Hi guys, I bought my XG not running on fuel very well at all, but great on gas. Over the past few months i have been trying to get it to run on fuel properly. After replacing the MAP sensor, TPS, Oxygen sensor, Idle speed controller, Injectors, Fuel pump, Fuel filter and cleaning out the throttle body. I am pretty close. (Gee this car was a mess!!)

I am currently experiencing a wandering idle and idle hang time. I checked my isc and at idle the voltage starts at 10.8 but then slowly creeps to 14v and closes completely and my idle drops as if my isc is disconnected. My oxygen sensor is also showing that the car is running rich. (showing 0.85v at ecu). So from this i reckon i have a vacuum leak. However NO HOSES ARE LEAKING that i can find.

After going through the vacuum hoses there are a few blocked off for the lpg. However the wierd this is that the PCV vent hose is not connected to the throttle body, it is connected to a vacuum tree on the inlet manifold after the throttle body!!! This is causing the PCV vent to rattle all the time for some reason. The vent on the throttle body has been blocked off with a hose and a bolt in the end. And the hose going to the purge solenoid (where the charcol canister is) has also been blocked off. (connected to inlet manifold and disconnected and sealed at purge solenoid end)

The hose coming out the of rocker cover at the back has just got a oil breather on it.

My questions for you are! (if you could please help)
1. Should the pcv vent hose be connected to the throttle body, not a vacuum tree on the inlet manifold?

2. Does it matter that the purge solenoid with the charcol canister is not connected at all on gas or lpg?

3. Do you think this could be the solution to my idle woes!!!!!

This is quite a common issue on E series falcons.

Firstly it is a good idea to change your PCV valve pickup position. You can buy a plastic base plate with hose fitting attached that goes under the ISC from Ford or a good LPG installer.
It comes with a balnk off grommet for the original position (I recommend you fit it with a hose clamp on it so it doesn't come off with the first backfire you have) So then fit the plate to the bottom of the ISC and plumb the PCV valve hose to it.
If you are running the metal PCV valve it will rattle cause they have different flow rates and springs when compared to the original plastic PCV.
I fit a restrictor to the hose to fix this problem and it will maker the metal PCV flow the same as the original PCV. You can use anything that will fit snugly inside the PCV hose and thye drill a 4 mm hole in it. This will still enable good crankcasen ventilation without allowing the PCV to rattle like hell.

Then you need to make sure your tune is right. Make sure engine is at operating temp. NO fault codes on a engine run test. BASE idle speed set correctly and Timing are all correct. All sensors must be reading correctly especially ecu coolant temp sensor. Make sure throttle body is cleaned.

Once this is all done you need to do a idle speed re-learn procedure. This is the fix for hunting idle and idle speed that hangs for a long time.

Pull the ground off the battery and leave off for 1 min.
Refit and start engine on petrol. drive vehicle normally for 5 mins.
Come back home and park vehicle.Make sure all accesories are off so no extra loads placed on engine.
Leave it in drive with AIR CON ON and handbrake on. Allow to idle like this for about 3 to 5 mins. Then place in neutral with air con on and allow to idle for another 3 mins. Then turn air con off and place in gear again. Allow to idle for 3 mins. The neutral and idle for another 3 mins.
Done.
Now switch car off allow to coool for a bit and then take it for a drive.
9 times out of 10 this fixes hung idle for me. The 1 time it doesn't is cause i have overlooked something that is wrong like coolant sensor reading (be sure to clean the terminals at sensor as they have a nasty habit of corroding and messing signal). Another one I missed was poor ECU earth.
Make sure ALL your earth's are perfectly clean. Any voltage drop on sensor or ECU earth's will play havoc with EFI control.

I have been working on E series falcons for many years now. I learnt this at Ford when I worked there as a 2nd and 3rd year apprentice and it has served me well all my career and I still use it sometimes.

Generally petrol performance degrades due to that side not being used very often - usually look at fuel delivery, pump, filter, regulator, injectors.
If it's running good on LPG, usually that means the ignition system is okay, as any weakness shows up on LPG more than petrol. Having said that, check plugs, leads, etc as it sounds like they mightn't have been changed for a long time.
Yeah, should be connected as per a normal petrol only setup.

Make sure the rear rocker cover breather is drawing fresh filtered air - if the hose is connected downstream of the mixer, it will be getting LPG/air mix - not too good if a backfire occurs. In this case, normally the hose goes to the air cleaner box.

Thank you "blownba" and "snap0964" for your quick replies to my questions. It has helped out heaps.

I'm going to go out on the weekend and get one of those isc plates to plum in the pcv valve. I can't understand why all the gas installers don't use this. It make more sense instead of blocking off the normal vent hose connection on the throttle body and moving it to a vacuum tree on the inlet manifold. Thus causing a vacuum style leak like it had in my installation.

Before i get the isc mounting plate, I thought i would just ask another quick question. What would happen if i just reconnected the pcv vent hose back to its original factory position on the throttle body? Is this bad for an lpg setup? In theory as it is sucking from the rocker cover and putting the vented gas back into the throttle body it shouldnt make a difference. The only problem i could see is that if the lpg was to go the other way and go into the rocker cover aswell as though the throttle body. This i'm sure would cause some problems? Feel free to correct me, i'm only guessing.

Also just to put my curiosity at ease. What would happen if i got rid of my gas ring and plumbed the lpg from the convertor straight to the throttle body (via the vent hose connection that i wouldnt be using as im going to get the isc plate)?. Would this be a way to get rid of the restrictive gas ring. Or would it be a way to blow up my engine and maybe myself aswell?????

Cheers guys, your input is really valued.

PCV hose normally goes to a vacuum tree on the manifold in a petrol only setup - my metal one's setup that way without any idle probs, although if it's giving hassles, try the plate as recommended. That pipe near the throttle body is for air into the rocker cover rear in a petrol only setup - not a good idea on LPG as mentioned, as LPG/Air will be flowing through there to the PCV. You'll find for the PCV valve there probably isn't much vacuum developed for it there - normally needs to be on the head side of the throttle body flow wise.

Most rings uses venturi effect to draw LPG into the airflow, so not a good idea. There are low restriction mixers like GRA, etc, but you may need to change the converter to suit also - you'd have to weigh up $$$ value.
The only way to remove the mixer completely is to go to LPG injection.

thanks guys, you answered the questions i needed. Cheers!!!