Greetings All,

Been dreaming of a low-cost exhaust analyzer. Does such a critter exist for the home mechanic? Lots of options in the $1500+ range, but that's way too rich for my blood. Maybe $300 tops for me?

I'd like something that can discern CO and HC levels at the tailpipe. I'd like to observe any changes in emissions as I make various adjustments. My truck still has to pass emissions testing here in The People's Republic of Oregon. It would be nice to have a general idea ahead of time before testing.

I've seen various homemade air/fuel ratio meters that are based on an oxygen sensor. If I got the A/F ratio in the perfect range, would CO and HC fall into place, or is that not directly related? Also, doesn't the sampling need to place close to the engine, such as at the exhaust manifold? Ideally I'd prefer something portable that works back at the tailpipe. My truck is non-catalyst.

What about a combustion analyzer, like an HVAC guy might use on a furnace? Could something like be used for a vehicle exhaust? I've seen some of those under $200.

 

Look for a used sun 105 or epa 75 analyzer. Both can be had cheap if you look as they are outdated.

 

Did you ask google ? lots of options depending on what you ask.


https://www.google.com/search?q=exha...VcfAwQQ4dUDCA0

 

CO and HC typically are tied to each other high Hydrocarbons begets high carbon monoxide. If you have rich fuel-air mixtures you will have high carbon monoxide. So really you can get away with just a CO meter

 

Yep HC or Hydrocarbons are just unburned fuel.

I dont know how many times as a state inspector on the dyno we've pulled the spout connector on GM trucks to get them to pass when the HC and CO were close but not with in spec. That switch to base line timing did wonders at cleaning up the results.

 

Thanks for the help, guys. Been poking around different sources online, but nothing real definitive. One big problem I hadn't considered is that nearly all CO detectors under $200 will have trouble responding to tailpipe exhaust for several reasons. They were never intended for the task.

One problem is the heat and humidity (at the tailpipe) are typically way outside the normal range for most detectors. This will skew the results dramatically.

Another issue is a meter is typically designed to measure trace CO in ambient air, such as in a commercial kitchen with gas appliances. If your kitchen already had CO at the same concentration as an exhaust pipe, you wouldn't need a meter to know. You'd already have one huge clue in the form of dead staff piled up on the floor.

I did find one English brand designed for automotive use, selling for about $250. I've been rethinking my cost/benefit calculations and I'm just not sure such an expenditure is worth it.

FWIW, I did own a Sun 75 sniffer, 20+ years ago. It was obsolete even then, and wouldn't stay remotely in calibration for any length of time. Maybe I just had a lemon, but I'm not sure I want to go through that again.

 

If you are talking about the Gunson one I own one , they have been around for ages and are proven and reliable units for what they are, they just have a slow response time.

But if you trying to fine-tune they will do the job.

And same on the Sun 75 all are now so old they need fully rebuilt and will drift otherwise. But getting a SUN 75 rebuilt is all but an impossibility as far as I am aware.

 

Why not have a bung welded into your exhaust system and get the innovate set up

https://www.google.com/search?q=inno...4dUDCA4&uact=5


Has your truck failed the test in the past?
Does it fail the test a lot ?
Or this just your OCD kicking in ?

 

That's a bingo! Except the correct term is CDO, alphabetized the way it should be.

The truck has always passed emissions testing. The last two times, it was kinda close, though. I get it, pass = pass. The margin doesn't matter, as far as the nanny state is concerned. I'd just like to stay on top it, that's all, but without spending an arm and a leg.

Think of my Quixotic quest as part of basic diagnostics, such as doing a compression test. I may not necessarily do anything with the result. It's more like establishing a baseline to see if anything changes. For example, I've got marginally low compression on one cylinder of my 351W. I have the numbers written down somewhere, but I'm locked into my easy chair at the moment so am working from memory. It was something like 120# versus 160ish on all others. I'm not about to tear the engine apart for repair as it runs very well. But as the mood strikes, maybe once a year, I'll do a compression test to keep an eye on it.

I had an episode a couple of years ago when the engine was very low on power. Seemed fine empty, but had trouble when fully loaded, struggling on minor hills. The truck had just passed an emissions test and there wasn't much margin to spare. I forget the exact details, but the two years previously the truck had passed much more readily. I found the vacuum advance actuator had failed. I think it was the vacuum leak itself causing the loss of power, not the loss of vacuum advance. Oh anyways, in retrospect, I also suspect the shift in the emissions test result was caused by this same vacuum leak. If I could run a reasonable facsimile of an emissions test at home, I suspect I could have caught the problem sooner. As it played out at the time, we had to turn back within the first ten miles of a long camping trip. Several days passed waiting for parts, etc.

