Thread: 91 dual fuel disco won't start

What sort of gas system?
Being a '91, it's almost certainly not an injected system.

Does it have a mixer?
If so, what type?
Backfiring can cause troubles in the mixer if it's a particular type.
Easy fix if it is.

Maybe post a photo of the gas system, or try to start it on petrol .. etc.

The MAF doesn't control anything while its on LPG so won't affect that. LPG backfires due to all sorts of factors, and it can damage a lot of hoses etc because the whole inlet manifold is full of gas/air mixture.

So to start with, inspect the components in the air intake for physical damage, splits, blown off hoses, damaged mixer diaphragms etc. Then take out the plugs and gap them to 0.7mm. If you can get it running adjust the timing to 10 degrees BTDC at idle, using a timing light.

Further help will depend on what type of gas system you have, there are lots of different brands fitted to these vehicles and they have many differences. Oh and you could of course be out of gas, inspect the tank's own gauge/s to see what's in there.

Some pictures will of course help, there is a "manage attachments" button on each posting page that will let you upload pics directly from your device.

Thanks guys for such a fast response
AK83:
Hi mate
As I said I am very new to LR's and LPG but I'm keen to figure out as much as I can
Im pritty sure its not the carby 3.5L
I've taken some pictures to help.
I'm not 100% if it has a mixer but I'm hoping you guys can tell me from the pics
(so sorry I'm so noob, promise I'll learn quick)



Bee utey:
Hey mate
Wish I had asked all this before I got a mobile mechanic to come out and help problem solve the issue,
Live and learn.
#1- So far the only damage I can see is:
one of the clips that connects the air filter to the MAF sensor is gone
I found No hoses disconnected when I had a good look just now,
When I bought the truck i did find a dodgy 'T' piece connector running right next to the intake. Of the 3 hoses that connected to the 'T' piece only 2 still connected and he had a stick shoved in the broken third entrance to it.
Mind you it still ran like this
I replaced it and found no difference.
I think it's some sort of oil delivery pipe??
This is the one I fixed....



#2- I'm really sorry bee utey but I can't seem to understand what you mean by
"gap plugs to 0.7mm" ??

The leads look a little old and run down
And they are just hanging, not neatly, cable tied in a couple places





#3 - I'm not 100% on the exact type of system I have ,
I know it's the basic LPG system by the looks of it
It sends gas to the intake
Gas tanks under the rear

a few pics which hopefully might help



what is this?



this is a zoomed in pic of the label on the thing in the first pic



gas tank under rear



same gas tank but looking at the top



LPG switch - car off



LPG switch accessories on , on LPG.
says nearly full ( was nearly empty when I bought it and I put 20L gas in it on the way home before it died, also added about 10L petrol the other day)



LPG switch accessories on,
on petrol.



this is her

Thanks again guys
Really appreciate all the help!!!!

1. That is a fuel injected engine. The generic type of LPG system is "simple mixer" type, ie it has no moving parts.

2. The mixer is the ring on the air intake, it mixes gas with the air that the engine draws in. The gas is drawn in by vacuum generated by air flowing through the mixer ring, similar to how a carby draws petrol into the air flowing through it.

3. The tee piece that you connected is correct the way it is now, it is part of the engine's crankcase ventilation system. Blocking it is pointless, because of the way the fumes run.

4. "Gapping" spark plugs refers to adjusting the gap between the electrodes that point into the cylinder heads, you will need a spark plug socket to remove and replace the plugs and a feeler gauge to set the gap correctly. I'm sure that a yoo toob search will show up some instructions.

5. The spark plugs leads look OK at a first glance, remove each end off firstly the distributor cap and then the spark plugs and inspect the terminals inside the boots. All metal contacts should be clean and shiny, black is a sign of a burnt out lead. Don't mix up the leads, the firing order must remain the same.

6. The mystery device is the LPG converter, (brand: OMVL) it converts high pressure liquid from the tank to low pressure vapour for the engine to draw in. It has two idling screws on one side, don't touch these until you've progressed with other things. There are two water hoses connected to supply the heat to vapourise the liquid LPG. Replacement ones surface on ebay for $50 to $200, there's a good possibility it's stuffed.

7. The gas hose to the mixer has an adjuster in it, that sets the maximum flow to the engine hence the power or economy. If you get the engine running, adjust the knob in and out and see if the power improves.

8. The gas tank has a gauge sender to the right of the tap, clean its face with a rag and see where the needle sits. You may need a mirror. If the sender is electrically buggered it will show always full on the dash gauge when switched to gas.

1. Thanks for clarifying that mate

2. Ok now things are starting to become more clearer, could the mixer be damaged from the backfiring ?
Are there any parts inside the mixer that need replacing ?

3. Ok, good to know that's all good now

4. Ok, I now understand gapping
I will purchase a gap reader and test all spark plugs tomorrow

5. I removed all leads as you instructed, all are clean and shiny
Only weird thing was 2/8 leads would not pop off with ease
And when I did get them off the metal part inside the lead was hard stuck on the spark plug





I'm guessing those 2 leads will need to replaced

If so I'll get them tomorrow

6. Amazing ,
Thank you
I now feel I at least understand what's happening here,
What gas parts are involved
(in my once apon a time mystery system),
and what they do.
So could I just use any heater hose the same diameter and length as a replacement ?? Or should it be specific to this type of system?
I'll look around tomorrow also for them if they can be any water heater hose

7. I didn't even notice that was there lol
Not sure if I'm getting ahead of myself here but When I finally do get her started I should be able to tune this system myself?? using the adjuster on the mixer hose,the idle screws on the converter, and adjusting the timing ??
That would be awesome

8. Ok maybe we have something here
After finding & cleaning the gauge
It's sitting on 1/2 while dash gauge says 4/4
So does that mean I need to replace the LPG electrical fuel gauge ?

Many thanks for all the help mate

=)

2. Mixers are usually machined from solid alloy and are not often damaged. Inspect it yourself for obvious damage.

4. Asking for a gap reader at an auto shop will get you dumb looks, ask for feeler gauges as previously mentioned.

5. Yes the leads need to be replaced. With practice you'll learn how to wriggle them off without pulling the connectors off.

7. I'm talking about the LPG converter, the hoses are just standard heater hose available anywhere. Lookie on ebay:

omvl | eBay

8. The sender unit on the tank probably needs replacing, its out in the weather after all, the dash gauge is probably OK. Example of a sender:

0 90ohm Axiom APA LPG Tank Sender Unit Tank Gauge | eBay

There's also the possibility that the LPG tank is out of date and needs retesting. Find the ID plate on the tank and see how long it is since the last test date. 10 years is the max allowed.