924Board.org

[ideola]

I received my Gunson Gastester this week, and finally had a chance to play around with it yesterday (on the 941) and today (on the 81 NA). These units can be readily had for new for $200 + shipping on eBay or Amazon. (Official website is here).

I was pretty impressed with the unit. Small, lightweight, easy to read from a distance, and seems to work exactly as expected. The manual is clear, concise, and easy to follow.

After fully warming up the car by taking a spirited 20-minute drive on the local twisties , it took me about 30 minutes for each car from start to finish to get the CO reading dialed in precisely to manufacturers specifications. The Gastester has a calibration feature that is quite sensitive...you have to calibrate it in open air to read 2.0% CO before you can begin testing the car. You also have to disconnect your O2 sensor (assuming you have one and that it is functioning) as per the instructions on the fender for setting fuel mixture. Otherwise, you will be chasing your tail trying to adjust things.

In any event, on the 941 (actually, a 1980 931 with the Lambda system), the best I could do was to get the CO to 0.8%. Specs say 0.5 - 1.0, but I couldn't get the readings to drop any lower than 0.8%, so I eventually left it there, figuring a little rich on a turbo won't hurt anything. On the NA, I dialed it in precisely to 0.5%. I figure on the NA, I don't need any extra richness in the fuel mix, and I particularly want to try to improve its fuel economy.

I have to reiterate what has been said in many other posts regarding air fuel mixture. The actual tolerance of the set screw is unbelievably sensitive. Barely a degree or two of change WILL affect the CO output noticeably on the Gastester. Achieving factory specifications requires some patience, and VERY, VERY fine tweaking of the mixture screw. Also, I had to re-calibrate the Gastester midway thru the tuning process for each car.

In any event, based on my initial experience, I am very impressed with the Gastester, and I think it is a worthwhile investment for anyone who has multiples of these cars. If you're in SE MI and want to give it a try, send me a PM.
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erstwhile owner of just about every 924 variant ever made

[Mike924]

^+1

I have come to the conclusion that my Gunson meter always reads 0.5 - 1.0% high. I set the Co on the '24 to the level in the Haynes manual, but when I compared the reading on my friend's wideband lamda meter, it read an AF ratio of 20! So we set it to an AF of 12 (on the rich side, I know ) and the reading on the CO meter was about 4%.

You do need to watch the 2% calibration setting; it does drift very quickly and takes at least 20 mins before it settles down to a steady value.

Also, count to three after making an AF adjustment before taking the reading, just to give the air plate time to settle down.

But, overall: the easiest way to set the AF on any car, and especially CIS motors.
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1985 Porsche 924 'Lux', Kalahari Beige (my ex)
1993 Porsche 968 Coupe, Midnight Blue, 6 spd

'There is no substitute for a little grease under your fingernails.' - Chrenan, 924board.org

[Jaf]

Hmm. I had fun with mine. Started off at something silly like 12 percent. Got it down to 2 percent which I figure is fine for an old car (think we're allowed upto 4 percent legally in the UK...oops wonder what I'm allowed in Spain?!). I checked it a few days later and it was at 2.5 but I was doing the test half outside so it was probably less windy that day as a third check was back to 2 percent. Might do the test again just out of interest.
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1978 924na

[Mike924]

Sounds like yours is just fine, Jaf.

I'd leave it at that.
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1985 Porsche 924 'Lux', Kalahari Beige (my ex)
1993 Porsche 968 Coupe, Midnight Blue, 6 spd

'There is no substitute for a little grease under your fingernails.' - Chrenan, 924board.org

[Mike924]

[scottc]

Have you re-registered your car in spain Jaf?
I was under the impression it wasn't necessary being an EC registered vehicle??

[Jaf]

[scottc]

Ahh that makes sense. Though how could anyone prove you've had the car on the road for 6 months?

My inlaws imported their Jersey registered Golf to spain when they moved there. Similar rule, but as Jersey isn't part of the EU, they can only use it for 3 months a year. I think they've been there for 3 years now, and haven't reregistered it.

I was quite suprised to find a lot more 'older' cars the last time I was there. Especially Renault 4's for some reason.

[El Chato]

Hi guys, comming over to the threat, I was wondering so has anybody tried of the other exhaust analyzers out there that are quite vintage as the car, wondering the pros and cons against those to a gunson tester, before I buy one, Ideolas explanation sounds great, a shop in Juarez can do the adjustment on the car they charge 300 pesos, like 24 dollars, but im not to happy if they just move a screw a couple of times. what do you guys think.

another doubt when ajusting to 0.5 I saw in ebay that it says they are acurate only to 0.5 so when ajusting do you go down in increments of 0.5 till it gets there and if too lean you get 0.0 or -0.5 ?
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1979 924 N/A, Snail Shell
1980 924 N/A
1976 924 N/A

It may be that your whole purpose in life is simply to serve as a warning to others.

Today's weirdness is tomorrow's reason why.

[Mike924]

If they do a good job of it, $24 sounds like good value for money.

The meter will give minus numbers, but this is usually a sign that the 2% calibration is off.

Does you car have a cat? The 0.5% value only applies to cat-fitted cars. Without one you need to look at 1.5 - 2.0% or so.
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1985 Porsche 924 'Lux', Kalahari Beige (my ex)
1993 Porsche 968 Coupe, Midnight Blue, 6 spd

'There is no substitute for a little grease under your fingernails.' - Chrenan, 924board.org

[El Chato]

I actually took it off, cuss running rich made it heat up a lot, and somewhere I read that fuel reaching the cat could mess it up, I was looking at the color tune spark plug another member used to set the A/F I think thats a better approach and keep the tool, is that just as good as the co readins to ajust it?
_________________
1979 924 N/A, Snail Shell
1980 924 N/A
1976 924 N/A

It may be that your whole purpose in life is simply to serve as a warning to others.

Today's weirdness is tomorrow's reason why.

[Mike924]

I've never had good correlation between using the Colortune and the Gastester. The Colortune tends to end up with the mixture on the rich side.
_________________
1985 Porsche 924 'Lux', Kalahari Beige (my ex)
1993 Porsche 968 Coupe, Midnight Blue, 6 spd

'There is no substitute for a little grease under your fingernails.' - Chrenan, 924board.org

[El Chato]

thanks mike924, I feel Ill go to have the guys do it properly after I adjust the valves and re torque the head and quick tune up.
_________________
1979 924 N/A, Snail Shell
1980 924 N/A
1976 924 N/A

It may be that your whole purpose in life is simply to serve as a warning to others.

Today's weirdness is tomorrow's reason why.