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Unread 08-26-2013, 06:55 PM   #1
scraper
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Engine runs fine until new Oxygen Sensor?

Here's the situation. I had a broken Oxygen sensor and I needed to replace my Cat, so I did both at the same time. Prior to the replacements the Jeep would start and idle fine. After the replacements the Jeep won't even start. It will fire a couple of times and sputter, but I can't get it running long enough to do anything.

I ran an error code check and nothing comes back. In an attempt to fix it I removed the throttle body and cleaned it and the IAC. That didn't do it. My fuel pressure is fine. Spark is good. Vacuum lines look good, but I can't get it running to check them.

I just can't figure out why a new Oxygen Sensor would cause the Jeep not to start and idle.

Funny thing is prior to replacing the oxygen sensor the jeep didn't even have one working. The old one was snapped in half and It ran just fine without it.

Any guesses what my issue could be?

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Unread 08-26-2013, 07:27 PM   #2
bigbossd1030
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If you suspect the o2 sensor. Unplug it and see if the jeep starts. That will eliminate that.

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Unread 08-26-2013, 09:24 PM   #3
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Quote:
Originally Posted by bigbossd1030
If you suspect the o2 sensor. Unplug it and see if the jeep starts. That will eliminate that.

Sent from my iPhone, probably because I am bored at work.
This.
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Unread 08-27-2013, 01:21 AM   #4
msprooch
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Try to unhook the battery for ten minutes to reset the ecm
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Unread 08-27-2013, 06:49 AM   #5
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Originally Posted by msprooch View Post
Try to unhook the battery for ten minutes to reset the ecm
I tried this and I unplugged the Oxygen sensor. Didn't fix it so it has to be something else and the oxygen sensor being new is just a coincidence. I will have to check everything going down the usually list to narrow this down. This is the YJ that sat for 5 years and I have replaced a ton of stuff, so chances are something I replaced a week or two ago needs to be readjusted. The list of things I have done to this jeep to get it in shape is really long. Which is why this is so frustrating. I thought I had it close to being trail worthy and then bam the Jeep tells me otherwise.
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Unread 08-27-2013, 12:01 PM   #6
Que89YJ
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You did the O2 sensor and the cat. Check the crank position sensor connector and wiring and the fuel pump connector. Listen for the fuel pump to cycle when you turn the key on-check pressure at the fuel rail. Check for spark at the plugs when cranking.
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Unread 08-27-2013, 06:07 PM   #7
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Originally Posted by Que89YJ View Post
You did the O2 sensor and the cat. Check the crank position sensor connector and wiring and the fuel pump connector. Listen for the fuel pump to cycle when you turn the key on-check pressure at the fuel rail. Check for spark at the plugs when cranking.
I pulled a spark plug today to check for spark and it's there. I also pulled the fuel line at the rail to check for gas and it is there and I can hear the fuel pump prime. The airways all look clear and I cleaned the throttle body. Jeep still won't idle.

Here's the funny thing and perhaps a clue. After I pulled the spark plug I put it back in and the jeep turned over and idled for about 5 seconds before it cut off again. The last two days prior to pulling the plug the jeep wouldn't even fire, let alone idle. So what does that tell us? Vacuum issue maybe?
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Unread 08-27-2013, 06:37 PM   #8
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This new O2 sensor you installed, was it plug and play or did you have to splice the old plug onto the new O2 sensor?
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Unread 08-27-2013, 06:43 PM   #9
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Originally Posted by laybackman View Post
This new O2 sensor you installed, was it plug and play or did you have to splice the old plug onto the new O2 sensor?
Your on to something here and I bet it is reference voltage related.
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Unread 08-27-2013, 07:28 PM   #10
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Originally Posted by jsawduste View Post
Your on to something here and I bet it is reference voltage related.
What I am really interested in is the OP states that the O2 sensor was 'broke' before the O2 sensor replacement. That isn't possible if the engine is controlled by the ECM is it? Not in my world.

scraper: Was that physically broken? Not plugged into the downpipe?
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Unread 08-27-2013, 08:32 PM   #11
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No O2 signal would have the engine staying in open loop. Not the best for drivability.
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Unread 08-27-2013, 08:53 PM   #12
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Quote:
Originally Posted by laybackman View Post
What I am really interested in is the OP states that the O2 sensor was 'broke' before the O2 sensor replacement. That isn't possible if the engine is controlled by the ECM is it? Not in my world.

scraper: Was that physically broken? Not plugged into the downpipe?
The old sensor was physically snapped in half on the part that sticks out of the exhaust pipe. So I was actually able to salvage the plug coming from the wiring harness and no splicing was required. Also I should note the jeep acts the same with or without the new O2 sensor being plugged in.
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Unread 08-27-2013, 09:17 PM   #13
Que89YJ
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You replaced the sensor did you disconnect the battery to clear the calibration and reset everything.
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Unread 08-27-2013, 09:30 PM   #14
Dake
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On the end of the fuel rail is the Fuel Pressure Regulator see if the vacuum hose is on it. I had the same symptoms and mine was just bad and flooding the engine. If Id let it sit for a couple hours it would start up just for a moment and die.
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Unread 08-28-2013, 04:04 AM   #15
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Originally Posted by Que89YJ View Post
You replaced the sensor did you disconnect the battery to clear the calibration and reset everything.
I did, I had the battery disconnected for about 24 hours and I even touched the positive terminal to the negative just to make sure.

About the fuel pressure regulator, can the regulator itself go bad? I ask because like I said the Jeep was running fine, then it went down hill real quick with idle problems, getting progressively worse in a very short period. I took it for a mile test drive, it was fine, then in the course of fixing other things in the garage, starting it and letting it run here and there it started to idle rougher and rougher, until now where it won't idle at all.
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