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View Full Version : Need Fast Help Again, Fuel Pump Relay!



juju4uofa
01-04-2006, 04:23 PM
Well, I took Badassbaldie's advice and tested out my relay and sure enough either it or the wiring is bad. I listened for my fuel pump while trying to crank the car and there was nothing. I pulled the harness off the fuel pump and tested for voltage while trying to crank and nothing. I pulled my relay and used to jumpers in the slots where the relay used to be. One jumper went from 2 to 4 (these are both grounds I believe) and the other went from 3 (which is always hot) to 1. When I did this the fuel pump ran. I automatically thought it was my relay but then I started wondering what prong number 5 was for. I assume it's the prong that gets the signal from the ECU telling the relay to complete the circuit. I got my volt meter out and put the positive lead in 5 and the negative in 4, it read nothing with the ignition off and negative 6 volts with the key in the on position. So, do I have a bad relay or is the signal bad. Or, am I completely clueless to what I'm doing? If it's my relay any idea where I could get one, Auto Zone doesn't carry one? Thanks guys so much, not having a car sucks!!!

I'm sorry if the pic is huge, I just reformatted and have no croping or resizing software installed

http://i18.photobucket.com/albums/b127/juju4uofa/FuelRelay.jpg

juju4uofa
01-04-2006, 04:52 PM
Whoa, I found a new relay online for $36. Is there a way to test my relay?

badassbaldie
01-04-2006, 05:31 PM
juju, Go to a VW or Audi dealer. They should have them in stock. Try the VW dealer first, they are usually cheaper. I think I paid $27 for mine.


Whoa, I found a new relay online for $36. Is there a way to test my relay?

Yes you can test your relay, but you need a manual and a pretty good understanding of electronics. I can e-mail you a copy of the testing procedures if you want. Easiest way to tell is buy the new relay and put it in.

juju4uofa
01-04-2006, 07:12 PM
I'm taking my relay to work tomorrow (Mercedes) there'll be someone there who knows how to test it. As much as I hate to spend the money I still think I'd rather it be that than a wiring issue.

cbass
01-04-2006, 07:19 PM
Juju4uofa, could you post a pic of where the fuel pump relay is located? I know the general area, but I want to know which relay it actually is.

Thanks.

4ingDrive
01-04-2006, 07:45 PM
A relay is just an electrical switch. An electromagnetic coil activates the switch. In the case of the fuel pump relay it activates two switches. I don't have the same numbers as you, my schematics are different.
Pin 15 is ignition power.
Pin S (red/blu) seems to be a ground signal from the ecm.
Pin 30 is constant 12 volt+
Pin 87a (grn/blk) goes to a 10a fuse and to the injectors.
Pin 87F (grn) goes to a 15a fuse then to the fuel pump. It also goes to another 20a fuse then to the n75, O2 sensors, fuel system diagnostic pump and the maf.

To test the relay use a 12v power supply or a 12v battery. Put either the + or - to the 15 and the other to the s terminal. You should hear the relay click. If it does that part is good. With the relay coil energised check continuity from term 30 to 87a then 30 to 87F. You should get contunuity between them. If not your relay is bad.
I hope I explained this ok I'm sleepy.

IKE20VA4
01-04-2006, 09:01 PM
can't you test it with vag com? it may have been something else. but in the output tests I thought fuel pump relay was in there....

maybe

badassbaldie
01-04-2006, 09:16 PM
Not bad for being sleepy 4ing. I understand but I have the wiring schematic in front of me.[:D]

cbass, here's a pic of the relay panel. The fuel pump relay is the one marked "372" (upside down):

http://www.audizine.com/gallery/data/500/6235relay_panel-med.jpg

mike-2ptzero
01-04-2006, 09:20 PM
My understanding was that the fuel pump only pulses 1 time(to raise fuel pressure) when the key is turned on, then only fully turns on after the car is running. But doesn't come on during cranking.

4ingDrive
01-04-2006, 09:45 PM
Originally posted by badassbaldie
Not bad for being sleepy 4ing.

Thanks, I thought I'd be in bed by now.


Originally posted by mike-2ptzero
My understanding was that the fuel pump only pulses 1 time(to raise fuel pressure) when the key is turned on, then only fully turns on after the car is running. But doesn't come on during cranking.

Not sure if it's off during crank or pulses.

juju4uofa
01-05-2006, 06:51 AM
Well, I finally got the relay figured out. Prong 3 (30) is full time power it runs to prongs 1 (87) and 2 (87a) and there is a switch in between. Prong 4 (86) gets a signal from the ignition and prong 5 (T) gets a signal from the ECU. These two prongs are connected with a solenoid in between them. When a power source is run through these two prongs the solenold closes the switch in turn providing power to prongs 1 and 2. So to test the relay you hook a power source to prongs 4 and 5 (one positive and one negative). You'll here a click which is the solenoid closing the switch. You should then have continuity between prongs 3 and 1 also 3 and 2.

