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PostPosted: Sun May 10, 2009 4:35 pm 
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After hanging around here for a couple of months to gain some knowledge of LPG systems exactly a month back I bought a very cheap Stag-4 kit off ebay.

On first examination of the Stag-4 system I was fairly impressed the ECU case, wiring and connector plugs were of excellent quality. As far as I can determine the only real difference between the Stag-4 and the Stag 300 is that the Stag-4 uses a much smaller case.

The reason I bought a Stag kit while they are not in in the high end of the market there are a lot of them about and they seem to work without problems.

For a tank I went for a 60 litre cylinder tank mounted directly over the rear axle behind the rear seats. The Rover boot would easily accommodated a much larger tank but keeping the weight down was a consideration as the mounting position will also raise the cg height of the car.

Installing the tank took longer than expected because most of the rear structure of the Rover is double skinned so after a couple of false starts the tank frame was re-drilled and heavy duty brackets made up to mount the tank.

6mm Polyflex pipe was used for the front to rear pipe run running down the right side of the car parallel to main brake pipes clipped at 300mm/1ft intervals with plastic P clips pop riveted to to the floor pan.

The vapouriser was located high on the right side engine compartment bulkhead adjacent to the power steering resevoir. The Stag ECU was located left side of the bulkhead adjacent to the battery on the removable section of bulkhead which allows for access to the pollen filter.

The Valtek gas injector rail was mounted on steel strip bracket spanning two pre-existing 6 mm tapped blind holes in the lower side of the plastic inlet manifold.
The inlet manifold was drilled about 25mm from gasket face with 4.5mm drill and tapped M6x1 for the nozzles.
Viewed from the front the manifold nozzle position were
Cylinder 1 4 o'clock
Cylinder 2 8 o'clock
Cylinder 3 4 o'clock
Cylinder 4 8 o'clock

With this layout the hose length between the injector rail and the inlet manifold was kept to an equal 110mm for all 4 cylinders.
These position allow normal access to the manifold retaining nuts and visual inspection from above without any dismantling.
The inlet manifold did not have to be removed for drilling, only unbolted from the head turned through 90 degrees --- the manifold ports were plugged with cloth ball pull-throughs and the head ports sealed with tank tape to prevent plastic swarf entering the engine.

The ignition switched supply to the gas ECU and RPM signal were both taken by splicing into the wiring for the coil pack serving cylinders 1&4.

The petrol injectors were rotated 180degrees to allow connection of Stag wiring
harness.

Wiring for the gauge and rear solenoid valve was looped out through the vent hose then back in to interior of the boot via the spare wheel well to run cable tied to the car's own wiring harness down the left hand sill.

One major problem with wiring this models is that it it uses a BMW style double front bulkhead and I could see no easy route pass wiring from the engine bay to the passenger compartment. After much head scratching I decided the best way was to roll back the carpet drill the passenger side foot well close to the centre tunnel just below the bottom of the fuse box cover trim panel. Suitable tight fitting grommets sealed with Dumb-Dumb mastic were used to prevent possible water ingress.

The fuel filler was fitted in the rear wing just aft of the existing petrol filler, standard 8mm plastic coated copper was used for the filler pipe.

Now to prepare the car I
(1) Did a compression test --- 180psi on all cylinders.
(2) Fitted New spark colder plugs NGK BKR7ES gapped to 0.7mm
(3) Ran petrol EOBD diagnostic scan to check for any fault codes and made note of live data values of fuel trims, MAP and Lambda values.

After all was ready for the first fill with gas -- and in spite of being a very experience engineer I made two classic errors
(1) I left the thumbwheel valve on the tank close
(2) I had forgotten to fully tighten the pipe union at the tank end on the main front to rear pipe.
Fortunately having read of others on the forum making the same mistakes I knew exactly what was wrong.

Put a few litre of gas in the tank -- then a check over revealed no obvious leaks so I filled the tank

Back home connected the diagnostic software entered the sensor and coil parameters and ran the automatic setup --- but it wouldn't run on gas. So I checked the operation of the solenoid valves and that gas was getting through to the vapour side of the system. But it still wouldn't run on gas.
After a few minutes thinking I restored manufacturers settings and after setting the main parameters, and I ran the auto set up and it worked. The gas metering nozzles are currently drilled at 2.1mm and the injector multipliers are between 1.3 and 1.4.

That was yesterday it has been running almost perfectly on gas ever since -- only fault seems to be running a little weak over 4,000 rpm but that should be easily tweaked when I borrow a laptop.


