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LPG  Conversion
January - February 2008
1991 Talbot Express 2.0L (Autosleeper Talisman)

See Also: Blank LPGA Safety Report and COP 11 Guidelines available in the for-sale section as part of the Manuals CD.  These 2 documents will save you a considerable amount of time and hassle getting the installation LPGA approved for insurance purposes.

Introduction:

After 9,000 miles @ average 20mpg in  3 years of ownership I finally decided to fit an LPG system. Despite the disadvantages of LPG what tipped the balance for me was a combination of petrol prices exceeding £1 per litre, and the availability of relatively cheap / proven conversion kits. Estimated fitting time was 2 full days. In reality this was nearer 8 days due to having to spend 5 days fabricating and treating tank the mounting rails which could be attached to the chassis underneath to support the tank. The floor of he van is wooden which would not be acceptable to mount the tank directly to it.

Tuning the Fuel Mixtures ( Air / Fuel Ratio):

The kit will come with simple set up instructions for tuning the mixtures at idle and high RPM (such as 3k). The basic mixer setup relies on the varying air pressure drawn through the mixer to draw LPG from the vaporiser (which acts like a diver's demand valve) in much the same way the carburettor draws fuel from the float chamber.  The relationship between mixer internal venturi size and the vaporiser's sensitivity are important in this respect. Too large a mixer and/or insensitive vaporiser will make it impossible to get the fuel mixtures within acceptable tolerances across all engine loads. Even with a well matched and tuned set up it should be noted that the limitations of this simple design mean a compromise is necessary. The basic tuning resulted in the engine running slightly rich under load which was good, however, due to the  my concerns that the mixtures might go weak as the tank emptied (and LPG Pressure drops) I decided to invest in a Lambda Probe and instantaneous Air/Fuel Ration gauge to give prior warning that I should switch to gas. Such kit is probably overkill but I like to be sure and it also made tuning the system on the road very easy without having to take it to a garage (and enjoy working on the van!).

Important: I destroyed 2 lambda probes due to afterfire (explosive backfire through the exhaust on the overrun) before I discovered that the problem was due to the air intake hose being mounted facing into the wind. What happens is that the throttle plate closes so the air being sucked into the engine is minimal, at the same time air is being forced into the air intake by the forward motion of the vehicle which results in a significantly reduced vacuum at the mixer. The mixer therefore feeds very little LPG into the intake on the over run resulting in a weak mixture that is too weak to ignite consistently so a lot of unburnt lpg/air is passed into the exhaust were it is ignited when the engine fires again (with a rather impressive bang, and a destroyed lambda probe). Simply re-locating the flexible air intake from behind the grill to point down wards cured this completely.

Tuning using a Lambda Probe and Gauge

The lambda probe and wiring harness was obtained from an Austin Metro down the local breakers yard. I liked this model as it has 4 wires (2 white for heater, 1+ve and 1-ve) and an easy to fit harness. The white wires are connected to the ignition and earth which provides a heating current to the probe. This is necessary to (a) ensure it gives a read out quickly from cold, and more importantly (b) to ensure it does not drop below operating temperature when the engine is idling. Another advantage of using a heated probe is that you can mount it further down the exhaust system. Personally I mounted it just below the exhaust manifold bracket as it gives near instantaneous response to exhaust mixture.

The Probe is a 0-1v type and fitted to the exhaust via a steel boss (large nut specifically for this purpose) bought of Ebay for £6. The probe is connected via the ignition to an LED Air/Fuel Mixture gauge temporarily mounted on the dashboard. This gives accurate Air/Fuel ratio readout at all engine loads and speeds enabling one to tune the system for optimum performance and give immediate warning if the mixtures go weak when the tank is almost empty.

Exhaust Boss and Lambda Probe

Instantaneous Air/Fuel mixture display temporarily mounted on top of dashboard for on-the-road tuning.
(The LPG Control Switch and fuel tank level gauge can be see mounted vertically below)

Peugeot/Talbot PCV
(Positive Crankcase Ventilation)

Picture of how NOT to install a mixer
(upstream of PCV)
 
 

The recommended positioning of the emissions take off (anywhere between the air filter and mixer will be acceptable).

The handbrake cable is temporarily pushed up out of the way in this shot.

1) Front-End LPG Kit,  Cost: £240

• Autronic Vaporiser
• Autronic AS-110 Control module and LPG Level indicator.
• M/F Mixer (32mm Venturi Diameter (originally a 27mm was used but restricted BHP to much)
• Voltran External Filler Unit
• LPG Solenoid (fits in engine bay between the Tank and vaporiser).
• 6mm Copper pipe x 1 Meter (this is the filler Pipe, not used)
• 8mm Copper pipe x 6 Meters (Tank to Engine pipe)
• 5/8" Water Hose + "T" Pieces
• Pipe clips and hose jubilee clips.
• Comprehensive fitting and set up instructions.
• Advice also provided via Email.

2) 4 - Hole full toroidal Tank (55L water capacity, 260mm x 230mm):
    Cost: £280 including all valves/fillers etc and electronic level sender.

