ThreeSheds Posted May 31, 2011 Share Posted May 31, 2011 I went to a wedding on Sunday in the RRC (3.9 on gas), about 120 miles. I have recently fitted a new vapouriser which involved moving all sorts of pipes and wires, and which I carefully (hah!) arranged to allow for the engine movement that occurs under torque, judder and off-road impacts. The journey down was uneventful, but just before I parked I had quite a hard bump when I failed to notice a speed hump and I thought to myself: "That's the first time my pipework and fitting have been tested by fore/aft engine movement". I set out to drive home and it was immediately apparent that something was wrong: It wouldn't pull beyond about 1/2 throttle, so I pulled up and - in the gathering gloom - I had a feel around all the pipes and connections. (I was wearing my light suit and a white shirt so nothing too extreme!). Set off again and still the same. But I appeared to be able to cruise at 60 so I soldiered on for a bit, but it was getting gradually worse. While driving I did some experiments and thought through a few things to try and diagnose he problem. Came up with loads of possibles and kept stooping to check this and check that, but all the time I was fixated on the stuff I had recently worked on. (I had proved it was the gas because it ran OK on petrol). Could I be out of gas? No - I had only done 120miles on that tank... After several hours of @rsing about (and a couple of kips since it had been a long day) I gave up, bit the bullet and drove home on petrol (ouch! My wallet!) Cut to Monday and I set out to fix it. Opened the bonnet and checked wiring, pipes, unions etc. Nothing. Stood beck and looked at it and suddenly FLASH! - could I be out of fuel? Well I thought, I had best check it even though I had discounted this the night before, maybe the new pipes etc had a leak or something?. So I checked the gas and lo! There was none (well no liquid anyway) - then I realised that I HADN'T filled it with gas just before setting out as I had planned because I had thought "It will just nicely get me there and I can fill up before I come back!. WHY, OH WHY had I forgotten that the night before (alcohol was not a factor, honest!) So I filled it up and presto - back to normal. What a wally! Quote Link to comment Share on other sites More sharing options...
Quagmire Posted May 31, 2011 Share Posted May 31, 2011 D'oh! The joys of LPG fuel tank gauges- you never can really tell 100% what you've got onboard... Especially annoying if the pump you last used didn't give you a proper fill and shut off after half the amount you would normally get in (I hate that!) What vapouriser have you fitted and how are you finding it? I cannot get my Bigas M84 to hold any tune whatsoever. I know what you mean about the feeling you get when having to drive on Petrol on great distance, you get this squealing sound from your pocket as your wallet has a mental breakdown... Quote Link to comment Share on other sites More sharing options...
task Posted May 31, 2011 Share Posted May 31, 2011 I always reset my odometer when I fill up with LPG, helps to predict when it's going to run out Quote Link to comment Share on other sites More sharing options...
Quagmire Posted May 31, 2011 Share Posted May 31, 2011 Me too- but the pump not filling thing still gets you then. Still better than forgetting to fill up though :D Quote Link to comment Share on other sites More sharing options...
ThreeSheds Posted May 31, 2011 Author Share Posted May 31, 2011 D'oh! The joys of LPG fuel tank gauges- you never can really tell 100% what you've got onboard... Mine is so bad that when I refitted the tank I placed it with best pipe runs in mind knowing that I wouldn't be able to see the gauge without removing a panel... I usually rely on the trip meter too, but recently I have been relying on what I call 'tanking' : When there are about 25 litres left the fuel-level float starts hitting the inside of the tank when the LPG sloshes about. It makes a sort of a metallic 'tank-tank-tank' noise - see what I did there? When there are about 10 litres left it changes rhythm to a double 'tank' When there are about 5 litres left it goes quiet again. The above is very convenient when you are in stop-start traffic, but doesn't work when you go through all three stages on the motorway... What vapouriser have you fitted and how are you finding it? I cannot get my Bigas M84 to hold any tune whatsoever. I couldn't get my old one to run right either - it was either too lean at the top or too rich at idle (or both). Now I have an OMVL R90E which is great - I can just do it by ear and get it running nicely - my mileage (which was pretty dire) has increased by about 20% too Plus, I still haven't done any proper tuning so either I am a tuning god or there is still more to come Quote Link to comment Share on other sites More sharing options...
Quagmire Posted May 31, 2011 Share Posted May 31, 2011 I'd never thought of listening to the tank- mine is in the loadbay of my 90 so it's right behind me!- I get the clank/tank/boing noise all the time but am obviously too dense to have noticed a pattern to the noises- will listen out in future Will checkout the OMVL then, mine is getting quite annoying- I recently made an adjustment to the mixture to get a better mixture under load, and my mpg crashed and burned as a result, and I have been struggling to get it back since. My last tank gave me 14.5mpg, so am on my way back to where I was, but it's just too hit and miss to do any adjustment with any real certainty. With my wideband plugged in I can literally make a small adjustment at idle, get it where I want it - and the next time I blip the throttle it ends up somewhere totally different! And i'm not talking about a 0.1 or 0.2 AFR difference, I mean like a whole 0.5-1.0! I then wind it back to where it was, and it ends up somewhere different again! Quote Link to comment Share on other sites More sharing options...
