Hello,
I've been having a long term issue with a misfire code. P0303
Because of the mil light, I wasn't going to pass NYS inspection.
I replaced most of the ignition parts, blah blah.
Did a compression test wet and dry, and #3 is consistantly 60 psi lower than all others.
Anyways I finally broke down and went to a professional.
I had reset the puter, checking valve springs. Took it in with 42 miles after reset and it passes inspection, because the mil had not popped yet.
I asked the mechanic to run a diagnostic as well, even if it passed.
He said nothing came up, had no answer, but he gave me a dressing down because of some of my mods.

Halo plugs
Dixie Caps
K&N filter
cat back split exhaust
DIY ram air design

He said that the ECM was not designed to work with these parts, and I was being a dope trying to re-engineer the truck.??????? That I should remove all mods, leave well enough alone and trust Chryslers engineers, they know more than me.
Now I had always read that the ECM will adjust to new data.
This forum is full of people modding.
My mods helped with gas mileage and pep.
60psi low means that the mil light is gonna pop again. The truck has only 44,000 miles on it, mostly highway. The mods have been in place since 10,000 miles. Because of the mods I think he passed it and chose not to investigate further, kept saying ECM might be bad.
I'm a DIY'er, always have been, intend to continue. Puters, cars, electronics....

So what am I suppose to believe here?

The truck has been very disappointing, but I'm not interested in going into debt for a new truck. The Dodge mechanics would not even put the right amount of oil in the pan, so I do not trust them.
The truck runs nice, except for the code, so I would have never noticed, except for the code.

Any thoughts appreciated.
ty

 

are you loosing oil? if its 60 psi didfference you have a problem with the headgasket or part of the head.

 

No sir, the plug is pristene, it still gets great gas mileage. All the plugs are good looking in fact. The code only pops at hot idle. It sounds good screaming down the highway, purrs sweet like.

Only test I have not done is a leak down, no compressor.
I pulled the valve cover just to check the valve springs.
I was hoping that an engine diagnosis, with a computer, would confirm the psi loss. He said that you can only do a psi test, manually. This flies in the face of info on net.?????????????????? He could have done more checking I think, like a leak down test. But, he just wanted to blast the mods. Like I said, I think he saw the mods, then went minimalist with the checks. No code, all good. Kept mentioning the ECM, said the mods required a flash upgrade for the mods to work with the ECM.
So I do not know what to believe.
Why's it so dam hard to find a mechanic that will talk to you and go the extra mile. They usually get paid for it.

Ultimately I needed an inspection sticker, I got it. But if I'm destroying the motor, I want to know.
The leak down will tell me if its a gasket? I will just build the test unit myself, and run down a compressor I guess. Its just everything I've done to date has failed, the professionals just are not much help, either.??????????????????????????????????????????? ???????????

 

the maximum variation of psi for the 3.9 is 40psi. so with yours being 60psi off you gotta have some sort of head damage. are you getting coolant mixing with oil? thats my thinking. but try swiching plugs to oem recommended. maybe your plug wire is bad. i dunno

 

All is new.
Only thing I have not changed or or physically looked at is the head.
No, the plugs are pristene.

 

Thanks for the info folks, but I was hoping to promote a discussion on what this ASC certified mechanic said.
I mean he was blasting a K&N filter add.
I realize that I can only push things so far without changing the computers parameters, but I don't think the little bit that I've changed, is that big of a deal. I read plenty that says the computer is a little adaptable.
Listening to the guy indicates that the aftermarket parts industry is a scam, but.....

 

Nobody?
Gentleman, come on now. 96 views and only Thunder responds.
Why is an ASC cert mechanic calling the aftermarket industry a scam? That to add a K&N filter is no good.

 

I have an '01 with a 4.7L and 193,000 mi. and I am getting ready to put the K&N on mine. I put a Specter that I got from autozone on it two years ago, that is a cheaper version of the k&n. I put a flowmaster exhaust on it last winter and it sounds and runs great. The only code I have is for the tps and that is because it is bad and I need a day off to go get the part. I don't know how much modding can be done before your computer can't compensate for it, but judging from what I have read on this site, it doesn't sound like you have gone far enough to find out. The thing that sucks is the aftermarket world seems to cater to the Ford and GM crowd and has little respect for those of us driving a Dodge. I still have not found a good place to find upgrades for my 4.7L.

 

Don't you mean ASE certified mechanic and not ASC? If somebody working on my car told me they were ASC certified I would be scared

 

oops, yes.