Is this right?

[peterdon]

I was swapping Land Rover stories with another guy yesterday, he reckons he had a V8 with LPG that did not have a seperate ECU. The change over switch had a module in it to change to gas at specific revs irrespective of temperature. This was the only control he had. I've never heard of this before, has anyone else?

[Sir Henry]

That sounds like his Landy was an early one with carbs rather than fuel injection. As such the LPG system would have merely used a mixer or an 'LPG carb' and all the switching would have to be done manually. In practice it has to be manual as you need a 'no fuel' position on the switch to allow the float chambers in the carb(s) to empty - unless the jets can be switched off electronically via an anti-run-on circuit. That's the same as I've had fitted to my '76 Silver Shadow. Although it works reasonably well without any feedback from the exhaust (open loop) I will soon be adding the closed loop controller to improve it.

[Clifford Pope]

It doesn't necessarily even have to have carburettors, although if a Rover V8 it probably does.

I have a Volvo 240 with fuel injection, converted to LPG many years ago with a simple open-loop mixer.
It's primitive by modern standards, but it works reliably, and gives good fuel economy.
When on LPG there is no ECU. If I switch over to gas it changes over if the revs are blipped to about 2000. I think the switch just turns off the injectors but leaves everything else running.

[peterdon]

It doesn't necessarily even have to have carburettors, although if a Rover V8 it probably does.

I have a Volvo 240 with fuel injection, converted to LPG many years ago with a simple open-loop mixer.
It's primitive by modern standards, but it works reliably, and gives good fuel economy.
When on LPG there is no ECU. If I switch over to gas it changes over if the revs are blipped to about 2000. I think the switch just turns off the injectors but leaves everything else running.

That sounds to be what he was talking about. I've not had a lot of experience with LPG (on my second vehicle now) but was under the mistaken impression that all had an ECU. It's a good thing to learn something new everyday

[Sir Henry]

Some earlier injected cars were fitted with the notorious Bosch K-Jetronic ("Konstant") injection system during the 80's. As it is almost entirely mechanical in nature it is usually just switched off when the engine is switched over to gas. Although it works fairly well (when it's working at all) it doesn't do much for improved power output or fuel consumption. However since it is normally found on larger engines such as the 5.3 litre, V12 Jags (~300bhp) or the 6.8 litre, V8 Rolls & Bentleys (~250bhp) power and 'economy' improvements rarely figure into the equation. Fortunately even a simple LPG mixer can work wonders on such engines when set up correctly and the addition of a closed loop controller can improve things even further. Even titchy little 3.5 litre engines (based on the ubiquitous Small Block Chevy motor as bought out by Rover/BMC/BLMC/etc.) can benefit from conversion to LPG.

[mat_fenwick]

titchy little 3.5 litre engines

Show off! Size isn't everything you know (as I keep telling the missus...)

[Sir Henry]

titchy little 3.5 litre engines

Show off! Size isn't everything you know (as I keep telling the missus...)

Just use an 'Angler's Ruler'. She'll never know the difference ... unless

Ps. I've owned a driven/ridden motors down to 600cc (FIAT 126), 150cc (Lambretta) and even 50cc (Chinky moped). I still prefer the more 'grown up' car with ... sphericals

[woody]

its quite a common type of switch, it just energises a relay to stop the injectors working,as alexander would say simples...... it would be an open loop system though.

[Talkingcars]

My '77 WV Scirrocco 1600cc ran very nicely on K-Jetronic, 0 to 60 in under 7 etc.............

[Tubbs]

Do you remember the fuel protests of 2000? When people blockaded the oil refineries and truckers the m25 ? Everyone was up in arms about fuel going over a pound a litre. Tony Blair said it was the closest the uk ever got to civil war in his memoirs.
Anyway we where 'open looping' anything we could at the time. We had no choice, it was all we could get hold of. Leonardo's where thin on the ground, the odd Econ ec lambda controller. But that was about it. Injection change over switch, emulator where required, relay where not and tune it up with a multimeter on the lambda probe !