Exhaust analyzer

Hello - I am a new member here from CanadaI have owned my 1972 350SL Djet for over 25 year, and I am active on the Benzworls and Peachparts forums in North America. Please excuse me using English.

On my own car, I installed a full time AEM wide band Air-Fuel ratio meter (pictures below) This makes setting mixture (%CO) easy. But many owners do not have such a meter. I read on this forum about a low cost infrared CO meter. Could anyone provide details of manufacturer and where such a meter can be purchased. This would help many D-Jet owners.

Hi Graham,

welcome to this website. English is absolutely okay, that is why I have translated my whole compendium to English. Mentioning benzworld: The only thing we do not appreciate is if someone copies drawings, pictures or tables from here and publishes them e.g. on benzworld as happened in the past with Norbert's measuring gauge for trigger contacts. Linking to this website is of course welcome. I know it wasn't you, so please forgive my statement.

Now when it comes to your qeustion regarding the AU tester. Yes I do use two infrared based ones. One is Gunson's professional gas tester. Thats i ssimiliar to this tester . Mine can additionally measure dwell and rpm. I bouht it second hand for 100€. And I own a Bosch ETT 08.14 gas tester as well. Both have an accuracy of roughly 0,5% which is good enough for not catalytic cars. Tomorrow I will buy a Bosch 4 gas tester ETT8.41. That has the big disadvantage that you need to recalibrate it allthe time with a verification gas. Let us see whether it will run at all. And it is only needed for catalytic combstion diagnosis.

There should be old Sun exhaust testers available in the US, similiar to the Bosch one. Intersting enough you can pay more for Bosch infrared testers than for a 4-gas tester. The infrared ones need no real maintenance other than maybe a filter.

Hi Graham,
I'm very glad I can Welcome you in this forum, too.
I know you're an active member in North-American forums

You wrote: "On my own car, I installed a full time AEM wide band Air-Fuel ratio meter (pictures below) This makes setting mixture (%CO) easy."
Never saw such an instrument before

Does this mean you adjust the mixture when driving, or just the mixture at idle?

Regards
Norbert

Hi Norbert,

no this is just a broadband sensor plus a meter. Americans like to work with air/fuel ratio and not with lambda. So 14 would be equivalent to lambda 1. Such devices are rather popular in American classic cars. A friend of mine uses it on his Adenauer and that made him find out that his fuel injection pump was too lean in high revs.

nordfisch wrote: Hi Graham,
I'm very glad I can Welcome you in this forum, too.
I know you're an active member in North-American forums

You wrote: "On my own car, I installed a full time AEM wide band Air-Fuel ratio meter (pictures below) This makes setting mixture (%CO) easy."
Never saw such an instrument before

Does this mean you adjust the mixture when driving, or just the mixture at idle?

Regards
Norbert

Hi Norbert,
As Volker said, on my car, I installed the AEM wide-band O2 sensor kit that comes with an AFR gauge. The sensor actually outputs lambda, I believe, but display is in AFR because that is what many understand better. I paid about $200 for the complete kit, but I have seen others for even less. But AEM and Innovate were the leaders at time I did install. I looked at Gunson and others, but really, I don't they are good enough and they would have even cost us more! I also found that measuring at tailpipe was inaccurate - I had back mixing of outside air. Measuring near engine is best.

Regarding adjustment. Idle, I did in garage by giving engine short burst and turning ECU knob from centre position until I got a suitable AFR (easy to convert from %CO to AFR and vice versa). I chose a high %CO (rich mixture) for idle - seems to help with hot starts. For load mixture, we adjust the MPS. Take car and run it at various loads. Check vs MB original specs (available in Technical data Manual) and decide on a suitable setting. So trial and error method, not adjusted while driving.