I checked my relay this morning and it unfortunately it is good. So, is it my ECU not sending a signal, my ignition not sending a signal, a stuck fuel pressure regulator which is telling my ECU there's already enough fuel, or something else in the wiring. I've said this a million times, but it sure does suck to do all this work to a car just to fix it, not make it better!!!

mike-2ptzero
01-05-2006, 08:49 AM
Originally posted by juju4uofa
Well, I finally got the relay figured out. Prong 3 (30) is full time power it runs to prongs 1 (87) and 2 (87a) and there is a switch in between. Prong 4 (86) gets a signal from the ignition and prong 5 (T) gets a signal from the ECU. These two prongs are connected with a solenoid in between them. When a power source is run through these two prongs the solenold closes the switch in turn providing power to prongs 1 and 2. So to test the relay you hook a power source to prongs 4 and 5 (one positive and one negative). You'll here a click which is the solenoid closing the switch. You should then have continuity between prongs 3 and 1 also 3 and 2.

I checked my relay this morning and it unfortunately it is good. So, is it my ECU not sending a signal, my ignition not sending a signal, a stuck fuel pressure regulator which is telling my ECU there's already enough fuel, or something else in the wiring. I've said this a million times, but it sure does suck to do all this work to a car just to fix it, not make it better!!!

This is how most all relays are wired up since 87 and 87a is the switch outputs and 86 and 85 are what control the switch. There is even a diagram of this on every relay. Problem wont be your fpr since it has nothing to do with telling the ecu if there is fuel or not because it is not wired up. Are you even sure that it is a fuel issue? Have you tried pulling the rail/injectors up out of the intake manifold and see if any fuel comes out of them when you first turn the key on. You could also check if it is working by putting a fuel pressure gauge in the feed line and see if the fuel rail gets pressurized when you turn the key on.


BTW is the ecu showing any DTC's at all?

badassbaldie
01-05-2006, 09:10 AM
You could also check if it is working by putting a fuel pressure gauge in the feed line and see if the fuel rail gets pressurized when you turn the key on.

I believe he tested the fuel pump directly (bypassing the relay) and he said it was good. Now that the relay was tested and working, he's probably got an ECU and/or power issue.


BTW is the ecu showing any DTC's at all?

I didn't have any when my car did the same exact thing.

JuJu, did you ever try disconnecting the ECU? If so, I would take Bitter up on using a stock ECU. I've also been told by some that the wiring harness can go bad too.

juju4uofa
01-05-2006, 09:14 AM
Well the relay won't send power to the fuel pump so I just assumed it's not getting fuel. Even if the fuel pump isn't consistently running without the car being on it has to run at least intermitently during startup. I haven't checked for pressure but I may do that this afternoon. I have a universal pressure guage and I need to get a T-fitting and a piece of hose. The pressure guage (if I'm not mistaken) reads from 0 to 100 psi, will this be adequate?

When my key is in the on position every once in a while I was hearing a clicking (which I found out was the relay) and my dash lights flicker a little. This sounds like a bad ground, although I haven't been able to locate one. Keith from APR told me to turn the ignition on again this afternoon and if all the lights come on expect the check engine light then it's my ECU. If in case it is, they'll fix it for free (minus shipping). It's good they'll fix it but I'd much rather find a loose ground. This would save me time and more importantly keep me from wondering what happened to my ECU and is it going to do it again.

Sorry, what are DTC's?

badassbaldie
01-05-2006, 09:24 AM
Sorry, what are DTC's?

Diagnostic Trouble Codes

juju4uofa
01-05-2006, 10:17 AM
I did disconnect the positive lead on my battery for about 5 minutes (I assume this reset my ECU) however nothing changed. I haven't noticed and DTCs but I'll look this afternoon when start working on it again.

juju4uofa
01-05-2006, 04:49 PM
I got home today and unplugged my battery and even unplugged my ECU. I hooked everything back up and turned the ignition on. The dash lights were on like normal except the check engine light instead of just being on it was flickering. Also, my fuel pump relay started clicking like crazy. I called APR and they got me to tap on my ECU while the ignition was on. You could tell it had a direct effect on how much the CEL flickered. So, they said it was the ECU and I shipped it off about an hour ago. I sure hope this solves it and am very pleased with APR's willingness to help me out and fix or replace it for free. I've been unimpressed with some of there employees, but Keith seems to know his stuff. I'll let everyone know if this fixes the problem. I should have the ECU back at least by Tuesday. Thanks again for all of your help.

juju4uofa
01-08-2006, 09:30 AM
Well, I got the ECU back Saturday morning. Unfortnately, I didn't specify which address so it went to my parent's address (my billing address). Anyway, I had some friends bring it to me today. I put it in and did a TBA, I tried to crank it and it fired right up. I drove around for a little while with no problems and then I gave it hell for about 15 minutes and still no problems. It's been cranked several time since I reinstalled the ECU. Thanks APR!!!!!