Golf MK4 1.6 engine softly shakes only when standing &on LPG

[77771234]

Hi Everyone.

I would sincerely appreciate your help. Got a Golf MK4 1.6 Petrol & LPG. Used normally for work. Runs perfectly quite on Petrol and LPG but when I am on LPG and stopped (not moving at all) I can feel soft slight shakings transmitted to the cabin by the engine. The shakings are almost un-recongisable still if you are careful you can feel them when stop at a traffic light or so. When the car is on LPG and moving it does not transmit any shakings. While when running in petrol no shaking whatsoever whether while moving or stopped. What could be the issue? Could it be its old LPG system or some air out flow? Have changed the spark plugs recently as well and still the same. Like said it runs perfectly well without any problem, just when careful and the car is stopped you can notice some shaking transmitted to the cabin from the engine which apparently doesnt run as smoothly on LPG. Would appreciate any opinion or suggestion. Thank you in advance.

[paintman]

Petrol & LPG usually run best at different degrees of ignition advance - LPG usually much more & I suspect this may be what's happening.

As an example, my 3.5EFi RRC has been on LPG for years. The LR factory manual gives dyamic timing for my MY as TDC +/- 1 deg @ 600rpm for petrol.

Setting by road test it's better & fine at 6 deg BTDC on petrol which gives better performance on LPG.

I can advance considerably more on LPG but when switched to petrol it's not happy at all so set at 6 deg as a compromise. There are gizmos that change the ignition when switching but I've never tried one.

I'd suggest that what you are experiencing isn't worth worrying about.

[77771234]

Thank you man. I hope as well, it is nothing to worry about.

BTW, was talking to a friend and he was suggesting that it could be a vacuum leak and as such it is felt much more on lpg rather than petrol. Could that be a reason for the shaking?

[E-bmw]

Assuming you have an MPI type LPG system with an ECU, it won't be advance unless it has been poorly set up.

It is probably worth finding your local LPG specialist & getting it in for a service & having it checked out, as a small gas leak when on LPG can cause this & I did have to have an o-ring replaced on one of mine on the car I had LPG installed on.

This caused the same as what you describe.

There is also a filter for the LPG which should be replaced as part of this service.