I'm trying to diagnose a problem w/ a 5.3 truck engine that is in in a Jeep wrangler. It is running a flashed F-body PCM running the 5.3 program.

When you rev it to about 2k + it revs somewhat smooth but you can hear a change in tone every half a second

when you go to drive it, it bucks/surges and sometimes wants to die (mainly when you arn't on the gas and then give it gas)

I've check for vacuum leaks, I'm not perfect, but I'm sure I have cleared up any vacuum leaks. I checked the fuel pressure and it is getting over 50psi. I also switched out the throttle position sensor w/ one off another engine and it still does the problem. I also switched the MAF on it- still does the problem

what do you guys think I should do? could it maybe be one or two bad coils? anyone know how to checked the coils?

let me know anything you guys think I should try and I will, I need to get this thing fixed!

 

Any codes being thrown?

 

Pretty sure it's in the tune, did u change throttle bodies? If so it will need to be recalibrated for airflow more than likely, mayb a tuner will chime in

 

yeah the throttle body was changed to an LS1 style (drive by cable w/ TPS and IAC sensors) it was also tuned for it

no codes are being thrown

this really has me stumped

also to add, it only does this when it is at full operating temperature, on a cold start up you can rev it up to 5k and it is nice and smooth

 

Then you need an adjustment to the tune. When it gets up to temp it goes into closed loop and aparently has a calibration issue.

 

I had this problem in my car when I just copied over 5.3 tune into my LS1 tune. It make my O2s switch too fast and it surged rich, then lean (probably 2-3 times per second).

 

so do I need to get it tuned?

I unplugged the o2 sensors and ran it in open loop and it ran flawlessly, so it is either the o2 sensors or the tune

what do you guys think I should do?

 

If is relatively stock, it very well could be a bad O2 sensor.

 

Either o2's or tune.

 

alright guys, well the o2 sensors are brand new (they are tucked away where you can hardly see them)

is it pretty involved to tune them in? I have a tuner, but he mainly works on f-bodies and not truck engines