sensor issue maybe

[Comanchejess]

Hey guys, I am having quite the confusing issue. My beloved 87 MJ has had a misfire for quite a while and I've been trying to run it down. After replacing my fuel pressure regulator, I thought my next issue was my MAP sensor. I replaced it, only to end up cleaning connections and putting the old one back on, as it wasn't the MAP sensor itself, but a vacuum line that ran to it that was cracked and split. After I tracked all that down, I noticed that when I plug the vacuum line at the back of the intake it seemed to run quite a bit better for a few minutes, but then she'll die. She also seems to be idling a little high, and even with the new pressure regulator is still running very rich. 

 

I have a Buddy who had similar problems in his tacoma. He changed the plugs and o2 sensor(s) and that seemed to help his truck. My exhaust is rusted through in several places, including right at the manifold, so I'm wondering if it could be an o2 sensor/exhaust issue or more of an intake/air fuel ratio issue or an issue with some different sensor or maybe the throttle body? I'm almost out of ideas here and anything can help. 

 

Thanks to everyone on here who reads my page and helps to track down these issues to keep my (mostly) stock Renix on the road. It's a cool truck and hopefully will be cool for years to come...

[JustEmptyEveryPocket]

2 hours ago, Comanchejess said:

including right at the manifold

Based on this I would guess your O2 sensor is seeing (or thinks its seeing) a super lean condition. It conveys this and your ECU dumps in more fuel to compensate.

 

The MAP vacuum line is also essential for getting the correct fuel and run conditions.

 

Fix your exhaust so that, at a minimum, there are no leaks before the O2 Sensor. Make sure the vacuum line to the MAP is complete and undamaged. Then report back.

[cruiser54]

Have you been to www.cruiser54.com and completed Tips 1 through 5 yet?

Checked to see if any intake manifold bolts are loose?

[mjeff87]

Id wager a bet that I could take my 9/16" offset box end wrench to any Renix era XJ/MJ and get a half turn tighter on every intake/exhaust manifold bolts.  Start there.