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Volvo 940 b230ft fuelpump relay clicking

Jonny940turbo

Jonny940turbo

New member
Joined
Mar 21, 2024
The problem started almost a year ago and it was really bad in the summer. Got the car running after a while searching why it wouldnt start but it was just a bad relay in the enginebay.
So, after i got it running car was just idling and out of nowhere rpms jump up and can hear the fuelpump relay click and the problem always came back when idling for a bit when it was ~10+°c outside. But in the summer of 2023 driving the car it suddenly started clicking the relay a bunch and car jerked really hard and almost didnt respond to throttle at all and was hard to keep running. Also the CEL flickers with the relay clicking. Have cleaned all enginebay connectors, new ECT sensor, EZK has been changed, plugs and ignition coil, the black slim box near battery, grounds are cleaned and new o2 sensor. Might not remember all thats done. Could it be with the ecu pin-9 cutting power to the fuelpump relay somehow? Also forgot to mention that fuelpump is wired with its own relay and switch. Ecu is 962.
 
The fuel ecu grounds the fuel pump section of the relay to turn on the pumps. So if the ecu is for some reason removing the ground that could be the issue. I would presume you have tried a different relay? One thing that can cause the ecu to remove ground is loss of the engine rpm signal from the EZK. It can also be a bad ecu. Is this a car with the immobilizer? That can also cause the ecu to shut down fuel if it thinks there is an issue.
 
Its a 1998 so it has the immobilizer from factory but i think the 962 ecu doesnt have it (not sure) and the ecu has chip in it, and factory ecu is 984 but someone has changed ecus in the past. And yes i have a spare fuelpump relay and a spare rpm sensor but changing them didnt help:/ The original fuel pump relay does not control the fuel pump anymore like i said it has its own relay in the enginebay but i bet thats not the problem because the main problem started before i had wired the new fuelpump in.
 
Be aware that on LH jetronic the fuel pump relay is a double relay inside the body of relay with a traditional shape. It's correct name infact is fuel ignition relay and not fuel pump relay.
The first relay is activated when you turn the ignition key to the ON position and so the LH jetronic is powered up, the second one is a normal fuel pump relay activated by the LH jetronic when it feels that the engine is running.
If you hear it clicking and the MIL lamp going on it could be that it is failing the first releay and the LH jetronic has been quickly switched off and on.
 
I'm not familiar enough with 940s, but a few simple things to try are:
- replace the ECU/EZK fuse, and inspect the socket
- try wiggling the ignition key while idling
- carefully inspect the ground wires, and bolts, going to the front+back of the intake manifold
 
I have checked all ground wires and tried another relay with no success. Its just so weird that when it was -20°c - -5°c outside i never had issues but now that its 0°c-5°c its getting worse again. Im thinking it might just be the ecu.
 
May be, but before condemning the ECU I suggest to make some Y wires to take the measures of the voltage to the coils of the relay. In the past I had a problem with this relay and I had to monitor it for a while due to the randomicity of the failure.
In this picture I used a multimeter but then I attached a simple DIY device made by two leds and resistors to easily diagnose if there was voltage when the relay switches off.
 

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That looks semi simple to do. But yeah the problem is quite random but idling too long triggers it more easy. sometimes it clicks the relay randomly while driving and when accelerating it jerks hard. Weird that the spare relay i have does the same thing. Fuse/relay box also doesnt look bad. Would be nice to get the problem sorted out even tho i will take the lh2.4 out and get a maxxecu at somepoint.
 
Moving to another ignition system seems to me an bit hazard if you have not identificare the cause of the failure before.
It could be also a wiring problem or a bad ignition switch, just for writing two possibilities.
 
I would try a different ECU if possible. I had to drive home 8 hours with an ECU that would turn the fuel relay off and on every 60 seconds or less. When I got home and threw a spare ECU in it went away.
 
So it might that the 962 ending ecu is bad.
Some site said that 962 ecu has injector controlling issues or something like that and fuelpump doesnt work.
 
apollokid said:
May be, but before condemning the ECU I suggest to make some Y wires to take the measures of the voltage to the coils of the relay. In the past I had a problem with this relay and I had to monitor it for a while due to the randomicity of the failure.
In this picture I used a multimeter but then I attached a simple DIY device made by two leds and resistors to easily diagnose if there was voltage when the relay switches off.
Click to expand...

I now have tried this method and the result was the relay not clicking anymore but the car still jerks like it used to. I made the Y wires and just grounded one of the two grounds coming from the ecu pins 20 and 21. Grounding the other pin didnt do nothing but the other one just stopped the relay from clicking. Im starting to believe that the ecu is junk.
 
By grounding the pins of the fuel relay coils the car can now be driven without problems?

If yes a faulty pin in the connector, a broken soldering on the PCB or a faulty transistor could be the main suspected.
In this is the case it should be easy and cheap to fix.
 
apollokid said:
By grounding the pins of the fuel relay coils the car can now be driven without problems?

If yes a faulty pin in the connector, a broken soldering on the PCB or a faulty transistor could be the main suspected.
In this is the case it should be easy and cheap to fix.
Click to expand...

