So I've known about my cylinders misfiring for a little bit now, and have just been trying to limp it around until I got enough money for a new PCM to be installed to fix the problem. But I've run into some issues.

First, I took the truck to get it smog checked, and it failed the first time not due to emissions but due to the fact I had a check engine light on with multiple cylinder misfires (which I thought was BS since the emissions were all perfect). I was told the misfires were due to my PCM not sending signals to the cylinders telling them to fire, so that needed to be replaced. I head down to the local Dodge dealer and get bent over for $1000 for my new PCM to be installed. Problem solved right? Not even close. The truck still idles and runs really poorly after the install. The only thing that changed was the check engine light turned off. The tech who worked on the truck says there might be dead holes in my cylinders, but they wont know for sure until I pay them $400 more just to test it. They also said if there were it would be around $3,000-$3,500 for a new top end on the engine or I might even have to go all out and drop a whole new engine in for $5,000+.

So I took the truck to try and get it smog'd again today since now I've got the new PCM in and today's my cut off date to get it re-insured through the DMV without having to pay a late fee. Since the check engine light is off and my emissions were all perfect before I figured I could at least get the thing to pass now and take care of all the insurance and whatnot.

Failed again, only this time it's because my emissions are too high.

So what could cause the change in my emissions from being fine before with a faulty PCM, to now being too high with a brand new PCM?

I'm really starting to get fed up with all these issues and I'm hoping I can figure out whats wrong with the damn thing since now I can't even sell it since it's got so many issues with the engine.

Any help or insight would be greatly appreciated.

 

Well first off, how long have you had the new PCM? It usually takes about 150-250 miles for the thing to "train" and begin to run closed loop off of readings from the various O2 sensors. Until that time, the PCM is running open loop, which is the same as when a truck is warming up and will dump more fuel. A richer mix will always put out more emissions.

But I question if the PCM was the problem, the misfires on a 4.7 usually point to a head gasket failure or head cracks, resulting in coolant mixing and misfiring.
How's your oil look?

 

Yeah it could easily be due to a head gasket issue. I was made aware of that as well from my oil looking like a milkshake. PCM's only been in for maybe 50 miles, so I might just have to rack up some miles and try and test again before my grace period for insurance is up.

Lets say I somehow do get it to pass smog, is it even worth paying for all this to repair it at this point? I'm at 100,500 miles on the thing already and I'm looking at a new head gasket, full cylinder replacement, or an entirely new engine if I choose to repair it. In my eyes it's starting to look like I might have to cut my losses and get rid of the thing.

 

Yep, I was pretty sure your oil was gonna be funky. If it's a head gasket, no big deal, a little labor intensive, but all will be fine with a replacement. Now if it's the heads, it can be costly to replace them, but do-able. It's usually not the block and I don't consider 100k miles old for a 4.7, hell the 4.7 HO in my Grand Cherokee is still breakin' in at 97,000 miles, LOL.

If you can go 50 miles without a misfire, it tells me it ain't bad and is probably the gasket...

 

It's misfiring all over the place, no way I'll make it 50 miles without that happening. I can clearly hear it through my exhaust you can easily feel the engine having issues as it's being driven. I'm gonna take it in today and just have the engine checked for all that so I can be sure of what it really is. I'm not sure I even needed a new PCM now which would really ruin my day if I find that to be true.

 

There were some 4.7 parts (including heads) in the classifieds. Might wanna check on them and see about picking them up as replacements.

 

i got a 03 dakota with the 4.7 v8 how bad is it to replace the head gaskets?