A handy fuel pump relay tweak

[johne]

By the way, is it normal when the multimeter is probed across both injector pins that the buzzer is set off during continuity test?

Yes. The resistance of the coil in the injector is very low.

John

[BrianSmith_S2]

Thanks john, thats reasuring to know my injectors are normal

lets just hope using the scope tomorrow i find something out.

[a4kquattro]

yep, knowing that the fpr is kicking on is helpful when troubleshooting no-start. I was also thinking of coming out with a simple product to show that the CPS is working, basically a little inline adapter with 3 pin male and female contacts and an LED in the middle that blinks when pulses are received.

I just use a scope, but it would take less time to use a test tool like that..

[BrianSmith_S2]

yep, knowing that the fpr is kicking on is helpful when troubleshooting no-start. I was also thinking of coming out with a simple product to show that the CPS is working, basically a little inline adapter with 3 pin male and female contacts and an LED in the middle that blinks when pulses are received.

I just use a scope, but it would take less time to use a test tool like that..

Yep, i agree. I feel a Forum project coming along

[S2central.net]

Aready 1-step ahead of Marc on that one with a wee little project that I started this week... Been kicking it around my head far longer than that, but finally found some time to scribble it down and start with a prototype. Few more parts on the way, but the idea is to make a couple of cheap little units to visually verify the presence of signals from crank & camshaft. I want to try and make something as generically useful as possible but don't want to engineer it to death as its going to need to be a low cost affair that has wide enough appeal to turn it into a useful gizmo to have in the glovebox. Getting it packaged nice and robustly at the right cost could be the challenge here but I'm not so worried about that for now.

[S2central.net]

Here's a pic of illuminated fuel pump relay - engine running - anyone can see !

[HPmuirt]

Here's a pic of illuminated fuel pump relay - engine running - anyone can see !

Cool, gotta guide with pics for us to copy?

Cheers n

Si

[S2central.net]

I don't have a formal guide as such, but its pretty simple...

The relay has these terminals numbered underneath:

30 - unswitched 12V
T - pulled to 0V by the ECU when it is happy the engine is spinning... connects to one side of solenoid
86 - other side of solenoid, connected to switched 12V
87 - to fuel pump and lambda heater
87a - to injectors, maf, isv, evap & wgfv

When you pop the hood of the relay you can see an internal ballast resistor - you can verify connectivity around the internals with meter. I might have a photo that I can annotate.

The 'T' terminal is one side of the resistor nearest the corner... solder the -ve (cathode) side of a 12V LED to that pin
Attach the +ve side the 12V LED to the 87 or 87a terminal... this is NOT the other side of the resistor

Drill a hole in the relay housing so the light is visible and thats about all there is to it. I used some heatshrink on the LED legs just in case it moves around... could have been really tidy with a little bezel on the cover - might do that another day when I try the bicolor LED version.

[S2central.net]

Here's annotated pic of relay internals...

87a or 87 : 12V LED anode
T : 12V LED cathode

[BrianSmith_S2]

The black/blue wire stays at 12V via the pump relay, but the ECU opens and closes a path to 0V for each injector - that will be the other wire at each injector, so placing the LED across each injector should see it pulse - never actually verified that the pulses are long enough to be visible by naked eye, but your scope will see them being triggered.

Just put a scope over injector no 1

Trace 1 is transition when ignition is first turned on, Trace 2 is from ignition on to engine turning over

I was expecting over 200mV at the injectors? any one know what voltage i should be seeing, and if it should be above 200mV, what could cause this low voltage?

Brian

[S2central.net]

Those injectors aren't being energised... either the ECU isn't triggering them or the fuel pump relay isn't activating... which is what I think is happening. Unless there is a break in the loom or bad earth.

Check again fuse 28 is OK and also check that you see 12V on the black/blue wire that enters MAF. This is fed by the 87a terminal on the relay. You can of course check for presence of 12V at the injectors in the black/blue wire with respect to chassis earth - not other pin on the injector as this only goes to 0V under ECU control.

87a also feeds 12V into blue/red wire (via fuse 24) on ISV, EVAP & WGFV.

You need to reduce the number of variables here - tape the damn relay closed if you can to verify that terminals 87 & 87a are both energised.

[BrianSmith_S2]

Those injectors aren't being energised... either the ECU isn't triggering them or the fuel pump relay isn't activating... which is what I think is happening. Unless there is a break in the loom or bad earth.

Check again fuse 28 is OK and also check that you see 12V on the black/blue wire that enters MAF. This is fed by the 87a terminal on the relay. You can of course check for presence of 12V at the injectors in the black/blue wire with respect to chassis earth - not other pin on the injector as this only goes to 0V under ECU control.

87a also feeds 12V into blue/red wire (via fuse 24) on ISV, EVAP & WGFV.

You need to reduce the number of variables here - tape the damn relay closed if you can to verify that terminals 87 & 87a are both energised.

Just put multimeter on black/blue wire that enters MAF and earth and and could only see 10.5V with ignition on.... dropping to 9.5V when turning over

[S2central.net]

Well I don't understand that... MAF is only energised by 87a terminal on the relay... unless there is a variant of the wiring on your early ABY that I don't have documented here. I am using schematic that applies from Oct'92 to Jul'94 that has served me well (other than known errors on POS wiring).

After shutdown it can take a few seconds before ECU relinquishes the fuel pump relay but it absolutely should be off when you just turn the key on.

Can you do the test again with relay unplugged as the only thing that should be actively enabling it is the ECU. This will verify if you are getting ~12V from that relay or somewhere else.

I say 12V but your values are lower - could be a weakening battery with all the cold cranking - but it wouldn't hurt to see what voltage you have there as you shouldn't be losing 2V across a healthy relay.

[BrianSmith_S2]

Well I don't understand that... MAF is only energised by 87a terminal on the relay... unless there is a variant of the wiring on your early ABY that I don't have documented here. I am using schematic that applies from Oct'92 to Jul'94 that has served me well (other than known errors on POS wiring).

After shutdown it can take a few seconds before ECU relinquishes the fuel pump relay but it absolutely should be off when you just turn the key on.

Can you do the test again with relay unplugged as the only thing that should be actively enabling it is the ECU. This will verify if you are getting ~12V from that relay or somewhere else.

I say 12V but your values are lower - could be a weakening battery with all the cold cranking - but it wouldn't hurt to see what voltage you have there as you shouldn't be losing 2V across a healthy relay.

Yep, i will redo the test tomorrow, but from what i can remember there was a 30 second or so delay between probing Maf and the ingnition last being on. I might go to G&S tomorrow and purchase another FP relay, it might not be faulty but no harm having a spare in the tool box

[S2central.net]

Would be interested to know what G&S charge for a relay like that - seem to recall they are silly money from Audi UK - its not unique to S2 but not a generic item to my knowledge.