Citroen BX Electrical Issue - Tachymetric Relay?
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Thread: Citroen BX Electrical Issue - Tachymetric Relay?

  1. #1
    Fellow Frogger! FedGrapes's Avatar
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    Default Citroen BX Electrical Issue - Tachymetric Relay?

    Hi Guys!

    I am having an intermittent electrical issue in the BX when I attempt to start.

    Turning the key enables everything as it should, then clicking over to the "Start" position engages the starter as it should. As the starter cranks, everything cuts out. The entire car loses power. It's as though the battery is removed, or a fuse is blown. Sometimes, the starter solenoid will only click before the car loses electrical power.

    The power will return anywhere from one to thirsty seconds later. It will return if the key is in the on position, or the off position (Sometimes the starter solenoid will click rapidly as power cuts in and out for a short time).

    I fiddled with the relays near the RHS front strut under the bonnet, and twice this has caused the car to start, but could still be coincidence.

    The issue occurred once a month ago, then twice within the last week, and today got to the point of completely preventing the car starting.

    Is this an issue that can be caused by the tachymetric relay failing? Or something else? To me it seems similar to symptoms others have described, but I can't understand the entire car losing power.

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    Potentially important notes:
    -The battery is healthy, and properly charged/charging.
    -The starter motor is less than 12 months old.
    -I fixed a fuel leak two weeks ago that required the movement of the filter and pump
    -New oil and oil filter were fitted two weeks ago. Oil is slightly over the full mark (250mL?).
    -NO issue has been observed while driving yet; if the car starts, it doesn't stop.
    -I haven't attempted a push start of the car while it's power is out.

    Thanks!

  2. #2
    Tadpole
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    Is the earthing system in ok ... Check /replace watching strap to engine?
    Remove spark plugs does it spin ?
    How olds starter motor?
    They are my thoughts and that's about all I have... I don't know what a bx but googles going to show me !
    Good luck


    Sent from my 3geesus using Tapatalk( it's ifail)
    Probably should put something clever here..
    oh well

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    Quote Originally Posted by FedGrapes View Post
    ...
    Turning the key enables everything as it should, then clicking over to the "Start" position engages the starter as it should. As the starter cranks, everything cuts out. The entire car loses power. It's as though the battery is removed, or a fuse is blown. Sometimes, the starter solenoid will only click before the car loses electrical power.
    ...
    That doesn't sound like a tachometric relay faulty. It only switches on the EFI and doesn't control supply to the rest of the car. A bad earth or something similar on the positive side is possible. Ignition switch cooked perhaps? Can you try another switch unit at the back of the lock?

    Batteries are also strange things as a multimeter reading can suggest it is quite OK and being charged OK too, but you only find out it has only a weak surface charge when you try to apply a decent load to it, such as starting. Test the battery as step 1 as it's really the most likely suspect. Get it load tested with a proper load testing device or swap it between another car and see if the problem moves with the battery.
    Last edited by David S; 25th May 2016 at 09:26 PM.
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    Now go make me a sandwich Hotrodelectric's Avatar
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    Is your car carb or injection? The tachymetric relay will only show up on the FI cars. I would think more of a battery problem. Check and make absolutely sure your battery cables are clean and firmly connected. Get the battery tested. Check for corrosion anywhere in the charge and start circuits. Make sure any underhood ground terminals are connected. Have you tried a jump start? Remember- with electrical, simple and stupid first.
    The measure of your character isn't what you do when people are watching- it's what you do when they aren't watching.

  5. #5
    1000+ Posts Ken W's Avatar
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    BXs don't have a tachymetric relay. There are two relays over on the RHS of the engine bay near the ECU loom and the diagnostic connector. One relay comes on with ignition on and start positions to power the ECU, the other comes on when the ECU senses a CAS signal and supplies power to the injectors and fuel pump. If you put separate fingers on each relay, you can feel them click in as the ignition is switched through each stage. I think it is normal to lose dash lights during starting.

