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No power to fuel pump. New pump and relay

7

77volvo242

Member
Joined
Nov 14, 2020
Location
California
I am not getting any power to my fuel pump (no buzz/prime with keys in and won't turn over).

I have tried swapping out both the fuel relay and the main pump itself.

I did notice that there was some slight melting around the fuel pump relay harness on the power in terminal. It does seem like there is still a connection, but thinking this slightly melted power lead might be a clue to what's going on.

The car is a '77 242, but the engine management is lh2.4 from a 1991 245, which involves the full fuel system as well as electrical harness and sensors. Fuel system was done by prior owner.

Any ideas what to check next?
 
Checked fusebox?

If it's not a fuse, break out the wiring diagram. Make sure you have power at the relay when you should (key on, etc). If you do, make sure you have power out of the relay, power at the fuel pump, etc. If power is missing at any of those points, figure out where it disappears to find the bad connection or broken wire. Pretty straightforward stuff. If you have power all the way to the pump and the pump still isn't turning, make sure there's a good ground connection from the pump back to the body.
 
Yes all the main fuses inside cab look good. Unless there is another fuse for fuel system located somewhere else I don't know about? But not getting any power at the pump with voltmeter.

Any idea which terminals should have power for the relay with key in ignition on? I think that's where I get stuck.
 
Get a diagram for fuel pump/LH relay. Power comes from the battery via the fuse holder at the battery.
 
If it has the complete harness from a '91, I'd look up the '91 wiring diagram and check out the fuel system diagram. Unfortunately since it's a swap it's entirely possible your car doesn't adhere to the diagram anymore.

In a stock setup there is a fuse in the engine bay for the fuel pump but they may or may not have kept it. OEM location would be a small white holder connected to the main battery cable - originally they were mounted to the fender but usually they have broken loose and are flopping around on that side of the engine bay by now.

20 amp fuse coming off battery - Volvo Forums - Volvo Enthusiasts Forum

Volvo 240, 740 & 940 - 20 amp fuse coming off battery - if you dont wanna read all that...the basic question is it necessary? what is it for? Ive been told it might be for an aftermarket stereo but i dunno it comes off the battery termal from the wire that goes to the starter. its just places...
volvoforums.com
 
Khrrck said:
If it has the complete harness from a '91, I'd look up the '91 wiring diagram and check out the fuel system diagram. Unfortunately since it's a swap it's entirely possible your car doesn't adhere to the diagram anymore.

In a stock setup there is a fuse in the engine bay for the fuel pump but they may or may not have kept it. OEM location would be a small white holder connected to the main battery cable - originally they were mounted to the fender but usually they have broken loose and are flopping around on that side of the engine bay by now.

20 amp fuse coming off battery - Volvo Forums - Volvo Enthusiasts Forum

Volvo 240, 740 & 940 - 20 amp fuse coming off battery - if you dont wanna read all that...the basic question is it necessary? what is it for? Ive been told it might be for an aftermarket stereo but i dunno it comes off the battery termal from the wire that goes to the starter. its just places...
volvoforums.com
Click to expand...
The 25 amp fuse connected to the battery is there and appeared good. But swapped it anyway.
 
There is an ignition amp which usually is mounted by the left inner fender near the battery. You can use a test light or a sensitive voltmeter and check at the input and output for triggering. That will lead you to which way to troubleshoot. If there is not input trigger then it is either wiring, EZK unit or bad crank sensor. If there is input triggering but no output that could be the ignition amp itself or parts further down in the system like wiring to the coil.

If you don't have spark the fuel computer won't ground the fuel pump relay to power the pumps. So I always start with spark. Have you tried to read any codes? Is the diagnostic box installed on the strut tower?
 
dl242gt said:
If you don't have spark the fuel computer won't ground the fuel pump relay to power the pumps.
Click to expand...
1980/81 VW Rabbit with CIS used a relay that sensed crankshaft pulses.

Since someone re-engineered his vehicle, I'd have to see WTF they did.
 
77volvo242 said:
Yes all the main fuses inside cab look good. Unless there is another fuse for fuel system located somewhere else I don't know about? But not getting any power at the pump with voltmeter.

Any idea which terminals should have power for the relay with key in ignition on? I think that's where I get stuck.
Click to expand...
The relay should always have power through the red wire at the relay. Pin 4 at the ECU connector and Pin 5 at the EZK connector should also always have power. When the key is turned to the run position pin 6 of the EZK and pin 15 of the ECU should have power. If you have power to the red wire at the fuel pump/main relay, grounding the blue/green wire should make the fuel pumps run if the relay works. The power out of the relay to the pumps goes through the yellow-red wire and passes through fuse # 4. Check all that and report back what you find.
 
84B23F said:
I recall VW relay had to "know" engine was rotating...fire prevention measure if fuel line was busted in an accident/etc.
Click to expand...
That's exactly why it was done the way it was. A safety feature to keep the fuel pumps from spraying fuel all over a wrecked car.

You could split hairs and say it doesn't need spark. What the ECU needs is an RPM signal. On Volvo K-jet that was delivered from the coil low voltage terminal.
 
You could have NO SPARK and still have the fuel pump relay work. I was correcting his comment that he was saying if the powerstage is bad, there will be no signal to the relay to turn the pumps on.. Which is NOT true

EZK gets the crank sensor signal and then tells the LH box that the engine is turning and then the ECM grounds the fuel pump relay.




5 minutes with a wiring diagram and a test lamp at the relay wiring should tell you whats going on.

Go jump the black/yellow wire to ground and see if the pumps go on.

Go open the relay and pinch the contacts closed and see if the pumps go. Leave the box open and go key on, and crank and watch what the contacts do.

BASIC electrical diag. Don't use a meter, use a test lamp.


Sorry lots of editing. Don't have too much time to post a well written post right now.
 
Last edited:
Go to ozvolvo.org/archive and download the 1977 greenbook and the 1993 greenbook (do a browser <Ctrl-F> search for 1977, 1993). The 1977 shows how the car was originally wired (2 separate main+fuel relays). The 1993 shows how the LH2.4 dual main+fuel relay is wired, but the main fuse is different from a '91 harness.

The recommended way of upgrading to LH2.4 uses just the LH2.4 fuel relay, and bypasses all the old K-Jet stuff. If you look at pg 9 of the '77 greenbook, it shows the 2 separate K-Jet main+fuel relays. Check the driver's footwell to see if these relays are gone - they should be. If not, it will take some tracing to see how LH2.4 was retrofitted.

When you turn the key on, do you hear the main/fuel relay click and then un-click a half-second later?
 
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