i am just thinking that since you replaced the engine something might have gotten mixed up - not familiar with the 97TJ intake but check and see if the fitting where the MAP gets plugged in is flowing air both ways with no restrictions (unplug at the map and blow/suck air thru it, then follow the line and make sure it is straight to the intake and no other things on it).

[SDWE61988]

I have a 95.  I am using a 4.0tb.  I used it on the other engine for almost a year before it blew.  Is your guage in the engine bay or did you run it through the fire wall and mount it somewhere inside the jeep?  I will have to definiately check the vac lines again. 

[sharpxmen]

it's inside on the dash, i will post a pic tomorrow with my dash and fuel rail so you can see how i did it.

[dunklervogel]

Strangely enough, I am also fighting a battle with code 51 ( aka p0171) A lean air/fuel mixture has been indicated by an abnormally rich correction factor

My symptoms are:
it is blowing black smoke (unburnt fuel) out of the tailpipe, dripping raw fuel as well.
Exhaust smells horrid and can even smell it a bit on the highway too its so bad
12mpg average when I used to get 17 average. 
Major loss in power.
Occasional backfire
Surges on acceleration.

I have been moving down the list replacing parts here is all I have done:

Replaced both o2 sensors
Replaced plugs and wires
Checked compression (all 4 cylinders are 145-150 psi)
Checked for vacuum leaks with a vacuum gauge (no leaks)
Ran injector cleaner through it.  After that tank of gas I used seafoam.
Pulled the injectors and inspected them, they appeared to be in good shape.  Tips were clean.  Checked to see if they were leaky by priming the fuel system with the injectors pulled.  None leaked when ignition was turned to on.
Checked air filter.. it is in decent shape so left it alone for the time being.
Checked fuel pressure.. steady 48 psi
Checked oil, looks good.

Still after all that.. the code remained.
Took off my cat and looks like the inside is melted.  Since I'm pretty much out of all other options, I said screw it and just went ahead and ordered a magnaflow cat.  Now I am just waiting for it to come in then will install it and see if the code still gets thrown.
If it does, then I am out of ideas.

[sharpxmen]

not sure if you did it yet, you might have but in case you didn't check the spark plugs and look at their color - make sure you remember where they came out from. Check the distributor cap and distributor, make sure there are no signs of wasted sparks. also check the wires and make sure they're ok

[sharpxmen]

not sure if you did it yet, you might have but in case you didn't check the spark plugs and look at their color - make sure you remember where they came out from. Check the distributor cap and distributor, make sure there are no signs of wasted sparks. also check the wires and make sure they're ok

sorry man, noticed that you had replaced the plugs - you should still take them out and inspect them - see what the color is or if any of them is wet (and if they all look the same or not).
does it idle in 3 cyl by any chance? you can check that by unplugging a wire at a time.

this is a long shot but i'll throw this idea in anyway: could it be a lifter/rod/rocker/valve issue? as i said, long shot - see what the spark plugs look like first and if they are all the same or major differences. Keep us posted.