Oldsmobile/Buick Repair: 87 3.8 olds (buick) 34# fuel pressure, throttle position sensor, digital volt meter

Question
I HAVE 87 OLDS CIERA W/3.8 SEQUENTIAL INJECTION.HAD LEAKING INJECTOR ENGINE CUTTING OUT AT LOW SPEED.THEN WOULD NOT START. NEW INJECTOR STARTED FOR A FEW SECONDS THEN STALLED.REPLACED CRANK SENSOR, STILL THE SAME.CHANGED FUEL FILTER.CHECKED FUEL PRESSURE, 34# CRANKING. AT FITTING ON RAIL.HAS SPARK.I SUSPECT PUMP OR PRESSURE REGULATOR BUT UNSURE HOW TO TELL WHICH ONE.I WAS FORMERLY A MECH UNTIL 1980 BUT DON'T KNOW A LOT ABOUT THE LATER CARS.ANY ADVICE WOULD BE APPRECIATED.THANKS DAVE

Answer
Hi Dave,
That system uses a pump and regulator to maintain 28-36PSI. I would say your 34 PSI is just fine, so pump and regulator are not the problem, nor the filter.
With good spark and good fuel pressure, I would next check for vacuum leaks.
The EGR valve could be stuck on some carbon, or the brake booster could be leaking.
At any rate, a vacuum guage could be helpful.

Next would be to check and see if the injectors have power with the key in run, and then if they pulse while cranking.

The throttle position sensor is another possibility, although slim. But if it is sending a wide open signal, the ECM could confuse it as a clear flood signal, and not inject any fuel. I am not positive that ECM does that, but it could.
The TPS is connected to three wires. One is a 5 volt refference signal from the ECM. One wire is a ground. And the third wire is from a potentiometer in the TPS, and sends a varying amount of that 5 volts back to the ECM to indicate throttle plate angle so it can adjust the injector pulse width.
If you have a good digital volt meter, and want to measure it, you have the 5 volts of course, and the ground. So from the third wire, at closed throttle you should have 0.4 volts, and at wide open throttle you should measure about 5 volts, or about the same as the refference voltage.
Throughout the travel of the throttle should vary between those limits, with no big jumps or breakes in voltage.

One other item in the fuel charge system that could make a difference is the MAF, or mass airflow sensor. The readings from that sensor determine the injector pulse duration, ignition timing, and egr valve operation.

And then there is always the timing belt/chain as a possibility.

And loose wire connections. But check the injector power and fuse first, and the vacuum.

Van