SU problem

[Mudhog1974classic]

Hi all,

I'm running SU's on a 3.9 Disco motor in my Classic rangie with dual fuel.

When I change from Lpg to petrol I get a splutter, which then when I turn the switch half way to Lpg again, the engine kicks into life until the petrol runs out!

Note: The truck run's fine on Lpg!

I have checked the Lpg control switch and it's working OK.
I have bypassed the Lpg all together and still the splutter.
I have checked the fuel filter and replaced it and still the splutter.

Can anyone help or suggest what to try :(

[Lotz-A-Landies]

Hi all,

I'm running SU's on a 3.9 Disco motor in my Classic rangie with dual fuel.

When I change from Lpg to petrol I get a splutter, which then when I turn the switch half way to Lpg again, the engine kicks into life until the petrol runs out!

Can anyone help or suggest what to try :(
A couple of questions: Does the LPG conversion have fuel cut off solenoids in the petrol line and are they functioning?
is there an electrical cut off to the fuel pump and is it working?
Is your electric fuel pump still functioning properly - the Bendix ones can be beasts at times (am assuming yours wasn't an EFI type with a submerged pump)?
Diana

[StuRR80]

Mine actually stopped as soon as I switched from gas to the middle position then to petrol (or striaght to petrol). I just thought it was because the carbs don't hold as much LPG as petrol therefore I stopped switching that way. Worked no probs from Petrol to gas.

Also, it may take time for the fuel pump to kick in and send the petrol back up the line to the carbs?

Only guesses from my experience but there IS a reason why my rangie's off the road at the mo... :angel:

[Mudhog1974classic]

A couple of questions: Does the LPG conversion have fuel cut off solenoids in the petrol line and are they functioning?
is there an electrical cut off to the fuel pump and is it working?
Is your electric fuel pump still functioning properly - the Bendix ones can be beasts at times (am assuming yours wasn't an EFI type with a submerged pump)?
Diana

Hi Diana,

1 The solenoids have been checked and are working
2 No electric fuel pump cut off,
3 Fuel pump is working normally and not an EFI type

[DEFENDERZOOK]

does it run on the petrol.....?


how long has it been since it ran on petrol......
and have the dampeners in the carbies still got oil in them.....?


if the carbies are working fine......then i would expect the splutter when switching from petrol to lpg......

[Mudhog1974classic]

does it run on the petrol.....?


how long has it been since it ran on petrol......
and have the dampeners in the carbies still got oil in them.....?


if the carbies are working fine......then i would expect the splutter when switching from petrol to lpg......

It was running fine on petrol about 4 weeks ago.
Will check the oil levels.

What type of oil do I use?

How full should they be?

[DEFENDERZOOK]

we use to use transmission fluid.......


as you drop the plunger in...it should have resistance just before the threads touch the carby......


so what you are saying....is....it wont run properly on petrol......?
but it runs fine on gas.....?

[Mudhog1974classic]

we use to use transmission fluid.......


as you drop the plunger in...it should have resistance just before the threads touch the carby......


so what you are saying....is....it wont run properly on petrol......?
but it runs fine on gas.....?

That's what's happening!

[Lotz-A-Landies]

Now to summarise:
You have checked the fuel filter and it is good/not clogged.
There is no electrical cut off on the electric fuel pump.
There are no cut-off solenoids on the petrol lines/or they are working O.K.
The electric fuel pump is working normally. (making clicking sounds & petrol comes out the end of the fuel line at the carbies if you disconnect it ?)
The solenoids on the LPG tank and evaporator are functioning.
The change over switch has been tested and is working O.K.
The symptoms: The car runs normally on LPG.
You switch to petrol - the engine dies.
you switch back to LPG the engine runs fine.
You switch back to petrol and the engines splutters runs for a bit and dies.
the engine wont start on petrol.

Is that correct?

Have you checked the needle and seat in the fuel bowl on the SU is not clogged? (The little cylindrical chamber with a hex nut on top to the side of the air inlet.)

Diana

[Mudhog1974classic]

Now to summarise:
You have checked the fuel filter and it is good/not clogged.
There is no electrical cut off on the electric fuel pump.
There are no cut-off solenoids on the petrol lines/or they are working O.K.
The electric fuel pump is working normally. (making clicking sounds & petrol comes out the end of the fuel line at the carbies if you disconnect it ?)
The solenoids on the LPG tank and evaporator are functioning.
The change over switch has been tested and is working O.K.
The symptoms: The car runs normally on LPG.
You switch to petrol - the engine dies.
you switch back to LPG the engine runs fine.
You switch back to petrol and the engines splutters runs for a bit and dies.
the engine wont start on petrol.

Is that correct?

Have you checked the needle and seat in the fuel bowl on the SU is not clogged? (The little cylindrical chamber with a hex nut on top to the side of the air inlet.)

Diana

It will start on petrol... but splutters... then when you turn the switch half way to Lpg it kicks into life until the petrol runs out....then when I turn the switch on Lgp the truck run's fine!

Brett

[DEFENDERZOOK]

sounds to me like its getting lpg all the time whilst its switched to petrol.....
the lpg only shuts off in the central position......so its getting both fuels when its switched to petrol
and its just flooding the engine.......

[Lotz-A-Landies]

Yours is obviously a different switch arrangement to mine, as I only have 2 positions and there is a timer in the switch.

The fact that it will run better on the intermediate position than on the petrol position is interesting.

In your system, do you know what happens electrically when you move to the intermediate position? i.e. what does it turn off (and "turn on" for that matter).

Spluttering sounds like a fuel mix problem. This is usually, too little fuel or too much air.

I would look for problems on any of the manifold vacuum hoses. Vacuum advance, engine performance guage if fitted, brake booster hose. (Rough running on petrol was a problem with my RRc recently, although an EFI engine, the problem was a small vacuum hose disconnected off the manifold plenum chamber sucking air.)

The other issue of a partially blocked needle and seat is still an issue worth checking. Wax can solidify out of the fuel if it is not run on petrol for a period of time, this will cause fuel starvation. Although that it runs on the intermediate switch position seems to discount that as a cause.

A third option is a distributor advance module malfunction putting the timing out slightly when on petrol - although unlikely.

Sorry I can't be of more help.

Diana

[Mudhog1974classic]

we use to use transmission fluid.......


as you drop the plunger in...it should have resistance just before the threads touch the carby......


so what you are saying....is....it wont run properly on petrol......?
but it runs fine on gas.....?

Well I checked the oil levels and found that they both needed oil.(a friend said to use 10-40 grade oil)
Man this is to easy...started the truck and turned the switch to petrol and nothing had changed... the splutter was still there....back to the drawing board.:wallbash:

So I decided to change the oil in the swivel housings
After doing this I thought I should take the truck for a run to help things settle. On the way round the block I thought I might try the petrol again...
switched the switch and the truck kept on running ....I didn't no if the switch was playing up or not, so I switched back half way to Lpg to see if anything would happen. Sure enough the petrol run out and I switched over to Lpg fully and everything was Ok. Drove on and repeated the petrol change over and it was working agian!!!:D

The small things really count sometimes!!!

Thanks to all for the helpful tips.

Brett

[Lotz-A-Landies]

Brett

Good to know you have it fixed and now I must check the oil in the SU's on my S2B engine.

Cheerio
Diana

P.S. Will file that one in the "usefull folder" in the brain box