Thread: rrc engine harshness 1500~rpm

Originally Posted by sven58

Hi all, my 90 classic (4.6) has a harshness in the engine in the range of 1500 -1800 rpm when driving thru that range on part throttle.
The sound /vibration was there before the 4.6 conversion but much less. Anything that can buzz or rattle seems to vibrate in sympathy.
I have ordered some softer engine mounts (bearmach anr 1808),as the new ones i fitted during the engine swap are much firmer .(2 different sets, 1 of them genuine.)Of course I threw the originals out.!
Has anyone had experience of the harmonic balancer rubber going hard with age? regards Steve

G`day ,

Does it use the std ignition system ?

Could the roughness be the engine missing through that range ?

Do you know that 4.6 are not balanced as finely as a 3.9. They depend on the crank angle sensor to measure the acceleration of each cylinder and the ECU to fine tune each injector to balance the engine pulsations.

Regards Philip A

No its not a misfire. New engine and megajolt coil pack ign. It was doing it with various ignitions mufflers engine mounts etc. Its just a harshness with a buzz/rattle. Engine mounts arrived 2day, thats my next step, thanks,Steve

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Originally Posted by sven58

No its not a misfire. New engine and megajolt coil pack ign. It was doing it with various ignitions mufflers engine mounts etc. Its just a harshness with a buzz/rattle. Engine mounts arrived 2day, thats my next step, thanks,Steve

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G`day ,

The factory set up can have a miss if the alternator wire runs close to the ignition amp and at around those revs so my questions .

The 4.0 ltr is not as well balanced as the 4.6 ltr , we have one of each one in an 84/5 and the other in an 94/5 , `ive never noticed any vibration , roughness ETC other than when a head gasket is leaking . Then they just have a roughness down lower in the revs .

If they are the normal type engine mounts the round ones i`d be surprised if there was any difference unless the engine is actually laying over and touching something at those revs .

It would pay to check whatever is on the other end of the crank to the balancer .

Does it use V belts ?

Hi i dont have a distributor, i have crank triggered coil packs, so Im discounting a misfire. I assumed all mounts would be pretty much the same, but there are softer ones out there. The bearmach version from the uk are supposedly softer. The remnants of my originals which i cut off are definitely softer. The genuine and aftermarket mounts I tried (stc434) have a hard rib in the centre which feels like steel, the originals have a soft rib which deforms under thub pressure. Ill just have to wait for them to show up. Thanks for the replies Steve

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I had a vehicle in last year that had a bad vibration after changing the drive plate. The torque converter ended up in a bad spot in the crank adaptor. The engine didn't vibrate on free revving, just under throttle at around 1500rpm. I ended up getting another crank adaptor machined up to get away from the wear spot.

To diagnose looseness at the converter nose, you could undo the converter from the drive plate, then manipulate it through the inspection hole in the bottom of the bell housing. Any free movement in the vertical direction would be suspect.

Yeah you could be right about the torque converter, when the new mounts arrive ill have a look. Cheers , Steve

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