fuel delivery - Intermittent

[Jonnycash]

I have been trying to track down this problem for a couple days now.
The car is a 92 svx 172K miles. All stock except for crank pulley.

With no symptoms leading up to this, the car did not start after being shutoff and parked for aprox. 3 hours.

-I checked the timing belt... seemed fine.

-Checked fuel pressure, by pulling the line after the filter off. Sprayed fuel from both the metal and rubber line.

-Checked spark by removing a plug and grounding it. (on the right side, away from spilled fuel.) Had spark.

-Checked fuses. Found #2 blown. Replaced it, car started and drove for 15 mins. Restarted after 1/2 of being parked. Car then restarted and drove fine for another hour, where it was parked at home.

-Car did not start the next morning. Checked fuse 2 again, was fine. After pulling the fuse and putting it back in, the car restarted and drove just fine.

-Car died later that night, this time while driving. Again pulled fuse 2 and replaced it... no start. Checked fuel pressure, none.

-Had it towed home.

-Replaced, Cam and crank sensors as well as maf, all one at a time cranking it over in between... No start. Checked fuel pressure, none.

-Let the car sit with no more work done, and it started. Ran for 1/2 hour in my driveway. Idled fine, and ran fine when I held the rpms around 2k. Shut it off and turnrd it back on a few times. Everything seemed ok.

-Drove it 50 feet down the road, stalled, no restart. Check fuel pressure, none. Let the car sit and read the forum on my phone for about 1/2 hour. Restarted, drove it home.
Sorry for the timeline, but just wanted to give as much info as possible.

The only consistancy is the fuel pressure, except for the first time, but I checked it until well after it didn't start.

Now I have disconnected the fuel line and stuck in a jug. Sometimes if I turn the key on I have fuel flowing. Other times none. It does not stop flowing(engine off) within 20 seconds (thats all the time I could check before the gallon jug filled up).

I have tried disconnecting relays under the dash while fuel was flowing in order to locate the fuel pump relay. No luck with that. I have checked the manual wiring diagram and component locator for the relay, but can't find one that matches the description.

I am thinking the problem is:
-Bad fuel pump relay
-Bad fuel pump
Hopefully someone can help me locate the relay. Also any other suggestions are welcome
Any help would be greatley appreciated.
Thank you!

[sowise]

Fuel pump relay is located under the steering column by the power steering ECU, front wiper relay, and main relay.

Fuel pump modulator is located under the rear speaker deck next to the rear wiper relay.

and obviously it could be the pump going south.

those locations are in the manual tho. Troubleshooting of the relay should be performed per the wiring diagrams.

If I were a betting man..wait I am I would bet on the fuel pump but thats because you can't go wrong upgrading it to a walbro.

[Jonnycash]

Originally Posted by sowise

Fuel pump relay is located under the steering column by the power steering ECU, front wiper relay, and main relay.

Yup, thats what I read in the manual. I have been under that dash trying to find a relay with the same color wires as what the manual states.

Originally Posted by sowise

Fuel pump modulator is located under the rear speaker deck next to the rear wiper relay.

I never even thought about the modulator. Will check that in the am.

Just another note... I cannot hear the pump running, and never have. I have also had other people listen for it, and they can't hear it... even when I have confirmation that it is pumping.

[oab_au]

If you turn the key on, you should hear the pump run for a couple of secs. Also check the earth for the pump modulator, it is screwed to the body near the modulator.

Harvey.

[sowise]

I don't know if the pump is as loud as some other makes and models, have to verify with others for certain though since it has been a while since mine was up and running. Should hear something with the rear seat removed though.

I can try and take a look under my dash tomorrow for the relay I have that area open so should be able to peek at both cars to check for any differences but they are both 92's so doubt there will be any changes.

[Jonnycash]

Originally Posted by oab_au

If you turn the key on, you should hear the pump run for a couple of secs. Also check the earth for the pump modulator, it is screwed to the body near the modulator.

Harvey.

When I turn the key on, I cannot hear the pump, even when it does run. I know it runs, because it is pumping lots of fuel. I will remove the seat and see what I can find. Thanks!

[Jonnycash]

I am reading 7.5-8 volts at the fuel pump with the key on and off.
I now have a new pump, and it runs when I put 12 volts to it, as does the old one.
Modulator?
What is the modulator's job, anyway?
Thanks!

[oab_au]

Originally Posted by Jonnycash

I am reading 7.5-8 volts at the fuel pump with the key on and off.
I now have a new pump, and it runs when I put 12 volts to it, as does the old one.
Modulator?
What is the modulator's job, anyway?
Thanks!

