Hayk

iTrader: (1)

As the title says, my fuel pump doesn't kick on when I move the key into the ON position. It only works when I crank the engine. I bought a simple Multimeter off of Amazon to test my electrical system.

Mastech MS8268

I followed the Factory Service Manual and checked my relays (EFI and Circuit Opening Relays).
It said to check for continuity between pins 1 and 2 (silver). I recorded around 92-95 Ohms with no beep. And there was no continuity between 3 and 4 (copper), as stated in the manual. Then it said to connect the battery to pins 1 and 2, and check for continuity between pins 3 and 4. I heard a click and there was a clear beeping sound. It was 0.6 Ohms, which is the same as touching my probes together. Does that mean my relays are good? I tried some other ones that looked the same, and they behaved in the same fashion.

I then went to the fuel pump connector and measured the voltage coming out of the harness. With the key ON, the meter was showing 0-400 milliVolts. You would see it grow to 400 and then drop down to zero. When I cranked the engine, it went to a steady 11.2 Volts.

Any suggestions? What do you think is stopping the battery from sending 12Volts to the pump in the ON position?

Hayk

iTrader: (1)

Here is my thought process. I'm not getting battery voltage at the pump, with the key on. Although I am getting power while cranking. Maybe the ignition switch is to blame? Maybe the power during the crank is actually coming from the alternator. Am I on the right track?

P.s.: checked all fuses for continuity. They're all good.

hzt30

Does this car start?

Most systems use a relay to prime the system usually for only two to three seconds when the ignition in in the on position then it waits for a high enough RPM signal to continually run the pump. Did you recycle the key to check for voltage? After the key is on for a few seconds the voltage disappears.

Hayk

iTrader: (1)

The car does start. I cycled the key a few times, same result.

I should mention that the alternator was replaced by the previous owner.

Edit: I would like to test my ignition switch in the same way as in this video. Apparently there is a wire responsible for the fuel pump.


Where is the ignition switch harness located? Is it also next to the fuse box?

hzt30

EFI RELAY - Closed with the ignition switch at on or start position.
CIRCUIT OPN RELAY - Closed with the starter running.
Circuit opening relay powers the fuel pump.

hzt30

The fuel is controlled by the circuit opening relay and the crank sensor (NE signal), and the ECU. When the key is turned to "on", the ECU energizes the circuit opening relay, and that cycles the pump on for 3 seconds to build up pressure for starting. The crank sensor counts the teeth of the flywheel and sends a signal to the ECU when the engine is turning. If the engine is not cranking, the crank sensor sends no signal to the computer, so the fuel shuts off after the 3 seconds.

Once the engine starts cranking, the computer receives a signal from the crank sensor. The computer sends a ground signal to the circuit opening relay via FC signal, and the fuel pump continues to run as long as the engine runs.

Hayk

iTrader: (1)

Thank you for that explanation. So are you saying that I should check if the CIRCUIT OPN RELAY is getting power(clicks) when the key is ON?

hzt30

Relay should energize for a few seconds than drop out when key is first turned to on position.

What exactly is the issue with the car, is it hard to start?

Hayk

iTrader: (1)

I didn't have another person to help me, so wrapped some wire around the relay terminals and ran it to the top. This way I could probe the relay while having it plugged in.

Here is what I saw:
I had my headlights ON when the key was in the ON position. Battery Voltage - 12.8V (OFF) and 12.3V (ON with headlights).

Note: I was incorrectly using my Voltmeter. Instead of having the negative lead on a known ground, I was measuring the potential difference between the pins. These measurements are meaningless. Please refer to my two pictures that are further down.

EFI
In the OFF Position:
Silver Pins - 0 Volts
Copper Pins - 12.8 Volts (Battery Voltage)

In the ON Position:
Silver Pins - 11.3 Volts
Copper Pins - 6 milliVolts

Circuit Opening Relay
OFF
Silver Pins - 0 Volts
Copper Pins - 0 Volts

ON
Silver Pins - 0 Volts
Copper Pins - 12.1 Volts


The car takes a little longer than normal to start. Part of that problem is a fuel pressure drop, but that's for another thread. I would like to regain the ability to energize my fuel pump, so that I could build up the fuel pressure without cranking the engine for too long.

Both relays look identical (same part numbers). I would like to see a picture of somebody else's engine fuse box, just so I know that I'm not missing anything.

hzt30

Since car starts and runs it appears that the EFI & the circuit opening relay are functional. The problem seems to be the FC signal coming from the ECM when key is first turned to on position. You can put your negative lead of the voltmeter on a good ground and the positive lead on the FC side of the circuit opening relay and check for voltage when key is first switched on.

When metering certain ECM circuits you need to have a high impedance meter (10 megohm or higher) so you don't blow the ECM drivers.

Hayk

iTrader: (1)

What is an FC signal? I was trying to find some relevant circuit diagrams in the FSM, but it doesn't seem to have anything.

EDIT: I was wrong. Pages 68-69 have the CIR OPN and EFI Relays with the ECM. I now understand what you were saying.

hzt30

The FC signal is the Fuel Control signal from the ECM. It is ground side control line to the circuit opening relay which controls the operation of the fuel pump.

The schematic that I posted is from a 1997 ES300 service manual.

Hayk

iTrader: (1)

hzt30, you have been a great help, thank you. I have already learned a little bit about wiring diagrams and the fuel pump operation. Just so you know, your picture is not showing up.

I went back and measured the voltage at each terminal on both relays. My negative lead was always on the battery ground.

KEY OFF: Everything was 0 Volts, except for EFI's Pin #5

KEY ON: Here is what I saw





Both relays are good. I have tried switching them, and I get the same result. As you can see, I get 12.6V on both sides of the control leads for the CRC OPN RELAY, but it doesn't close Pins 3 and 5. I have verified the measurement by having someone turn the key, while I was connected to Pin #3.

Is this a confirmed FC Signal issue? I don't know where the computer is located. I'm guessing I will have to check the Green/Red wire for continuity. And I don't think I have a high impedance meter.

hzt30

My fuel pump control circuit picture is back.

So you are saying that you never get the initial 2-3 second FC signal from the ECM? Everything looks as it should with key on and engine off but after the 2-3 second prime time.

The green/red wire is good all the way back to the ECM because the engine will never run without this FC control line. It looks like the ECM isn't sending the initial FC signal with the initial turn on.

Hayk

iTrader: (1)

Okay, having your picture as a reference makes a little more sense. What voltage measurements would I see, if I had an FC signal during those first 3 seconds? I did not probe Pin #2, when I had someone turn the key. I probed Pin #3(output), thinking that if there was a signal, I would see 12.6V.

I think I'm misunderstanding how a relay works. On the control side, do I need to see 12.6v coming in and 0V(ground) going out? Should it look just like the EFI relay with the key ON?

EDIT: The more I think about what I've done and what you've said, the more it makes sense. In order for a relay to close, I need to have power on one side and ground on the other. That's why when I was testing for continuity, I had battery positive on one pin and battery negative on the second pin. So the computer grounds the relay for a few seconds, at least that's what it's meant to do. I haven't probed the relay with the engine running, I should do that to see how it's supposed to be.

If there is no ground signal with the Key On, does that mean my ECM is faulty? Can it be reprogrammed/reset?

Also, I now understand how a voltmeter works. My measurements in post #9 are worthless, because they were done incorrectly.