fuel pump keeps switching off, ideas?

[duff5000]

Hi everyone.

92 efi stopped while driving it the other day. After some searching on here i found the way to bypass the relay for the pump and was able to drive it home. Interestingly when i got home and pulled the wire i had running from the battery the car still kept running (i expected it to stop straight away if the relay was faulty)

Since then the car starts and runs a bit but you can hear the relay clicking off and on every so often. The engine either misses or stops depending on how long the pump is off for i guess. I swapped the pump relay and the same thing still happens.

What could be turning the pump relay off? There seems to be more clicking from the engine bay while this happens but i havent worked out exactly where or if it is a relay or just the fuel pressure going high then low that is doing it.

Any ideas?

Thanks.

[Spetz]

Do you have an alarm/immobilizer?

[duff5000]

Nope.

[rumpfy]

page 1059 of the manual (4 cyl MPI) shows the 'engine control relay' at pin 2 supplies power (12 Volt) to the fuel pump.
As a first step, confirm that the pin has 12 volt when the pump should be running.
The particular relay seems to have 2 coils and at this stage I'm not sure what the two coils do. One of the coils is activated when the transistor in the ECU goes into conduction, and at pin 7 of the engine control relay, the voltage at this point should be zero when the transistor is conducting and hence the relay must be conducting.
check this details and see what happens.

[Tlmitf]

Sounds like either you have a broken trigger wire, or the component controlling the triggering is defective.

Grab a multimeter and check the conductivity of the trigger wire, more than likely it is broken at some point along its length. Depending on how much effort you want to put in finding the break determines how much wire you need to replace.

Basically what the bloke above me said.

[duff5000]

Sounds like this is going to be a fun job. Any idea why the pump relay is so complicated? I assume the relay is doing more than just a simple off/on function but not sure what. Car runs fine with 12v going to the pump connector on the firewall but i am pretty sure bypassing the relay with a switch isnt going to be a good idea long term.

Any idea what would be making clicking noises around the intake area? Not sure is there is anything there that would be triggering the relay to go off and on. Ill do some more testing. EDIT: looking at the wiring diagram there is a purge valve in there somewhere controlled by the same relay.

Downloading the manual now as i cant find where i saved it from last time i needed it. Ill work out what the trigger is for the relay and see if it is flicking off and on as well.

I did get the spare from a wrecker there there is always a small chance it has the same issue. You would think a relay either works or doesn't, 2 being intermittent sounds like the relay itself isn't the issue.

[veeone]

Relay is energised when you turn the key to start and then should switch from that to alt circuit once the alternator excites.
This way if you have an accident the alt stops working and electrical supply is cut to the fuel pump to prevent fuel spraying everywhere if a line is cut in the accident etc.
Might be dirty contacts in the relay....swap it out and see if it still does the same.Eliminates that then go from there if the problem persists.
Clicking in the intake area is not the fuel pressure relief valve making noises is it?? Vee

[duff5000]

Thanks, that makes sense.

I swapped the relay with one from the wreckers and the problem is the same.
I guess the connector to the ECU could have some corrosion. A bad connection to the ignition switch could cause issues as well i imagine

Not sure where the clicking was coming from, Ill have to get someone to start the car so i can listen for it again. Often stalls before i get the chance. Actually the other day it was still clicking away after the car stalled which is weird.

[veeone]

Might be that alternator connection. I think the ignition key would be ruled out if it is the fuel supply only and not spark as well as the fuel pump runs off the alt once engine running and key only provides power to pump while cranking. Vee

[duff5000]

Good idea, ill check those connectors.