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Discussion Starter · #1 ·
I noticed today when I started up my Jeep that there was a knocking noise that sounded like it was coming from under the PCV filter under the valve cover. I never noticed it before and I installed a Howell TBI last week. I don't know if one has to do with the other. It is a steady knocking. Any ideas what it might be. It is a 4.2L 258 in my '87 YJ. The engine has about 90,000 miles on it. Is this the first signs of trouble? Thanks for the advice in advance.

Donny

1987 YJ 258 I6, 5 Speed, TFI Upgrade, MSD 6A, TFX Exhaust, Smitty Sure Steps, Howell Fuel Injection1999 Cherokee Sport, Stock
 

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Discussion Starter · #3 ·
What does that mean? Is it something I can diagnose on my own or should I take it to my mechanic? Is it ok to drive the Jeep like that or will I cause damage?

Thanks.

Donny

1987 YJ 258 I6, 5 Speed, TFI Upgrade, MSD 6A, TFX Exhaust, Smitty Sure Steps, Howell Fuel Injection1999 Cherokee Sport, Stock
 
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It's probably a lifter not holding enough oil pressure, or it may be the engine can't hold pressure. You could put a quart of atf in the motor oil and hope that there is just some yukk blocking the lifter from getting enough oil, and the atf might clean it out. It's not good, but probably not the end of the world.

 

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You'll hear a ticking noise if a lifter is not able to leak down or does not pump up with oil.

A noisy lifter often is an indication of an oil pressure problem. A noise may occurs when the engine is first started because a lifter has drained when the engine was off. When the engine is shut not running some valves are held open. This puts spring pressure on lifter. The lifter bleeds down. After the engine starts the oil flows under pressure back into the lifter and the noise halts.

Other reasons for lifter noise may be:

A. Intermittent noise at idle:
Dirt in the lifter check valve or wear the valve's worn out.
B. Noise at idle, and it goes away as engine RPM increses.
1. It's wear between the lifter body and the plunger that's out of spec.
2. It could be caused by Low oil pressure, or;
3. Thin oil.
D. The Lifer is quiet at idle and the noise increses with RPM.
1. The oil's full of air. Too much oil in the crankcase and it's being beaten to a froth, and the froth's sucked up into the pump.
2. A bad pump letting air siphon in... and spreading it into the oil gallies. E. Lifter noise at ALL engine RPM.
1. Dirt buildup inside the lifter body.
2. Varnish buildup inside the lifter body.
3. A worn cam
4. A worn Rocker arm.
5. A worn pushrod
6. Low oil volume.
8. Thin oil, wrong viscoity, or too high a temp thinning it out.
9. Worn Oil pump.

It's going to be hard to isolate a bad lifter without teardown. You could purchase a mechanics stethscope and try to narrow down the noise. A good visual inspection of the lifter is usually necessary.

 
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