4.0 engine knocking

[rovercanus]

Hey everyone. I just posted this on pirate and copied it here to get a variety of opinions.
I have a 2000 d2 4.0 with 62k miles on it. I've had it for a year and run synthetic oil in it for about 11k miles. I'm running a K&N oil filter. 20w40 Castrol Syntec
Recently, in the last couple thousand miles I get a knocking noise. At first I thought it was exhaust leaking as it was not a sharp rap but lately it increased in volume somewhat. Not real loud but more noticable by me.
On start up and idle the engine sounds fine, when it's put in gear the noise increases and when I start to move I start getting the louder, I hate to say it, metalic rap.
I was thinking connecting rod since it happens under load but the noise goes away after running under load for a few seconds which sounds like a lifter.
I'm running seafoam in the oil to see if it frees anything up.
The noise isn't always consistent either. Some days I'll get the rap, others I don't.
If it is a rod, can I get away with just changing the bearings for now? I know it's cheating but I really can't afford a tear down. If it's a lifter what is best to free it up.
I need to change out an engine mount, maybe it would be a good time to open up the sump and check the oil pick up tube.

 

[andrewv]

Check it with a scope to really get an idea of where the rap is coming from. We had one that was driving us nuts, as it sounded like it was coming from the oil pan. We then thought maybe it was something in the transmission, resonating through the pan. We took the inspection plate off, and voila! There is a small allen screw on the flywheel that serves no purpose, and sometimes it will tick against the starter. You can try taking that out and see if it helps, but if it doesn't, you could have a cracked flex plate. This is, of course, assuming that the noise is back there and not in the engine.

 

[rovercanus]

What are you refering to when you say flex plate?
It definately sounds like it's coming from the engine but the ex had a cherokee that had transmission noise that transferred to the engine. Where do I check for the screws?

 

[andrewv]

Flex plate is on the back of the flywheel, in the transmission. On the bottom of the trans, there is an inspection plate held in place by 3 screws or so. Take off the plate, start it up and put it in gear to see if it's louder. Does it always do it in gear? Worse in reverse? Never in park? Does it sound like something is bouncing around?

If the above are true, you will then need to remove the inspection plate on the front of the transmission housing. Turn the engine by hand and look for an allen screw about the size of a pencil eraser. It it's been hitting the starter, you may see a nick in it. Try taking it out and see if the noise goes away.

This all assumes you can get the vehicle on a lift and get it over your head. Otherwise ! Call me at 303.810.9401 if you want to discuss further.

 

[rovercanus]

I didn't realize an auto transmission had a flex plate. It's worth checking out the fly wheel bolts, it could very well be coming from there.
It doesn't always happen when it's in gear.

 

[andrewv]

We've always called it a flex plate, but it could be called a "tyre" for all I know It doesn't always happen in gear, but does it NEVER happen in park? There's only one of those screws, by the way.

 

[rovercanus]

It will do it in park.
I was refering to the bolts that hold the torque converter to the fly wheel.

 

[D Chapman]

You sure it's not an exhause leak? Or a loose O2 sensor?

 

[rovercanus]

I'm hoping it's an exhaust leakbut I'm finding no evidence of that yet.
I'll check the o2 sensors.
I was also thinking of an alignment problem because of the broken motor mount.

 

[D Chapman]

I bet that is all it is. I have gaskets at the house if you need one. Also, since it's getting cold, if you need a garage to fix your mount at, come on by.

 

[rovercanus]

Thanks Dan. I'll do it at the shop at work. Most of my tools are there. I guess I'll wash the mud off the bottom first so it doesn't poor into my eyes!
I'll take a closer look at the gaskets when I'm under there.

 

[andrewv]

Figure it out yet?

 

[rovercanus]

Not yet.
When I do my engine mount I'll kick around the exhaust system again.
If I don't find it I my check my oil pick up tube in the sump, even though I'm not getting oil pressure light.
Then one day I'll need to change my valve cover gaskets, at least then I can check the upper valve train.