3.8 Mommyvan off idle knocking...

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pishta

pishta

I know I'm right....
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yeah, yeah, dont come knocking! No really, its making a knocking noise just off idle and when power braked to put load on motor. It idles fine, just a random knock and runs great on the road, no noise whatsoever. Just did a 800 mile desert round trip and no issues but its bugging me and my driver wife. I have heard "chain whip" but that sounds BS to me. If that loose, what would it hit and wouldnt it be worse at higher RPM's? or throw a code sue to timing fluctuations? rod knock (but only off idle?) water pump or idler? A/C pump (does it when A/C is off too) or bad A/C clutch? Replaced alternator decoupler already and seafoamed it today, cant tell if it did anything yet, but it was alot of fun! Idles fine, runs great. this is a stock pic but shows nothing the chain would hit to me. Where is the magnum Mopar tensioner! Can I get it this far down while its still in the 06 van? Seems this pic is missing half the chassis.
November14th2010002.jpg
 
My 2008 Jeep Wrangler 3.8 engine started knockin at 18K. They had to put a short block in it.
 
Have you checked side play on all of the connecting rods? Endplay on the crankshaft?

There was a running change (around 04) where they made the timing chain THINNER by about 1/8" (cost reduction). This also required that the timing chain cover also was changed also to accomodate the extra thinner chain. To use the older (slightly thicker) timing chain, you would have to get an older timing chain cover to work with it, they are not interchangeable.

There was also a batch of thin wall blocks (they were 3.3L). When they were tightening the drain plugs on the blocks (one each side) with a pneumatic air gun, they would crack the block and fail the air test afterwards. They were able to get them through using an electric driver to run in the drain plugs. I would not recommend removing drain plugs on these blocks, instead remove a cup plug to drain the blocks. You may crack the block reinstalling the drain plugs if you remove them.

Also make sure you set the cam sensor in the timing chain cover correctly when you put the timing chain cover back on. It is very sensitive and cause it not to start if the gap is too big. They came new with a felt pad that would get knocked off by the cam sprocket. That felt pad was used to set the gap on the cam sensor and the felt pad would just fall into the oil pan.


Could your noise also be caused by the trans or suspension?
 
My wife had some funny knocks like that on a 3.5L and then the arm on the tensioner idler pulley broke a while later. Never figured out why that would cause a knock, but it never did it after a new idler was put on.
 
Well pishta, I have to say since you didnt tell us what van this is, I dont know if you can get it that far in the van. My sisters 93 Voyager with the 3.3, no way!

Beware, her van had the same thing happening at 182,000 miles. Before we could investigate a rod got pulled out the bottom of the number 3 piston. Still have pictures of the piston shrapenal too lol!
 
Might be a wrist pin. My Neon's been dooing that for over 200K miles now. I even re-ringed it at one point for other reasons - everything was fine aside from the noise which sounds similar (but higer pitch and higher in the engine) than a rod noise. It's not present once the rpms climb beyond 1500 or so.
 
Well, wrist pin is easier than a crank if its on the front bank, rear and I'm F'd. Did you get the title? 06 minivan. I may pull pan sun AM if I have the time after a radiator swap and injector o-ring..all before 1300. Kinda smell like gas once in a while. It sound like a heavy knock, I'm guessing crank related..:-( I'll pull belt off and see if it subsides ruling out according drives and water pump.
 
I too had a 3.8 that developed a very light knock, only at idle at around 190,000 miles...Funny thing was, it seemed to start with the only non Mobil 1 oil change I ever did on it (Wal-Mart house brand full-syn, they were out of Mobil 1). I never got into to it to check it out... ran perfectly to 230,000...Then my daughter got hit head-on and totalled it. I had no qualms that it would have continued on for a long time to come, it never got any worse in those last 40,000, and at 230,000 I still didn't need to add any between changes.
So much for me being helpful...
 
pishta said:
Well, wrist pin is easier than a crank if its on the front bank, rear and I'm F'd. Did you get the title? 06 minivan. I may pull pan sun AM if I have the time after a radiator swap and injector o-ring..all before 1300. Kinda smell like gas once in a while. It sound like a heavy knock, I'm guessing crank related..:-( I'll pull belt off and see if it subsides ruling out according drives and water pump.
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Somehow I missed the '06 part. Well I'm out as far as how much you can do in the van. My sisters 93 we pulled the engine through the top, don't know about an '06.
 
