Please Help! I am writing to you about a problem I am having with my dual fuel 1994 Mitsubishi Magna ts 2.6. I have owned the vehicle for just over a year. Although 20 years old, the mileage is low, now 105000. Shortly after I bought the car, I had gas installed as a cheaper alternative. I continued to use petrol for short periods after the conversion but about two months later a problem developed with petrol usage. The engine starts and idles fine on petrol, but after a short (few seconds) of driving, starts to miss and worsens if I try to continue on petrol. The car runs perfectly on gas. This has been the situation for about 7 months now. I always start the engine in petrol mode, and then switch to gas when the 'missing' kicks in. I have asked several different mechanics, but no-one can give me a lead as to what the problem might be. One oddity that I noticed is that on 2 separate occasions, the engine ran perfectly on petrol until I reached my destination ( about 20 kms) but each time when I re-started the car the problem was back.

I have tried a few experiments which tend to add to the puzzle. I switch to petrol at 100 kmph on a hill. The engine doesn't kick in at all until I have slowed to about 60 kmph and then it ignites, but is missing furiously. At this point the 'check engine' warning light comes on. Also, I can travel along in petrol at about 40 kmph but as soon as I encounter a rise, or need to increase power, the stuttering increases so that the vehicle becomes undriveable. I have not tried to persevere to see if I could crawl home ( say if gas failed), and hope I don't need to .

Assuming efi?

Let the gas run out, then see how it behaves on petrol. If it runs well with an empty gas tank, chances are there was still gas getting into the engine when switched to petrol. ie the missing is from an overly rich mixture of petrol + gas.

EDIT: probably easier just to turn the gas off at the tank, and try running on just petrol for a while.

Alternatively, just get the car to the missing stage, switch off and remove a spark plug, and see if it is running rich.

If you confirm it is rich, get the gas-off solenoid (or whatever it is officially called) replaced.

You could also try toggling gas on-off a few times until that solenoid decides to seat properly,if that is the problem.

Pretty much trial-and-error until you narrow down the fault, I'm afraid.

Thanks Madmax, and yes it is efi! Ok, I'll check out the solenoid, thanks.

Thanks Madmax, and yes it is efi! Ok, I'll check out the solenoid, thanks.

Also have a look at the wiring under the bonnet if the control box is easy to get to. I've seen one install where all of the problems were due to badly made spade connections to the control box.

Sounds like a fuel problem to me.
Generally there is a relay that switches off the petrol fuel pump when you switch to gas and that may have dirty contacts and affecting the fuel pump when you switch back to petrol.
May even be a clogged fuel filter or even the pump itself on the way out.
As it runs perfectly fine on gas the ignition system is ok.

I can travel along in petrol at about 40 km/h but as soon as I encounter a rise, or need to increase power, the stuttering increases so that the vehicle becomes undriveable
Needs more fuel for the hill and not getting it!!!!
There is a small chance the injectors are on the way out as well i had a set start playing up a while back and had a misfire on revving the motor and no power going up a hill. Started and idled fine!!
When injectors were tested they told me the vehicle should not have been running at all.Goodluck vee

Hints : http://www.go-lpg.co.uk/Hints.html

OK, I turned off the gas completely and there is no change at all. Also checked the plugs, and it's not running rich. Wiring to the gas instal is fine. I'm beginning to think it must be an injector problem.