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PostPosted: Fri May 20, 2016 7:29 am 
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I have a Cologne 2.8 in my Scimitar and it has never been particularly good. There is a definite loss of power and smoothness in use that isn't there on petrol. I have done all the servicing and adjustments, including trying an ignition advance and even swapped out the engine. I have adjusted the mixture setting by ear, although it was previously set by an LPG specialist. However, I don't know for sure what the CO should be set to and I suspect it was set lean as per an injected vehicle. As an example, the CO on petrol is meant to be between 2 and 3% and I wondered if that would be the case for LPG too? Fuel consumption is poor, I get 90 miles for around 32 litres around town and I would have expected more. No sign of leaks or other problems.

Any other suggestions for making the LPG better would be gratefully received. I would even travel a realistic distance to someone who is used to N/A installations.


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PostPosted: Fri May 20, 2016 10:27 am 
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Open or closed loop? I suspect open with no lambda feedback. CO would normally be lower than on petrol but not by a huge amount althouh using a lambda sensor to set it up is more accurate. Have a look here http://www.diy-lpg.co.uk/articles/files ... -loop.html for setting up an open loop system.

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PostPosted: Fri May 20, 2016 11:01 am 
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Interesting information Gilbert, thankyou. Perhaps I need to buy myself a wideband Lambda sensor. In the meantime I will hijack the CO meter at my MOT station and at least set it up that way. Not sure what CO to aim for on LPG, 1% perhaps?


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PostPosted: Fri May 20, 2016 10:54 pm 
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I'd say 1% is probably a little lean, even taking various other things into account. Think i'd aim for about 1.5 - 2.0% as a starting point, make sure the bias is right or as near as possible across the rev range and then take it for a test drive. You may find you have to alter the bias to regain mid-range ortop end then re-tweak the idle - it's trial and error until you get it to run the best you can really.
If it runs fine across the rev range with 1.5 - 2.0% on idle and leans off when cruising then i think i'd stick with that, if not tweak whichever way you need to.

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PostPosted: Sat May 21, 2016 10:10 am 
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Scimitar wrote:
Not sure what CO to aim for on LPG, 1% perhaps?
That's the thing, really.. Like Gilbert said, compared to petrol CO may come down a bit on LPG but would have to guess what CO level would provide correct mixture. Meanwhile a lambda probe would tell you when the engine is running correct mixture. Plenty open loop systems are set up by the methods Gilbert pointed to and those methods usually give good results.

Simon

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PostPosted: Mon May 23, 2016 3:07 pm 
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Well I think we may be getting somewhere. Original setup showed weak mixture on the nearside bank. I believed it to be a problem in the head and as I was replacing the engine, didn't worry much. The carburettor was a new genuine item.

I fitted a new powerplant and re-installed the carburettor to it and went for an MOT today. Once again there was no way that the nearside bank would set up due to weakness. I could hear a whistle too, which suggested an air leak. Spraying brake cleaner around gave a reaction at the carburettor base on the rear nearside so it was taken off. The rear part of the base was banana shaped! If anyone but me had installed it, I would blame heavy handed installation, but it was done properly with the spring washers just compressed.

A replacement has been ordered for tomorrow and the supplier has agreed to inspect the original. I am sure they will say it has been abused, but at least the issue should resolve. Thanks to everyone for their suggestions and I will report back when done.


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PostPosted: Tue May 24, 2016 6:31 pm 
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Well one step forward and two back.

I wasn't able to setup the CO again. This time both banks were running but at 3000 RPM it leaned out terribly. I could get about 3% at idle with adjustment of the power valves and it went to almost nothing at speed. Bias control appeared to do nothing to improve matters. Looks like I may have to go back to the original dealer as I can't find anyone else locally.

Moving over to petrol, once again it was horribly rich. Mixture screws were nearly all the way in to achieve less than 3%. They should be around three and a half turns out. I did find that .50 idle jets are fitted where I expected .45s, so that will not help. As the MOT station wanted to close I had to abandon at that point.

