I really need some help at my the end of my rope on this one.

Have a 4.2SC 120K on the clock, running like a dog, lumpy and rough at certain points in the rev range but floor it and its smooth and pulls like a train.

I do sometimes get the following errors codes:

Lean running both banks
Random misfires on various cylinders especially 3 and 6 but across all.

I have so far done the following.

Replaced all spark plugs
Replaced all coil packs
Replaced ignition systems capacitor
New MAF
new MAP
new oil filler cap
new o ring for dip stick
Checked for vacuum leaks

Any ideas where to go now?

When i had random missfires on my old bosch 4.0 p38 i changed like you coil packs leads plugs etc it was the same on lpg too so i didnt at the time think it was electical however because the lpg learns data from the petrol ecu thats why it was the same on both fuels it turned out my petrol ecu was f.....ked the famous mark adams discoverd this for me

Have you checked the exhaust sensors at all? Alex

2018 Skoda Kodiaq vRS
2009 Caterham Supersport Race car
2007 M5 Touring
2005 Range Rover Vogue SE Supercharged
2004 SL55 AMG

Not had any exhaust sensor errors come up on either bank, but could check them, will plug in the Gap and see what reading I get pre and post cat see if they are at least changing. Good suggestion as troubleshooting guide does say possible exhaust leak.

As for the ECU I guess it could be that as it is the same on gas and petrol but surely that would have wider affects. I will clear the learned data dn see if that fixes it

I would check the exhaust sensors to identify the values. If they are running lean you may well have an air leak in the intake manifold area. It would also explain the lean running errors you are getting.

That was my issue the ecu i was told that basicly the lpg ecu takes readings feom the petrol ecu such as o2 readings and air flow readings as sugested about the air leak thats also i good point if there is more air than needed going in thwn the ecu,s will compensate and try to ajust the fuel mix

Right just checked Gap and can only see live values for post cat bank 1 o2 sensor, not idea how to read the rest that one shows 96 or 97% regardless of throttle position or load, is that normal?

As for air leaks thats what I'm trying to work out but not found one yet.

I have replaced MAP and MNAf and both now have readings that change under load and throttle position both mv and air flow.

Sensors should fluctuate with throttle movements

anyone know how to see all the values with the GAP tool?

Latest update, replaced all 4 o2 sensors and no difference.

Have also done a compression test on all cyclers and all around the same range.

Looked and looked and looked for an air leak somewhere on the vacuum system or air intake, no luck not even with carb cleaner squired everywhere.

Also checked all the plug gaps all good.

Run great under full throttle lumpy under a stable constant throttle position.

I still think its un metered air some where, have ordered a new PCV valve which will arrive tomorrow.

Anyone got any other ideas.

Have you got a exhaust blow even a sloght leak before the sensors will confuse the readings etc

Nothing obvious but how would you check for a small leak?

Have a good look for signs of black soot around the manifold joins etc