Assumption (please verify) - Factory says setting should be 383 OHM for the CO screw at the MAFs Question 1: In a Motronic 2.5 1989 vehicle with no cats (stock Euro) a trip on the Dyno, showed that 340 OHM is the ideal to keep the CO, HC and NoX within the limits specified in the owner's handbook - is this excessively rich? Question 2: What is a "big" difference 5 ohms, 10 ohms etc. I heard +5 ohms (388 ohms) is "very" lean and steps of +5 ohms are a "LOT" - can you give your opinion? Question 3: In catalyzed vehicles, the CO pot is ignored as the O2 sensor is the mechanism by which the ECU regulates fueling, if so isn't the assumption that the CO screw is wired in-line wih the injectors wrong? Question 4: My MAFs were set to 340 Ohms and the exhaust pipes look like this - In real ife a bit darker the camera strobe lightened them up a bit) - what's your opinion? Car revs up perfectly and is a great drive... Thanks to you all in anticipation of great replies. Marco Image Unavailable, Please Login Image Unavailable, Please Login
That's pretty rich. I would try turning them up to about 360 and see how it runs. However, it could be your cam timing also. The Euro cars run different cam timing than the U.S. cars. Less valve over lap if I'm not mistaken.
When O2 sensors are used, the CO pot has no effect. Otherwise, when O2 sensors are not used, the CO pot value will adjust your CO emission. However, no two cars will have the same resistance to get the same effect. Engine condition plays a significant role in the overall emissions level when you are doing a 4 gas analysis. In the old days, the CO screw was actually an adjustable air pathway within the Jetronic Air Flow Meter. In the Motronic, it is a potentiometer.
It is an Euro spec. If there is less overlap, does this mean there is an ability to use a richer mixture - I guess there is less time for fuel and air to enter the cylinder. Noob - I noticed on the Motronic 2.5 circuitry that grounding pin 20 sets it up for non cat mode. For no other reason than that of smell reduction, I wantet to get a pair of 200 cell metal core high flow catalysts - no name brand, and stick them on. I'd connect the standard O2 sensor on a home made loom incorporating the O2 heater (connected to the Fuel injection circuit as is on cat stock cars), disconnect the earth on pin 20 and connect the O2 sensor on to 28 and 10. I'm holding off until I can gt 2 sets of wideband gas analysers which can act as narrow band O2 analyzer simulators, feeding the ECU a signal based on the wideband analysis AND offer Cat EGT functionality. Would I need to change cams etc. to stick the high flow cats or can they just b "bolted"? Image Unavailable, Please Login Image Unavailable, Please Login
