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LPG Failure


Well-Known Member
June 30, 2009
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'99 UK spec - LPG soon!
Happy New Year gentlemen (and Ladies!) of the forum!

I've got a bug! Well the Explorer has. I've been suspicious of this for a while but this week has finally become conclusive.

I've got a 98 with a Lovato single point LPG system. It's an old system with a ridiculously small tank but as you all know, a new one costs more than the truck so there we go.

Anyway, it's been a temperamental SOB for a while and has - on occasion - been known to completely shut down the LPG system for no clear or apparent reason. When I say this, the physical presentation is that all the lights on the switch unit go out and it runs on petrol (Aarrgghhh!!). Then later, again for no obvious reason, it just comes back next time you switch on.

It was sporadic and very occasional and as such, I never fully investigated it. Since Christmas though, it's staken on a new slant and over the past few days, I've seen it for certain - it drops out on running right turns!!

What I mean is any right turn that's enough to create a side of side-force. If you stop at a junction and turn right, no problem but if you don't have to stop and a similar junction, all the lights go out, it switches to petrol then when you straighten up, the lights come back on (in petrol) then when you get over 2000 rpm, it switches back to gas.

It's done it today four or five times without fail - I can almost do it to order!! It even did it on a bend and an island.


All suggestions very gratefully received!


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It's obviously a loose electrical connection to either the control box or more likley the switch over relay.

AS I expect you know, on single point systems, you switch over to gas at 2000 rpm.

the control box reads the RPM (from the red lead connected to the ignition coil) and detects when 2000 rpm is hit. - this input is also used to make sure the engine is running and not stalled when running on Gas.

so first check the connection from Gas control box to the coil is good and not loose or broken (get the car running on Gas and then wiggle the wires).

Second on the wiggle test is the + feed into the control box wires.

It has to be a loose supply wire as the box goes into reset on power on and switches to petrol.

have fun



Thank you very much - not only for the answer but for confirming my preconception of the guys who actually would have something to say about this. I had three of four names in mind in no specific order and you were certainly in there!! Seriously though, I did admire and respect the depth of detil you got into on your own system so I'm all ears!!

Now, when you say control box, are you talking about the nastly little switch unit inside or the Leonardo gizmo under the bonnet?

If there's any relevance, the tank unit on mine is FUBAR and so I have no gauge (driving on the trip clock) and (consequently I think) it doesn't automatically switch back to petrol when it runs out of gas (but that's only my assumption and I'll stand correction).



the control box is the leonardo box under the bonnet.

it is highly likley there are 3 or 4 boxes under the bonnet

the Leonardo control unit
the switch over relay (you will be able the hear the click on switchover
an Injector emulator (failure of this will cause a DTC to be generated as it fools the PCM when running on Gas but won't cutt off the system
A voltage regulator that feeds a fixed voltage to the IAC Valve when running on gas (you may not have one of these and in any case it only effects idle speed)

The switch unit may or may not be the problem, but if it is it is only a switch that can be replaced.

I'm pretty sure the Leonardo does not switch back to petrol if you run out of gas, in any case it is not the tank that would make the switch but an electrical pressure sennor that elecrically triggers a control unit.

Hope this helps


If you don't have them you can download installation instructions for the Leonardo here

(dead links)


Indeed there are at least four boxes - there's the Leonardo (Electronic Feedback System AEB175), the emulator (Lovato EMU2.6), a Lovato "Adattore Sensore AEB336 and another little gizmo which I think eliminates fault codes or soemthing. I can't make it out on the photo I've got here.

I've got photos of the whole lash-up - sorry, "system" but I don't think I;ve the means to post them. If you'd like a gander, just tell me how or let ma have an email address or something.

Now I'm more inspired, if it's dry-ish, I'll have a proper look at the weekend.



system diagram (but not including all the peripheral boxes)

(dead links)

Hi Jon

I received the pictures, the one below has all the elements in.

Item 2 is the control box (system processor) I would check the plugs for corrosion and do the wiggle test with the engine running on gas.

Item 3 is the square wave emulator that fools the PCM into thinking it has a control feedback from the petrol injectors when running on Gas - a failure of this one would only mean getting DTC's when on Gas

Item 1 is either the switchover relay (does it click when you switch over to gas?) mine also had an LED to show it had switched over- if so then again check plug for corrosion and do the widdle test

Item 4 is a strange one I can read OBD2uFIX but the AEB part number is hidden behind the pipe - can you check and post it.

When you are wiggling wires , don't forget the other end of the wire (perm and switchs + connections

have fun


(dead links)

Hi Jon

I have a couple of ideas bud..

I would solder all the crimped connections for starters (above 1) and everywhere you can see em ..

check where the switch / gauge comes through from the engine that the cable hasn't cut / broken stretched

have u checked the tank connections, exposed to the elements down there , assuming it's under the car

good luck

Right gents, thanks for the input. I've had a rummage and have mixed results to report.

The cornering problem was the permanent live. The Jim Henson "installer" had taken it frmo the battery terminal pinch bolt which on mine is a flanged head. He'd got a ring crimp under the bolt head but somehow - even with the bolt and clamp tight - the crimp wasn't being gripped and was moving enough to break contact.

New crimp, nyloc and washer - sorted!!

Only now we're back to an old problem where the lights on the switch unit all go out indiscriminately but I can't be sure whether it switches between fuels or not as you don't feel any change occur.

I've a feeling this might be the switch unit itself so I think a replacement is in order since I've been around most of the connections now and lo, they ARE soldered (so I can't moan too much!) and I've re-made the main ones.

By the way Jim, the unidentified article is (I think) AEB 442.

Now, on to inlet manifold gaskets...........

hi guys...

I have this exact same problem...same system but different car...

JonC... i hope u see this but highly doubt it as your profile shows your last visit here was FEB 2014...

anyone else know how jon went resolving this problem?