Shudder under hard acceleration

[choppedliver]

Hi all,

Just recently noticed a there and not there shudder from the rear left under hard acceleration in 2nd (straight line). It's not always there and it's only really brief and if I have the tune on it's a bit stronger/more readily occurs.

I'm wondering as I write this if perhaps it TC/wheel spin, but what's odd is that it feels like it's the left rear, but the right rear is the one that more readily spins. The weather is cool in Sydney and the car is definitely making more power and traction is lower.

I will monitor and see if it get's worse. I searched and found nothing comparable so I'm guessing it's in my mind or it's the weather.

Thanks

Byron

[vtl]

If its wheel spin you should see the DSC icon blink in your instrument cluster.

[choppedliver]

It happened again under mid acceleration in 3rd today, so it's not wheelspin. I need to do some proper testing on a smooth road.

B

[DR-JEKL]

Hmm perhaps it could be a dead diff?

[choppedliver]

Did some more diagnosis today and I think a call to Advan is in order.

I could only test in 2nd and 3rd, but the vibration comes on somewhere around 2750 and finishes around 3200 or so from application of half or more throttle. It's more pronounced with the tune on, and doesn't appear below or above.

My current thinking is coil or spark, but it revs cleanly to redline no issue so I'm not sure about that.

I managed to repeat it in 3rd over and over again, so that will help diagnosis.

B

[DR-JEKL]

Sounds like the smart thing to do just in case it's something more serious!

Just out of curiousity have you had the wheels off recently?

I remember a while ago a member had a vibration issue, he had loose wheel bolts (maybe go and check them!)

[Jim621]

Sounds like perfect rev range when the boost peaks so you have the highest compression pressure - so id suggest its the spark is missing, and causing a misfire.

First thing would be to check the spark plug condition (the tips might be eroded enough to modify the spark gap).

Regards, Steve

[choppedliver]

So I took the car to Advan, and we did points/plugs, but did not fix the issue. The points/plugs certainly got the engine back to it's original smoothness which was an excellent result.

There were several possible causes for the shudder, but Pete suggest putting a couple of tins of Liqui moly through the engine. the first did nothing, but a good thrash last weekend suddenly clear the injectors and voila it's back to it's old strong self.

So very happy with that result.

Byron

[totti84]

How many KM's do you have?

Have you cleaned your valves or considered it?

[choppedliver]

70,000kms. As long as it runs ok I don't see the need. It pulls very well. I haven't dyno'ed it recently or taken it to the drags but if feels the same as it did at 40,000.

Byron

[totti84]

I'd highly recommend you clean your valves, you will probably free up 10-15kw.

You'll appreciate it when you see how bad they are!