Factory dual fuel AU getting bad economy on both fuels and won't rev hard

[Bushbasher]

The short version -

- Fuel economy bad on both petrol and gas
- engine won't rev past 4k RPM on petrol
- at 4k RPM it runs clean at 1/2 throttle but grumbles and labours at full throttle
- engine won't rev past 5k RPM on gas but runs clean all the way at WOT although wheezy
- all ignition electrics good
- both fuel systems appear to be good
- had a gas tune
- had injector cleaner
- replaced fuel filter
- replaced crank angle sensor
- cleaned TPS
- cleaned TB
- no vacuum leaks
- exhaust from cat back is less than 3 yrs old and still looks as new, no rust, tarnish or dents
- when the gas tune was done it was plugged in to a diagnostic unit and didn't throw any codes.

any ideas why it won't go and is getting crap economy?

** replacement cat will be picked up tomorrow and fitted.



The long version -

This has been ongoing for over 12 months now to varying degrees. I think I've sorted it out and it comes good for a tank or 2 then starts getting worse again. The failure to rev hard is a relatively new symptom and I'm not sure if it is coincidental, symptomatic or something I've now caused.
Ok, I'll start from the beginning of this latest attempt to cure the bad economy issue. The wagon runs on LPG 99% of the time so I originally thought it was a gas only problem but it can't be, more on that later. ok, the wagon was getting very sluggish, especially at higher revs above 3500rpm and was just running out of stem completely by 4k and the economy was going away plus going up even a shallow rise it was starting to struggle and was downshifting like it was leaning out or something so I got a gas tune done. This didn't seem to make much difference. Then I got a whiff of gas one day so thought it was leaking gas which explained the bad economy and possibly the poor performance if it was leaning out so I traced the leak and fixed it. No change. Then I decided it might just be that the old donk was getting tired so I did a dry compression test on the cold engine. The results were disappointing with 2 cylinders at 90psi and the others at around the 115-120psi range. So then I did a wet test to see if it was the rings or the valves and squirted some oil down each pot and did the test again and all the pressures came up to around the 150psi mark, so rings not valves, bugga! I've subsequently done a compression test on a fully warmed up engine and all compressions came in between 170-180psi so definitely not a compression issue. This is where I discovered it wasn't a gas only problem as when I started the car back up and took it for a drive to clear out all the oil in the cylinders I decided to switch it to petrol to help wash the cylinders down to help clear the oil and discovered the engine wouldn't rev past 4k. Then I realised the engine was struggling to get to 5k rpm on gas. Thinking I had 2 separate problems now I thought I'd fix the gas problem first so just thinking it was the plugs fouled with the oil I put in to the cylinders I changed them for no change. Then I thought it was running a bit lean at high RPM so I gave it a full turn on the high speed adjuster to see if it would help but no joy. So I was stumped. Plugs are good, leads and coil are good, everything runs ok at low RPM just bad economy 420km from 68L highway when it should be closer to 520km. So I turned to the petrol side and I firstly tossed a bottle of injector cleaner in the tank and replaced the fuel filter as it's never been done in 350k km but it made no difference to the problem, still won't rev. So I thought I'd do an economy test just to see and only managed a paltry 600km highway from a full tank. So now I'm thinking it has to be a problem common to both fuels so first I thought it might be a faulty crank angle sensor not letting the timing advance under load so it's been changed, for no joy. I'm confused as to how it can pull to 5k RPM on gas and do it cleanly yet only pull to 4k RPM on petrol and at anything over half throttle the engine grumbles and shudders like the timing has been retarded too much. Put it in gear and floor it and it'll pull to 4k and only run clean to half throttle yet hit the gas button and suddenly it runs clean and continues to rev to just under 5k although slowly and wheezy like it's leaning out. So now I'm picking up a replacement cat tomorrow to see if that makes a difference but If this doesn't fix it I'm running out of ideas.

Anyone got any ideas where to look next? ?



Cheers
Bushbasher