So that's my basic motivation, a lazy man's way to keep tabs on the overall engine health and watch for any trend changes. I'm not looking to hot rod the engine or anything like that. And I think it would be slicker than snot if I had some low-buck way to do so.

 

If that is all you are doing all you is the CO meter then. As it will tell you how efficient the combustion is. Be aware the Gunson unit at $250 when you get it you will feel like you just got screwed, there is not much to it and it is not what you would call, of robust construction and is rather delicate. The unit was originally made in the 80s and has not changed since and still uses a segment LED display for the read-out. So put in the context of a low coast exhaust analyzer from the 1980's it's construction is bang on as to what you would expect. But not up to the standards of today's lower-cost tools.
Is it something a commercial shop is going to get by with ? HA not by a long shot. Is it ok for the DIYer that needs an automotive exhaust gas CO meter to set, dial-in or tune carbs on occasion? Absolutely

 

Four+ years later, an update with a half-a**ed solution:

Had a little trouble a few months ago getting my truck through emissions testing in The People's Republic of Oregon. HC levels were above limits. A normal person would have just taken their vehicle to a shop for testing and any necessary repairs/adjustments. Myself? I'd rather hang onto my ManCard, thank you very much. I renewed my search for an affordable means to check HC and CO levels in the exhaust. I knew I could make the adjustments, but still needed some measurement method to make sure I was going in the correct direction.

Did I find a perfect solution? Not really. Adequate? Workable? Yep and yep, at least for me. I picked up a couple of cheap handheld testers. I found used units on eBay for maybe $25 each, IIRC.

For HC (HydroCarbons, i.e. unburnt fuel), I went with a Mestek CGD-02:


This is not the latest model, and upgraded versions are now available. Poke around and I'm sure you can find something better. One big limitation with this model is only shows LEL, which means Lower Explosive Limit. There are tables which let you convert this value to PPM (Parts Per Million), which is criteria used for emissions testing. However, these charts are kinda hard to interpret, and vary depending which fuel is present. I gave up trying to make any sense of that, and simply went by a lower LEL value meant less HC in the exhaust.

For CO, I went with a TopTes CT-300:




This unit worked very well. I chose this one because it covers 0-5000 PPM. Most similar testers only covered 0-1000 PPM. One drawback is this unit does not have the long flex probe, but I thought the greater range was more important.

Lots of similar testers out there, and not too expensive either, especially if you can find them used. Some models have rechargeable batteries, but if expecting very infrequent use like I am, I'd recommend regular batteries you can remove when not in use. No point in paying extra for rechargeable batteries that may self-destruct in storage and leave the unit unusable when needed next time.

More details of my testing travails in this this thread:

https://www.ford-trucks.com/forums/1...***-valve.html

 

I'm sure you can come up with a hose attachment to fish down the tail pipe to feed the sensor.

 

Funny you should mention that. I played around with this idea. I rigged up a hose and plenum arrangement. The two testers plugged into the plenum and a shop vac was used to draw exhaust for sampling. I was busy patting myself on the back for such a brilliant idea. And then I turned on the shop vac. This put a slight vacuum on the plenum, as intended, but unfortunately the HC tester went berserk. Shut off the vacuum and the tester returned to normal. For whatever reason, at less than ambient atmospheric pressure, even with clean fresh air, the HC tester went nearly full scale high. I even tried reducing the vacuum by opening a port downstream of the meter, but no joy. Even the slightest vacuum caused trouble.

The CO meter worked fine, but not the HC tester. Maybe if I spent more than $25 on it?...

 

I'd give you a pat on the back too. But I would not have thought about using vacuum. Why would that be needed ? I'm not familiar with how that works. The testers we had at work, I thought we just waved through the air or tuned them on. Even when I used to do the semi-annual test, we just opened the test bottle of gas and put it near the sensors.

It's been over 5 years since I last did that.
Funny story, sometime about 2012 I got fed up with the "calibration procedure" of the Facilities Engineer, who I had known for decades, put in the semi-annual PM. (periodic Maintenance procedure) and made up my own simple step be step cheat sheet. To test the O2, N2 and H2 sensors around our Lab and Test Cells. I had given a set to some co-workers over in the Space Suit test area. One day I got fed up, because I found out the Factory guy's had an outside vendor do all the sensor testing. My Foremen inform me, he had heard about how my cheat sheet made the process so easy, from the guy's in the Space Suit test area, that there was no need to pay some outside Vendor to do it.

I was known for thinking outside the box, and coming up with fixes for things or shortcuts that worked.

 

When I had my shop our "Sun like machine" had a 2 gas checker and it did have a vacuum pump to pull in the tail pipe gasses but the machine was at the front of the car and I dont think the exhaust would be able to get pushes to the machine. I remember it having a think stone filter just before the hose went into the machine.
Kind of wish I still had the machine just to play with now that I know so much more on how it could of been used
Dave ----