Why isn't my tachometric relay working? - NOW SOLVED

[Hen]

OK, so I got round to wiring up a tachometric relay this evening (to my stock 4AC sprinter if it matters at all). Everything seemed to go ok until I started the car to check it was working. And it wasn't. So firstly, has anyone successfully used a VK tachometric relay to run their fuel pump?

I used the tachometric relay I pulled from a VK at Pick-a-part. And followed the wiring diagram given by BradW in this thread, which is shown below too.



I've checked the wiring a few times over and am sure that the pins I have connected are:
30 - Fused IG+
15 - Fused IG+
1 - Wired to negative post on coil
31 - Ground (chassis nearby)
50 - STA from starter solenoid
87 - Not used
87b - Currently not connected to anything, just checked with a multimeter.

The relay goes clickity-clickity-click while the car is running, and the voltage measured on the output pin (87b) floats around from 3 up to 11VDC. But as soon as you put any load on it (a relay coil was all I had handy) this pin immediately drops to 12V.

I've checked the signals on the incoming pins and they seem to make sense. And I've tried two different relays. I've even replaced the tachometric relay with a normal relay. It goes clickity-clickity-clickity too, but can actually drive an output.

I'm a little puzzled now and wondering if I have misunderstood something about tachometric relays. Does anyone have any suggestions that may get this working?

Thanks
Hen

** EDIT - And to save any newcomers reading all the way to the end, I'd wired the relay socket incorrectly. I used the pin layout on the relay and assumed these referred to the socket layout, not the relay.

[thechuckster]

i thought the point of these was to close when the engine was running not cycle on/off in time with the engine? so the fuel supply is only enabled when motor is running or cranking.

Am assuming that by "clickity-clickity-click" you mean it is furiously clicking away when powered up?

30 should be a fused battery supply not IGN switched

87/87B should go +12V when it gets a STA or Coil(-) signal otherwise it should be off.

the STA signal could come from the STA signal from the ignition key and it should be a +12V

are you sure the supply to the coil(-) pin is correct?

[Hen]

Yeah, I noticed that I'd used IG+ rather than +B for pin 30 when I was writing the above post, however I see no reason that'd make a differrence here.

And yes the Clickity-clickity is the thing furiously turning on and off when the engine is running.

I was immediately suspicious of the coil negative trigger since it is the hardest pin to test, but it is a 200mm run directly off the coil -ve terminal, so I'd be suprised if it had issues (and yes, I double checked which was +ve and which was -ve)

Will have more of a poke later on today to see what I can uncover.

[DoctorDubb]

For a start that wiring looks good:


So far i can only see you have tested it with the engine running and not during cranking. If you test it during cranking then hopefully you can isolate wether its the coil trigger or not:

Does the relay go Clickity-clickity when the engine is starting i.e. when the starter is engaged?
If No -
Does the fuel pump work/prime (or get 12V at the 87/87a) then? If Yes - coil trigger is an issue (or a dodgy connection inside relay - i.e. see if you get it with the other tacho relay). If No -could be three things - bad STA source (bout doubt it as this wouldnt introduce an issue while the engine is running) pin 15 (IGN) is not hooked up properly /cant draw enough current / dodgy fuse or bad earth

If Yes -
Could be faulty relay - bad earth or bad IGN source Test these pins and make sure your getting correct voltage at these pins.

The only idea i can think if its the coil trigger is to try a slightly longer or shorter cable or different thinckness etc as you can get some weird effects with AC on lines or even interference.

Hope this sorta made some sense.
Cheers,
Steve

[Pure_In_Sanity]

You dont have pins 50 & 1 swapped around, by any chance?

[roadsailing]

Ben, why dont you just do it the easy way, using two relays switched in parrallel, one off the ignition signal, one off the oil pressure sender?

and why do you need a fuel pump for a 4AC, piss off the mech pump or is there a surge tank setup already? if there is a surge tanke and a mechanical fuel pump, the two switch method will work very well, you could even just run the oil pressure switch because there will always be fuel in the surge tank (might need some way of priming it though of course)

[Hen]

Wanted to run a tachometric relay because I think they are a neat solution, plus the 4AC doesn't have an oil pressure switch, it's got an oil pressure sender, so there'd be some rooting around to get that method to work.

However if I can't get this relay running it's my next shot. I'll check over the things suggested to see if I can sort it out. Nice diagrams there too thanks Dr.

Hen

[Hen]

OK, again the problem was caused by my stupidity. I'd been looking at the pin assignmnet on the relay body and using it to wire the relay socket. Of course the pin assignment referred to the pins on the relay, so I had wired a mirror image. And because the pin layout is symettric everything looked like it worked.

So i swapped the pins around (1 and 15, also 50 and 31) and things now work.

Thanks all for the constructive input

Hen

[Omar]

Just need to clearify the connection.
30 to Battery +(ve) via fuse
15 IGN ( which should we use?)
1 Coil - (can we tap from ignitor? or is it direct from coil?)
31 to Battery -(ve)
50 start feed fm ign switch (If we turn the key)
87B to Fuel Pump

I just manage to get the used SAAB tacho metric relay with
15 / 50 / 86 / TK / 14 / 31 / 87 / 87B / 30

[Omar]

Just need to clearify the connection.
30 to Battery +(ve) via fuse
15 IGN ( which should we use?)
1 Coil - (can we tap from ignitor? or is it direct from coil?)
31 to Battery -(ve)
50 start feed fm ign switch (If we turn the key)
87B to Fuel Pump

I just manage to get the used SAAB tacho metric relay with
15 / 50 / 86 / TK / 14 / 31 / 87 / 87B / 30

Anyone please...

[RA35GT]

Just need to clearify the connection.
30 to Battery +(ve) via fuse
15 IGN ( which should we use?)
1 Coil - (can we tap from ignitor? or is it direct from coil?)
31 to Battery -(ve)
50 start feed fm ign switch (If we turn the key)
87B to Fuel Pump

I just manage to get the used SAAB tacho metric relay with
15 / 50 / 86 / TK / 14 / 31 / 87 / 87B / 30

G'Day Omar,

15 is just a +12V that comes on when the ignition is on. (The coil+ if handy)

1 should be connected to a coil-. (It may work when connected to the ignitor but you would have to try it)

50 should only be +12V when the key is in start.

[Omar]

Thanks mate for ur fast respond
So I will try to tap 1 to igniter -ve &

[dori81]

couldnt you connect it to the crank angle sensor instead of the coil? also does a tachometric relay allow for fuel prime? THREAD DIG I KNOW!

[Suavemechanic]

not stupidity , i did that as well , seemed like the right way at the time

[dori81]

turns out u wire it to the longer green wire out of the big plug on the igniter pop the cap open and theres a green wire in there longer that the others sorta curled up in there splice it into that! how ever my relay clicks abit when i drive unsure whats going on there also i can here my fuel pump prime either :S