Hey, I've acuired a 2001 Dakota 4x4 4.7 with random misfire issues. Replaced fuel pump (didn't have right pressure) coils, plugs and injectors. Cleaned throttle body and intake manifold, all sensors cleaned or replaced and replaced all existing vacuum lines. Still throwing a 0300. Compression check good. I noticed a vacuum line that looks like either it' open or possibly even missing a part? It' near the battery compartment. Any idea what this runs to? Couldn't seem to find it on the vac line diagragms.

 

Just a vent tube, probably for the front axle. Just stick it up somewhere out of the way.

 

yea that's the front axle vent line.

What cylinders are misfiring to give you the 0300 (multiple misfire: see other codes)? You might have to look under pending codes to see what else is being suspected.

I don't see anything about O2 sensors. Have you serviced/looked at/replaced them? The upstreams generally detect misfires on these trucks, though i could have swore the 4.7 had dedicated knock sensors.

 

I replaced both downstream sensors and brake booster. Definitely misfiring though. Not when accelerating but when maintaining speed and rough idle. Slight gas smell from exhaust. CEL blinks when maintaining speed as the misfire get bad. Cylinder 1 and 2 misfire codes and 0202 injector circuit malfunction. Harness is new and injector as well so I'm assuming the wiring is bad. Gonna work that out soon. New belt chirps when turning, need to diagnose that as well.

 

The upstreams are what sets the misfire, not downstreams.

Can you feel the misfire, or does the computer only think it is happening?

Given that last bit, you might have a PCM that has bit the dust. Injector malfunction is a pretty generic code. Also, being the front 2 cylinders also gives me some question marks.

Squealling belt is probably a bad belt or tensioner, belt is getting bogged down form the power steering pump when turning.

If you can't feel the misfires, I'd look at the upstream O2's and double check that #2 injector harness. Might be a good time to look around and buy a handheld scanner that can do live data streaming (I just bought one, have not played with it)

If you can feel the misfires, then I'm wondering of these's something up with how the ignition is picking up the signal from the crank sensor, or if you have a valvetrain problem going on.

And being a 4.7, you might pull the valve covers off. Valvetrain issues are very common.

 

Can definitely feel the misfire. Truck shakes when it happens and idle is pretty bad. Pcm looks to me to be a new remanufactured put on by the previous owner. I' starting to suspect a burnt or bent valve but I hope not. May take it somewhere to get it diagnosed. Can a loose belt cause misfire? At idle the lights flicker. I am wondering if the alternator is not getting the right amount of speed and thus not sending enough juice to the plugs.

Total symptoms are bad idle, fuel smell coming from exhaust, bad fuel economy. When I floor it, it doesn' miss a beat and I can actually keep the 0300 code from throwing when driving that way. Misfire is felt at idle and when feathering the pedal to maintain speed.

 

Your options are rather limited on the 4.7 . I would still pop the valve covers off and make sure there's no foolery going on in there. A bad set of cam lobes or a rocker trying to fall off the pedestal will do weird things.

If you can feel it, then it's not an electric glitch. There's something going on. Since you already put coils in it, that *should* rule out spark. Air is a safe assumption. That leaves fuel.

Is he PCM a 3 plug or 4 plug? Jot down the numbers that are on it (should be a mopar P number if the reman didn't cover it up).

 

Well there' a new fuel pump and filter and I've replaced all vacuum lines. Not sure what else to check with air. It' a 3 port. Remanufactured Sticker says mopar p/n R6040239AG

 

That part number crosses over right. Without a scan tool it's hard to say what is going on then. I'd still pop the valve covers off if you can and ensure there's nothing up with the valvetrain. Aside of that, it will take a shop with an advanced scan tool to see what's up.

 

I'll start with the shop as I am having to drive it right now and will see if they can isolate the problem. If not guess it' time to pop the tops and start feeler gauging. Thanks for your time