Dyno Day 20020316 - Van Data - 4-Gas

During the Rolling Road tests a 4-Gas test was also done.
In my, then newly acquired, experience doing a RR without hooking up a 4-Gas-tester doesn't have much point.
The graphs show you what goes wrong (lack of power at a certain power-range), but the information on the burnt (or not) gasses tell you what may be going wrong.

Unfortunately the 4-gas tester wasn't an integral part of the RR-testbench. As a result it's not possible to superimpose the data of the 4-Gas test to that of the RR. The 'raw data' was given to me on a printout and entered in a spreadsheet to produce the following graphs:

CO CO2 O2	HC

By using one of the RR graphs that's also plotted against time (the x-axle on the graphs above are seconds), one might be able to get some reference points, but it would be hard to find an exact starting point (second #1 in the above graphs was not the same point in one of the runs). As it is the starting points of the graphs above were used to 'overlay' the various graphs in one picture.

What these graphs do seem to show is a consistency in readings.
It doesn't look like there is a problem in 4th gear that's not there in 3rd or All gears.

To better understand what these readings were telling me I did some searching on the Net and found the following documents that explain a thing or two on combustion gasses;

The 1st 3 documents require Adobe's Acrobat reader
and were found at an US Toyota Motor Sales site
(c) the respective copyright owners

So what did this tell me ?

HC value
This is basically the amount of unburned fuel that's coming out the back.
For my Van it should be around 400ppm. As you can see in the raw data, the initial value was some 2400 or 6(!) times as much as it should be.
As the value never came close to 400 this (partly) explained the 'afterburners' in my tailpipe.
This value is a bastard to trace as it can have all sorts of causes, ranging from to lean or to rich a mixture to mechanical problems.

CO value
The CO value indicates partially unburned fuel.
This one is much easier to trace as it's always a result of a mixture that was too rich; there wasn't enough O2 (Oxygen) to convert to CO2 exhaust gas only.
During the year 'MOT' the CO value is measured.
My Van can get away with 4.5% but the Haynes manual mentions a value between 1,5 and 3%. Usually this means the carb settings have to be tweaked a bit before testing, as it doesn't really run well on too lean a mixture. There was no initial CO value given, it was measured during the RR tests.

CO2 value
As mentioned above, CO2 is what you want to come out of your exhaust as it's the end result of a good burn; the higher the better.
It's linked to the CO value, but can also be influenced by other factors and thus is a bit harder to trace.
I haven't found a reference yet as to what the CO2 level should be for my Van.

O2 value
O2 is Oxygen. Any of this coming out of the tailpipe is a waste basically; it could have been used to burn more fuel.
Too much O2 is often an indication of a lean mixture or an airleak.

Lambda value
As the above documents explain, the Lambda value is a calculated value.
Since my Van is an 1980 model and not equipped with a cat it's not of much interest here.

Looking at the data it shows that the HC, CO and O2 values are too high.
Strangely enough the test run where it all went 'south', in 4th gear, is the one showing the best values for HC, CO and O2.

As the RR run in 4th gear indicated something seriously (as in mayor, not really serious as in may kill the engine) wrong, I decided to have that sorted first and then see what the values would be. As it is the values do not clearly point out a certain failure that could be causing the problem.

So what now ?

(c) 2002 Anne, DynoJet and respective owners