WANTED: DIY Exhaust Gas Tester/Analyser.

Message

Sir Henry · #1 Post by **Sir Henry** » Sat May 09, 2009 1:20 pm

As above, but no silly prices

yohimbe · #2 Post by **yohimbe** » Fri Jun 05, 2009 9:20 am

look here, I have installed several of these kits in my cars.
http://www.14point7.com/

jalfrezigazee · #3 Post by **jalfrezigazee** » Fri Jun 05, 2009 3:57 pm

where do you get them frokm in the UK?

yohimbe · #4 Post by **yohimbe** » Fri Jun 05, 2009 5:46 pm

i just ordered it direct from Canada, just read the page. I think 5 bucks to the whole world.

Sir Henry · #5 Post by **Sir Henry** » Sat Jun 06, 2009 2:00 am

Since I posted the above I've 'picked up' a Gunsons Professional Exhaust Gas Analyzer. This has helped a lot but doesn't indicate the level of unused O2 in the exhaust.

yohimbe wrote:look here, I have installed several of these kits in my cars.
http://www.14point7.com/

Is that what these kits do? and do they display in percentages or just high/low?

jalfrezigazee · #6 Post by **jalfrezigazee** » Mon Jun 08, 2009 12:03 pm

if you want to know about O2 readings then why not get an air/fuel gauge plumbed in, will have readings all the time then not just when you want to analyse it. Cheap enough from ebay

Sir Henry · #7 Post by **Sir Henry** » Mon Jun 08, 2009 3:53 pm

I've just had a gander at the air/fuel gauges on eBay and they all require some kind of Lambda sensor in the exhaust. Since The Old Girl is well pre-Lambda (1976) fitting one would be problematical at best.

jalfrezigazee · #8 Post by **jalfrezigazee** » Mon Jun 08, 2009 9:46 pm

some of the kits on ebay come with a lambda probe and the boss you can weld onto the exhaust. Or you can buy them seperately for about £25 I think

Sir Henry · #9 Post by **Sir Henry** » Mon Jun 08, 2009 10:22 pm

I'll consider adding such a gauge when finances and other work (multi-gauge to fit and some wiring to fettle) permit.
I assume that the lambda probe needs to be as close to the exhaust manifolds as possible/practical?
On The Old Girl that would be at the side of the sump where both down pipes join to enter the main run under the car.

jalfrezigazee · #10 Post by **jalfrezigazee** » Tue Jun 09, 2009 12:23 pm

you would put it anywhere after where all the pipes jon into one pipe. Distance isnt an issue as the chemical composition of the exhaust should not change as it cools (I think

) If the reading was being used by a computer to change fuelling then location would have to be near the engine so the change is as soon as possible

Sir Henry · #11 Post by **Sir Henry** » Tue Jun 09, 2009 2:45 pm

Pretty much as I thought. However I am given to understand that lambda probes need to be really hot to work properly and the gasses in the exhaust system cool rapidly as they move along the system.

Gilbertd · #12 Post by **Gilbertd** » Wed Jun 10, 2009 12:33 am

Which is why lambda sensors have an inbuilt heater.....

yohimbe · #13 Post by **yohimbe** » Wed Jun 10, 2009 7:34 am

all wideband lambdas do have a heating, and that are the only ones you can use for exhaust gas analysis, the small band only thell you lambda one, rich or lean.

SimonHobson · #14 Post by **SimonHobson** » Fri Jun 12, 2009 7:53 am

My portable tester is simply a bit of pipe with a lambda probe boss. To use it, just stuff it up the exhaust and secure with the bolt, run the cable in through the tailgate or whatever route is convenient.

I only use a standard zirconia probe, so yes it's more or less just "rich-lean" indication, but it's surprising how much information you can glean from it. In practice, it isn't a step from rich to lean, there is in fact a band where it's possible to infer the difference between "barely lean" and "more lean" - so when you are close to the correct setup, it does in fact give you quite a good reading. I'd seen wideband sensors before, but been put off by the price, I think these 14.7 kits seem pretty good value so I might invest.

At the moment I just use a voltmeter and plug the heater circuit into the fag lighter socket. On my list of "round to it" jobs is to add an led gauge for convenience.

