Fuel Pump Relay - Socket Voltage Checks?

[peterz123]

Ok - maybe old guy or someone that's done this can steer me here -

problem: 2003 A4 B6 1.8t no fuel pressure at rail, I need to know if all the sockets are powering correctly at the relay, so I can isolate it to a possible bad new relay

- New OEM Fuel Pump, New OEM fuel Filter
- New Fuel Relay from auto zone " 167" relay diagram looks correct - 1 large vertical blade (87) , 1 large horiz blades ( 30) 1 middle blade (86) 1 small blade (85) at top
- No power at Pump plug
- No power at fuse
- Pump runs when "hot wired" directly from 12v source and auto ground
- No codes in vagcom

I searched and read an old thread and checked the Fuel pump relay socket, there is 12 V at the Horiz, indicating good 12v from ecu - in the older thread old guy says to check the lower horiz for control voltage but there are no connection to the lower sockets - there is 12 v at the top horiz medium socket - it looks like the really isn't working as the input voltages are there ebut the output to the fuse is not, but I'm sure I'm checking it correctly

thanks

[Seerlah]

Easy check. Pop the cover off. If the relay plate does not open and close rapidly while cranking the car, then there is a coil issue on the relay. Or, hold the relay closed manually (use something non-conductive, like a plastic pen) and see if the car turns on. When you release the pen from the plate and relay does not stay in the closed position, then that also confirms you have a power (potential) issue.

A relay is nothing but a switch. It works by a magnetic coil that pulls the contact plate closed. That magnetic coil need two potentials to be energized. If it does not close, you have a potential issue or the coil itself is compromised. Since this is a new relay (even though not OEM), I would sway from the coil itself being an issue. Or...the Autozone relay is crap or the incorrect one (high probability).

[peterz123]

Easy check. Pop the cover off. If the relay plate does not open and close rapidly while cranking the car, then there is a coil issue on the relay. Or, hold the relay closed manually (use something non-conductive, like a plastic pen) and see if the car turns on. When you release the pen from the plate and relay does not stay in the closed position, then that also confirms you have a power (potential) issue.

A relay is nothing but a switch. It works by a magnetic coil that pulls the contact plate closed. That magnetic coil need two potentials to be energized. If it does not close, you have a potential issue or the coil itself is compromised. Since this is a new relay (even though not OEM), I would sway from the coil itself being an issue. Or...the Autozone relay is crap or the incorrect one (high probability).

looks like maybe a bad relay- I used a toothpick to manually close the contact and the pump started running it does not stay closed - the part looks correct based on the old one but I bought it in a pinch to see if it would resolve the issue- need to get an oem relay on order - thanks

[old guy]

Sorry but I have to ask the obvious question. You have a good fuse?

[Seerlah]

That should have been a first. And these ideally should be tested for continuity vs the eye method (though clearly blown ones is a given)

[peterz123]

Yes, good 20a fuse - seems like the obvious can always be elusive after working in a cold garage all day putting a head on and the car back together only to have no fuel pressure

[Seerlah]

If your fuse is good and my method for checking worked, it is either a bad relay (coil) or a potential issue. Pin out will be on the relay cover. Check voltage at those pins before replacing. Could be a wiring issue. Also used oem relays can be purchased on eBay for cheap versus $50 at the dealership.

[peterz123]

If your fuse is good and my method for checking worked, it is either a bad relay (coil) or a potential issue. Pin out will be on the relay cover. Check voltage at those pins before replacing. Could be a wiring issue. Also used oem relays can be purchased on eBay for cheap versus $50 at the dealership.

Thanks, your suggestion of manually closing the really contact closed the circuit and fired up the pump, but it doesn't stay closed or cycle with key on-off, which leads me to think that since there is 12 V present, there there is something hinky with the relay- I'll check the voltages on the other contact have an oem (#167 pn 191906383C ) on the way and I may given time, stop by the junkyard and see if I can find one to get past his and get the car out of the garage and get mine back in - hard to believe anything has changed in the wiring, it was working fine before the belt sheared about 10 teeth, but with a new timing belt, rebuilt head installed, new fuel pump, filter and associated new hardware, tentioners, rollers and disassembling half the car, that I messed something up in the wiring

[Seerlah]

You don't check it at the relay. You can do that for testing the actual relay (outside car with 12v source). But right now we want to test if the pins themselves are getting any voltage. You check it at the female terminals that the pins to the coil of the relay go to. Only thing you can do at the coil with the relay out the car, for what we are checking for, is to check for resistance (I suggest you do this anyways). And unless you know exact OHM specs, you will be limited. If it has resistance, it works. If it doesn't, then it doesn't. But a bad coil isn't necessarily an on/off thing (though really is). It could be something like the coil not creating a large enough magnetic field to close the relay. That is why specs are important.

You set your meter to DC voltage. With engine off, place the prongs into the 2 female terminals that the coil of the relay would go. First just go to the start position to see if there is any life (if the pump would have primed, it would have shown voltage on your meter). But since the pump does not prime each time you place it in the starting position, you would need to crank the engine to see if there is life (will show voltage reading, then zero, voltage reading, then zero repeatedly rather fast). I'm sure there is a better method, but what I would have done. Actually, I would have just swapped in a spare used OEM from ebay but you get the point. Also unplug your injectors during this to not have them spray fuel and flood your chambers.

If somebody has a better method, please post. Pretty sure my method won't make his meter too happy.

