VT has flat spots on fuel, works FINE on LPG???

[lordmuz]

Hi all,

I bought my VT a year ago, and at the time it was a cheap buy, neither running 100% on petrol or LPG (It is factory LPG, with an IMPCO gas mixer). Over the last 12 months, i've got the LPG system sorted (the converter needed a new sponge and a couple of parts relpaced). The LPG side works sweet. No hesitation on acceleration, idle is nice, plenty of power.

Now, to the fuel side..... Fuel has major flat spots in the low RPM range (during take off etc) but all through the rev range (low RPM at low speed is more noticable). If you're travelling at 100k's an hour and put your foot down it seems fine on petrol. But if you are taking off from a standstill, even if you plant it and let it rev to 5,000 rpm you can feel the flat spots.

Here is the list of things i've done to try to rectify the fuel system at low RPM:
1: New fuel filter
2: New spark plugs
3: New air filter
4: New ignition leads
5: New throttle body & IAC valve
6: Cleaned Plenum Chamber thoroughly
7: Replaced PCV valve
8: Replaced all injectors with new ones
9: Replaced fuel rail
10: Replaced fuel pressure regulator
11: Replaced fuel pressure regulator vaccuum hose that connects to plenum

See this thread for more details about my experience changing the injectors, fuel rail, and FPR and cleaning the plenum (with lots of pics) if you're interested:

http://forums.justcommodores.com.au/vt-vx-holden-commodore-1997-2002/93638-howto-replacing-fuel-injectors-cleaning-plenum-chamber-vt-commodore.html

I have cleaned the MAF sensor with CRC MAF sensor cleaner. The ECU is not reporting any fault codes.

However, when you try to take off from a set of lights (especially if you floor it), it surges and doesn't feel right at all. If I drive on LPG it is perfect. My VS (other car) is really beaut on fuel (it has an aftermarket LPG conversion). Runs excellent on either petrol or LPG.

Although I don't use petrol much (prefer LPG due to cost), I want the car to run right on either fuel.

Can anyone suggest what else I can look at - i'm running out of ideas. :bang:

 

[buzuki]

id tip AFM, its prolly had backfires and blown the arse out of it.

 

[lordmuz]

id tip AFM, its prolly had backfires and blown the arse out of it.

Considered that, so I swapped the MAF from the other commodore (VS) with the VT. Exactly the same result. The VS works fine with either MAF. I sprayed the connector contacts with CRC contact cleaner etc etc.

Any more tips?