My 85 Z28 305 TPI is having some issues. I have replaced the TPS now for a 4th time but this time it has not fixed the issue. Prior it would run rough, put out black smoke, and not run unless you were hard on the gas. If I adjusted the TPS it would clear up but come back later. Then the car just stopped running, long cranks, starts sometimes but extremely rough and cuts right off.

Replaced TPS yesterday and upon checking the voltage ground is good, gray wire has 5.06V, but the blue wire with the OHM meter set on 12V was .08 at idle and like 1V at WOT. I figured I must have the meter wrong to read it so I changed it to 9V and the blue wire ranged from .22 to .44 idle and 2v to 4v at WOT with the sensor in different positions.

I was told that the sensor is bad when it does this but its brand new out of the box. Could it be something else? Any help on this is greatly appreciated.

 

Of course be sure that the connector is solid and that your pin tension is good. The TPS should read .5V +/- .05V at closed throttle, and 4.5V at WOT. The MAF sensor and circuit cause alot of trouble on these cars. Check MAF voltage. I assume you have wiring diagrams so I wont tell you which wire to check at. The MAF voltage arnge is about .5V key on engine off, 1.4- 1.7 at idle, and about 4.5 at WOT. On any EFI sensor, be sure you use a DVOM with 10Mohms/volt imput impedance for accurate readings and so you don't create issues with the ECM when testing.

If MAF and TPS test okay, take a close look at your injectors and or distributor. Injectors and HEI dist are also common failure items. I have seen both cause symptoms similar to yours. Do you have a scan tool. Anyone working on an EFI system should own one. You of course need an OBDI compatible tool. These can be spendy new but since they've been around for 25 years, you can now buy older units for cheap on Craigslist. My favorite is the SnapOn MT2500 "brick". With a scan tool you would want to watch BLM and integrator, TPS and MAF while the problem is occurring.