[peterz123]

You don't check it at the relay. You can do that for testing the actual relay (outside car with 12v source). But right now we want to test if the pins themselves are getting any voltage. You check it at the female terminals that the pins to the coil of the relay go to. Only thing you can do at the coil with the relay out the car, for what we are checking for, is to check for resistance (I suggest you do this anyways). And unless you know exact OHM specs, you will be limited. If it has resistance, it works. If it doesn't, then it doesn't. But a bad coil isn't necessarily an on/off thing (though really is). It could be something like the coil not creating a large enough magnetic field to close the relay. That is why specs are important.

You set your meter to DC voltage. With engine off, place the prongs into the 2 female terminals that the coil of the relay would go. First just go to the start position to see if there is any life (if the pump would have primed, it would have shown voltage on your meter). But since the pump does not prime each time you place it in the starting position, you would need to crank the engine to see if there is life (will show voltage reading, then zero, voltage reading, then zero repeatedly rather fast). I'm sure there is a better method, but what I would have done. Actually, I would have just swapped in a spare used OEM from ebay but you get the point. Also unplug your injectors during this to not have them spray fuel and flood your chambers.

If somebody has a better method, please post. Pretty sure my method won't make his meter too happy.

thanks I thought you were suggesting I test the actual contacts of the relay with the cover off and plugged in to see if there was an open circuit within the relay or coil- Actually the first thing I did was test the female connectors for the relay to see if the 12v was present (ecu) to the main horizontal connection as well as the control voltage to the upper horizontal connection- there is 12v at each connector- the potential for small upper horizontal connector escapes me I don't have a pin our or diagram but I think I'm just looking at a bad relay with a known good one to test against - by manually closing the switch on the relay with a toothpick, the pump fires up with key in pos 1 so there is power to the relay the wiring and fuse there eon back are fine

[Seerlah]

Seems you got it figured out!

You never tried to fire up the car yet (with the replacement relay)?

[peterz123]

Seems you got it figured out!

You never tried to fire up the car yet (with the replacement relay)?

should have typed "without" a good relay - stuck until I get the new one

[peterz123]

One last question before I head to the junkyard- , you say that if I manually engage the relay- plugged in with the cover off ( I did and the pump works) I have a coil and a power issue or one or the other? how many twelve volt pins are there at the relay, there is 12v to the large horiz blade, I assume the vertical is the other connector which energizes the fuel pump, these are the two sides of the relay coil, then there are two more connectors at the top a very small one and a medium sized blade- the medium has 12 volts with the key on, is there a voltage to the very small pin I assume that once the relay coil contact / circuit is closed that the small pin gets a control voltage of some sort from the relay back to the ECU? Not sure to know where I go with this if a new relay behaves the same, I've always had relay issues as simple fixes either there's power or the relay is toast. Have you seen a thread on the correct power on sequence -i.e. ignition switch power then ecu then fuel pump on, off etc I couldn't find one - it's pretty tight in there so I can't really see any cold coding or gauge on the wiring

[peterz123]

OK new relay is in and same issue- there is 12v at the large horizontal blade/pin but no 12v gets applied to the vertical blade when the key is turned. I can manually close the relay contact and the pump starts, but the relay will hot hold the contact closed so I'm missing a voltage somewhere- ECU? I have Spark and Check engine light at position 1- camshaft position sensor? There are no codes, is there a way to test the CPS? Visually it looks fine spline and teeth also look fine

[Seerlah]

You would need someone who knows the schematics to tell you how that other potential to the relay coil gets introduced. Can't really help you here. Good luck!

To test the cps I think you can check resistance. Take sensor out and mimic the tone ring gaps with a piece of metal (place to sensor). I'm on my phone right now but will look up resistance in ohms you are looking for. It's posted in a thread in the b5 section somewhere.

[Seerlah]

Here you go. Starting at post #17 down it tells you how to check with a volt meter. You are actually looking for voltage and not resistance. I goofed.

http://www.audizine.com/forum/showth...1#post10300691

[peterz123]

You would need someone who knows the schematics to tell you how that other potential to the relay coil gets introduced. Can't really help you here. Good luck!

To test the cps I think you can check resistance. Take sensor out and mimic the tone ring gaps with a piece of metal (place to sensor). I'm on my phone right now but will look up resistance in ohms you are looking for. It's posted in a thread in the b5 section somewhere.

Update- Ok I looked at this from a number of sides, at the relay if there are a few voltages there it should work- the one component which will kill the control voltage to the relay is... The camshaft position sensor- Mine looked fine and the teeth were straight and unmarked I ohm'd it to ground and it checked fine. Luckily, the CPS is the same part on the allroad, so I pulled a near new CPS off my allroad put it on the A4, pulled the fuse and checked voltage- you guessed it- 12 v at the fuse, put the fuse back in and turned the key, pump started humming, turned the key to position 2 and it fired right up and ran like a top. Then it gets weird, I put the good CPS back in the AR and the old one back in the A4 and again it fired up and ran like a top - fires up in half a turn and runs smooth as silk. Thanks for your help- seems like CPS can be a tricky beast and cause a few gremlins

[Seerlah]

You have to be a brave person to own an Audi, let alone two. Or have mental issues

Just joking...but I'm really not! Fun factor being the reason not taken into consideration. Glad you got it figured out.

[peterz123]

You have to be a brave person to own an Audi, let alone two. Or have mental issues

Just joking...but I'm really not! Fun factor being the reason not taken into consideration.

True, the AR tuned to perfection, not leaking a drop of oil with both K4's pushing you back into the seat as you eat a boxer S for breakfast makes it worthwhile.. somewhat. thanks agin.