Fuel pump relay ??

Sun May 06, 2012 9:37 pm

Ok so at no point does it run through the engine ecu? Where does the ignition switch get its supply from? A direct feed straight from the battery?

Sun May 06, 2012 9:46 pm

Ignition switch gets its live feed from a stud inside the fusebox. The stud is a hex. cap bolt, and you can see the head of the bolt in the deck of the fusebox. Don't turn this bolt.
The stud is in turn fed by one of the smaller red wires connected to the battery, if the battery is front mounted, or by one of the red wires connected to the large stud in the 'phantom battery terminal' on the bulkhead if you have a rear mounted battery.

Sun May 06, 2012 10:17 pm

Yep that all makes sense, thanks. My point is that we agree the DME relay switches on the engine ecu yes? And obviously without it nothing will 'run' blah blah blah. Maybe it's because I've been around newer cars too long but I was under the illusion that it was a similar process with the systems on these cars, where as far as the engine ecu goes, it controls everything including engine starting. I did listen to you when you said there wasn't a relay for engine starting but I took that in the form of there's no relay on the main starter motor cable side. I wasn't aware it was a seperate direct solinoid feed, newer stuff switches through ecu's and obviously if this was the case with my problem then the DME relay wouldn't be directly responsible for starter motor cranking but if it wasn't powering the ecu then starting wouldn't occur.

As I said I assumed this was the case but clearly it's just a very simple process. I under estimate peoples knowledge and I apologise.

Sun May 06, 2012 10:29 pm

On an E30, the green wire from the ignition switch connects to part of the engine ECU, and this part of the ECU in turn switches on the DME relay. The DME relay then turns on the rest of the engine ECU, which activates the idle control valve, (which people tend to think is the fuel pump priming.) Nothing else happens until the ECU sees pulses from the crank position sensor.
"Newer stuff", up to and including EWS3, at least, runs the black/yellow through a relay in the EWS module as well, but is otherwise pretty much the same as on the E30.
I presume the reason for this is to stop the uninitiated cranking the engine until the battery dies, if the EWS hasn't been unlocked for some reason.

Sun May 06, 2012 10:40 pm

Grrrmachine wrote:Can you show me which parts of the Wiki you're referring to, as you've definitely misunderstood something. Neither the DME relay nor the ECU itself have anything to do with the engine cranking, so if there's a part of the Wiki that makes you think there is, then I need to know so that it can be amended.

Also, if your battery is only showing 12.2V, something's not as it should be:

http://www.e30zone.net/e30zonewiki/inde ... ge_Battery

And did you even try the Diagnostic Plug start? If you had, you'd have saved yourself all that messing around with relays in the first place.

The only prob I found with the wiki is when it tells you what you should be looking, I.e 'you should see 3 relays side by side, the relay you require is the one on the right' As Brianmoooore said things can get moved around over the course of 20 odd years by other people. So you select the right hand relay for example as stated by the wiki but in the past they have been moved around so technically you might have hold of the left hand one.

So you could be doing tests on it, and it's not even the correct relay your testing. (I'm just using this as an example though)

But it could be wires bunched together or pipes moved about etc... Do you see what I mean?

As for battery yep I'm aware its not the correct voltage, sorry what I ment was its was ok enough to crank the engine over and wasn't at 9 volts or something.

Sun May 06, 2012 10:48 pm

170sport wrote:Disconnect your fuel feed to your fuel rail and turn ur ignition on, you will get lots of fuel coming out and the crankshaft wouldn't have turned a single degree.

your not 100% correct. my m42 does engage the fuel pump with ignition on as you said to pressurize the system. but if the battery has been disconnected or engine stalls due to certain issues such as lack of fuel the fuel pump isnt turned on by the DME until a signal is received from the crank sensor probably for safety reasons ..

Sun May 06, 2012 10:53 pm

Yeah that would make sense for vehicles which have factory fitted push button start control. Or keyless start. I used to work for Audi and despite them being rivals I assumed they used similar systems, clearly not ha!

Sun May 06, 2012 11:09 pm

balilu91 wrote:
170sport wrote:Disconnect your fuel feed to your fuel rail and turn ur ignition on, you will get lots of fuel coming out and the crankshaft wouldn't have turned a single degree.
your not 100% correct. my m42 does engage the fuel pump with ignition on as you said to pressurize the system. but if the battery has been disconnected or engine stalls due to certain issues such as lack of fuel the fuel pump isnt turned on by the DME until a signal is received from the crank sensor probably for safety reasons ..

Yeah that's understandable, obviously the pump will stop when the crank stops spinning and when it see's the engine cranking then it'll start to supply fuel again.

But as Brianmoooore says it could be the iscv I'm hearing? The more I think about it the more plausible it is. but It's just not as loud as the fuel pump, but I'll leave my e30 overnight and listen what noises it makes tomorrow morning on a cold start up. as where on the subject

Sun May 06, 2012 11:32 pm

Audis are weird! The A3 I have here primes the fuel rail when you open the driver's door.

Mon May 07, 2012 12:19 am

Easy way to spot the fuel pump relay;it's the one with a green/violet wire attached to it's bum!

DME relay has 5 connections...

Mon May 07, 2012 6:30 am

daimlerman wrote:Easy way to spot the fuel pump relay;it's the one with a green/violet wire attached to it's bum!

DME relay has 5 connections...

And this info is in the Wiki on the Troubleshoot page.

I know what the OP is saying about identifying parts on the car, but each instance does have data to confirm. For example, on the Fuel page:

"The fuel pump relay SHOULD occupy the middle position; to confirm, check that the relay has a green/violet wire feeding it."

Mon May 07, 2012 7:28 am

Brianmoooore wrote:Audis are weird! The A3 I have here primes the fuel rail when you open the driver's door.

They are complex, you'll be amazed at how many function and settings you can have with just the key!

Mon May 07, 2012 7:33 am

Grrrmachine wrote:
daimlerman wrote:Easy way to spot the fuel pump relay;it's the one with a green/violet wire attached to it's bum!

DME relay has 5 connections...
And this info is in the Wiki on the Troubleshoot page.

I know what the OP is saying about identifying parts on the car, but each instance does have data to confirm. For example, on the Fuel page:

"The fuel pump relay SHOULD occupy the middle position; to confirm, check that the relay has a green/violet wire feeding it."

Yeah I agree that's the correct to actually confirm.