Thread: STARTING WOES GAS/PETROL

The trouble with Impco systems is that if you switch off the engine on gas a considerable amount of gas remains in the converter. This causes flooding if you then attempt to start either with petrol assistance or on straight petrol.

Most likely your petrol assistance time is set too high. The petrol assistance should be less than one second. Find the time adjustment on the Peel box and turn it right down. For hot starts you need no additional petrol at all as gas is still present in the air intake on shutdown.

If you wish to start on petrol you need to clear the gas by changing to petrol before shutting off the engine. Also pausing with the key on for 1-2 seconds after turning the key to ignition may help, to time-out the petrol assistance. It depends on how the box is hooked up. If it is hooked up to gas switch power you should be able to observe the petrol light on the box go out. If it is hooked to the gas valves (after the safety cut-out) you will observe the petrol light come on as you begin cranking.

Best thing to do with an Impco system is to bin it, and put on an European converter and mixer. Then the flooding problem should be greatly reduced. Also you may find a large improvement in performance as the Impco mixer is very restrictive, especially at low engine speeds.

Lastly make sure your MAF (mass air flow meter) remains powered when running on gas. It will run poorly on petrol if swapped while running, if the MAF is disconnected on gas. Test for 12V at the brown/orange stripe wire at the MAF plug while running on gas. You may have to run a separate power supply for it off the live side of the injector cut, if it is wired that way.

Wow, bee utey, what a reply! Given me much to investigate.
I've not noticed the petrol light go off or on at any time except when I switch it, so I'll observe a little closer.
A few questions if you don't mind -
I've avoided switching from gas to petrol while running cos I was told it immediately puts the car into limp-home mode. Is this true?
You say a European converter and mixer will give better performance - so would you think this expalins why the car sometimes feels good and responsive yet at other times, for no reason obvious to me, it feels sluggish? Same with gas economy - sometimes 300k from my 65 litres'ish of gas, other times barely 220.
LAstly, when testing for 12V at the MAF, this is with the MAF unplugged while running?
Thanks for sharing your knowledge - gives me some confidence I might work out this beast yet.

The only way switching from gas to petrol on the move will put your ECU into limp home mode is if the MAF is disconnected by the injector cut, which is what you have to test for. Switching off the ignition and restarting on petrol resets the limp home mode.

You test for power by peeling back the rubber boot on the connector and sticking the multimeter probe in with the said brown/orange wire. If there is no power there on gas only you snip the wire and connect a new feed to the MAF from a point before the injector cut relay where power is present on both fuels.

Varying performance could be due to a number of issues, including a seized distributor advance. All dissies should get a drop of oil under the rotor button once every 10,000km. Hardly any mechanic ever does this and in consequence the advance gets very sticky and reluctant to move. Check the advance is working smoothly by timing light with and without the vacuum advance hose connected. You could also have issues with the gas mixer, especially if oily fumes are being fed into it.

The eurpoean converters run with a fixed size mixer which has no moving parts so it is always at the maximum available size opening. To get optimum economy from a gas system you need a system that has separate cruise and power adjustments. Most modern vehicles do this with an exhaust gas sensor and a fuel processor. They may gain you up to 20% extra range over a basic system.

The injector cut relay may or may not be part of the switch. Peel have various types of inj cut relays and switches. Look for adjustments in the side.

Ok. So I know what my weekend job is now. Many thanks.

The MAF plug seems to be a moulded thingy with no rubber boot ie cant get to the wires. But, if I disconnect the MAF when running on petrol, the engine chokes and dies; if I disconnect the MAF when running on gas, no change. So this would suggest the wiring issue?
I also checked the vacuum hose to the fuel reg - and fuel oozes out of the reg nipple. So I think new fuel reg required.
Also sucked on vacuum advance - no resistance, so that's probably cactus as well.
Can't get rotor off so can't oil dizzy - but suspect the advance spring problem may have already happened. have to get a timing light I guess to check, plus a new rotor.
Oh the pain, the pain.