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Old 07-10-2003, 02:45 PM
Senior Member
Join Date: Sep 2002
Posts: 2,486
Hi 96C280, good question. The Star Diagnosis System ( SDS ) is simply a quick and accurate way of checking for trouble codes, and looking at all the input signals, sensor values, etc. of a particular system. In your case the first thing I would look at would be the "Hot Film Voltage" value in HFM-SFI. Mass Air Flow sensors can fail in more ways than one. If the voltage is a steady 5V it would almost certainly cause the surge/hunting you describe. I've only seen a handful of these failures though, mostly on vehicles with bad engine wiring harnesses. Keep in mind that a MAF failure such as this is completely different from the "lacks power/Check Engine light/PO170/173 code complaint. This type of fault develops over a period of time due to degradation of the hot film material. As I said, this would be the first thing I would check, and it would only take a few minutes. Next, I would check ASR, E-GAS, CC/ISC ( depending on what your car is equipped with ) for codes. I would look at the potentiometer voltages in the throttle actuator as well. Again, this would just take a few minutes. I could use SDS to run the motor in the throttle actuator as well, while I watch/listen for smooth operation. I could also road test the vehicle while observing the actual values. The biggest benefit of having SDS is that it saves time. It also allows me to observe several signals/inputs simultaneously.Before SDS we used the Hand Held Tester ( HHT ) which was nearly as good as SDS. Before the HHT came along in 1992/93 I would need to gain access to the control unit to be tested, then connect bulky/unwieldy test equipment and use my DMM to measure voltages, resistances, etc. If I wanted to check more than one signal at a time I'd need additional DMM's. It would also make road testing/observing much more difficult. I hope this explanation helps. Good luck with your car.
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