Bobsteriffic Posted May 30, 2016 Share Posted May 30, 2016 1992 WD21 here, I've got a bit of an engine misfire. At first it wasn't very consistent, but over the past week it's slowly been getting a bit worse to the point where it misses almost always when it's running or idling. Over the course of the last two days I went through and spent time servicing the: - spark plugs - checked spark plugs wires (all functioning as they should) - fuel filter - air filter - checked oil (last change was around 3000 miles ago) and transmission fluid levels - distributor cap & rotor When I pulled out spark plug #6 it did have a slight black film on it and smelled very strongly of fuel, which then led me to change the fuel filter. When I put the new plugs in, nothing changed. But when I swapped out the filter, the truck initially ran a bit smoother, but then started missing again after it warmed up. Either way the tune up seemed to help it a lot, but it still misses and I'm definitely missing a cylinder just based on the shaking and lack of power. I just ordered a new O2 sensor to replace hopefully on Wednesday, but I just wanted to see if anyone on here has any other insight into this. Thanks to everyone in advance! Link to comment Share on other sites More sharing options...
adamzan Posted May 31, 2016 Share Posted May 31, 2016 Unplug the o2, and start the truck. If it runs better, you know that's what it is. If one plug is more rich like that, could be the injector is leaking. If it is, fix it quick or it will thin out your oil and wear down the cylinder walls. Link to comment Share on other sites More sharing options...
Cuong Nguyen Posted May 31, 2016 Share Posted May 31, 2016 It could be a poor faulty ground for the man sensor. It's a common issue. Also, you could have a faulty injector. They can become dead or stuck open. Sent from my SAMSUNG-SM-N920A using Tapatalk Link to comment Share on other sites More sharing options...
Bobsteriffic Posted May 31, 2016 Author Share Posted May 31, 2016 Unplug the o2, and start the truck. If it runs better, you know that's what it is. If one plug is more rich like that, could be the injector is leaking. If it is, fix it quick or it will thin out your oil and wear down the cylinder walls. By unpluging the O2 do you mean completely remove the sensor? Or just unplug the wiring harness (wherever that may be)? If it's the latter, where's the plug located at? Or should I just attempt to track it down by following the wire back up to the engine bay? Link to comment Share on other sites More sharing options...
Bobsteriffic Posted May 31, 2016 Author Share Posted May 31, 2016 It could be a poor faulty ground for the man sensor. It's a common issue. Also, you could have a faulty injector. They can become dead or stuck open. Sent from my SAMSUNG-SM-N920A using Tapatalk Yeah, I also thought it might be the injector. I'm really hoping it's not that though, thanks for the insight! Link to comment Share on other sites More sharing options...
adamzan Posted May 31, 2016 Share Posted May 31, 2016 By unpluging the O2 do you mean completely remove the sensor? Or just unplug the wiring harness (wherever that may be)? If it's the latter, where's the plug located at? Or should I just attempt to track it down by following the wire back up to the engine bay? I'll make it easy. If it has never been messed iwth it should be in that "tree" of connectors on the passenger side. 3 wires. It will have that wierd jacket o2 sensors have on them. Unplug it there, fire her up, and test drive it. Link to comment Share on other sites More sharing options...
Slartibartfast Posted May 31, 2016 Share Posted May 31, 2016 Another vote for the #6 injector. Link to comment Share on other sites More sharing options...
byob Posted May 31, 2016 Share Posted May 31, 2016 A 02 sensor will not cause a p0306 but more likely an p0300 dtc. I would ohm the injectors-11.0-12.0 is new. Anything near 14.0 or above is faulty. To verify the cap and wire set are decent mist water on them to see if you get arching. Link to comment Share on other sites More sharing options...
Bobsteriffic Posted June 1, 2016 Author Share Posted June 1, 2016 Thanks to everyone for the responses! Unfortunately I'm so busy this time of year I'm just going to send her into the shop on Monday to hopefully have a compression check ran and then go from there. Thanks again! Link to comment Share on other sites More sharing options...
Bobsteriffic Posted June 6, 2016 Author Share Posted June 6, 2016 Just wanted to post a quick follow-up response, it was the #6 injector. You guys are damn good at identifying things on these rigs. Thanks again! 1 Link to comment Share on other sites More sharing options...
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