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PostPosted: Mon May 11, 2009 7:58 am 
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Joined: Fri Jun 29, 2007 2:28 pm
Posts: 1131
Location: Northants.
Nice to see another succesful DIY on here. You were very thorough with the set up, I just ran a auto calibrate on my Zavoli and luckily it worked. Things I learnt, the spuds can be just over 2 inches from your petrol injectors, the pipes also don't have to be all the same length and the spuds can also be at different angles and in slightly different places. Alas I had no choice with this because of the complex manifold on the Vauxhall engine and my lack of planning. I also find the rubber boot you have to fit behind the filler is token because when you release the gun the excess enters you car through the rear vent.
Also I learnt that cashiers poop themselves when they see LPG shooting in a thin streak across the length of you boot from a first time leak.
Have you had a inspection yet?
I used Tann Autogas in Finedon, Northants. They were helpful and charged £85 for a full LPGA certificate. They just got me to fit a larger exhaust shield for the tank but gave me the ally sheet to do it with. Apart from that it passed.


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PostPosted: Sun May 17, 2009 8:13 am 
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Joined: Mon Apr 21, 2008 3:54 pm
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Tweaking the multiper curvre didn't fully cure the mid range weakness problem, but bumping up the regaulator output pressure from 1.2 to 1.3 bar did. I have noticed that you can hear the gas injectors operating more noticeably at the only slightly higher pressure

I think I may re-drill the nozzle size from 2.1 to 2.2 or 2.3 mm and reduce the pressure , rough clculations indicate 2.2 mm should be spot on but I have 2.3 drills in the tool box and 2.2 would have to be ordered.


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PostPosted: Sun May 17, 2009 9:02 am 
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Joined: Fri Jun 29, 2007 2:28 pm
Posts: 1131
Location: Northants.
The Stag 4 kit looks really impressive for its' small size with the ecu being not much bigger than a packet of fags and the tiny vapourizer with built in solenoid/filter. They are a bargain on ebay at present.
I almost bought the AC Autogas system which is the same as the Stag 300 from ebay. The Stag 4 though would have saved me no end of trouble but it was not available at christmas as my Zavoli reducer and AEB ecu are quite big and this made them very hard to fit in the compact front end of my Zafira.
Profess Autogas in South Wales are one of the main importers of the Stag system me thinks.
Good luck.


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PostPosted: Wed May 20, 2009 2:11 pm 
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Joined: Mon Apr 21, 2008 3:54 pm
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I found had a flat spot between 3000 and 4000 RPM under full throttle conditions lambda readings confirmed the car was running weak in this speed/load range. I tried playing around with the gas injector multipiers with a little success but could not get the petrol and lpg injector curves to match at the extreme high load end of the scale.

Next move was to bump up the varouriser output pressure, this worked to some extent, but I wasn't 100% happy with this as a solution, so the I decided to bore out the metering nozzles from 2.1mm initial setting which was right at the bottom end of the kit manufacturers recommended size range for the engines power output per cylinder. Initially I had intended to step up to 2.2 or 2.3 or even 2.4mm however I found reports on the web the Vauxhall Omega 1.8 owners were using nozzles with larger bores up to 3.0mm, I also found that the manuals for other kits based around the same regulator and gas injector rail recommended bigger bore nozzles.

As a result I have now drilled the nozzles to 2.5mm and brought the gas pressure down. I adjusted the gas pressure down to bring the gas injector times in line with petrol injector tmes --- multipiers are now in a range between 1.1 and 0.9.
The flat spot is completely gone, engine response and performance is identical on gas and petrol --- when idling on gas is smoother and less prone to hunting when the AC turned on than it is on petrol.
Lambda readings taken via EOBD are identical both in closed loop and open lop modes. I suspect the bigger nozzles were required because the Rover 1.8 engine uses fully sequential injection.

Result I am one happy camper.


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PostPosted: Wed May 27, 2009 6:35 pm 
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Joined: Mon Apr 21, 2008 3:54 pm
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Car is returning 27.5 mpg on gas better than I expected, as on petrol 30 MPG is the norm.

However as the weather is warmer perhaps 31 or 32 on petrol would be nearer the mark.

I have still got a flat spot with WOT in the mid RPM range untill the engine is fully hot, and having tried bigger nozzle size and increased pressure I have come to the conclusion the vaporiser can't keep pace under these conditions.

It is a Tomasetto Alaska which most kit adverts claim is rated at 140 bhp but is in fact only rated at 134bhp by the makers which should still be be enough to cover a 118bhp car but I suspect it isn't so I might try fitting a Bigas RI-21 vaporiser.


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