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hi just a newbie on here its probably been asked before but gu 4.8 poor throttle response on petrol perfect on lpg throttle body was seized but is perfect now replaced air flow meter with after market one and it was worse any idea's please.and the valves have all been replaced with stainless and seats so head is perfect.
 

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Hi mate - I had a problem with my 4.8 and gas, the opposite to what you've got though. Mine was fine on petrol, stalling and lacking power on gas. Turned out to be a dud stepper motor on the regulator causing the problem but I became fairly familiar with the LPG electrical system during the process and don't recall there being an input for the MAF on the gas system? It had connection for Lambda (Oxygen sensors x2), RPM and throttle position only. Other wiring in the system was to disable petrol injectors, gas shut off solenoid, and the gas tank level gauge.

Could that be the issue? MAF problems not presenting on gas because the feedback from MAF isn't used by the LPG system?

Mines a mixer type, not injected. Injected seems use the feedback (MAP - Manifold Air Pressure in this diagram: http://www.autogas-lpg.co.uk/file/1_wiring_diagram.jpg ) so this only applies if you have a mixer type system, not injected.

I'm no expert but this fits with the symptoms you describe. If it was mine, I'd ask someone in the know what the ramifications of running with the MAF disconnected would be - I know it'll trigger engine warning in the ECU that will need to be cleared at least. Try it with the MAF disconnected on LPG and if it's still fine, start looking at the original and replacement MAF sensors.

We have a Commodore (VE) which has MAF issues from time to time, throws up an engine warning and goes into "limp mode". I bought some MAF cleaner aerosol (I actually use some electronics/PCB cleaner I got from Jaycar, much cheaper). Remove the MAF sensor, give the hot wire a spray, let it dry, put it back in, clear the error and it's usually good for another 6 months. If I just clear the error, it'll happen again within a day or so.
 
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