    With the engine cranking, you should be able to feel the fuel pump whirring away. We have been battling dodgy fuel pumps and wiring giving only about 7 volts at the pump of late so this is something to check. Many of our BXs now have another relay with control wired in parallel with the injector relay that supplies fused battery power direct to the fuel pump that is also locally earthed.

    A complicating factor is the mongoose security alarms fitted to most of these cars in Australia. Exactly what model do you have - TRI, TRI 122 or TZI?

    Cheers Ken
    Last edited by Ken W; 26th May 2016 at 08:30 AM.
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  6. #6
    Now go make me a sandwich Hotrodelectric's Avatar
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    Quote Originally Posted by Ken W View Post
    BXs don't have a tachymetric relay. There are two relays over on the RHS of the engine bay near the ECU loom and the diagnostic connector. One relay comes on with ignition on and start positions to power the ECU, the other comes on when the ECU senses a CAS signal and supplies power to the injectors and fuel pump. If you put separate fingers on each relay, you can feel them click in as the ignition is switched through each stage. I think it is normal to lose dash lights during starting.

    With the engine cranking, you should be able to feel the fuel pump whirring away. We have been battling dodgy fuel pumps and wiring giving only about 7 volts at the pump of late so this is something to check. Many of our BXs now have another relay with control wired in parallel with the injector relay that supplies fused battery power direct to the fuel pump that is also locally earthed.

    A complicating factor is the mongoose security alarms fitted to most of these cars in Australia. Exactly what model do you have - TRI, TRI 122 or TZI?

    Cheers Ken
    The things I learn. Wonderfuls stuff , Ken. I know the BX was available with carburettor. You didn't get that there?
    The measure of your character isn't what you do when people are watching- it's what you do when they aren't watching.

  7. #7
    Fellow Frogger! FedGrapes's Avatar
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    Thanks all for your responses!


    Quote Originally Posted by haulrs View Post
    Is the earthing system in ok ... Check /replace watching strap to engine?
    Remove spark plugs does it spin ?
    How olds starter motor?
    They are my thoughts and that's about all I have... I don't know what a bx but googles going to show me !
    Good luck


    Sent from my 3geesus using Tapatalk( it's ifail)
    Earth strap checked; it works on another vehicle. It's fairly new, but was a Superc**p purchase.

    Spark plug removed, but it didn't restore electrical power itself.

    Starter motor was a new unit installed 12 months ago. I hope it's not the culprit... I don't enjoy the journey to access it!

    Quote Originally Posted by David S View Post
    That doesn't sound like a tachometric relay faulty. It only switches on the EFI and doesn't control supply to the rest of the car. A bad earth or something similar on the positive side is possible. Ignition switch cooked perhaps? Can you try another switch unit at the back of the lock?

    Batteries are also strange things as a multimeter reading can suggest it is quite OK and being charged OK too, but you only find out it has only a weak surface charge when you try to apply a decent load to it, such as starting. Test the battery as step 1 as it's really the most likely suspect. Get it load tested with a proper load testing device or swap it between another car and see if the problem moves with the battery.
    I'll see if there is a spare ignition to try. JohnW had an extensive collection of spares that came with Amelie, and I'm sure I saw some in one of the boxes!

    I inspected the connections at the battery, and the cables leading from it that I could follow. They seem to be healthy. I re-made all the connections taking care to insure good contact.

    The battery sits at 12.55 volts when the car is off, and when the car loses power. Cranking is very healthy, and takes the voltage down to 12.3v. When running, the car sits at 13.35v, independent of revs from 1k to 4k. Batteries that I've had in the past with low CCA have all had a larger voltage drop, and an effect on the cranking speed. I'll do a switch of the battery this evening to double check it.

    Quote Originally Posted by Hotrodelectric View Post
    Is your car carb or injection? The tachymetric relay will only show up on the FI cars. I would think more of a battery problem. Check and make absolutely sure your battery cables are clean and firmly connected. Get the battery tested. Check for corrosion anywhere in the charge and start circuits. Make sure any underhood ground terminals are connected. Have you tried a jump start? Remember- with electrical, simple and stupid first.
    Injection! I don't have any carbs here at all! The BX TZI uses the 1.9L DKZ engine seen in the 205 GTI.

