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Ford 2.9 Weird unexplained issue


Deercamp

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Hello ranger station i recently bought a 1988 bronco ii 2.9 5 speed that had been running like crap, My issue is when warm my truck idle surges at around 400-550 sometimes if i give it throttle it will go back to 900. (this sucks when driving in town and stop and go traffic on hills) it feels like it's about to stall, my truck shakes. When i bought it temp gauge wasint working i replaced the sender and sensor and problem went away for a day sense then i have replaced fuel filter and Fuel pressure regulator problem still occurs. Also i bench tested my fuel injectors all seem fine. I bought a obd1 reader for it and it reads no codes it is weird because i unplugged the o2 sensor (it ran the same) and still won't throw any codes. It runs fine when cold and starts right up. Also this has happened a few times, I would be driving fine and when i switch to say 3rd gear it will rev but not go it will sputter with accelerator fully depressed for about 5 seconds then it will "launch" and go fast almost feels like it wasint getting fuel then suddenly gets a few shots of nitrous (i know that sounds weird) Or somthing was plugged up in the exhaust and it shot it out. Sorry i'm new to all this and stumped that it won't throw any codes, I'm going to check fuel pressure today. Does this sound like a electrical issue? Any help will be greatly appreciated.
 


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adsm08

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This is almost 100% an electrical problem.

Check the oxygen sensor ground. It is a eyeleted wire bolted to the back of the passenger side head. I have had one run like you describe with that ground damaged, even if the sensor was unplugged.

If that is ok on the driver's side inspect the pink/black wire for the fuel pump. I haven't worked on an 89+ extensively, but it the wire routing is anything like the 86-88 then the wire passes near the frame and can rub if things get disturbed just wrong. I have also had this happen where it was rubbed and grounding and it produced roughly the same symptoms as the O2 ground.
 

Deercamp

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Thanks for the reply, i fixed my issue! it wasint the o2 sensor ground but you gave me the idea to check all my grounds, sure enough the ground that's on the upper intake and goes to the firewall was loose i pulled on it and it came right off, i got a new connector on there and tightened it back up also i cleaned a bunch of connectors that had corrosion on it. My bronco runs better then ever! I've been fighting this issue for a month now thinking it was a fuel issue. Thanks again!
 

adsm08

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2WD / 4WD
4WD
Tire Size
31X10.50X15
And that is the ground for almost every sensor on the vehicle, so no surprise that it would make it run screwy.
 


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