Complete LPG testing

[Gilbertd]

An ELM327 can be a useful tool on an OBD-II car, and communicates with the car's own engine management computer system for all of its data.

Have you thought about where you might plug it into your carb-equipped car?

Different poster Ross, this is the guy with the Carina fitted with an open loop, closed loop system. Confused me slightly at first too

[junkcatcher]

Most ELM327 interfaces sold are imperfect clones nearly the pro grade software refuses to work with it.

Usually the cloned interfaces are supplied ciomplete with software that isn't so picky and will do the job. For a 4 cylinder engine you want to look at the the graphed live data output from B1S1 and the short and long term fuel trims and compare the results between petrol and lPG

[cors]

An ELM327 can be a useful tool on an OBD-II car, and communicates with the car's own engine management computer system for all of its data.

Have you thought about where you might plug it into your carb-equipped car?

Different poster Ross, this is the guy with the Carina fitted with an open loop, closed loop system. Confused me slightly at first too

Neither the less i shall use the opportunity .This car has more sensors than i care to know about but i have not found one on the exhaust. which is a bummer.BUT i think the exhaust manifold has a few strange closed thread holes that might fit an adapter to take the plug. I need to get my camera out and do the pics i want but i am an Aussie and the winter has thrown me a little considering i am working on the car in a open parking lot.(need to toughen up a bit).

Also there is a pollution system on the exhaust that once as operating temp is reached, the coolant that goes through the inlet manifold heats up a vacuum hose connection that allows manifold vacuum to operate another vacuum assisted valve.
This valve opens and lets manifold vacuum suck exhaust fumes into the inlet manifold for a second burn, im guessing i could use that place because the pipe that goes from the exhaust to inlet manifold is full of carbon and the system doesn't work anyway.
My van does have a catalyst converter though, poor quality i suspect.

[greg.ray]

"You can make a crude exhaust gas analyser using a generic 4 wire lambda sensor in a piece of steel pipe that can be fitted onto the tailpipe. The sensor will have 2 white wires which are for the heater so need connecting to 12V, a grey wire which is signal ground (connect to 12V negative) and a black wire which is the signal wire. The signal wire will give a voltage. 0V means the engine is running weak, 1V means it is running rich. It will actually flip flop between the two extremes when it is correct and stay at one reading or the other if it is wrong. You'd need to allow it to heat up for about 20 seconds before it will do anything sensible. You'll probably find that a multimeter with a needle is easier to read than a digital one. It will be slow reacting because it will be analysing gas that has travelled the length of the exhaust system, rather than as the engine is at that precise moment."

With regards to this, can someone explain how this is produced exactly. It sounds like a very nice idea if I can make my own. Also, in terms of what readings you get, what would be the expected normal readings exactly?
Thanks
Greg

[Gilbertd]

There's a picture at the bottom of Simon's page here http://www.diy-lpg.co.uk/articles/files ... -loop.html. It consists of a length of steel pipe of the right diameter to be a reasonable fit inside your existing tailpipe. It has a clamp welded to it so it can be clamped to the exhaust pipe to stop it falling out and a threaded boss welded to it to allow a lambda sensor to be screwed into it.

The lambda sensor will give an output of 0.1V if the mixture is lean and 0.9V if it is rich. If the mixture is correct it will flip flop between the two about once a second. It is the average you are looking at, if it hangs at one end of the scale or the other, the mixture is wrong. However, bear in mind that this will be of little use on a car with a catalytic converter as the cat will clean up the emissions. It needs to be before the cat, so is fine on a car that has had the cat removed or is too old to need one but not a lot of use on anything that does have one.

[rossko]

The lambda sensor will give an output of 0.1V if the mixture is lean and 0.9V if it is rich. If the mixture is correct it will flip flop between the two about once a second.

Gotta qualify that in this context....
A standard sensor probe will indeed say low for lean, and high for rich. It doesn't really have a "just right" output, only high or low. That might sound less than ideal, but in fact its a very useful property for electronic closed-loop engine systems which continuously adjust the fuelling. Its much less useful as a test tool out of its natural home.

In most closed-loop engine systems, it will indeed normally be seen to flop from one state to the other and back at regular intervals. The system varies the fuelling by a very tiny amount to keep the sensor popping from one state to the other, that way it knows it is hovering about the 'just right' state. Bear in mind a closed-loop system already has its own sensor permanently fitted to the exhaust, so you wouldn't really need this tool to begin with.

In a few closed-loop systems, the fitted sensor is of a so called 'wideband' type. This type will give readings at a number of mixture settings, its much more like a true lambda measurement than the high-low two states of the standard sensor. The fuelling control isn't continuously hunting up and down by tiny amounts, it seeks the right level and maintains, only correcting when the sensor signal wanders off target. Monitoring the sensor output should a give pretty steady output, then.
If you stick a high-lo sensor up the tailpipe of a car running wideband, you will not see flip-flopping, you will a steady 'lean' or 'rich' signal .... because the high-lo sensor is incapable of signalling 'just right'.

Finally, on an open-loop car - and that includes almost all Carburetter and early fuel injection systems - there is again no hunting around for the 'just right' state, so again the hi-lo stuck up the tailpipe isn't going to flip-flop. It will tell you rich or lean of course - but you will have little idea if 'rich' means 0.01% rich (which really is as close to perfect as you are going to get from this kind of system) or 30% rich (its flooding and running like a pig).

