Thread: P38A bad vibration in engine

Originally Posted by DEFENDERZOOK

i was gonna mention the flex plate too.......

but i would start with a harmonic balancer.......



you gonna be home this weekend......i might try and pick up that pump to get it out of your way.......

I'm free!

Ron

Originally Posted by rangieman

a long shot but could it be the flex plate cracked or broken

years ago i had a falcon the torque converter came loose and that thing shook like hell

I had considered that. I replaced the flex plate not long ago after it broke (200 km from home!). The noise prior to complete failure was totally different, it clattered and banged but not in anyway in time with engine rpm. As the engine rpm increased, the engine smoothed out and the noise went away.

Ron

Maybe I have an answer.

On Friday, Derek from Modern Motors at Dungog (ex-LR dealer) had a play with the car and he thinks it's misfiring on 1 and 2 cylinders. Removing the injector electrical plugs on those cylinders made almost no difference to the running of the engine. There's good spark to both cylinders.

As the problem is evident on LPG and petrol, it has to be mechanical or an electrical timing problem on those cylinders. They don't share the same coil so it isn't that. The car has a new coil pack.

The timing is set by the flywheel reluctor ring passing by a crank angle sensor.

So this arvo I put an oscilloscope on the output of the crank angle sensor.

This is what it looked like.



From the left (disregarding the first spike), the first pulse with the different shape is the one that sets up the timing. The reluctor ring has a missing tooth (intentional) to to identify TDC on no. 1 cylinder. Those pulses are 10 degrees apart - there's 35 pairs of teeth (don't forget there's a missing tooth to make up the 36 needed).
From the workshop manual:

The output signal from the CKP sensor is obtained from the magnetic path being made and broken as the reluctor ring teeth pass the sensor tip. The reluctor ring has 35 teeth and one missing tooth spaced at 10° intervals. The missing tooth is positioned at 20° after TDC.

.
Note, however, waveform 1-1/2 pulse further to the right. It's smaller than all the others. I wonder if it's being misread by the ECU and upsetting the timing.

Tomorrow I'll remove the crank angle sensor and examine the reluctor ring. I suspect one of the teeth may have broken away which will mean gearbox removal and replacement of the flywheel - the reluctor ring isn't available separately - naturally! It ain't cheap. I'll replace the flex plate at the same time.

Any comments?

Ron

assuming youve eleminated

the TC and drive plate
the harmonic balancer
ancillaries
Valves not sealing proplery at higher RPMS
then given that wave form the 2 dips are possabley the answer...

However these can be cause by the harmonic balancer if its not playing the game vibrating the timing ring (lots of different names for it) If your donk has it mounted on the harmonic balancer.

Also check the cleanliness of that ring We had a falcoon come in last week hissing and farting like you wouldnt believe and 2 minutes with the gurney to clean up the never been cleaned engine had it running like a dream again.

Originally Posted by Blknight.aus

However these can be cause by the harmonic balancer if its not playing the game vibrating the timing ring (lots of different names for it) If your donk has it mounted on the harmonic balancer.

The reluctor ring is on the flywheel. I'll remove the bellhousing cover plate today and check it.

I can't check the flex plate nor TC until the gearbox comes out. If it comes out, the flex plate will be replaced as a matter of course.

Sticking valves is a possibility. These engines are quite bad for fouling the valve stems and causing problems with the valves not sealing. LR later came out with a carbon breaker design and some cars had them retro-fitted under warranty. It was only done if the custmer complained.

Ron

Well, good news, bad news.

I put the car on the hoist and had a look a the reluctor ring. Yes, the low signal was from the welded pole.

The spacing between the arms of the pole was a greater than the others. Closing it up brought some improvement. Adjusting the others which were higher levelled their outputs to the same as the others.
But it didn't fix the vibration.

However, removing the cover plate from the front of the bell housing allowed noise to escape. More anon.

Shortly after, another ex-LR dealer mechanic (DefenderZook) turned up to give me a hand. He noticed a clicking from under the car. He couldn't work out from where it was coming. But I was pretty sure.

So I removed the small disc cover plate from the bottom of the bell housing and a piece of steel plate fell out. Uh-oh. It looked like flex plate.

Yep, we rotated the flywheel and soon found the flex plate was broken away around one of the bolt holes.

Oh well. It's good that it confirmed my long held suspicions that the plate had failed. It's bad 'cos it means taking the tranny out this week.
I'll order a flex plate and flywheel/reluctor ring tomorrow (public holiday today).

That's 16,000km from this plate, 15,000km from the previous plate. Why?

Ron

why....?



to let you know that you have 15,000kms to get rid of it before it breaks again........

its an auto thing...

real flywheels have a decent amount of meat in them so they can deal with all the crap we deal out to them...

in seriousness its a rotational stress thing..

If you dont get the mounting bolts all to exactly the same tension,
if the thing is off center by a piddle fart
if you over tighten the bolts to the tc
if theres a weak bit of metal or a heavy part in the plate

its going to be out of balance, it spins pretty quick and has torsion put onto it from near the edge. (also having it driven against the starter doesnt help it.

normal flywheels are quite so bad as they have more metal and the drive is transferd out from nearer to the center.

These are all compounding factors, you could have just managed to pick the 2 bad ones out of the batch.... (itd be about my luck too)



And I dont even get to bag autos on this one as this is all before any part of the auto.... Bugger.

best of luck with the repair job.