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Discussion Starter #1
Planning to install afr gauge on my 72.

For those that have done it, did you weld in the bung while installed on the car? And at what location-Im assuming the best spot is one of the down pipes.

I’m wondering about working clearance or if I would need to remove the down pipe.


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I looked into doing this on my down pipes but have put it on the back burner as the clearance is not good. Ideally the bung needs to be welded to the upper part of the pipe between the 10 and 2 o'clock positions to ensure condensation does not collect on the sensor. So realistically this need to be done with the down pipes off the car.
 

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I had muffler shop weld in a bung. I decided to put it after the crossover pipe and just before the resonator. I figured that this might provide some mixing. Otherwise if on downpipe, you would just be monitoring one bank.

The other consideration, is how you will route the wiring from the sensor to the gauge. As you can see from the pictures in the attached link, I decided to come up through a hole in the tunnel. Just big enough to get the connector through.

Some manufacturers sell a clamp on bung. It's a piece of pipe cut in 1/2 with bund already installed. Goes on with clamps and I suppose some hi-temp sealant.

I have had my AEM AFR gauge installed for what must be about 10 years. After the initial adjustment of the MPS and the ECU (for idle mixture), I have not had to make any more adjustments. Best add-on I have made for the Djet!

Good luck with your install.

https://www.benzworld.org/forums/r-c107-sl-slc-class/1528846-450sl-engine-issue-3.html#post4219942

 

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Discussion Starter #4
Thanks for the reply And link to photos Graham.

That looks like a lot easier access than the downpipe.

Like you, I just want to use it to ensure mixture is set properly. So I initially started looking for portable CO2 monitors but the AFR gauge seems to be the most cost effective solution. I may not even mount the gauge - just remove and plug the bung after I set the mixture.

Looks like you’ve been running yours for years. Have you had to replace the sensor ever? That seems to be a common failure. I’m also leaning toward AEM.


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Like you, I just want to use it to ensure mixture is set properly. So I initially started looking for portable CO2 monitors but the AFR gauge seems to be the most cost effective solution. I may not even mount the gauge - just remove and plug the bung after I set the mixture.

Looks like you’ve been running yours for years. Have you had to replace the sensor ever? That seems to be a common failure. I’m also leaning toward AEM.
I have not had any problems with my AEM unit.

It is interesting to have it installed. Setting mixture takes a bit of time so it is nice to have the numbers right in front of you. The %CO MB quotes is different depending on engine load. Also different at idle. I am sure I posted the numbers elsewhere on this forum. My car now runs well under moderate load at about 14.0 AFR.

At idle I set it quite rich. This, along with increasing fuel pressure, overcame the hot start problem that is caused by too lean a mixture. Changing fuel pressure requires MPS adjustment to get all mixtures right but helps the djet run better. (I thig I am at about 32-34psig)

At one time, engine was running lean (on meter). I thought meter might be wrong. I added injector cleaner, and the number came back to normal. I just like to see the AFR!

Anyway, just some examples of how a built in wideband AFR can help. (By the way, make sure you get a wideband meter like the AEM)

By the way, this is the clamp on bung. About same price as C$50 weld job!
https://www.summitracing.com/int/parts/avm
 
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