The V8 Owners Forum -

Hi all,

My 3.9 Discovery 1 has started to misfire/judder really bad below 2000 rpm and at light throttle. Seems to go away at higher rpms

It is particularly bad on a cold morning and results in a big drop in power / judder.

The system is a Bigas Sequential (SIGN).

I have replaced the plugs to NGK BPR6ES and gapped to 0.8

New leads

New distributor, rotor, cap and ignition module

New coil

Could it be a sticking injector?

I have purchased a data cable to hook into the Bigas ECU.

I have taken a video, I apologize for the shakey video and background/road noise (It's an old squeaky land rover :/)

https://goo.gl/photos/j3eyGBk1VDk43atj8

Air leak or poor electrical connection somewhere would be my starting point.

You say you have new HT leads, if they're standard then ditch them and get good quality 8mm leads.

LPG puts a lot more stress on the ignition system so any weakness will show up on LPG but may not show when on petrol.

I had a judder at high load / speed, which after replacing lots of ignition components turned out to be the MAF. Petrol was fine, LPG juddered.....

Chris.