You'd be suprsied how much an O2 makes things go haywire, i would deff check em if theyre original....mine were shot and for weeks the truck "did what it wanted" idled funny, misfires always from different cylinder combos, the truck would slow down when i was hitting the gas, mpg was horrible, etc..

 

All hardware is on as it should be. The 02 makes sense. It is original and was not replaced after the plenum repair. May be awhile till he gets it done, since he retired he dosen't get in a hurry for anything.

 

i am haven the same problem with the random missfires and sounds like a hugh vaccum leak at times i have changed plugs wires,idel air sensor and nothing has fixed it.is there a way to check each o2 senser at home with lil tools,cause auto zone says they cant find out witch one or if all are bad?

 

Check all your injector o-rings at the intake. There's your source. If you can't find it anywhere in the lines and, even if a vac reading proves to be good at around 17-20 on the gage, it's most likely at the intake ports.

Check by taking a rubber hose up to your ear and place the other at the injector at the intake port. It will hiss when you get to it. Usually the two rear ones on either side.

The vac leak is the root cause for misfires due to the fact that it's allowing more air in. It's leaning out your fuel mix thus causing it to run lean. When it runs lean, you get misfires.

The O2 sensor is supposed to monitor the output and if it senses lean A/F mix, it feeds back x-amount of voltage to the ECU. Then the ECU adjusts the mix so it reads better at the output. But, the problem is, the other chambers that have the leaks are still running lean thus causing misfires while the remaining chambers are running richer.

At the final output, the mix looks good to the O2 sensor. But, it's not good at the chamber level as it's still lean due to a major gross leak. In that case, it is not enough of an adjustment to correct the problem of a lean mix in one or more of the chambers and, as a result, you get misfires.

Chris

 

I never thought of an injector o-ring being the cause. I'm having a similar problem thats been driving me nuts for a while.

 

It sounds like my idle when my O2 sensor went bad. Replace your Pre-cat O2 sensor.

 

It's something that is not well know I suppose. I had it happen after putting in a new set of injectors not too long ago. I had a high rpm at startup and knew I had a vac leak someplace. I put a gage on it and it read fine. No issues though the rpm range. But, I could hear it. I was quite aware about injectors leaking but, I have never had it occur on my truck. I got out the tube and there it was. Took seconds to find it.

Upon pulling them out, I wanted to find out why it was leaking. The o-rings that were shipped with the injectors were undersized by 25 mils on the OD. The max allowable is 15 mils deviation. I yanked out both rails and replaced every single o-ring with some high quality o-rings. Problem solved.

Always remember, tops leak gas, bottoms leak air.

 

I think thats probably one of the problems with mine, but it isnt the worst of it. When mine starts up, it has a fairly high and a little shaky idle. It sucks air like crazy for a couple minutes until it is driven a mile or so up to about 2000-2500 rpm. Once its been warmed up, it only makes a very slight and hard to hear sucking noise, that I presume to be an o-ring. Pre-cat O2 sensor has been replaced with a Bosch, new IAC, new Coolant Temp Sensor. I guess that leaves the AIT sensor.

 

The AIT would throw a code 23 if it was out of range. That should not be an issue. Check for vac leak or, air in your fuel lines. Air in the fuel lines will cause a shake. Also, a lean mix would also cause a shake due to an imbalance across the cylinders.

 

Tried some WD-40 on the vac lines to see if I could get it to rev a little, and the idle stayed consistent. I bled the fuel lines not too long ago when my dad used his injector cleaner. I pretty much had to because I got one hell of a shake, but this isn't like that.