If I use a test light at the fuel pump and it shows power while cranking engine, does this mean that its a good circuit and the pump bad? 1991 mercury capri

USA CAR,NOT tOLD yours.nor "e"code, series3 code.
e21 ,1975?
2.0L
320i. the "i' only means fuel injected 320d is diesel
what matters more 'e" code, e21 up.
No year told,
NO ENGINE told, nOR GAS OR DIESEL.?????? i= gas.
first we test fuel last , not pumps first (sorry but i cover that)

the engine must be good, no bad engine burns fuel and run.
next is (gas engine) spark must be good or if diesel glow plugs.working.
then comes fuel checks last. (all this is basic basics 101 stuff)
the PCm cuts fuel for many good reasons.
but we test fuel pressure cranking, on any dead engine using a tool called fuel gauge ( PSI or in Europe BAR/kPA)
CRANKING ONLY
IF THE FUEL PUMP RELAY IS DEAD, MOST TIMES THAT MEANS
THE PCM IS CUTTING FUEL ON PURPOSE.
TOP CASE PCM SEES SPARK DEAD AND MUST BY LAW CUT FUEL FAST.
if car has bad TPS sensor and it sends 5vdc to the PCM for throttle angle (100^%) or WOT false signal the PCM cuts fuel
or the PCM sees IMMO not happy it cuts fuel. or spark and on some cars even cuts cranking, on my car it cuts fuel after 3 second run
if IMMO KEY FAILS.

other simple tests, is Test fuel.spray
if engine good and spark good, test fuel works.
see? but no engine told
and spark plugs all tested for good spark..
on on all uSA cars here, 1996 up any OBD2 scantool works
so we scan it first. see why the PCM cut fuel???
as it can for many reasons,
on gasoline engine top causes are P03xx DTC errors
for sure CMP or CKP sensors failing it cuts fuel 1or2 ways.

NO CAR TOLD at all.
47 year span , sorry can not guess.

The year the first BMW 320i was manufactured was 1975
Max Nebular car.

fuel is cut to prevent CRASH and burn as seen on TV, endless.
by law and pure hard LOGIC. deep inside the PCM.
and more.

Bad wire harness or bad pump

And then it runs good? If yes, there is a problem in your fuel pump circuit. It could be a bad fuel pump relay, but the circuit clearly has a problem. The engine computer should signal to the relay to send power to the pump when you are trying to start it. In fact when the key is turned to on, the computer should activate the relay and turn the pump on for about 2 seconds. That puts enough fuel pressure at the engine, so that cranking the engine over should start it- no fluid needed.

How do you know the fuel pump is good ? Did you do a fuel pump pressure test with a test gauge ? Did you test the fuel pump electric circuit ? Is the check engine light on ? There is a fuel pump relay under the hood engine compartment . The right front behind the headlamp are four relays , the one to the left is the fuel pump relay .I'll send a link to a video on testing the circuit !There also is a fuse in the wiring near those relays , it's power for the fuel pump relay ! Or you have a bad fuel pressure regulator ! A plugged catalytic converter could do this , need to pull the O2 sensor an do a back pressure Test ! Fuel Pressure Test Exhaust Backpressure Testing How To Diagnose Exhaust Restrictions EricTheCarGuy

`Probably the fuel pump in the tank has stopped working. Verify with a check for power at the gas tank connector: When the engine is cranking, the fuel pump wire should have power on it-use a test light or voltmeter. If the wire has power, but pump will not turn on, the gas tank will have to be removed to replace the pump.
Just by turning the key to on, not start, will or should cause the fuel pump to come on for about 2 seconds to pressurize the fuel lines and put gas under pressure against the fuel injectors. If you don't hear the pump buzz on for a brief time, you know you need to check the fuel pump circuit. Check fuse, check fuel pump relay...but the easiest way to verify a bad pump is to check fuel pressure, or check for power at the gas tank when the engine is cranking. No power is a fault in the circuit (fuse, relay, wiring), power available to the pump but no pump means the pump will have to be replaced .

Check the injector fuse. With key on, injectors should have constant power available to them on one wire. The other injector wire is ground wire. With constant power to injectors, all it takes to pulse the injectors is for the computer to ground the injector ground inside the computer for a split second, and pulse occurs, causing fuel to spray out the injectors.
So if injectors aren't working, either the injector drive circuit (the power to injectors) or the injector ground circuit is lost. You can buy a cheap "noid light" at any auto parts store, and check the injector circuit. Just plug the light into the injector connector and crank the engine over. If the light is blinking, circuit is good. If no light, the circuit has a problem, either on the drive side or the ground side.
Here's a way to check the ground circuit separately. Use a test light clipped to the Positive battery post. Probe the ground wire terminal of the injector connector while the engine is cranked over. The test light should be blinking-meaning the computer is grounding the circuit normally and would be causing the injectors to pulse, if power is available to them.

Pressure in the rail indicates the pump is working.
When the key is turned on, the pump will come on for about 2 seconds to pressurize the fuel system. Then pump will shut off and not come on again until the engine is cranked. When cranked or when running, the pump will be on full time. To check if the pump is getting a signal, the engine must be cranking over. Or you may pick up that 1 or 2 second signal when the key is first turned to on. Is this the way you checked for power to the pump? How much pressure are you getting at the rail? Any pressure at all means the pump put it there.
Injector circuit test: Use a testlight and ground it to the engine. Pull off an injector connector and turn key to on. Probe the two wires to the injector. One wire should have power and light the testlight. If it does, the power side to injector is good. If nothing there, the injector drive circuit is out.
If you got a steady light on one wire, then check the injector ground circuit. Move the testlight lead from ground to the positive battery post. Now probe the injector connector's wire that did not light the testlight, while someone cranks the car over. If working right, the testlight should now be blinking, meaning the computer is properly grounding the circuit for injector to pulse. If both tests pass, the injector circuit is working right.
Good luck.

Check your injector circuit. It will also let you know if the PCM is allowing the injectors to energize. Here's how:
Pull off one injector connector. Turn key to on. Use a test light and clip the black lead of tester to ground, Use the tester's probe to probe both wires in the injector connector. One of the wires should have power and light the testlight, meaning the injector power circuit is working. Now for the injector ground circuit.
Move the black lead of testlight to the battery positive post. Now probe the wire in the connector that did not light up. Have someone crank the car over. When cranking the test light SHOULD be blinking, meaning the PCM is properly grounding the injectors to work. If both wires passed the test, your injector circuit is good.
If it's not working,either the power circuit from ignition switch to injectors is out (no steady light), or the ground circuit from injectors to PCM is not working (no blinking light).
Good luck, post back with results for further assistance.

you can have someone tap on gas tank while trying to crank it ,,if it try to start,, its the fuel pump,, while they are under there have them listen for a hum when you turn the key switch on, if no hum fuel pump bad

There is no fuel reset button on this van.

To test the circuit before removing the tank, you will need a voltmeter or cheap test light. Disconnect the connector at the fuel tank. On the harness side, locate the gray wire (fuel pump wire). Connect the test light to a good ground. Have a helper crank the engine over. While engine is cranking, the gray wire should have power. If it does, and the pump is not turning on, then the pump must be bad and need replacing. If there is no power on the gray wire with engine cranking, the circuit is the problem, not the pump. Go back and find the fuel pump fuse in the junction block (the fuse relay block where the fuel pump relay is). Check the fuse, also check if there is power going to the fuse. This fuse should be hot at all times. The circuit goes from battery to pump fuse to fuel pump relay to gas tank and the fuel pump.