Innovate have a 2 sensor unit that would be good for our V-8s! They also have portable meters.

www.innovatemotorsports.com/

Hi Graham,

we are just doing an experiment here in Germany. Rennstrich8 (Tobias with his racing 280CE) with an M110 with increased bore has tried to adapt his car. While this is principally possible by tuning the ECU on a test stand, I have advised him a - as I believe - better solution. He will install a lambda sensor and an old lambda control unit to adapt. There are actually two different versions available. One that changes the water temperatur sensor resistance and one that acts similiar to the idle-run potentiometer to influence the basic injection pulse.

Unfortunately we have no results yet. I am also eagerly wating. But I consider such solution better than an A/F ratio meter as it is self-adaptive. Tuning the MAP sensor is easy to access on type 3 MAP sensors, but you are very limited as you can only parallel-shift its load-curve. And it can well be that such a sensor will not fit the car next door anymore as tolerances of sensors, ECU and MAP sensor just add up to be too lean or too rich.

Sounds like it will be a challenge to get optimum mixture across all load ranges.

A number of Djet owners (and some K-jet owners) have gone to Megasquirt. With that you can map your mixture however you wish and at same time eliminate all the expensive Djet parts. There are probably other aftermarket replacement ECUs that are even better (but more expensive) www.peachparts.com/shopforum/vintage-mer...runs-megasquirt.html

But not racing, I am happy with Djet especially with full time AFR (or Lamda) read out and manually adjusting the ECU and MPS.

At present, I have noticed my AFR gauge reading higher than it did before. In other words, engine is running leaner. Fuel pressure is still same. Injectors may need cleaning, but perhaps something else could cause lean running?

Hi Graham,

lean in that respect means more oxygen. I would check ignition dwell and timing before I do anything else. Secondly an injector spray that is imperfect or too low could cause less combustion and more oxygen.

I don't have points. Converted to Pertronix 1885 several years ago. So no dwell to adjust

Timing also should not have changed. But it could be that centrifugal advance might be sticking (it did once before and I had to free up weights). That would give me less advance at higher speed/load. I will check timing! I may also have an air leak, so will check vacuum as well.

Along with the lean mixture, I also notice reduced power. But only when engine is really warmed up and has been on a long run. At normal temperatures, car is still quite lively.

Hi Graham,

actually I do not believe in a need for Pertronix on MB's D-Jetronic cars. They are (with few exceptions on early 250CE) always equipped with transistor ignition. That is why contacts do not have any current load and will not burn down as in other cars without transitor ignition. Using Pertronic with tranistor ignition module of Mercedes-Benz will just use double transitor switching. So even n original cars dwell will not change. Main failure will be coating on contacts due to low current or oil and fat. So I just wanted to point it out as a possible source.

And yes you are correct to verify everything else before you go to D-Jetronic components. A leak onn MAP sensor woulld create a richer mixture. That's why I did not mention this as a possible problem.

It is true that Djet points will not burn out because they operate at low voltage. But the fibre rubbing blocks still wear and therefore the points gap (and dwell) changes over time. Pertronix module completely eliminates this at a very low cost.

Pertronix also eliminates any effect of distributor bearing wear and shaft wobble.

There is really no negative to having double transistor modules. But a positive is that the Pertronix can completely replace the expensive MB module, if it fails. Just a few simple wiring changes required. Many owners have done that and at same time installed the Pertronix Flame Thrower coil (with apparently improved performance). I have not gone that far yet, but have the coil ready!

So as you can see, I am quite a believer in the benefits Pertronix can offer I just wish there was a similar replacement for the trigger points!

Hi Graham,

I also believe in Pertronix and will install it in my fin tail convertible. It does not harm to do it in transistor ignitions too. I just wanted to point it that there are little benefits. And yes I wish there was a solution for the trigger points as well. Jaguar / Lucas did that. But people were not too lucky with Lucas's quality of that solution either. So far I could not get hold of a Jaguar trigger point, neither the reed relais version nor the hall sensor version. I could only acquire an ECU and will analyze how they have interfaced those sensors.