This all started at once, so I'm guessing something failed. In fact, it happened sometime while I was at work--it drove fine in the morning, crappy in the evening.

The truck never really liked to idle in the cold, but it has gotten substantially worse with an audible random miss. The idle improves as it warms up, but the random miss remains. It isn't a big miss, but I can feel it and see the tach drop about 100 RPM when it happens.

And this evening, while hauling a load of firewood up a big hill, it was knocking slightly. I had knock issues before, but running 89 octane gas seemed to cure it. Now it's knocking slightly even with the 89. I sure as hell don't want to feed this thing premium!

I'm thinking it has to be ignition related, but the distributor, wires and plugs are new. How about a cam position sensor? Failing cat? The front O2 is new, but the rear one trips the CEL now and again.

Any thoughts would be much appreciated. Thanks in advance!

 

plenum gasket ever been fixed ?
pinging is often related to that, especially since your ignition is all new.
you might try stepping up octane to 91-93 to see if that reduces ping.
cam position - i doubt it.
cat - probably not.
IAC or TPS - maybe.
other vac leak - maybe.

 

I'm actually more concerned about the stumble than the knocking. The knocking could be a lot of other things, and what I heard may or may not have been knocking. Could the plenum gasket cause a random and very slight miss?

 

i don't know. may not be related - but i've got a 98 ford explorer that blows intake seals every 60k miles like clockwork. when it does that, it goes very lean, which flips out the computer, which goes into some kind of default mode, and idles like crap, and turns on check engine light. some code for left bank lean, right bank lean.

my 01 ram will idle cold at around 1000 rpm, and gradually drop to 600 as it warms up.
you might want to pull the plugs to see if you have any fouling ?

 

check your o2 sensor wiring. I had a similar issue but mine was intermittant and it turned out that I had o2 heater fuses and one of them blew because of a short. swapped the fuse, re-insulated the wiring and it was all good.

another suggestion is to set your tps voltage. drill out your tps mounting holes so you can have some movement in it, put a v-meter on the signal wire and dial it in for .7~.75volts.

 

OK, some additional information:

#1, starts right up, idles at proper speed, doesn't surge wildly (every few seconds it drops 75-100 RPM), but the exhaust sounds like chug-chug-chug-chug instead of its usual steady V8 burble. Under light throttle, it is rough and only smooths out at higher (15+ MPH) speeds.

#2, I can smell gas and/or something burning when I start it. Mostly smells like gas.

#3, the plenum is damp inside, but there's no pooled oil. Does this count? For the record, it's pretty much always looked like this, even when it was running perfectly.

#4, while checking the plenum, I fired it up and on the driver's side, there's an irregular tap or click or pop noise that coincides with the stumble. I'm positive that it isn't the injectors nor the valvetrain (which are regular ticks like a clock), and I can hear it better from underneath by the starter. I've been thinking that I had exhaust leak because as I drive, I can hear tapping down by the E-brake under load (it's worse when it's cold), but this sounded different at idle from inside the engine compartment. Could an exhaust leak cause all this?

#5, when it's cold, it bucks noticably when it shifts into OD at about 35 MPH. This started with everything else.

#6, it's definitely knocking. I just squirted 5-6 gallons in it the other day just to get home--could this just be some bad gas? I've never experienced bad gas before, even after a long period of storage in one of my other cars. I'm going to fill it up tomorrow and see.

Pulled codes @ AutoZone: the usual P0138 that I've had for a few months and have been ignoring (post-cat O2 sensor) and a new one: P0307, which is the cylinder #7 misfire. Cleared codes and the CEL came back within 5 miles (I don't know which one came back, but I'm guessing the misfire). Which one is 7 on Mopars?

I'm going to check plugs and wires (even though they're new), but I don't think they're the problem--this started all-of-a-sudden and is consistent under all operating conditions. I'm leaning towards a fuel or sensor/processor problem now.

Keep the suggestions coming! I sure appreciate it.

 

I dont think the exhaust leak would cause a bad miss like what your experiencing... the #7 cylinder is right above the starter though which would make you think the ticking noise is coming from #7. after you check the wires and if you find they are ok, you might want to do a compression test on that cylinder to see where it's at. I had the #8 exhaust valve seat let go which caused a pretty big miss.. no compression in #8. probably not your problem but worth mentioning.

 

sorry to hear of the problems....

it sounds like you are going about it in a systematic way
...which is good and shows your ability.

since you already suspect one side of the V8
you might consider doing either a
static compression test
or perhaps even better
a running 'dynamic' compression test
on those 4 cylinders
http://misterfixit.com/dyncompr.htm

Cylinder #7 does have a bad reputation for problems
including cracks in the combustion chamber

It is a matter of opinion
but you may end up pulling the valve cover on the suspect side of the V8
and whether to do this first or later is up to you.

If you pull the valve cover first,
you might quickly see
a broken valve spring, rocker arm problem, bent push rod, etc.

I do remember other owners who have found that the Magnum 5.9 V8 pushrod end
has worn clean through its rocker arm seat,
and when this happens
a missfire occurs...but it is a relatively easy repair

I like to do non-destructive things first
so I would probably do the compression tests first
before pulling the valve cover because of the wires/mounts/clamps
that have to be moved out of the way.

I might also do a air leakdown test on the driver's side cylinders
and listen carefully for where air might be escaping.

I might also do a swap of sparkplug and wire from #7 to #5
just because it is relatively easy
and as a check to see if the missfire might follow this swap
and it would give me a chance to closely look at the sparplug deposits.

good luck

 

Thanks for the advice, everyone.

First thing I'm going to check are the plugs. I'll pull #7 (I assume the driver's side cylinders are 5, 6, 7, 8, yes?)and have a look at it. If something looks bad, I'll swap them out. Don't know what kind the stealership put in when they removed the broken one. That will give me a chance to check the wires, too (which should also be new).

I'll pull the coil wire and see what's going on in there, too. I believe the coil is newish--I did that and the TPS when the truck was relatively new to me (12,000 miles ago).

I'll clean out the distributor cap.

HankL suggested a compression test and a leakdown test but since the miss is really so slight, I don't think it's internal--that'll be a last resort. However, since others have suggested that a valve spring and/or pushrod might be damaged, I'll check those. Since Hank suggested that the pushrod has a tendency to wear through the seat on the rocker arm, I guess I'll pull the valve cover and have a look around. I can see how that could cause problems if the valve is only opening partially or intermittently.

And I didconsider a leaking injector, so I may pull those and see if there's a leaker. My engine is rusty as hell for some reason (I think my truck was a plow in its previous life), and perhaps the fuel rail has corrupted an O-ring. Does this happen often?

And finally a fresh tank of gas.

Good thing it's 28 degrees here in Cleveland with that horrible ice storm from the midwest rolling through for the next few days... [:@]

Thanks, guys! If you have any other thoughts, I'd love to hear them.

 

drivers side is 1,3,5,7

also VWandDodge (Gary) had issues with crap in his fuel rail, that is something else to consider. there are screens on top of the injectors to keep dirt particles out, when you have them apart, clean them with TB cleaner.