We went through this on a Chrysler 3.8 that I bought to fix and resell. It was a wrist pin in our case. Mechanics that had looked at it before has varying diagnosis that were all over the place. Might want to purchase a mechanics stethoscope before you tear in to internals of it.
 
Out the tops going to be tight if i decide to get into it. Pan pull should tell something. 06 was in the body of text, my oversight. Seems majority run fine with this random idle knock forever. I'll post with findings. Thanks all.
 
I think some of the accessory drive pulleys will crack and have a start IP or idle knock.
 
Remove the plug wires one at a time and see if you can pinpoint what cylinder its on.
If the knock doesn't go away with one wire, it could be something totally different.
Those alternators have some sort of clutch drive behind their pulley. Those will scream sooner than knock but could create a knock sound in belt tensioner reaction.
Who knows.
From my old school experience...Timing chains did slap the inside of the timing cover. GM timing chains would wear through their sheet metal cover and toss all the oil before the chain would jump a tooth.
 
Good idea, that should pinpoint what cylinder to check, cross my fingers its in front if anywhere.
 
Dont remove spark plug wires!!! Youll be dumping raw unburned fuel into the exhaust and the catyletic converter will clog/meltdown/catchfire. Not to mention you could ruin your 02 sensors

Get an OBDII diagnostic tool and one by one deactivate each fuel injector.
 
/6 Matt said:
Dont remove spark plug wires!!! Youll be dumping raw unburned fuel into the exhaust and the catyletic converter will clog/meltdown/catchfire. Not to mention you could ruin your 02 sensors

Get an OBDII diagnostic tool and one by one deactivate each fuel injector.
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Hmm, well I pulled each plug wire in the front momentarily and there was no knocking this morning. And in doing that, I pulled every plug wire crimp off the cable! Aww forget it. If it starts to act up again, ill look into. Its running fine now. a little knock between 1200 and 1500 is minimal. My breeze knocked since day one (45K) off idle and its still kicking (and ticking) 120K miles later.
 
pishta said:
Hmm, well I pulled each plug wire in the front momentarily and there was no knocking this morning. And in doing that, I pulled every plug wire crimp off the cable!
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So now you have to get a new set of plug wires?


Maybe use some dielectric grease on the tips of the plugs before installing the new wires, so they will come off easier if you need to in the future.
 
Does it have an alternator decoupler pulley? I've had a few go bad, and it sounds like internal engine noise.
 
Already replace the alternator decoupler, huge difference when that was fixed. New plug wires, yes. I think the wires were just cheap, dielectric would not help as the crimp still rotated on the plug tip. Probably due anyway.
 
pishta said:
Already replace the alternator decoupler, huge difference when that was fixed. New plug wires, yes. I think the wires were just cheap, dielectric would not help as the crimp still rotated on the plug tip. Probably due anyway.
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No, my point was to use dielectric grease on the spark plugs, so the boots, crimped tip will come off easier if you have a need to remove them in the future.
 
OK so maybe I'm an idiot. I think I can pull plug wires at/off the dist' cap one at a time and allow every cylinder to lack spark a few strokes without dumping a half gallon of raw fuel into the exhaust.
I'm amazed at the fuel mileage they get if the fuel is going that fast.
 
They had distributors in '06?:poke:

Sorry just being a pain in the :bootysha:

I wasnt calling you an idiot or anything just relaying what I have been taught.
 
/6 Matt said:
They had distributors in '06?:poke:

Sorry just being a pain in the :bootysha:

I wasnt calling you an idiot or anything just relaying what I have been taught.
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Hey Matt, check this out... LOL!

[ame="https://www.youtube.com/watch?v=n7zfnbdyAW8"]Sean Penn/Jeff Spicoli - You dick! - YouTube[/ame]
 
/6 Matt said:
They had distributors in '06?:poke:
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well, they have coil packs with 6 leads coming off them......Im out. The van runs fine. noise has become blasse to both of us. It is what it is. Thanks all, ill look into replacing pistons when I determine the thing is worth fixing.
 
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