not long ago bought a '99 mazda b2600 daily with factory duel fuel...
problem is, its been using fuel, whilst switched on gas. when i first got the car, the thermostat was stuck open, thought that may have been an issue, but didnt help.
the 'factory' systems were an option, and sent to a nearby gas fitter to be fitted, as most 'factory' options are.
its all impco stuff, with mazda cast into some of the adapters alongside the impco logo, and has two switches that need to be flicked at the same time to change from gas/petrol.
it only starts on petrol, even when hot. will start when switched on gas, run for a sec then die, like as though ignition has been cut or something.
so anyway, i took it to a gas specialist cos i cannot be assed with it and dont know too much about how these systems work, and he said that...
the gas computer is ****, its supposed to switch injectors off, and keep fuel pump running to circulate fuel.
because the comp is buggered, someone has done a dodgy fix, and the second switch is turning the fuel pump off, but injectors continue to open, and pressurebuilding up in the fuel tank is causing fuel to continue to be injected in while still on gas. if i drive with it on gas according to the proper switch, then flick the fuel pump switch to on, the car just dies.
checked both pins on one of the injectors, and both pins have power when either on gas or petrol (what should i expect to see, i figured one is power, the other is a pulse wire, although neither gave a pulse, as its batch injection and was idling at 1500 to keep it going on 3 cylinders while i checked it i didnt expect to see it pulse). havent had a chance to check fuel pump yet, and cant hear it either so i'll need to check the actual wiring.
so basically, what i'm wanting to know, does this seem like a plausable diagnosis? he is finding out a price on replacing the computer for me this week...
Thanks,
Dave

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Dave W

The 1600

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Gas systems can be a pain in the arse... i got rid of my old Panel Van for pretty thing that yr car is doing...

I'll have a look tommorow at work to see if we have a computer. What year is the bravo?

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its a 99 b2600/bravo. its the actual gas computer, not the mazda one. impco brand. dunno what model or anything.

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Dave W

The 1600

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you shoud have 2x mixture screws on your convertor.

one is idle/start (little 'un), the other driving (big 'un).

most "tuners" wind the idle screw in and the driving screw out to compensate, causing flooding at low RPM and garbage fuel economy.

or they just wind it in to make you start it on petrol and it idles crap @ low rpm when on gas, so the idle gets wound up to compensate.

seen it four times now. each time all it took was 3 laps around the block playing with the big'n'little screws.

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***OUT OF ACTION***

Impco systems are fitted with a Lambda solonoid which is designed to work at idle only. As the converter is a simple converter and has no adjustments you can make the idle cycle by setting idle mixtures lean then applying vacum to the breather of the converter and forcing it to richen up and then lean out again to get a fluctuating idle. What happens normally is that either the solonoid will flog out holding vacum permanantly to the converter causing it to stall from running rich or the lpg pcm will die of old age and the same thing pretty much happens.

It all sounds a bit complicated the way I have explained it but I am finding it difficult to explain. But try this. Disconnect the vacum hose from the converter and plug the vacum hose to stop any potential manifold vacum leak, leave the convertor disconnected (this will allow the diaphragm to breath freely). You will need to compensate the mixer idle adjustment because of this (1/2 turn anti clockwise) to richen it up slightly. This mod will bypass the lpg pcm for an impco lpg setup. These systems have no control of the lpg under acceleration as it is a 'constant depression' mixer setup much like an SU. Electronics are for idle only on this setup. This may be why the car is not idling on gas.

I have seen it many times before but internet diagnosis is like phone diagnosis, it is always etter if the car is in front of you.

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Some people play hard to get... I play hard to want!

My dad's got a B2600 on dual fuel. The injectors are f**ked though, so it only runs on gas. Bloody BBQ fuel. Been through two sets of injectors, a reco motor and several fuel pumps in the past few years. Good cars when they work, but a pain when they break down, which in my opinion is a little too often.

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the processors not worth much.its the wiring up job that add cost.
mazda fitted a system that was sorced in australia.
its uses impco bits.my mate had one that the engine died before warranty run out.
he had it done at his cost as it was obvious that the original system wasnt up to the job.
he sold it to a lation after lots of KM and they replace the AFM when one day it run out of gas and would only idle on petrol.

the start on petrol bit then change over is to stop backfire and destoying the air flow meter.
when changing to gas the impco system wont have any primmed up read to go.systems I worked on dont swap over intill 1500rpm.cOLD START primmer is available for impco convertor that solves starting issues.

injectors die as they dont get used most of the time.

if someones got a switch to turn of the pump then what else have they dodged up.

looking at a injected vapour system myself.not a lot of dollars.
i found the impco works fine when new and last a long time--when it gives drama you find its well worn out.landi based systems tend to need adjustments and servicing so when its worn out you already know.

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