Running rich after O2 sensor change - Page 7 - JeepForum.com

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post #91 of 99 Old 11-04-2012, 07:58 PM Thread Starter
Bad_Dog
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Reset computer: Engine idles fine. First few trips - and this does involve the engine getting up to temp, stopping and cooling down and then starting back up again - the engine idles fine and throws no codes. Then I'll start it up and it'll idle rough. When it does that, I check and it's now throwing code 52. It doesn't take weeks, just me driving it about three round trips to work, or so.

But you're right, it doesn't make sense that I can drive a handful of trips and it idles fine (and there's no gas smell). And then boom, idles rough, gives 52, and I smell gas when I get out of the Jeep.


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post #92 of 99 Old 11-04-2012, 08:25 PM
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Reset computer: Engine idles fine. First few trips - and this does involve the engine getting up to temp, stopping and cooling down and then starting back up again - the engine idles fine and throws no codes. Then I'll start it up and it'll idle rough. When it does that, I check and it's now throwing code 52. It doesn't take weeks, just me driving it about three round trips to work, or so.

But you're right, it doesn't make sense that I can drive a handful of trips and it idles fine (and there's no gas smell). And then boom, idles rough, gives 52, and I smell gas when I get out of the Jeep.
I wonder if the MAP sensor is the cause of your problem? When it is running good is fully warmed up and the codes are cleared pull the vacuum line off of the MAP sensor and see what happens as far as idle is concerned and what code it throws. I do beleive that a MAP sensor malfunction can trigger a code 52 and casue a rich fuel mix to happen.

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post #93 of 99 Old 11-04-2012, 08:55 PM
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OK, just some more reading...on your thread. SDGBASSE in post 43 layed out what you need to do to test the MAP sensor.

If the MAP sensor checks out go back through the postings here in and re-read everything QUE89YJ wrote. This man knows his YJ's!

My only thought is if it is fuel related and mechanical in nature like a pinched return fuel line, why doesn't it happen as soon as you go into closed loop mode when the engine heats up the first time?

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post #94 of 99 Old 11-05-2012, 07:36 AM
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You either have a fuel pressure issue which you eliminated with the presssure readings or a bad injector. Sorry it took so long to get back. My car got hit and I had to piece it back together.
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post #95 of 99 Old 11-05-2012, 12:28 PM
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You either have a fuel pressure issue which you eliminated with the presssure readings or a bad injector. Sorry it took so long to get back. My car got hit and I had to piece it back together.
This!

Get a fuel pressure gauge and read the pressure at idle, then shut off the motor, watch for pressure to leak down. There is a spec on exceptable leak down. I don't know it off hand. If you are above that threshold you either have fuel leaking back to the tank (bad regulator) or leaking injectors.

Sorry I do not know the spec on leak down nor fuel pressure. Should be in a haynes.

Generally the ECU wont throw a rich condition code until it has seen it x number of miles or start ups or hot cold cycles. Which is why it takes a few trips for the code to set.
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post #96 of 99 Old 11-05-2012, 12:29 PM
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My only thought is if it is fuel related and mechanical in nature like a pinched return fuel line, why doesn't it happen as soon as you go into closed loop mode when the engine heats up the first time?
In open loop the ECU ignores the O2 and is using a set table for fueling. It wont throw a code until it goes closed loop.

Mechanically the only reason he would be running rich is a leaking injector, or bad regulator allowing to much fuel pressure to the injectors.
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post #97 of 99 Old 11-05-2012, 12:37 PM
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Yep that is exactly what I meant WHY J. The fuel pressure should be able to hold 20+ Psi for 20 minutes aftwer shutting it off. I am betting it doesnt.
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post #98 of 99 Old 11-05-2012, 01:10 PM
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Originally Posted by Why J? View Post
In open loop the ECU ignores the O2 and is using a set table for fueling. It wont throw a code until it goes closed loop.

Mechanically the only reason he would be running rich is a leaking injector, or bad regulator allowing to much fuel pressure to the injectors.
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Yep that is exactly what I meant WHY J. The fuel pressure should be able to hold 20+ Psi for 20 minutes aftwer shutting it off. I am betting it doesnt.
How come this DTC does not set during the first open loop to closed loop cycle? Leaking injector or a bad fuel regulator problems do not come and go, right?

It would be nice for anyone to came up with the right answer. The OP just wants his YJ running right!

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post #99 of 99 Old 11-05-2012, 03:21 PM
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Do the bleed down test on the fuel pressure. I bet it's not going to hold pressure.
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