4.0 ohv slight vibration at 2100 rpm

[Vincenthdfan]

Hello all,
I havent been on here for a while since getting my 93 Ranger XLT back together. I've been out enjoying it...man it sure drives nice and pulls hard with the 5 speed conversion and 97 4.0 engine I installed.

However, I noticed the other day when running down the freeway above 65 mph and at 2100 rpm, there is a buzzy/imbalanced feeling coming from the engine.

Its not in the drive train, its definitely coming from the engine...it never did this with the original 93 engine installed.

Then, when I accelerate to 2500 rpm's I can hear a pronounced rattling sound, almost like a detonation sound, in fact it almost sounds like valve float when you over rev an engine?

Again, it never did this with original engine so it's puzzling?

This engine is in very good condition, has around 125,000 miles on it and runs really well, except in these rpm ranges.

I do feel a slight tremble at idle too, not real bad, but certainly not as buttery smooth as one would expect from an engine with all new plugs & plug wires installed.

I'm wondering if it could possibly be a fuel injector causing a lean condition in one of the cylinders....thoughts?

 

[RonD]

I had that on my 1994 4.0l, it was the fan clutch.

Start cold engine, and let it run for at least a minute, then shut it off, this frees up the clutch
Or test on warm engine after its off

See if you can wobble the fan, if you can it is causing the 2,000+ RPM vibration

 

[Vincenthdfan]

I had that on my 1994 4.0l, it was the fan clutch.

Start cold engine, and let it run for at least a minute, then shut it off, this frees up the clutch
Or test on warm engine after its off

See if you can wobble the fan, if you can it is causing the 2,000+ RPM vibration

Good idea...unfortunately, I already replaced the fan clutch when I did the motor swap (water pump too).

 

[RonD]

New just means "never tested" now-a-days , it used to mean "tested and works", lol, not any more

Test it for wobble, its free

 

[Vincenthdfan]

New just means "never tested" now-a-days , it used to mean "tested and works", lol, not any more

Test it for wobble, its free

I just went out and removed the belt and checked not only the fan clutch, but the new water pump bushings/bearings...no play.

Especially after I thought back about what you mentioned RonD...I remember the sloppy original water pump causing the exact high frequency buzz you mention before I changed it.

This is doing the exact same feeling as it did then, but its a light throttle application buzziness I'm feeling around 2100 rpm...hard to describe.

The 2500 rpm chatter only happens at that light throttle application too...very odd??

 

[RonD]

You could see if its fan belt related

Test and see if you feel it after Cold start of engine, at 2,100rpm or 2,500

Then when you have the time and engine is COLD
Remove fan belt from crank pulley
Start engine and see if you can feel vibration
If not then its coming from a pulley

You can run a COLD engine for a minute or 2 without the water pump, Battery Light will stay on
But no longer than 2 minutes