ThreeSheds Posted June 1, 2011 Author Share Posted June 1, 2011 My old one (can't remember the make) was similar in terms of adjustments. I decided it needed a good clean-out, but couldn't get a gasket set for it so I bought the OMVL (for less than £80) from here. One thing about the OMVL I don't like much is the breathing arrangement for the back-side of the diaphragm - this really is quite a large hole (about 12-14mm perhaps) with no easy way of protecting it from water etc. and if water goes in there it will really buggerup your mixture until it evaporates (there is no drain unless you unbolt it and turn it over). My plan (before hitting any deep water) is to pipe a breather to the (near-by) snorkel tube, but it needs to be a fat pipe (to allow for easy-quick throttle changes) and I don't know yet how I will fix it to the rear cover - glue looks favourite... Tuning for me is mainly an ear job. I do have a narrow lambda feeding into an array of LEDs, but I find that it runs better if I use that as a guide only and then play around a bit. At the moment it's running quite nicely and I am only making minor adjustments before each run and then making real world drivability checks. I have found in the past that for a stable idle and better pick-up off idle I need it a tiny bit rich (gauge flicking from green to red), and for cruising economy I set a bit lean by the gauge (not enough to affect the 'feel'), although technically lean, the plugs look great at this setting. Roger p.s. When I changed my vap I also moved it over to the intake side to shorten the gas-pipe run - I don't know how much difference it made but it should lead to improved throttle response I think... Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted June 1, 2011 Share Posted June 1, 2011 .... My plan (before hitting any deep water) is to pipe a breather to the (near-by) snorkel tube, but it needs to be a fat pipe (to allow for easy-quick throttle changes) and I don't know yet how I will fix it to the rear cover - glue looks favourite... ... I must confess to knowing absolutely nothing about vapourisers however the thought did cross my mind that the breather is I assume to keep one side of the diaphragm at atmospheric pressure.... if you pipe this into the snorkel (I may have misunderstood what you meant) then when you accelerate there will be a lower pressure than atmospheric due to the suction of the engine, won't this mess up your fueling? My apologies if I am talking out of my ar$e here. Quote Link to comment Share on other sites More sharing options...
ThreeSheds Posted June 1, 2011 Author Share Posted June 1, 2011 I must confess to knowing absolutely nothing about vapourisers however the thought did cross my mind that the breather is I assume to keep one side of the diaphragm at atmospheric pressure.... if you pipe this into the snorkel (I may have misunderstood what you meant) then when you accelerate there will be a lower pressure than atmospheric due to the suction of the engine, won't this mess up your fueling? My apologies if I am talking out of my ar$e here. Not at all! You are bang-on. That's a very relevant point but one which I have considered and I think that it wouldn't be a problem for the following reasons... The breather is designed to keep the 'other side' of the diaphragm at atmospheric so that there is a relative difference between that and the vacuum caused by the venturi. It is the difference that is important in determining the amount of gas going into the system. Normally there would not be a snorkel in the system, and the pressure difference would be mainly due to the venturi and a little from the air filter, and normally the breather and the engine air intake would be experiencing roughly the same conditions (both being under the bonnet). In my proposed case there is possibly (as you said) extra vacuum due to the length of the snorkel and the Bernoulli effect, but also I think, at times there will possibly be extra pressure (at speed or when experiencing gusts of wind) - either way the addition of a snorkel I think, introduces a fair bit of variability into the intake pressure. Because of that, I think that connecting the breather to the snorkel pipe would actually allow for more consistency of the required pressure difference, and hence allow me to then adjust the mixture more effectively. The Bernoulli effect would of course tend to lead to the mixture going lean at higher engine speeds, but would at least be consistent and so I hope that I will be able to compensate for that with the settings. Hope so anyway (If not I'll put it back as it was ) Roger p.s. The other thing I briefly considered was piping it into the intake between the filter and the venturi so that the only determining factor in pressure difference would be due the two Bernoulli effects - one from the speed of the air through said venturi and one due to the speed of air through the intake tube, but this would be physically quite difficult to do so I thought that the snorkel pipe was near enough. Hope this all makes some sense... Quote Link to comment Share on other sites More sharing options...
Gromit Posted June 2, 2011 Share Posted June 2, 2011 If you read all of the above, then you are probably now here: Wiki - Bernoulli's principle Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted June 2, 2011 Share Posted June 2, 2011 ... In my proposed case there is possibly (as you said) extra vacuum due to the length of the snorkel and the Bernoulli effect, but also I think, at times there will possibly be extra pressure (at speed or when experiencing gusts of wind) - either way the addition of a snorkel I think, introduces a fair bit of variability into the intake pressure. Because of that, I think that connecting the breather to the snorkel pipe would actually allow for more consistency of the required pressure difference, and hence allow me to then adjust the mixture more effectively. The Bernoulli effect would of course tend to lead to the mixture going lean at higher engine speeds, but would at least be consistent and so I hope that I will be able to compensate for that with the settings. Hope so anyway (If not I'll put it back as it was ) ... I must admit I had never thought about the increased variablility of pressure caused by the snorkel and how your approach may actually compensate for this, looks like you have thought quite a lot about this! I'll be very interested to hear the outcome of this mod once you work out how to attach the breather, mostly for my geeky side really :-) Quote Link to comment Share on other sites More sharing options...
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