1997 3.9 Engine Knocking
1997 3.9 Engine Knocking
06-02-2008, 03:17 PM
The vehicle tends to crank over 4-6 times before she fires and when it does catch, I can hear this knocking sound coming from either the front of the engine or at the bottom and the sound does not go away. Sounds more in the front.
What might this issue be as I am new to the 3.9 and do not know a whole lot about the common problems with these engines.....
06-02-2008, 08:01 PM
It could be a spun rod bearing. Does your oil pressure drop off significantly after the engine warms up?
06-03-2008, 07:11 AM
Oil pressure stays the same.
I have an auto stethescope and I chekced around the bottom of the oil pan and towards the top front of the oil pan and the noise seems to be more prominent around the front top of the oil pan.
06-03-2008, 06:36 PM
You might have gotten lucky, it sounds like it could just be the timing chain tensioner instead of a rod bearing.
06-04-2008, 06:44 AM
After you stating info about the oil pressure, I actually paid close attention while driving yesterday and the oil pressure is up and does not come down even after warm up, when I give it fuel it stays the same, the pressure does not fluctuate in any way.
Although the guy I bought the truck says he runs 20w50 in there, I have only had it a month and have yet to switch oil.
What is the average cost of a new timing chain and tensioner and how is the install for timing?
06-04-2008, 08:52 AM
About $100 and 6 hrs. of time to do it yourself.
About $600 to have a shop do it.
Oh, and get that 20w-50 out of there as soon as you can. It's costing you at least 1 MPG and is straining your oil pump along with it's drive shaft and your timing chain.
06-04-2008, 03:58 PM
I'm thinking the bearings are bad and the PO used 20-50 to prolong or cover up the prob. Try the right oil and see what the pressure does then.
06-04-2008, 07:54 PM
If the bearing are worn (or spun) the oil pressure will drop off significantly after the engine warms up. That is why I had asked how the oil pressure was. Since the pressure is holding high and steady, one can safely assume the bearings are okay.
The 20w-50 is another story. If the PO ran it year round, it would've prematurely stretched/worn the timing chain and it's gears. (In the winter 20w-50 is like molasses until it gets hot.) This is due to the fact that the oil pump is driven off of the camshaft, which in turn is driven by the timing chain.
06-08-2008, 07:11 PM
I think you should remove the cover for the timing chain. Advanced or Auto Zone have a tool loaner program. It would be cheaper to borrow a harmonic balancer puller from a friend.
This will save you a lot of money. If you live in a hot climate the oil isn't that bad in a cold climate it will cause you problems in the winter.
Pull the cover and tell us what you find.
06-08-2008, 07:22 PM
I took ALLORO's advice and drained the 20w50 in place for Valvoline Max Life 10w30. The knock has went away considerably and the oil pressure is still the same. The knock is still there but not as prominent. I am not too concerned at this point as it does sound alot better....
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