OK...here it is. I can floor it, run it as hard as I want on flat ground and no knock. 30 seconds into a hill and it starts clacking. only a 4% grade or higher. 30 degree cold night, 90 degree day...same same. When I crest the grade and head downhill (I do this drive every fri and sat, you go from a 6% up hill to a 6%+ downhill in 30 seconds) it's still there if I give it 1/2 trottle or more. Then, after a 1/4 mile or so down the hill, it goes away, but it's gradual. 92 mazda navajo, 5speed, 4L ohv. Full oil(15W40).
Almost seems like it's starving for oil, like the clack when it hasen't ran for a couple days, that first second after it starts, but oil psi is good on the gauge. Any thoughts.

sounds like it may be time for a new motor...how many miles are on the truck?

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I have a similar situation, but I am unconvinced that the noise is engine knock. Could it be the transmission rattling, or perhaps an old exhaust heat shield that has come loose?

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1993 XLT 4x4, 4.0 liter, Auto, 149,000 miles, reg cab, stereo, air shocks.

There is one thing the 4.0s have that causes them to display a knock. Not saying its the same problem but it can cause it. Recently I was hearing a knocking or loud tapping noise that seemed to go away when I revved it up. I did some research on it and discovered that they have a timing chain tensioner that wears out and can cause it. I replaced it and my noise has completely gone away.

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1994 Ford Ranger XLT Supercab 4.0 5 speed 3 inch suspension lift 31/10.50/15 Dakota Definity M/T

Hope not. odo says 40,000. Missing a 1 or 2 for sure. I had to put a trans in it about 5,000 ago.

I'm also having a similar problem but only when my engine gets hot. Get a knocking when trying to get power from it at low rpms, if you rev it up past 3,500 rpm no knocking. Its a old '94 4.0 ranger and at one time sat still for almost a year. Going to look into that timing chain tensioner

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1994 Ford Ranger XLT 4.0L 4X4
140,000 miles

Possible clogged oil pickup tube?

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2000 Ford Ranger XL 2.5L 5-speed RWD 3.73 open - 122,000+ miles
Total Payments: 8/12
Buggman LED 3BL/CARGO, stang dome, Buggman Stang Dome LED conversion, Buggman LED Brake Light conversion, Throttle Cable Mod, Line-X O.T.R., Coil-Pack mod, Air silencer/snorkel removal, expo lit dual-visors
Coming Soon: OHC & auto-lamps/auto-dim mirror
2.3L Headgasket/TIMING/Water Pump replacement guide
Haha

That's about what I was thinking. Marvels mystery oil? Any other suggestions?

Valve clatter. My 94 4.0 does it. Only going up hills though. As crazy as it sounds my mechanic told me to use premium gas to keep it quiet and so far it's worked great and the motor is smooth and silent

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94 Ford Ranger
V6 4.0L 2WD
Rough Country Leveling Kit
Hydro 8000 Shocks
31x10.50x15 Yokohama Geolander ATS
15x8 Cragar Soft 8s

Huh!?! Gonna put some octane boost in it before I do the hill tomorrow and see what she does. Does sound like valves, but I never considered octane as a cure. If that helps, sea foam here I come. Thanks all.