Exhaust Gas Analyzers

[jrwilson]

My car's idle is way high, and also it has cold start problems and jumps a bit in RPM at first start up for a few seconds - all of this tells me I'm running a bit rich and I need to adjust the mixture and idle screw.

I'm supposed to only set the mixture based on %CO at idle on a warm engine.

I can't take my car to the mechanic easily as they are an hour's drive away and there's no way to get home while they have my car so it's basically an all-day adventure, so I'm looking for ways to do this in my driveway. Ideally I'd like to be self-sufficient in this anyway and not have to rely on expensive, faraway mechanics.

I've seen the Gunson Gastester which isn't horribly expensive, just wondering if anyone can recommend it or another hobbyist level device I can use to do so.

I do have a wideband O2 sensor but it goes to an analog gauge inside the car so it's hard to get an accurate reading on it. Also it only reads one bank.

Also, I'm wondering if anyone has a link to the procedure for the initial setting of the mixture and idle screws so I can start from a "known" state.

[76FJ55]

Originally Posted by jrwilson

My car's idle is way high, and also it has cold start problems and jumps a bit in RPM at first start up for a few seconds - all of this tells me I'm running a bit rich and I need to adjust the mixture and idle screw.



I do have a wideband O2 sensor but it goes to an analog gauge inside the car so it's hard to get an accurate reading on it. Also it only reads one bank.

You state the symptoms indicate rich, what does the wide band tell you?

Most people have gone to a wide band O2 instead of using an Exhaust gas meter, so it sounds like you should already have the tools you need. you may need to supply your wide band with unswitched power so it can already be powered up and online before starting.

[Funracer]

I am on my second Gunson Gastester. Accidentally knocked the first one off a stool and it broke, so don’t do that. The GG does, I think, give a somewhat accurate measurement but it says results are +/- .5 which is a lot. Cannot remember what number you are looking for on a 78 but on my 83 the range is .4-.8% CO so a variance of .5 is pretty significant.

Read the instructions several times to get the hang of how to use it. There is also a GG video on YT.

I too have an analog AFR gauge. The GG is much more sensitive. It will display very small changes in the mixture screw that you wont see on the AFR.

Initial setting of the idle screw is easy. Clockwise til closed, then CCW two full turns. That should get you in the neighborhood.

Lots of info here and online about initial mixture setting. Not sure you need that though if your car is already running. Just start it, warm it up then set the mixture with the GG. Assuming everything else is working properly, and with CIS this is a large assumption, you are done!

The GG is not perfect but it does the job and way cheaper than some of the other CO testers. New GG are $250-$300 occasionally one pops up on the forum here for less.

[Ltanderso]

You should probably first verify your fuel pressures and timing . Id also confirm that you don’t have any vacuum leaks. After you check those boxes, you can then move to AFR and final idle adjustments.

[Schulisco]

https://forums.pelicanparts.com/porsche-911-technical-forum/1161561-co-gas-analyzer-la-borrow-rent.html#post12249026

https://forums.pelicanparts.com/porsche-911-technical-forum/1142246-co-analyzer.html#post12031605

CO must be between 1,5 - 3,5% for US cars out of 1978 & 79.

Thomas