Lambda reading zero on petrol ok on gas

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sandyt

Well-Known Member
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1,615
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Wraysbury Nr Heathrow
Morning all right Eric from here brought his thor engined 4.6 over and we hooked up to Lynx. He is getting really rough running on petrol but ok on gas.
So on petrol lambdas are showing 0v all the time fine on gas and the maf is only showing 16 kg at tick over on petrol. Am I right in thinking that all the sensors are ok due to the fact it runs ok on gas ? leaving the problem with the fuel distribution on petrol ie fuel rail pressure injectors etc ?
Ta for any help
 
Lengthy running on gas can wreck the ECU fuel trims tothe point of almost no running on petrol.

This is due to the burn cycle of gas and petrol being different, the ECU is trying bring the fueling back into line byt basing its results on what the sensors are telling it from running on gas.....so when on petrol all the fuel trims are out if whack.

Try resetting the fuel trims and see if that works, if not it could be dirty petrol injectors through lack of use....gas tends to gum them up.
 
Thanks Saint yes reset them and they lasted about 2 mins then went back to zero my thoughts are like you injectors filthy on another note looked at a 2007 supercharged on 80k miles looked and drove ok so maybe just maybe but then what would I do with the time
 
You've got to reset the fuel trims and drive it on petrol alone until the fuelling is sweet. Then drive to your lpg tuner and get the system mapped to the current good petrol fuel trims.
 
sandyt.

Don't know if the MAF reading is used on Gas but, mine was running like a bag of sh**e (petrol only). MAF reading 15 on idle which is low. Fitted new Bosch MAF and it's now running perfect. New MAF reading 22 on idle.
If Gas doesn't use MAF reading it could be your problem.
 
16KG is too low for the petrol trims to cope,replace the Maf with a decent one,recheck the airflow.Look for 22-25kg at idle,more than 90kg at 3000rpm,engine hot,all loads off.
 
Sandy, I did loads of reading on the net too & agree the Maf looks suspect. I took a chance & ordered a new Bosch one. It made a huge difference but then needed the adaptive fuel trims reset. A friend with a Solus diagnostic did that & it showed a misfire on 5 & 8. A new set of plugs cured that. The O2 were still not switching correctly so we put the original O2 sensors back. Hey presto.... They work & it goes like a rocket. Just need the gas reset now to match the petrol. Looks like it was the Maf but also faulty or incorrect o2 sensors. Let's see if Island 4x4 refund. Thanks again for you help. I am sure I will see you again. If I can help, please call or if you need my car to test anything.
Eric
 
Perhaps the calculated "demanded torque" and actual torque being delivered is more in line with the what the gearbox programming is expecting?
 
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