Yep - it's a misfiring cylinder (sorry - had to state the obvious). Could
be due to lack of fuel (clogged/non-functioning injector/damaged injector
wiring/failed PCM), lack of spark (fouled plug, bad wire, bad distributor
cap), or lack of compression (stuck/burnt valve, blown head gasket, cracked
head) - just to name a few possibilities.
Quick tests to eliminate problems are: swap plugs and wires #5 to #7 (on
both ends - plug end and distributor end). Clear the codes, and run it
again. If the misfire moves to #7, you've got either a bad wire or bad
plug. Next bleed the pressure from the fuel rail (either through a test
port, or pull the fuel pump fuse and run the engine till it quite), then
unbolt and pull up the driver's side fuel rail, and swap #5 and #3 (#7's
harder to work on) injectors. Put it back together, and see if the misfire
moves to #3. If so - bad injector.
Next thing would be to perform a compression test, at least on #5, but I'd
do the whole left bank (so you have numbers to compare to - do the other 4
if you're ambitious). If compression is low (<130lbs., or greater than a
10% difference compared to the other cylinders), a leak-down test is in your
future to determine where the compression's going. At that point, you get
into more serious engine work.
Of course - there's always the off-the-wall type of causes... a friend's
truck started running rough, acting like it was down a cylinder. He was
also hearing some valvetrain noise. After doing some basic tests, we pulled
the valvecovers (not as easy on a V-10 - damn intake plenum), and discovered
a missing (yep - MIA) pushrod, with a rocker arm just flapping loosely back
and forth, doing not much of anything. Pulling the lower intake manifold
revealed the missing pushrod laying at the back of the lifter valley,
minding it's own business (and slightly bent).
Sometimes, you just never know until you tear into things...
Tom is right, literally could be anything and you could even get
misleading successes. I chased a P0307 problem on a 97 RAM 5.2L for over a
year. With the help of this group we tried many things and several times
thought we had it nailed until the problem came back a few days, weeks, or
few months later. Always on the same cylinder and progressively harder to
keep it cleared for any length of time. ONE OF MY SYMPTOMS we discovered
late in the diagnosing was that once we had the code cleared (just by
resetting it with a scan tool) we could keep it cleared by never allowing
the engine RPMs to *ever* fall below 800 (i.e., holding your foot lightly
on the gas while at a traffic light).
Solving this could be as easy and cheap as rerouting & separating your
plug wires to prevent cross-firing; it could be as hard and as expensive
as a cracked cylinder head. Cylinder misfire codes can sometimes be really
tough to accurately diagnose because as we discovered there are so darn
many variables that can cause it. We ended up finally going to a dealer
where they did a full top end overhaul, replacing both cylinder heads
(complete, all new heads, valves, springs, rockers, plugs, wires, etc). I
honestly cannot say with any degree of certainty that the dealer actually
"pinpointed" the cause as much as they literally shotgunned the whole top
end by replacing literally everything it could possibly be. Only after
teardown did it become evident that the #7 intake valve seat was cracked.
Hopefully yours won't be as difficult or as expensive to find.
Like I always tell folks..........
start diagnosing from where the last guy stopped,
or.....take his word for it that what he checked.....
(I refer you to yer original post)
~takes a toke.....sips his crownroyal~
You *REALLY* lucked out! My P0307 ended up costing over $2k after a
year-plus of trying just about everything. Just goes to show the wide
range of things that can cause a cylinder misfire code.
With your luck you might want to pick up a lottery ticket.
Understood. I had a similar costly experience a number of years ago with a
Chevy -AFTER- putting in a brand new (not rebuilt) long block. Worst
mistake I EVER made aside from buying the Chevy in the first place. The
initial 100K was uneventful but it sucked a valve at 105k. Silly me,
rather than sell the bones for scrap I thought the pristine body and
never-smoked-in interior was worth dropping a new mill in it. Then the
tranny went... then the rear end started howling. Somebody ended up with a
P.O.S. '69 Camaro with a whole bunch of brand new parts in it.
Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here.
All logos and trade names are the property of their respective owners.