It's back, and this time back with a vengance.
P0307 (cyl #7 misfire)
Those who have followed my plight know this saga began a year or more ago.
Various things at various times have solved or rather mitigated the
problem to a greater or lesser extent for a while, but this time it's back
and not quite but almost a steady-state hard failure. Clearing the code
and it comes right back within the first 5~10 miles of town driving.
'97 Ram 1500 5.2L, 80k miles
Work done over the past year to date: (all Mopar parts)
new rotor cap
plug wire rerouting TSB applied
flushed injectors (several times)
cleaned combustion chamber
checked compression (135~144 lbs all cyls)
52.8 psi fuel pressure
swapped #5 & #7 injectors, problem stays on #7
Problem seems to occur most often when decelerating from 25~30 mph to a
complete standing stop in gear, i.e., approaching and then sitting at a
light with your foot on the brake. All of a sudden you feel a faint
flutter in the idle and 10 secs later the MIL lamp is on. Sitting in the
shop idling in gear and you can see the misfires counting up, 8~10 in the
course of a couple minutes, all on #7. The only code being set is P0307.
What next, Doctor?
Real simple - it's on the back of the throttle body. Two Torx screws and an
electrical connector. While you're at it, just remove the whole throttle
body (four bolts from the top, once you take the air cleaner off), strip off
the IAC, the MAP sensor, and the TPS sensor (all remove the same - just a
couple of screws), then give it a good thorough cleaning with some TB
cleaner. When you put it back together, leave the IAC uninstalled. Plug
the electrical in, and while holding it, have someone turn on the ignition
(but don't start the truck - it will rev to redline!), and watch the
movement of the IAC pintle. It should cycle all the way out, then all the
way in, then settle to a position somewhere in the middle. This should all
be smooth movements. If it's not, or if in doubt, you can try cleaning it
as well, but a replacement isn't that much money, either.
Before embarking on this, pick up a new throttle body gasket - 50% chance
you'll trash the old one while removing the TB.
Well, 100% chance of trashing the old TB gasket so your suggestion to pick
up one paid off. Harder to get my ass up in there to reach everything than
it was to R&R
Okay, all squeaky clean now. Had lots of carbon. Tried the IAC test OK.
Reassembled, drove over to Autozone to have them clear the code. Darn
thing coded again sitting in their parking lot idling. MIL lamp didn't
come on but the code came up again on their scanner within 1 minute of
restarting the engine. Trans in Park, idling w/AC on. Shut the eng off,
cleared it again and restarted once more. Idling it comes backwithin a
Cleared it again. Restarted the truck again and immediately kicked the
idle up to 1500 RPM. Sat there 2+ minutes at 1500 rpm wasting $2.59/gal
gas, all seemingly well. Let it idle back down and it gave a P0307 almost
What's next? Could the plug maybe be fouled again? This is beginning to
get a little tiring.
I just went through a similar experience and found that one of my engine
valves was running right at the end of the range of a hydraulic lifter
and as the engine got hot stopped the exhaust valve from totally closing
causing a misfire. Ended up taking that engine apart twice. The second
time took .025 off the end of the valve and problem went away. Yes
before I did this I replaced the Idle Air Control motor which didn't
help at all. I also was going to replace the MAP sensor before I
determined it might be a valve but didn't so saved that $50. After the
second assembly I ended up with a tappet noise but found I had only
installed it backwards so it didn't have chance to pump up. 5 weeks
later I believe I might have an engine that will go another 75,000
before it will need much work.
Good luck, Ron
Ahhh yes, the old "grind .025 off the valve stem trick. Had to do that
once to a 396 Chevy motor with solid lifters that got a little
over-zealously cammed and the springs were going into coil-bind, popping
off keepers and dropping hardened-steel valves deep into fragile aluminum
places where they weren't welcome. Sucking a valve at redline while
reaching for 2nd gear makes a very distinctive sound. The second time it
happens, the phrase "Awwwshit!" just doesn't seem adequate ;-)
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