    Simple and stupid checks have been done to the main cabling under the bonnet. Battery is getting a second opinion this evening. I'll be looking at the ignition barrel soon.

    Quote Originally Posted by Ken W View Post
    BXs don't have a tachymetric relay. There are two relays over on the RHS of the engine bay near the ECU loom and the diagnostic connector. One relay comes on with ignition on and start positions to power the ECU, the other comes on when the ECU senses a CAS signal and supplies power to the injectors and fuel pump. If you put separate fingers on each relay, you can feel them click in as the ignition is switched through each stage. I think it is normal to lose dash lights during starting.

    With the engine cranking, you should be able to feel the fuel pump whirring away. We have been battling dodgy fuel pumps and wiring giving only about 7 volts at the pump of late so this is something to check. Many of our BXs now have another relay with control wired in parallel with the injector relay that supplies fused battery power direct to the fuel pump that is also locally earthed.

    A complicating factor is the mongoose security alarms fitted to most of these cars in Australia. Exactly what model do you have - TRI, TRI 122 or TZI?

    Cheers Ken
    Good to know about those relays. It's incredibly difficult to match actual locations to the wiring diagrams before you know what's what! No Tachymetric (tachometric?) relay? Or is it just called something else? I thought it was just a relay that cut out the fuel pump when the engine was off, even if ignition was on.

    I'll check the pump whirring when I get a second set of hands. Should it start only when cranking, or does it run to prime the system at key turned to "ignition" too?

    I'll check that voltage to the pump this evening. Not sure if mine has had a relay installed for it.

    My starter motor has a relay now, to reduce current flow through the key barrel.

    I have a BX TZI Break. Original security has been removed. I'm fairly certain the system in the car is aftermarket. It's radio frequency on the remote locking, not IR.

  8. #8
    1000+ Posts Ken W's Avatar
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    If your ECU light is staying on for 5 seconds or so after the engine starts, it means there are stored fault codes in the ECU. If you hook a grounding lead onto one of the pins of the diagnostic port, you can read the fault code as it flashes out on the ECU light.

    The Mongoose immobiliser/alarm that was fitted in Australia to all BXs is an RF system and uses a small rectangular remote control. There may be a push button in the glovebox that is used to override the system.

    Here is a thread for some more links

    Citroen BX TZi ECU diagnostic codes

    Cheers, Ken
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  9. #9
    Tadpole
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    Is it possible for someone to help me too please...I dont want to take over this post though so excuse me...I have a BX19 GTI that will not start. It was running. I washed it and now it will not start,
    It has spark, but the only way I can get it to run is pour petrol into the manifold vacuum hose.
    Someone told me it will be the fuel injector relay or tachythermo relay but I have searched everywhere for one and cannot for the life of me find one, please if anyone can help that would be magical. Thank you in advance.

  10. #10
    1000+ Posts Ken W's Avatar
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    Hi Brownfrog,

    In Australia, all EFI BX's were supplied with an ECU that uses and oxygen sensor so they are all different from the GTI system. I think your system is covered by the Haynes BX Manual. If sounds like you have interrupted the signal that triggers the injectors or makes the fuel pump run.

    Cheers, Ken W

  11. #11
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    Reminds me of grief that I had with my BX quite a few years ago. No start. So the usual sequence of checks - spark ? OK. Fuel - no good.
    This was checked by undoing the high pressure fuel connection to the injection rail. Take care if/when you do that, even after the ignition is off, if the pump is OK then the line will be under pressure. If no pressure then go to the pump. Relatively easy, lift up rear seat and remove cover over pump. In my case there was electrical supply to the pump but the contacts were dirty and corroded. 800 wet/dry paper and electronic clean and lube spray solved the problem. Worth a look.
    rimzit

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