Now probe positioning. If you use it for feedback control, then you really need it as close as possible to the engine. It will work anywhere, but if there's a large lag between fuel change and feedback signal, then the mixture tends to hunt at idle. This also applies to the intake length - when I was on dual-carbs, I had a longish inlet tract between the single mixer and the engine. If you have multiple mixers, then my feeling would be that you need multiple probes positioned so that each one can feedback to one mixer - if I were doing a dual carb setup again, I'd use two feedback systems (I never did manage to get the twin mixer setup on my Disco to work right).

If you have a setup where it's not guaranteed to have a uniform mixture across all the cylinders (eg multipoint injectors, or multiple mixers and one feedback system) then you'll need to get the probe in at the first point where all the branches come together - you don't want one cylinder (or group) to run lean because they aren't being monitored.

jabran · #15 Post by **jabran** » Wed Jun 17, 2009 11:10 am

@Simon

Is there any effect on the reading if the lambda is at the exhaust tip in cat systems?

I use the 14point7 kit myself actually (not for lpg tuning) and it very accurate, took it to a mates MOT garage who had just had fresh setup done so his machine would have been correctly calibrated and the readings were on par.

I only use the wideband on my own cars but would be good if I could bung it in my mates cars for a bit of tunign if there isn't a major effect in the reading. What size pipe is best?

yohimbe · #16 Post by **yohimbe** » Wed Jun 17, 2009 11:55 am

yes it is possible but you should use something like this

SimonHobson · #17 Post by **SimonHobson** » Wed Jun 17, 2009 1:12 pm

jabran wrote:Is there any effect on the reading if the lambda is at the exhaust tip in cat systems?

Err, not sure ! But do cars with cats not also have lambda probes for their ECUs ?

From Wikipedia, a 3way cat does the following :
* Reduction of nitrogen oxides to nitrogen and oxygen: 2NOx → xO2 + N2
* Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 → 2CO2
* Oxidation of unburnt hydrocarbons (HC) to carbon dioxide and water: CxH2x+2 + 2xO2 → xCO2 + 2xH2O

Logically, it would seem that a probe downstream of the cat could have the readings affected. If you have a lot of NOx then you'll read oxygen that wasn't in the exhaust, but if you've got CO or HC then you'll read less oxygen. No idea how big the effect is likely to be.

What size pipe is best?

I don't think it matters much. It has to be big enough to take the probe, and small enough to fit in the tailpipe. The main thing is that it needs to go far enough up the tailpipe that you are pretty well guaranteed not to get any fresh air going in the pipe and upsetting the reading.

yohimbe · #18 Post by **yohimbe** » Wed Jun 17, 2009 2:52 pm

that is right, it is more oxygen, but not much. i.e. volkswagen uses a wideband in some models after the cat to check if it works correctly.
but in your case it ist no Problem I would to some logs before lpg to have the basis and tune your lpg ecu to the same values.

Sir Henry · #19 Post by **Sir Henry** » Wed Jun 17, 2009 3:51 pm

As money's too tight to mention

at the moment I'm holding off buying/installing an air/fuel ratio gauge. For future reference most of the gauges seem to need '3-wire' lambda probes: So ... what's the difference between the 3-wire jobbies and the 4-wire versions that currently seem to be all the rage on eBay

SimonHobson · #20 Post by **SimonHobson** » Wed Jun 17, 2009 4:08 pm

Sir Henry wrote:As money's too tight to mention at the moment I'm holding off buying/installing an air/fuel ratio gauge. For future reference most of the gauges seem to need '3-wire' lambda probes: So ... what's the difference between the 3-wire jobbies and the 4-wire versions that currently seem to be all the rage on eBay

When talking about Zirconia probes, they come with 1 to 4 wires.

1-wire - unheated, signal ground is probe body (ie exhaust pipe)
2-wire - unheated, signal ground is separate wire
3-wire - heated, signal ground is probe body
4-wire - heated, signal ground is separate wire

For most applications 4 wire would be preferred - that way you can take the sensor earth back to the ECU and avoid any errors due to volt drops in wiring. That's something people often forget about.

I once had occasion to measure the volt drop in the earth wiring of a conversion I'd done. Although the wiring was quite adequate for the current, there was about 0.7V drop due to the current for the 4 solenoid valves and lambda probe heaters. I hadn't expected that much, and it didn't do much for the ability of the system to control mixture