The modulator is controlled by the ECU to switch a resistor into the 12v ground line from the pump, to reduce the pumps out-put, when full fuel delivery is not needed. Reducing the flow prevents the fuel from heating.

Harvey.

[Jonnycash]

Originally Posted by oab_au

The modulator is controlled by the ECU to switch a resistor into the 12v ground line from the pump, to reduce the pumps out-put, when full fuel delivery is not needed. Reducing the flow prevents the fuel from heating.

Harvey.

Ok, Thanks.
So does that mean that the modulator may be working just fine, putting out 8 volts?
I am stumped. The pump run at 12v, but not the 8v that its currently getting.

[oab_au]

Originally Posted by Jonnycash

Ok, Thanks.
So does that mean that the modulator may be working just fine, putting out 8 volts?
I am stumped. The pump run at 12v, but not the 8v that its currently getting.

Idling, light throttle, the resistor is in circuit, so 8v is about right. When the pedal goes down and the rpm rises the resistor is bypassed for a 12v supply, for full pump out-put.

Can't say why it won't run on 8 volts, it should.

Harvey.

[Trevor]

Originally Posted by Jonnycash

I am reading 7.5-8 volts at the fuel pump with the key on and off.
I now have a new pump, and it runs when I put 12 volts to it, as does the old one.
Modulator?
What is the modulator's job, anyway?
Thanks!

You should not be measuring voltage at the fuel pump with the ignition key off and when the fuel pump relay should be open. Please confirm.

If there is voltage, the fuel pump relay must be stuck closed, or there is a short circuit in the wiring bypassing the relay.

On which wire at the fuel pump are you measuring voltage? You could be measuring a reduced voltage via the pump windings from the black wire to ground, in the event that the modulator and or resistor is not grounding the pump as it should.

You should be able to read close to 12 volts from the blue wire to ground with the ignition on.

The pump should run at full speed if you ground the black wire connection. Did you confirm running at 12 volts in this way or by making a direct connection to the pump? If not, make this test.

[Jonnycash]

Originally Posted by Trevor

You should not be measuring voltage at the fuel pump with the ignition key off and when the fuel pump relay should be open. Please confirm.

If there is voltage, the fuel pump relay must be stuck closed, or there is a short circuit in the wiring bypassing the relay.

On which wire at the fuel pump are you measuring voltage? You could be measuring a reduced voltage via the pump windings from the black wire to ground, in the event that the modulator and or resistor is not grounding the pump as it should.

You should be able to read close to 12 volts from the blue wire to ground with the ignition on.

The pump should run at full speed if you ground the black wire connection. Did you confirm running at 12 volts in this way or by making a direct connection to the pump? If not, make this test.

It was indeed the relay itself. I suspected it from the start, but the relay I was checking turned out to be the starter relay. The manual says the fp relay is to the right of the steering column. It is much to the left of it.
Once I located the fp relay, I held it while cycling the key, it clicked. I then grounded my volt meter, and checked the yellow wire, 12 volts there. Checked the blue wire, while cycling the key, 0 volts. I then ran a jumper between the 2 and got 12 volts at the pump.
I guess I will just call my new pump and strainer preventative mantainance

[Jonnycash]

Also,
Thank you to everyone who was so willing to help me out!
I hope one day i will be able to help you fix a problem.

Thanks again,
Jon

[Trevor]

Originally Posted by Jonnycash

Also,
Thank you to everyone who was so willing to help me out!
I hope one day i will be able to help you fix a problem.

Thanks again,
Jon

Kia ora Jon,

Pleased to help you and also that all is fixed. Your message of thanks is specially appreciated.

Cheers, Trevor.

[Jonnycash]

OK. So, appearently a problem still exists within the fuel pump curcuit.
I put the new relay in and all was well.
Today, I heard the pump running after I shut the car off. I checked the voltages, here is what I found:
Blue wire
12v with relay unplugged or plugged in, key on and off. (constant power)
Yellow
12v constant ( i believe it should be)
Black/white
12v only when key is on (same with relay plugged or unplugged)
Green
12v only when relay is plugged in and key on.
I unplugged the modulator and resistor, didn't change anything.
I unplugged the main fuse link in the fuse box and the pump was still running.
I unplugged the fuse (1st small 30amp green clear top, up from the main fuse link), and the pump stopped.
I am going to try and track down wires and find the problem. In the meantime, I am willing to listen to everyone's ideas of what might be going on here.
Thanks again!