Hesitant 5.3

Crazybiker51 · September 25, 2014

Had a similar issue with my old 98 until the engine threw a rod bearing a week later so I scrapped it

I feel like I'm beating a dead horse posting however every thread just leads to a dead end

My 2000 5.3 idles fine however when accelerating it's hesitant and will miss until I lay off, however not every time it will do it and will run smooth for miles with no issue, it will do it at all speeds when it does.

Just drove it 900 miles nothing changed nothing got worse, of course got 15mpg

Engine is throwing cel for all 4 o2's, I can clear the codes, light will stay off until I really hammer on it making it miss real bad, however no misfire code appears.

Replaced everything on the 98 and never got anywhere, I don't want to repeat the same with this thing, however I haven't tested fuel pressure on this one yet since I'm out of town, I did clean maf sensor seemed to smooth it for a test drive and that was it, scanner is a Mac unit and says maf reading is fine aswell as fuel and everything else other than o2

Folically Challengjed · October 15, 2014

How are the plugs & wires? I had a '98 5.0L that had the exact same symptoms. The wires were shot, & a new pair had it purring like new. I believe that was around 105K miles.

If bad plugs/wires are causing it to miss, unburned fuel would be sent on through to the 02 sensors, causing them to show that you're running rich. And though it's just a guess, you might not being showing a misfire code, because you don't "hammer it" very often, or for a very long duration when you do. It's my understanding that the computer has to document a certain number of misfires before it actually throws a code for it.

It also might not hurt to do an oil change, in case some of the unburned fuel has leaked-down into the crankcase.

Just a thunk.

FC