Runs on LPG not on Petrol

[Hamsteh]

Hey folks,

So I was running low on lpg the other day, flicked over to petrol (while on the move) and had zero combustion - it just died away. LPG is running fine, but had zero luck on petrol at all.

Today I've been playing with it a bit and managed to get it to fire after priming 3x, and it ran seemingly fine for about 3 seconds then stopped instantly.
I've only managed to get it to fire twice and both times it stopped almost immediately. Most of the time I get nothing, not even a splutter.

Things I know/have checked:

• Fuel pump appears to be priming
• Work fine on LPG
• I cleaned IAC a few weeks back (so I perhaps damaged it?)
• Tried unpluggin MAP sensor - no change
• Don't think it's CKS as this kills LPG also

What do we think? Googling suggests a few options including IAC, PCM, factory immobiliser.

I'm still running tests but thought I'd throw it to the brains trust while I'm at it.

Cheers folks,
Alex

[offroadfreak]

My XJ does the same thing, will be interested to read people's opinions

[rainman]

I would be looking at fuel pressure/ blocked fuel filter.
runs after you prime it 3 times, then stops. = no fuel pressure@ injectors?
IIRC the immobiliser stops ignition.
Pretty sure the iac is used by the pcm to maintain idle rpm when the extra load of the Air con comes on(among other things). Does it run at idle at with the ac on ok with lpg?

other wise could be worth looking at the box on the LPG side that disables the injectors.
Good luck with it

[Richard buttocks]

How old is the petrol?

[Hamsteh]

Originally Posted by rainman

I would be looking at fuel pressure/ blocked fuel filter.
runs after you prime it 3 times, then stops. = no fuel pressure@ injectors?
IIRC the immobiliser stops ignition.
Pretty sure the iac is used by the pcm to maintain idle rpm when the extra load of the Air con comes on(among other things). Does it run at idle at with the ac on ok with lpg?

other wise could be worth looking at the box on the LPG side that disables the injectors.
Good luck with it

Thanks for the help mate, yeah I'm going to borrow a mate's fuel pressure tester tomorrow to check primed pressure in the rail. The thing is it doesn't reliably start after priming. It's only done that twice with a decent break in between.

LPG runs basically fine all the time. I've had an intermittent rough idle with some missing for the past 6 months or so (which is why I cleaned the IAC to see if that would help). I should have mentioned that I have previously damaged my CCV ports in attempting to remove them so there's likely some sort of vac leak there too - but its been like this for at least a year.

How old is the petrol?

That's a good question... the jeep doesn't get driven much at the moment so it's certainly got at least a month or two on it. That said, I've definitely had much older fuel without any issues.

Appreciate all the help so far folks, I'll be testing fuel pressure tomorrow hopefully and see where to go from there.

[bleetnblurt]

relay fuel cut out or solenoid
they do need to shut fuel off when they run on LPG

[Hamsteh]

Okay so updates from today:

My mate's pressure kit did not fit the XJ, probably due to them being Porsche specialists...

BUT! It started on petrol first try and didn't stall out at all. I stopped and started it a few times with no dramas and drove the whole way home on ULP.

We plugged in his scanner and got three codes, two of which were the MAP sensor and Manifold Temp sensor (which I unplugged to determine if they would cause a shutdown). The third was "O2 sensor 1/1 input voltage maintained above normal operating range". Now I don't believe O2 sensor would cause a no-start?

Another thought I had, is that I may have bled the fuel rail a little while testing fittings on the schroeder valve?

Finally, its possible that there was some gunk/etc that has cleared itself up.

At the very least I'll be dumping the fuel that's in there and replacing my fuel filter.