[1994v12]

I've had this exhaust gas analyzer for years, it was at a yard sale for $10. NOS brand new never used in the box.
so...today, calibrated it, zeroed it, and connected to my 1994 V12 S600
after starting up the car cold (dash temp gauge read 114 degrees F in sun), it warmed up quickly, went into closed loop
initial reading was 13.8 air/fuel ratio.
the air filters, snorkels, factory MAF sensors are in place and plugged in.
pretty damned good, considering it has NO CATS, blocked EGR, and disconnected air pump.
it also has no muffler, only the resonator, listen how quiet the car is.
realize the restriction that was reduced, by axing the cats and mufflers.
here's the video, and a still pic of the gauge when car went into closed loop.
as you can see, the system is very good at limiting emissions, without the cats, egr, or air pump. CO (carbon monoxide) is only at 2%

 

[1994v12]

after fully warming up motor, a few minutes later, it hit 14:1 A/F ratio !
and only 1.5% CO reading. amazing.
this is without cats, egr, air pump.
it's also very quiet while idling, with no muffler, only a resonator.
makes you think why all that junk was on there ?
here is the video

 

[1994v12]

video of the engine, showing the MAF's connected. this was before it hit 14:1
I uploaded it so may as well show it. also shows general condition of interior, body, paint...
Snap-On MT2500 scanner is in back seat....we'll get to that eventually, a road test with the scanner connected....cracked the throttle a few times and the A/F momentarily fell a bit...
an OBD2 car idles lean, then goes rich when you hit the gas.
a carbureted car does the opposite, it idles rich, and goes lean when you hit the gas....which is what this car does on speed density as well, which you will see next...

 

[1994v12]

when I pulled the air filters, the mixture richened slightly to 13.9:1 A/F ratio
reason- MAF's sensed slightly more air coming into engine,
and intake air temp sensors cooled slightly,
ECM picked it up, and compensated by richening the mixture.
that's just how sensitive an OBD2 system is.

 

[1994v12]

next step, pull both mass airflow sensor plugs...
system resorts to speed density tuning, using the MAP sensors vacuum signal
a/f ratio drops to 11.65:1
richer for an ODB2 car, but actually NORMAL for an old carburetor car !
in those days they idled rich, then went lean when the throttle was opened.
it was at this point, that the car made the most wide open throttle power !
and burned the rear tires into 3rd gear with open pipes, then caught....
the downside, less gas mileage.
both sensor plugs are pulled, here is video
car still idles smoothly, quiet.
I'd recommend anyone having an MAF harness problem,
to unplug the MAF's and see if it solves it, you can then drive the car on the backup system, until you get it fixed. or indefinitely, if you wish...

 

[1994v12]

here's the gauges at this point...no thermostat in this car.
as you can see it's sitting right at normal operating temp without a t-stat anyway
so much for all the corrosion, etc. nonsense...from not getting hot enough, etc....

the A/F gauge did climb to 11.9 eventually, with the MAF's plugs pulled

 

[1994v12]

look at temperature on dash thermometer, 114 degrees F. what did I tell you guys about NEPA summers ?
and we have 83 percent humidity today.

 

[Mender]

next step, pull both mass airflow sensor plugs...
system resorts to speed density tuning, using the MAP sensors vacuum signal
a/f ratio drops to 11.65:1
richer for an ODB2 car, but actually NORMAL for an old carburetor car !

Seeing that it's a sequential fuel injected engine with minimal overlap at idle and long runners and not an old poorly tuned carbed car, 11.65:1 is way rich. Over 4X the CO so wasting fuel!

That shows how far off the speed density tuning is for this engine. Best to leave the MAFs plugged in and let it have the 14.0:1 that it likes.

But at least you're having fun. Nice car too.

 

[Mender]

after fully warming up motor, a few minutes later, it hit 14:1 A/F ratio !
and only 1.5% CO reading. amazing.
this is without cats, egr, air pump.

And is a direct result of the AFR, so not amazing, just physics. The cats, egr, air pump, etc take care of the bad stuff after that.

 

[1994v12]

plugged MAF's back in, mixture returns to 13.8 a/f

 

[1994v12]

after all this time sitting idling, in the 100 degree sun, temp started climbing up to 90 degrees C on dash gauge, so I wired up the cooling fans for good measure. not that it's ungodly high, the car calls for an 87 degree C t-stat. when the fans are on, the mixture richens to 13.5 A/F ratio. it may be programmed into the ECM that when the fans are on high, the mixture is richened up a bit to protect the engine from a meltdown, as richer fuel will tend to cool down an engine.

 

[1994v12]

previously I had swapped in a pair of S320 MAF sensors, they are nearly identical to the S600 sensors, but slight calibration difference in resistance on a 1 or 2 pins...the big difference I noticed, the car was QUIETER when driving.
most likely ? meaning the S320 MAF's are calibrated slightly leaner. general rule of thumb is, richer mixtures cause the engiine to run louder. will have to drive it with the Snap-On MT2500 plugged in to verify. bottom line is the S320 MAF's can be used in a pinch, if you can't get S600 MAF's. I've done it and drove the car for months on the S320 MAF's. if you want to race someone with your S600, unplug the MAF sensors. the car will be quicker at wide open throttle, and richer across the board in fueling, running on speed density. if you're having problems with the MAF wiring harnesses, do the same. see if it runs ok, until you get around to the laborious task of repairing the harnesses. if it does work, you may just want to DRIVE IT THAT WAY permanently, and let someone else down the road do the harness repairs ! save a lot of time, money, grief, sweat, cursing.