When Should The Tachymetric Relay Click?

[Guest antgel]

Today's project is to get a little further into cold start issues. I have the lid off the tachymetric relay and I can only see it switching when the ignition key is turned to the start position (i.e. the starter cranks). Is it not /supposed/ to click on at the ignition position, so that the rail gets primed? I can see some wires have been bodged in the area, so best to ask.

 

What is strange is this - when the ignition is switched on, and I manually close the relay contact, I still can't hear the fuel pump. Does this car have the quietest fuel pump ever or have I misunderstood how the system works?

[Guest antgel]

Here's the latest. When I bridge the connector with some wire, I can hear the pump run when I turn the ignition on. No need to lift the seat to hear it. But, the car still doesn't start from dead cold. So my relay /may/ be faulty (depends if it is meant to switch at ignition), but it's not the cause of my cold start problems.

 

Next up is a coil test, and new cap, rotor, plugs, leads.

[TEKNOPUG 3]

The fuel pump will turn on when you turn key to "ignition" - you'll here it click on - lift the carpet if unsure. You won't here the fuel pumping until you try to start the engine.

 

I would say that the tachy relay is at fault - a common problem. This would have nothing to do with cold start though - it would be like this all the time.

 

The relay also controls the ignition circuit - I imagine that is the part of the relay that you can see switching?

 

Run a search for "SAD"

[Bassman 1]

From my understanding, when the key is turned to start, the tachymetric relay is not in the circuit which is why a car with a faulty relay (i.e. mine) will still start but then die when you release the key. Once you are running, the ECU is controlling the tachymetric relay and I believe it pulses it on and off as required, so it might be hard to see it moving, but I've never tried to look at one whilst the engine was running.

 

If one of the pins looks a bit scorched, have a look at the solder joint on the back of the PCB, it is probably dull in appearance. Try re-soldering it to get a better connection, worked a treat on mine.

[TEKNOPUG 3]

That's incorrect AFAIK. I've had trouble in the past with tachy relays and I'm sure it's how I described it. If the tachy relay is at fault, the car will not start. If it does start then the tachy relay is working and something else is to blame. If you have a immobiliser it will tap into the same cicuitry and can cause similar faults.