If your getting wierd electrical stuff going on in your engine bay like relays ticking and your motor cutting out and bucking, try opening up the harness beside the valve cover and follow the six black grounds for the injectors till they join up with one. this connection will probably look fine but you will have to redo this connection. try ring connectors with a bolt through them and add another ground wire to them, attach this ground to the firewall ground for the engine, sand all the paint off under the bolt.After that add a battery cable to the firewall bolt and run this to the neg post on the battery. this solved all funny sensor, fuel, and driveability problems for me....this fix should work for 87 to 91 4.2's,with multi port fuel injection.