Very frustrating!


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PostPosted: Tue May 24, 2016 7:00 pm 
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If the bias won't do anything, I would suspect a restriction in the supply pipe, a vaporiser that is full of heavy ends or a vaporiser that is grossly under specced for the car. What vaporiser are you running on it?

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'96 Saab 900XS, AEB Leo, sold
'93 Range Rover 4.2 LSE, Lovato LovEco, sold
'98 Ex-Police Range Rover 4.0, Singlepoint AEB Leo, my daily motor
'97 Range Rover 4.0SE, eGas multipoint, a project.....

Proud to be a member of the YCHJCYA2PDTHFH club.


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PostPosted: Tue May 24, 2016 7:31 pm 
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This is the vaporiser unit which I think is an OMVL. I have moved the output from upper to lower port and didn't notice any residues.

Not sure which is the idle mixture control?

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PostPosted: Tue May 24, 2016 8:29 pm 
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If that's an R90E, and I can't be sure from that angle but it looks like it probably is, the top one is the idle bleed and the lower one is the main bias. Idle bleed allows a small dribble of gas through in case there isn't enough suck to draw gas in at low revs and should ideally be screwed fully in. That way you are running on the main bias all the time. It does look to be a very old R90E though. The most recent ones have a pair of 6mm headed adjusters while the previous version had an 8mm idle bleed and a 10mm main bias. Never seen one with the bias inset like that. Main bias will have a spring behind it while the idle bleed is just a tapered bolt.

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'96 Saab 900XS, AEB Leo, sold
'93 Range Rover 4.2 LSE, Lovato LovEco, sold
'98 Ex-Police Range Rover 4.0, Singlepoint AEB Leo, my daily motor
'97 Range Rover 4.0SE, eGas multipoint, a project.....

Proud to be a member of the YCHJCYA2PDTHFH club.


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PostPosted: Tue May 24, 2016 8:45 pm 
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Bias control has been shrouded with a short stub of rubber hose by the PO. Are you suggesting that I should be looking to replace the vaporiser? It will be the only component not yet replaced!

I have not touched idle bleed at all, just the bias and power valves.


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PostPosted: Tue May 24, 2016 9:26 pm 
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You could but it won't help if the problem is down to a restriction in the gas supply. An R90E is good for getting on for 300 bhp so should be adequately rated. When they start to go they usually supply too much gas rather than not enough. The bit of hose explains why it looked like it was inset in the picture, presumably it was put there to stop it from vibrating out.

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'96 Saab 900XS, AEB Leo, sold
'93 Range Rover 4.2 LSE, Lovato LovEco, sold
'98 Ex-Police Range Rover 4.0, Singlepoint AEB Leo, my daily motor
'97 Range Rover 4.0SE, eGas multipoint, a project.....

Proud to be a member of the YCHJCYA2PDTHFH club.


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PostPosted: Tue May 24, 2016 10:15 pm 
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They can vibrate out if unscrewed far enough. If unscrewed that far in the first place that might point to too large venturi on the mixer (and you have a lean mixture?) or spring missing from the sensitivity screw. If the idle bypass screw needed to be undone that far there'd definitely be some sort of problem.

Simon

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PostPosted: Wed May 25, 2016 12:23 pm 
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I have replaced the petrol pressure regulator today and it seems to idle well enough.

It runs on LPG and I can tune a reasonable idle both on the power valves and on the bias. So I need to see if I can get back on the analyser to see if it will set up correctly.


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PostPosted: Thu May 26, 2016 8:09 am 
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You need to follow the steps in the link I sent you. Set the power valve once and then adjust the vaporiser so the same power valve setting is correct at idle and then at higher revs. If it is still going lean, and you can't adjust it out, then start looking at restrictions in the gas supply.

