The other day I had a weird failure where one of the coil packs melted down. I was able to drive home on six cylinders, and fitted a spare one (thanks to David Hallworth for that!). Now the problem is that while it runs just fine on gas, it does not run on petrol at all. There's fuel at the rail, there are no faults logged, it just cuts out dead when switching to petrol. Plugging in the diags, everything reads perfectly. I can't think of anything that would take out just the injectors without showing other signs of distress.

Anyone ever run across this before?

Hmmmm, possibly the lpg ecu hada fit when the coil went down, when I first got mine it went into melt down and wouldn’t switch between either, otherwise the petrol ecu isn’t getting a signal, can you check that the pump is running or give it a manual boost of 12v, pressure might be at rail, but if it isn’t pumping it won’t work

As you've got a Leo fitted then the LPG system and petrol system are virtually totally separate. I suspect you've disturbed something and broken a wire somewhere, either the common feed to the petrol injectors or something in the vicinity of the emulators.

Well, it did have fuel at the rail, and now it doesn't. Relay is pulling in, pump isn't running (if I jumper the relay I don't hear it start). I guess I'm dropping the tank then! Anyone got any experience with this?

Lots of possibles with this one.

The coil could have been melted if the Leo's rpm wire (which will connect to a coil) shorted to earth at some point, may be worth checking this wasn't the case, could have accidentally fixed such fault changing the coil pack.

Can't remember what fuses run what on a P38 but shorting a coil pack to earth could potentially blow a fuse that runs some aspect of the petrol system, probably unlikely because would expect a relevant fuse to run the ignition (so wouldn't run on LPG either).

Emulators as Gilbert said.

Only other things that spring immediately to mind for this are forgetting to plug in the MAF (or ducting) / If an emulator isn't used (and yellow wires are used to disconnect petrol injectors) an issue in the Leo might have first caused the coil to burn, might now be causing Leo's relay (that joins / breaks yellow wire connection) to be unable to join yellow wires.

There are all sorts of ways of disconnecting petrol injectors if emulators are not used, yellow wires can be used directly or control a relay / a relay could be controlled by the blue wire.

Check positive feed to petrol injectors, check negative pulse at petrol injectors.
On either Gems or Bosch the fuel pump relay is switched by the petrol ECU which provides the relay coil's earth. I've known the petrol ECU to work perfectly except not provide the negative to the relay so the fuel pump never runs so obviously means it won't run on petrol (but will on LPG)... You've already ruled this out, I mention it because I was once called out to fix a P38 that would run on LPG but not petrol which (if memory serves) they said had recently had a failed coilpack. Wonder if a shorted coilpack could cause the ECU to fail in the way that sees it no longer provide the fuel pump relay coil earth. Discussed this with Gilbert before, he said he's known a P38 ECU to fail in the same way too but I don't know if that was after a failed coilpack.

Dropping the tank isn’t that bad to do, especially if emptyish, otherwise get some ply and place under the tank on trolley jack, the other route is dare I say, cut the floor.
I cut mine as I had 3/4 of a tank, took longer to pull the rear side panels , seats and carpet up than to change the pump after, I only cut 3 sides so it flapped back down and was sealed with tiger seal with tape over the top, I would check all other avenues first, seems strange to suddenly go pop.

Doh! I should've refreshed the page before continuing to write a reply after breaking off in the middle of writing it.
Seems a good chance a broken pump was the cause of the engine not running earlier?

I'm not sure if the two are linked or not. The misfire was definitely down to the coil pack. I guess I'm dropping the tank to at least have a look.

Check the inertia switch first. Power to the pump goes from the relay to the switch and then onto the pump. If you are dropping the tank, get yourself some 8mm ID fuel hose first, the steel fuel pipes often rust above the tank so you might as well replace them while it's dropped. I had to do those on the SE as the return had rusted through so it was pissing petrol out as soon as the engine was started. As said, dropping the tank isn't that difficult as long as you have a spare jack to lower it down, I didn't even need to disconnect the filler hose.

If you replace any fuel line, get some decent Codan R9 stuff or something, not the generic crap available on eBay/Halfords etc...

Check my thread on here about our red one nearly catching fire because of dodgy fuel hose used at the back of the engine. Or Google it - plenty of examples of it failing. Even the generic R9 stuff is known to be dodgy.

Any suggestions where to get quality stuff from? I bought some 8mm from Pirtek (it's right next door to where I work and needed it quickly) and it's already showing signs of cracking.

I bought Codan 7.9mm ID hose from a local company. This is the stuff you want, https://www2.codan.com/node/28273 and I would have thought somewhere like Pirtek would stock it If you ask for that specific hose you should get it rather than some generic fuel hose..

Sloth wrote:

If you replace any fuel line, get some decent Codan R9 stuff or something, not the generic crap available on eBay/Halfords etc...

Or LPG stuff suppliers whom I've warned many times about supplying 'fuel injection spec petrol hose' that bellows like a balloon if subjected to more than about 1 bar pressure. Which they've done nothing about.