Sadly the car still jerks even tho the relay is not clicking so grounding the wires just takes the relay clicking noise away so the relay gets power all the time but nothing changes;(
 
Remember that the fuel ignition relay activates not only the pump but also the ECU itself so it could be that the cause of the clicking is that the ECU have an instable power supply or a problem in receiving the rpm signal from EZK.
If I were in your situation I whould start to monitor the injectors signal to see if when the realy clicks also injectors stop to work.
 
apollokid said:
Remember that the fuel ignition relay activates not only the pump but also the ECU itself so it could be that the cause of the clicking is that the ECU have an instable power supply or a problem in receiving the rpm signal from EZK.
If I were in your situation I whould start to monitor the injectors signal to see if when the realy clicks also injectors stop to work.
Click to expand...

But when i grounded the relay using the Y wires the injectors should get power still because the power goes through the white relay. They still might lose the signal when to open?
Im going to try other ecu first just because its the simplest thing to do first.
 
I've translated this for you from the notes I wrote when I had a problem on this relay some years ago and I had to reverse engineering the wiring diagrams of the car to understand how it works the LH Jetronic system:

  • PIN 4 of the control unit (diagnostics) is always powered by + 12V
  • contact 3 of the injection relay is always powered at +12V
  • when you turn the ignition key +12V is sent to PIN 35 of the control unit which in turn sends PIN 21 to ground, contact 4 of the injection relay then goes to ground (followed by ground on PIN 21 of the control unit) and thus the relay switch closes, sending+12V to:
    • contact 6 of the injection relay
    • PIN 9 of the control unit
    • coil of the Radio Suppression Relay
    • PIN 5 of the air flow meter
    • idle valve coil ...
  • And finally at the end: with the engine running, the EZK ignition control unit sends the engine rpm signal to PIN 1 of the LH Jetronic injection control unit which causes PIN 20 (also of the injection control unit) to be grounded. Contact 2 of the injection relay thus goes to ground and the switch closes, bringing +12V to contact 5 of the injection relay which in turn brings +12V power to the lambda sensor and fuel pump

Knowing how the system works it could be easier now to understand that the clicking of the fuel ignition relay could have different causes:
  1. bad relay, but this I think that can be excluded since you have hard wired it and also if it stops to click the car still runs bad
  2. unstable ECU power supply (if ECU loose power supply it powers off and stops to keep the realy active)
  3. unstable RPM signal from EZK (if ECU doesn't feel the engine running it stops to deliver fuel)
  4. bad wirings or bad connectors
  5. bad ECU
I had suggested you to check the signal of injectors since if you have a scope or a graphical multimeter is should be a pretty easy job but it cannot be the only nor the last check to do (eg. if also injectors stop to work when the realy clicks it may be due to an unstable power supply or an unstable rpm signal so the next step should be to monitor in real time the rpm signal)

If you have easy access to a known working spare ECU trying to replace it could be a quick and easy test also if it let you to exclude only the last possibility
 
apollokid said:
I've translated this for you from the notes I wrote when I had a problem on this relay some years ago and I had to reverse engineering the wiring diagrams of the car to understand how it works the LH Jetronic system:

  • PIN 4 of the control unit (diagnostics) is always powered by + 12V
  • contact 3 of the injection relay is always powered at +12V
  • when you turn the ignition key +12V is sent to PIN 35 of the control unit which in turn sends PIN 21 to ground, contact 4 of the injection relay then goes to ground (followed by ground on PIN 21 of the control unit) and thus the relay switch closes, sending+12V to:
    • contact 6 of the injection relay
    • PIN 9 of the control unit
    • coil of the Radio Suppression Relay
    • PIN 5 of the air flow meter
    • idle valve coil ...
  • And finally at the end: with the engine running, the EZK ignition control unit sends the engine rpm signal to PIN 1 of the LH Jetronic injection control unit which causes PIN 20 (also of the injection control unit) to be grounded. Contact 2 of the injection relay thus goes to ground and the switch closes, bringing +12V to contact 5 of the injection relay which in turn brings +12V power to the lambda sensor and fuel pump

Knowing how the system works it could be easier now to understand that the clicking of the fuel ignition relay could have different causes:
  1. bad relay, but this I think that can be excluded since you have hard wired it and also if it stops to click the car still runs bad
  2. unstable ECU power supply (if ECU loose power supply it powers off and stops to keep the realy active)
  3. unstable RPM signal from EZK (if ECU doesn't feel the engine running it stops to deliver fuel)
  4. bad wirings or bad connectors
  5. bad ECU
I had suggested you to check the signal of injectors since if you have a scope or a graphical multimeter is should be a pretty easy job but it cannot be the only nor the last check to do (eg. if also injectors stop to work when the realy clicks it may be due to an unstable power supply or an unstable rpm signal so the next step should be to monitor in real time the rpm signal)

If you have easy access to a known working spare ECU trying to replace it could be a quick and easy test also if it let you to exclude only the last possibility
Click to expand...

I have forgot to mention that i have also changed the EZK a while back. I had a black one but now i have the gold with stock chip.
 
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