4.2l engine knocking

Dropped the gas tank down a little to take a peak. Think I found my return line issue. If I’m not mistaken, that pinched soft line is the return line.
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My theory on why this became an issue all of a sudden?

Rusty bondo’d skid plate that was flaked apart plus no hold down straps to hold the tank to the skid plate plus driving around hitting bumps eventually lead to layers of rust and debris build up under the tank that pressed the tank up into the crossmember/tub and pinched the line. Any returned fuel couldn’t return and increased pressure.

That’s my story and I’m sticking to it. At least until I get my new skid plate and new soft lines installed and the problem persists.
 
Caver Dave said:
Isn't that "Mr.Gasket" device post-filter a regulator?
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yes sir it is. It seems to be helping with the running issue. However, the upstream lines seem to be under greater pressure than they should be because of the regulator.

Waiting on the new skidplate and hold down straps to reinstall the tank. Hopefully have all that by 2:30 tomorrow.
 
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Little update.

Couldn’t for the life of me get the fuel pump outlet compression fitting to seal up and not leak. Tried two different hardlines fitting, one being new. Nothing. Pulled he pump, exchange it on warranty (I’m still suspect of that pump being a major culprit), cleaned up all my softlines, routed new softlines on the tank, went to install the new skid plate… my dumb ass ordered a 15 gallon skid plate and I apparently have a 20 gallon tank. So I used some fencing wire and wired the tank up in place while I wait for the new skid.

So now, I fired it up with the new MC2100, filter, pump, softlines, pressure regulator, and…. All is GREAT.

I did find the supply and return lines pinched above the tank. I’m halfway thinking someone installed an aftermarket 20 gallon tank, and used the OE 15 gallon skid, compressing the whole assembly up tight to tub. If that’s even possible.

Now to wait for the new skid plate and it’s back to the knocking issue. That should prove fun I’m sure. But hey, it’s running smoother and easier than it has since I bought it.
 
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I need an update on this! I have an 84 CJ seven with a knocking in the same scenario as you. I’ve heard from someone else it could be chain slop but I’m very fearful to dig in. I’ve got three kids and not a lot of garage time these days!
 
Alexthephotoguy said:
I need an update on this! I have an 84 CJ seven with a knocking in the same scenario as you. I’ve heard from someone else it could be chain slop but I’m very fearful to dig in. I’ve got three kids and not a lot of garage time these days!
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The engine knock? Still clacking away. I said fawk it, run it till something lets loose. It’s definitely my #5 piston slapping around. The only fix for that is a rebuild and boring out of the cylinder. Still debating on what engine I want to put in. For now, run what ya brung.

If you’re trying to diagnose it as being piston slapping around, run the engine and unplug spark plug wires. Listen for a change in the slap. At idle mine was quiet, pulled the plug wires and it started slapping. I’ve heard of the reverse as well.
 
I've got a 30k mile all aluminum 5.3 waiting for my 258 to die, but it just won't. My theory is, AMC used all kinds of parts from other manufacturers including Buick for engines at one time. It's not a stretch to believe they would have used a GM engine in 83 when my CJ was built if it was cheap for them to do so.
 
willness33 said:
I've got a 30k mile all aluminum 5.3 waiting for my 258 to die, but it just won't.
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willness33 said:
I've considered a 360 as well but I have this LS already paid for. 360 would adapt to my brand new ax15 a lot cheaper.
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I'm playing with the idea of swapping an aluminum LS into my loaner car if you ever want to get rid of it :D
 
willness33 said:
I've got a 30k mile all aluminum 5.3 waiting for my 258 to die....
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And this is the other part I wrestle with. My #5 piston slaps like a cheap pornstars cheeks that just won't quit. I know it's gutless, and would take a good deal of investment to get any kind of power out of it, but it would be fun to do it and say that it's original. Then have a level of comfort that the damn thing will never die in my lifetime. there's something about straight 6 builds that does intrigue me.
 
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mbalbritton said:
And this is the other part I wrestle with. My #5 piston slaps like a cheap pornstars cheeks that just won't quit. I know it's gutless, and would take a good deal of investment to get any kind of power out of it, but it would be fun to do it and say that it's original. Then have a level of comfort that the damn thing will never die in my lifetime. there's something about straight 6 builds that does intrigue me.
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Anything short of v8 sound and giddyup wouldn't fulfill my dream for this rig. I could be talked into a vortec 4200 with a sushi slicer after a few beers, though. The 258 will probably never die and I'm going to get all of the good out of it.
 
440 Mopar big block is pretty exciting - just sayin
 
mbalbritton said:
The engine knock? Still clacking away. I said fawk it, run it till something lets loose. It’s definitely my #5 piston slapping around. The only fix for that is a rebuild and boring out of the cylinder. Still debating on what engine I want to put in. For now, run what ya brung.

If you’re trying to diagnose it as being piston slapping around, run the engine and unplug spark plug wires. Listen for a change in the slap. At idle mine was quiet, pulled the plug wires and it started slapping. I’ve heard of the reverse as well.
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Drive it to Canaveral next month and meet me at the port lol 😂
 


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