I have a 2004 Dodge Dakota with 5 speed stick and a 3.7L V6. 2WD.
I hadn't started my truck for about a month and we had a few sub zero days here. When I went to start it the battery was dead. I jumped it and got it started but noticed a very loud noise coming from the engine. It sounded like something was going to come out through the top. It has 135,000 miles on it. I replaced the spark plugs but the same noise is present. I finally found that if I unplug the coil on CYL#6 (rear cylinder on passenger side I think is #6) the loud knocking stops although the engine runs rough whether or not #6 coil is plugged in. Any thoughts?

Thanks in advance for your ideas!

 

Your description and how the sound was manipulated sounds like it could be a rod bearing issue.

 

Thanks for the reply!
I guess I am thinking of this wrong.
I figured if it was a mechanical issue, it would make the noise whether the cylinder was firing or not.
Thought I would swap coils with another cylinder to see if problem followed.
No go, #6 still makes the noise when the coil is plugged in.
Could extreme carbon buildup cause a similar problem?

 

OK. first of all I bought a code reader.
OBD II PocketScan Code Reader Model CP9125
It's pretty basic but it reads the codes.
The only codes it read were showing when I had coil connectors pulled loose and the IAT sensor - high voltage, which I also had pulled loose.
I ran the truck several miles and it popped and knocked the same way as before.
When you accelerate, there is hesitation before the power kicks in.
It also runs pretty rough but not to the extent of dying.
Shouldn't it be throwing some codes if it is in any way an electrical issue?
I read it again when I got back home and there were 0 codes.
I just thought that because the knocking/popping stopped when I took the coil connection off that it was electrical.
Thanks for any help/thoughts!

 

You do appear to have a bad rod bearing. One test is to pull the plug wire and see if it goes away. Electrical problems won't make a knock.

Is it possible that something got into the engine? Water or oil maybe? It may have caused a hydraulic lock that bent the rod?

You can try the easy stuff first. Pull the valve cover and verify that valvetrain is working correctly.

 

I'm going to go with a hydro-locked engine, or you had water in the oil and the water froze.

 

Why does it not make the noise with the coil connector unplugged?
When the cylinder is firing it is putting a load on the rod and associated bearings and such?

 

correct. Without ignition, the piston is just freewheeling.

 

Yep magnet is probably right. Check your oil to see what color it is(milky etc). If you don't have the proper anti freeze levels then the water can freeze and expand in the block causing it to crack.

 

How was the oil level when you started it? If it was low to begin with and it's been sitting for a long time....

Usually when I have a vehicle sitting, I pull the injector or fuel pump fuse so it will crank for a while without starting. The idea is to get some oil circulated via cranking before cold start RPMs.