What I'm saying is, don't expect much from this for your use case.
In reality, the sensors aren't completely hi-lo, there is some degree of variation i.e. 0.0V probably means very lean, while 0.2V is probably close to spot-on ; especially if it suddenly tips to 0.7V, which might be equally close to spot-on but on the rich side. So some information can be gleaned, but you'd need a good understanding of how the sensor works, and an appreciation that every sensor is slightly different, and the capability to estimate what effect having it the "wrong" side of any catalyst wil have, to get anything really useful from it.

If you're not asleep yet, you might be thinking "aha, what I really need is one of those wideband lambda sensors" and that is quite true, a much more useful tool can be made. It will still lie if there is a catalyst upstream, but the biggest problem is the cost of these types of sensor.

Finally, don't forget all applies only in steady state conditions, i.e. cruise or idle. Under hard acceleration things go rich by design, on the overrun things go lean by design. Don't imagine there is a fault if you observe that happening, but you can you use the tool to check that is happening as it should.

[greg.ray]

Would the gunsons gas tester be any use in these circumstances at all? It does give an indication of how an engine is running, but I am not sure if this is of any use in a fuel injected car such as mine with a lambda sensor.

With thanks
Gregory

[SimonHobson]

Would the gunsons gas tester be any use in these circumstances at all?

Personally I didn't find one very useful at all.

To start with, you can't really drive around with it set up - and you need to be able to load the engine to get good results. Secondly, I didn't even find it that reliable (it tended to block the pipe with condensation) and when it did work, I couldn't really relate the readings to what I was doing.

Whilst the "lambda probe up the tailpipe" approach is quite crude, it does in effect give you a pretty direct reading - if there is oxygen in the exhaust then it's lean, if there isn't then it's rich (you aren't likely to get it 'spot on').

[cors]

As i found out my van does not have a lambda sensor.
I will pick up my new lambda sensor tomorrow and will try and create my testing equipment.
borch sensor. 4 wire unit.

[MarkJones]

Would the gunsons gas tester be any use in these circumstances at all? It does give an indication of how an engine is running, but I am not sure if this is of any use in a fuel injected car such as mine with a lambda sensor.

With thanks
Gregory

The gunsons gas tester i think tests gas to plus or minus 0.5 percent accuracy..in days when cars had carbs and less stringent emissions it was a great tool

so it could be reading 0.3...and you may need to get it to below 0.3 to pass the tests ..but because of its inaccuracy ..you don't know if you are there or not...it may actually be 0.8

so you need a gas analyser with plus or minus 0.1 accuracy or better .

but the gunsons will tell you that you are way over ..so that you can do some more work to get it nearly right ..

i have a snap-on one ..and its hard to know whats going on ..as the idle levels drift all over the place at tick over unless you keep putting it through a prolonged fast idle to clear it ..

BTW just because it has two digits past the point does not mean its accurate...proper 4 gas garage machiines have a self calibration built into them ..they have a store of calibration gas to compare

all the best.markj

[rossko]

..in days when cars had carbs and less stringent emissions it was a great tool

To be fair, he does have a carb.
Don't matter cos he's cobbling something else now

[cors]

Finally got a pic of the new sensor.Next i will pick up an Analogue multi meter.

I know you guys have seen them all before but its kind of a big deal for me considering i live in Russia and no one around me cares.

[SimonHobson]

Finally got a pic of the new sensor.Next i will pick up an Analogue multi meter.

I know you guys have seen them all before but its kind of a big deal for me considering i live in Russia and no one around me cares.

Yes, I guess we do take things for granted here - like ordering stuff for next day delivery etc. I've been watching a series called Ice Road Truckers which is an American program about truckers on the ice roads in northern America (first two series are in Canada, next two are in Alaska). When you realise that there are communities there that don't have any road connection to "the rest of the world" for like 10 months of the year does make us seem very soft here in the UK. Need something, well order it now and it can be delivered when the ice comes in 6 months - can't see that going down well in a country where people blame the council for not keeping every road completely snow and ice free for 365 days a year

Interesting that your kit comes not only with self seal crimp butt connectors (you crimp the terminal, then use a heat gun to shrink the sleeve), there appears to be at least one connector in there as well.

[Gilbertd]

I've been watching a series called Ice Road Truckers which is an American program about truckers on the ice roads in northern America

C'mon, be honest and own up. You're only watching it because of the tasty blonde driving around in 40 odd tonnes of truck....

[MarkJones]

They are behind here in the uk ..

There is another series called IRT deadliest roads ..set in india ..

also look out for "Gold rush Alaska" episode 8 on friday

All the best.markj

[SimonHobson]

I've been watching a series called Ice Road Truckers which is an American program about truckers on the ice roads in northern America

C'mon, be honest and own up. You're only watching it because of the tasty blonde driving around in 40 odd tonnes of truck....

Err, I couldn't possibly comment. Hmm, I wonder why Lisa got chosen to be one of the featured drivers

They are behind here in the uk ..
There is another series called IRT deadliest roads ..set in india ..
also look out for "Gold rush Alaska" episode 8 on friday

Looking forward to them - got my MythTV box set to record them as soon as they appear.

[cors]

Dont hesitate to feed me knowledge >if i get good at this i will try a harder install next time!

[Gilbertd]

You're making this one pretty hard without any input from us.......

[cors]

You're making this one pretty hard without any input from us.......

How true, i hope not to offend anyone and put them off posting their ideas.
Today i get my Analogue MM

And here it is.Ok i think i heard word of using some components, resistors i think.will keep searching

[cors]

Hello.

Can anyone help me to find a schematics to build the tester?. I am unsure what to look for .

regards