Why 4-Hole?: LPG tanks come in either single-hole or 4-hole varieties. The 4-hole tank costs considerably more (in this case approx £100) and offers several important advantages:

• The Blow-off safety valve is significantly larger giving it an added margin of safety. Whilst single-hole tanks meet minimum requirements 4-hole tanks exceed these.
• They are supposedly constructed to a higher standard, using thicker metal and stronger around the valve fitting areas (though I've not been able to confirm this).
• It is easier to fit and get a god seal on the smaller threaded individual parts and they are easier (and cheaper) to replace parts should an item fail rather than having to replace an entire multi-valve unit.
• Having a separate filler they can be fitted with a large-bore flexible filling hose that allows them to be filled up considerably quicker than a single-hole tank and at a rate comparable to that of petrol.

Tank Size: This gives the largest capacity that would fit between the chassis rails under the van without fouling the handbrake cable (height). The actual gas capacity is 44L (LPG tanks cannot and  must not be filled to more than 80% capacity) which equates to 9.68 Gallons. You should not run an LPG tank too low because this leads to a lean (weak) mixture towards the end as the gas pressure drops, Therefore assuming 90% of the 44L gas capacity is usable this gives 39.6 Litres usable (8.7g) and an estimated range of approximately 143 miles on LPG with a little in reserve. 4000 miles later I can confirm this is the case.  Of course if it runs out of LPG one simply switches to Petrol.

3) Large-bore flexible filler hose for Tank: (Shown picture above right. Although relatively expensive at an additional £20 the filler hose allows one to take advantage of the 4-hole tank's ability to fill 50% faster than a single-hole multivalve tank. It doesn't make a lot of difference but with the relatively small tank fitted to the van I anticipate filling up more regularly, especially on long journeys, and (as Mr Tesco would say) every little helps.

Cost Summary of Conversion:

The lubricant bottle is mounted in the engine bay behind the front grill just below the RH Headlight. The vacuum hose supplies the lubricant via a 'T' piece (supplied)  into the emissions pipe that enters the inlet manifold below the carburettor. This location ensures all cylinders get an equal measure.  The system is very easy to set up and uses approximately 1ml per Litre of fuel. I can confirm this consumption rate is accurate and that 1L of Flashlube last approx 3,500 miles on LPG. 

The FlashLube kit was purchased new from an Ebay supplier at a very reasonable £40 inc a 500ml bottle of oil. I have since purchased additional lubricant for approximately £12 per litre. I use genuine Flashlube as they made the kit but there are alternatives that are very slightly cheaper. 

Picture of Flashlube dispenser installation to go here.

Revised plumbing to Vaporiser (Coils now removed at insistence of LPGA Inspector despite previous inspector insisting on them being there!). Feed pipe deliberately curved to reduce stress.

• 6mm copper Liquid LPG Feed pipe entering top of the Vaporiser.

• 17mm Rubber LPG Vapour pipe (to mixer) exiting the top of the mixer.

• 2 x Water hoses can be seen at the front (the ones with the yellow strip).

• Also on front of the mixer is the 12v solenoid valve.

• The air intake hose (large black one) can be seen repositioned below the heater pipes.

Note: The round black item in the bottom RH side of the photo mounted beside the vaporiser is the actuator for the cruise control (supplied by Conrad Anderson))

Lambda Controlled Powervalve Kit (left) and installation of control module (far left)

Voltran Filler mounted discretely in the side skirt (can be seen in the dark grey just forward of the gas locker)

In this Photo:

 LPG Mixer ( mounted in-line in the Carb-Airbox hose), 32mm Internal Diameter. Note Emissions air intake has been blanked off and relocated upstream of the mixer.

Lambda Controlled Power Valve Mounted in 17mm LPG vapour hose going into the side of the mixer). This item can be tuned to act as a standard fixed power valve should the electronics fail.

Petrol Shut off solenoid (blue item). This item also has a manual override lever should the LPG Electronics ever fail.

I spotted this set up on a series 1 (pre 1991) Autosleeper Talisman in a car park so took some photos for your information. As you can see the tank is a cylindrical model,  mounted on 2 x angle-profile rails just in front of the rear axle. The tank is secured to the rails by standard steel straps and the two rails are bolted through the chassis on either side. An impressively simple mounting method.

Pros: This  set up almost certainly allows a larger LPG tank to be fitted giving improved range.

Cons: It puts the weight of the tank and LPG contents much further rearwards almost over the rear axle. 

Personally I find the vehicle already very light on the front particularly as I do a lot of steep climbs, sometimes in the wet when any lack of traction can be a serious issue with precipitous drops off single-track mountain roads. Consequently I do not want to transfer any weight to the rear if it can be avoided. Nevertheless I think this is impressively simple mounting method and certainly worthy of consideration.

Also of possible interest ... this vehicle can be seen fitted with the Grayston coil spring assistors (see the "How to" section of this webpage for further details on this and AirRide suspension options).

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