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'96 Saab 900XS, AEB Leo, sold
'93 Range Rover 4.2 LSE, Lovato LovEco, sold
'98 Ex-Police Range Rover 4.0, Singlepoint AEB Leo, my daily motor
'97 Range Rover 4.0SE, eGas multipoint, a project.....

Proud to be a member of the YCHJCYA2PDTHFH club.


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PostPosted: Thu May 26, 2016 11:13 pm 
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Just been reading through this thread again and it jogged my memory cell! When i first got my Jeep, it was running horrendously rich at idle (3.9%) on gas and then going down to 0% at about 2500-3000rpm. Amongst all the other problems i've found with it, the mixer was partially blocked (more than half the holes were solid with heavy ends or similar) and to clear it, i disconnected the vapour inlet hose from the mixer and squirted carb cleaner through it.
This improved matters considerably resulting in much smoother running throughout the rev range and once i got the idle down to a more sensible level, the mixture leaned off a bit under cruise conditions but was still at about 0.7% if memory serves. Bear in mind i was using a Gunsons Gastester and by that time i had my suspicions about it although having found the blocked mixer i wasn't so sure so the figures might not be accurate but are a guide to what was actually happening.

Could be worth investing a few quid in a can of carb cleaner to give it a try - very often the solution to things like this really is that simple.

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PostPosted: Fri May 27, 2016 8:25 am 
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Most kind Dave, I will look into that. The mixer was recently replaced but still worth a look! I have the car booked in at the specialist in Stonehouse next Thursday. Hopefully they will be able to double check what I have done and make sure all is well. Then off to France on Saturday, so the last thing I need is melted pistons!


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PostPosted: Fri May 27, 2016 8:27 pm 
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A bit more experimentation today. I took the carburettor off again and made absolutely certain that it isn't leaking air around the gasket. I also setup my new Innovate AFR meter with an exhaust sniffer.

Results from that once again showed that getting the fuel rich enough was impossible. The offside bank was able to be swung either side of optimum. I took off the nine month old mixer and inspected / cleaned it with no improvement.

Setting the carburettor to the typical 3 turns out gave correct figures both sides, so that tended to suggest a problem with the LPG delivery. As the mixer is fed with seperate pipes from the power valves, I tried setting up again with the old mixer which was a single feed design. Interestingly enough, I was then able to get reasonable figures both sides, but not consistently.

I looked at the twin mixer again and noticed that it doesn't fit securely on the top of the Weber, but rocks from side to side. Dressing the high spots back didn't seem to achieve much. As the old mixer snapped in securely, I decided to stick with it for now.

Setting up again showed the idle going lean, which the bias control made no difference to. Nor did it make any difference at speed, although it had been effective previously. Final job was to drop the idle speed a bit and then the idle mixture went off the clock at the lean end. I wonder if the wideband sensor hasn't enough emissions to read correctly? I don't have CAT's by the way.

Other notes..

Setting the engine up by ear gave readings that showed very lean, so until I can get it onto a CO meter, I will have to reserve judgement.


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PostPosted: Fri May 27, 2016 8:33 pm 
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Partly restrict air flow into the mixer with something (not your hand) temporarily to see if that causes the mixture to get richer.

You will have read Gilbert's suggestions (and link) on how to calibrate... So 'by ear', can you make it go too rich, so engine revs start to fall away again / or do rpm's increase the further you unscrew the sensitivity screw?

Simon

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http://www.Lpgc.co.uk
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PostPosted: Fri May 27, 2016 10:17 pm 
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I may be speaking out of turn here but on mixer systems on engines originally fuel injected, it seems common practice to use RTV sealant to ensure a gas tight seal between the mixer and throttle body. I would think this would be the same on carb fed engines or some other method of seal such as a gasket between the mixer and the carb.
If that is missing then not all the airflow at any given time would pass through the mixer so the mixture on gas could be variable to say the least.
Perhaps worth looking into or maybe Simon could advise?

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