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We discovered one of the temperature sensors may have been grounding out on the engine so we fixed that. We determined that the pressure switch is working as it was designed to (whether or not its design is compatable with my car is another question). We took it for a test drive and almost didn't make it back. It lost so much compression trying to come back it was probably only running on 1 or 2 cylinders....we forced it back and are back at square one...help? Becky '69 AT FI Fastback > At 12:37 PM +0000 3/8/98, northaven@worldnet.att.net wrote: > >When I reach freeway speeds it will sometimes be fine for a little > >bit, but then will experience progressively worse power losses until > >the car is just gasping to remain running. > > When it's losing power is it still fairly smooth, or does it cut in > & out, in & out? I have had worn distributor shafts that have made > for very erratic behavior. You could check for this by pulling the > cap & rotor, and try wiggling from side to side the shaft that the > rotor was on. (Note that it should *rotate* a bit for the advance > mechanism, but not wobble in such a way as to open & close the > points.) > > >Is it possible my pressure switch is bad if it is giving the reverse > >responses? > > I don't know (from other independent sources besides Muir) what the > electrical response of this switch should be when it's good. It > *may* be that Muir has things reversed. Note that "high vacuum" > corresponds to the throttle completely or mostly closed (like when > cruising on the highway) and low vacuum--no suction--corresponds to > flooring the gas pedal. > > Note that the pressure switch, only on early cars, helps tell the > brain when you've floored the gas pedal so that it can enrich the > mixture--that is, hold the injectors open a bit longer. Kind of > like a carb's accelerator pump. In 1970+ models, this function is > incorporated into a fancier throttle position switch that measures > "flooring the gas pedal" a bit more directly. That's why later cars > both have no pressure switch and different throttle position > sensors. > > You might look to other portions of the system that influence > mixture--that is, injector duration. This includes both temperature > sensors--the one on the intake air distributor and the one on the > left head. These are little semiconductor devices whose resistance > *decreases* as temperature goes up. If one of these sensors is > disconnected, then that will be a very high resistance--that is, the > brain will think that things are very cold, so it will enrich the > mixture by holding the injectors open longer each time. (I don't > know if they more typically fail by giving zero or infinite > resistance...) > > Are your spark plugs getting fouled due to too much gas, or are > they nice & tan? Has your mileage changed drastically? > > Also, the manifold pressure sensor, the main gauge of the amount of > air entering the engine, can cause all sorts of problems if faulty. > > >I have new plugs, cap, rotor, points, condensor, coil, etc.... > > How new? And have you double-checked the timing and dwell (point > gap) *today*? Probably not your problem, but you really need to > confirm these before proceding with injection diagnosis. > > >could it be my fuel injectors themselves? > > If you've done the Muir inspection, then you've confirmed that the > resistance of each one is a few Ohms. Mine typically read about six > Ohms, measured at the harness. One text indicates a maximum > tolerance of 25 Ohms. Other possible problems with the injectors > include leaky injectors or clogged/uneven spray patterns. I don't > think that anything you've told us would point directly to a problem > with the injectors. > > When was the last time you replaced your fuel filter, near the fuel > pump under the front end? (Don't put a regular cheap one here--the > correct one is required, and costs about $6 or $8.) > > Press on! Good luck! > > -Greg > '69 & '71 Squarebacks > '63 Beetle > >