Running lean bank 1

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Matt334

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So I recently bought my 2000 wrangler Sahara second hand, I put in new catalytic converters, no throwing code for running lean on bank 1 and gas mileage is down, no leak in line, looking for any advice, anything will help
 
What does your fuel trim look like, is it high and does it drop when you raise the idle? (check long term and short term both)
 
B1Toad said:
What does your fuel trim look like, is it high and does it drop when you raise the idle? (check long term and short term both)
Click to expand...

It does have a rough idle, and the rpm tends to stay high for a few moments after I let off the gas
 
Matt334 said:
It does have a rough idle, and the rpm tends to stay high for a few moments after I let off the gas
Click to expand...

If you have a way to check fuel trim we could see if it is high and if higher RPMs lower it, if so you likely have a vacuum leak.
 
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Since you have a rough idle I'm going to say a vacuum leak is a good possibility,
 
How’s your O2 sensors? Some of the cheaper sensors tend to give the TJs issues. If you buy NTK or Mopar they will be the best you can get
 
If yours has the mini cats on the side of the engine and they are not bolted tight to the exh manifolds, it will create an air leak that will cause the O2s to show lean. Check the cat to manifold bolts.
 
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Those are good posts- I’d wonder if the leak is pre cat maybe- spray wd-40 around the intake and see if it revs- especially where vacuum hoses plug in- if you have cruise see if it works- that indicates a vacuum leak too.
 
Sometimes it can be hard to use WD40 or propane trying to find a vacuum leak on a computer controlled engine, you have to be quick because the computer will compensate for the added fuel pretty quick. Best way is to be watching fuel trims as you do it, fuel trim will drop quick when extra fuel is introduced thru the leak. I've also seen people use a squirt bottle with water, you can see and hear the water when it gets sucked in.
Another cause for the lean condition and using extra fuel can be the MAP sensor damaged or leaking vacuum, it's not at the top of the list but it does happen. I bought a MAP sensor once at Autozone for my son's truck and it was bad, cost me hours of troubleshooting before I swapped it with one off my truck and figured it out. It was the first and last sensor I have ever bought from a box store, lesson learned.
 
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B1Toad said:
Sometimes it can be hard to use WD40 or propane trying to find a vacuum leak on a computer controlled engine, you have to be quick because the computer will compensate for the added fuel pretty quick. Best way is to be watching fuel trims as you do it, fuel trim will drop quick when extra fuel is introduced thru the leak. I've also seen people use a squirt bottle with water, you can see and hear the water when it gets sucked in.
Another cause for the lean condition and using extra fuel can be the MAP sensor damaged or leaking vacuum, it's not at the top of the list but it does happen. I bought a MAP sensor once at Autozone for my son's truck and it was bad, cost me hours of troubleshooting before I swapped it with one off my truck and figured it out. It was the first and last sensor I have ever bought from a box store, lesson learned.
Click to expand...

Good post-

I have a scanner that reads fuel trim- pretty insightful. Was having cat issues and got into it some.
 
If you can't/don't have a scanner that reads fuel trims, starting fluid works better for me than WD 40 or water.

You can always do a smoke test to check for vacuum leaks also.
 
A smoke "machine" is a fantastic diagnostic tool! I after many years of not having one finally built one a few years ago (Many good tutorials on youtube) I had most of the stuff already, had to buy the steel gallon paint can, nichrome wire, teaky torch wick and vinyl tubing. For a $20 investment, what an amazing pay off! My buddy owns a shop and has his Snap on smoke machine that he paid $1000.00 for and uses it regularly, he just shakes his head at my $20 version then says well mine is a tax write off LOL...
Vacuum leaks
Exhaust leaks
intake leaks
pressurize fuel system (smoke off)
etc etc
 
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