LPG Discussion Forum

I like to understand stuff and with that in mind have been looking at fitting a simple narrow band Lambda sensor and a meter to my 1988 VW T25 Camper, (flat 4 watercooled carb engine). I have a stainless exhaust with a blanking plug But researching on here (and elsewhere) tells me that type of setup is of little real use.

Hence my question = What type of gear do the pro's use to tune open loop systems ?

Wide band and AFR perhaps ?

Exhaust gas analyser for those that still have anything to do with open loop systems. There's nothing wrong with using a narrow band lambda sensor either fitted in the exhaust or hung on the end. The only thing is you have to get it reasonably close by ear first. Hold the revs at around 2,500 rpm and adjust the power valve for maximum revs on a fixed throttle opening. Let it drop to idle and adjust the idle bleed screw on the vaporiser for a stable idle. Do this a couple of times and it won't be far out. Have a look at http://www.diy-lpg.co.uk/articles/files ... -loop.html for a bit more info.

Once you have it right by ear a quick check with a wide band sensor will just confirm that you are right.

Open loop systems are the same as carbs to setup in that sense.

Once you have it right by ear a quick check with a wide band sensor will just confirm that you are right.

Open loop systems are the same as carbs to setup in that sense.

We use our ears, feel and decades of knoledge. After that we check it's driveability and adjust it wherever neccisarry. Then we tweak it on a gas alnalyser.

This is good info and I have previously read the DIY LPG article.

Being a bit old school I appreciate the "by ear" method and use it to good advantage on some of my other projects (motorbikes in particular) especially for ignition timing.

However, I have 2 of these VW water-cooled campers, one has a single power valve, but the later conversion has dual power valves, one for each carb choke, and it setting these up correctly that I would like to get my head around.

Why did you not say and the answer is simple.

Pull out that Y with 2 adjusters and replace it with one that only has one adjuster. It will never be 100% right with a twin adjuster.

Ah, that's interesting ! And easy for me to try out

What are the 2 valve setups for then, or are they just considered by the pro's to be simply not as good ?

In my opinion they have no purpose but a lot of teh equipment supplier send them out.

Just by ear, tacho and driving feel myself. I don't think there's much in the way of knowing how fluctuations in temperatures in water, air, gas, etc will affect the mixture even if lambda is set spot on at the time of calibration.

If getting the mixture bang on is of concern to you, consider installing a boss for a permanent lambda into the exhaust and adding a closed loop ECU and stepper motor - Done this on my old camper (Peugeot not VW) because I wanted to be sure the mixture was right when driven flat out (at 60mph!) on the motorway (2L engine pulling a large coachbuilt). Bit of work but re-assuring to know mixture is OK. I don't go to these lengths usually when converting carb vehicles, just thought it worth it on the camper.

Simon
LPGC

My '88 caravelle has the twin powervalve setup too and its been a nightmare to get correct. Vacuum operated second choke on the pierburg hasn't helped either.

Yes setting up twin power valves is a right mare, as dai (c.s) says just put a single y power valve in and you should be good to go. You have to look on a vaporiser / reducer as a carb. For all intents and purposes its got an idle jet (air bleed/ bypass actually) and a main mix jet. And its got a big diaphragm that gives it more gas on vacuum from the engine.
Its a very simplistic way of looking at it, but it helps with tuning.

Cheers Tubbs.

I doubt there is anything wrong with my setup, it was re-adjusted by the installers after a bedding in period. It's just that I like to understand stuff I have

Zebedee wrote:Vacuum operated second choke on the pierburg hasn't helped either.

Yes, it was that reason the I considered a wide band sensor and AFR gauge, so I could monitor it under real road conditions, until I saw the price of the kit! (bearing in mind I don't need any of this, I am just learning / playing ) btw, Are you on the VW T25 "80-90" forum ?

Yep, same username too.
Theres a thread of my LPG install on there.