Gti6 Fuel Rail Problem

[gti-si 0]

Right, very weird problem. I'll do my best to explain,

 

As far as I can tell the engine IS wired correctly. Ive got switched live to Pin 14, lambda, got the fuel pump feed from the relay etc. So the wiring in theory is bang on. Now when I turn the ignition, the relay engages and sends the 12v feed to the fuel pump. The pump primes, however, it runs continuously. At first I figured something must be wrong, and wondered if it was receiving a permanent live instead of switched. After thinking about that I realised it shouldn't make a difference. The object of priming is to pressurise the rail, correct? So I drew my attention to the fuel rail...Here, fuel is flowing straight into the rail, and out of the return pipe back into the tank. If I crimp the return fuel pipe, the rail pressurises and the pump stops, so I assume thats the pump primed.

 

What is causing this? Is there a valve in the rail or is this the role of the pressure regulator? I've never researched any of this before so completly in the dark. If so would this point to a knackered regulator, or have I got it wrong and my wirings b**locks?

 

Sencond, i've no spark or fuel on cranking...I have searched, and found these possible causes.

 

1. Double Relay - When I apply 12v switched to pin 14, the relay clicks, and then relays the 12v feed the fuel pump, I'm assuming because of this, it is working fine.

2. TDC sensor - How can I check this? I remember seeing a guide recently on how to check all the gti-6 sensors (resistances etc) but cannot find it again, any one know what i'm talking about and where it is?

3. ECU - How can I check my ECU isn't kanckered? I bought it as unlocked from jonnie205..If it was locked in actual fact, would I still get a feed from the relay or would it just cause no sprak?

 

Any other possibilities?

 

Thanks,

 

Si

[GLPoomobile 958]

Well I can't speak from experience but common sense (and going by recent forum shenanigans) would suggest to double check you've got the fuel lines plumbed the right way. Should be 10mm supply and 8mm return.

 

If that's OK then I 'd guess at a dodgy regulator. I'm don't know the ins and outs of how they work, but surely if it's allowing fuel to flow through it with the engine off, then it wouldn't be building pressure in the line so must be faulty. Think about it, if you let a hose trickle water it's at low pressure, put a finger over the end to block the flow and the pressure in the hose builds until it overcomes the pressure applied by your finger and is allowed to squirt out the end again. Your finger is the pressure regulator and the hose is your fuel rail. Does that make sense?

[gti-si 0]

Cheers Steve, nice anallergy, that is how I thought it might work, but wanted another opinion. It seemed the logical answer that it could only be the pressure regulator. I'll get a new one when I'm in the money, see how that fairs.

 

I had doubled checked and checked again that the lines were the correct way around, I'd been watching Garry's thread so made sure I had connected it up correctly.

 

Anyone any ideas about the lack of spark/fuel?

Edited May 19, 2008 by gti-si

[Spiky 37]

can you remember ALL the wires you've connected?

 

your fuel pump "should" only prime for about 10-15 second MAX sometimes less

 

if it is priming all the time, then, there is a problem,

 

both mine and rossi's primes as i said,

 

you sure it's a switch'd live to pin 14??

 

what other constand lives have you run???

[Spiky 37]

.

 

 

and to add as above

 

rossi's car, someone had swapped the fuel pipes at the rear of the car.. IDIOTS...lol

 

as said, the pipe nearer the front of the car is the return (8mm) and the rear pipe is (10mm)

 

 

hope that helps

[jonnie205 1]

i think what si is trying to say is does the pump prime for a given length of time or does the pump prime until a certain pressure is reached in rail then the pump will shut off?

[Spiky 37]

i think, its for a given amount of time,

 

asthe pump or regulator would not know how much pressure is in the lines as there is no fuel pressure sensor

[jonnie205 1]

it could be that the pump has an internal pressure regulator and it reaches a pressure then cuts off?

[Spiky 37]

there's a VERY slim chance,

 

even when's rossi's lines where the wrong way, so the pump was feeding the rear of the regulator (brick wall afectivly), the pump still "tried" to prime

 

probably didn't do the pump any good, but was a only a few second at a time and didn't happen many times so ok

Edited May 20, 2008 by Spiky

[gti-si 0]

I can't see why it would prime for a certain amount of time rather than until it's at pressure. What is the point of priming the fuel pump if it isn't to build the correct pressure in the rail? The rail has fuel flowing through it and out of the return, and this shouldn't happen...Can't see it being the wiring as that would suggest mechanical failure?

 

I've 100% that pin 14 has a switched live and the fuel pipes are definatly the right way, checked those. Also connected the switched live for the lambda and the other purple wire, can't remember what it was for. I have tried without some of these connected and it's still the same. I can't see it being anything else but the regulator.

 

Just need to figure out why i've no spark now

[Spiky 37]

IF and pugs dont have one,

 

the fuel system had a sensor to tell the ecu what the pressure was before the reg, it could stop and start the fuel pump.

 

but remember the prime is to prime only, and when the engine is running the fuel pump is running 100% and pressure is controlled by the reg

 

so so the prime is to get the pressure up before the engine starts,

 

if you now have no spark, i'd say your double relay is fooked

[gti-si 0]

Hmm, if I post you my relay, wanna try it for me?

[Spiky 37]

send it over

[taylorspug 7]

Check for corrosion on the double relay connections, ive had an S16 loom play up recently because of corrosion in the pins. Wasnt getting spark or fuel, traced it back to the relay, then gave it a technical wiggle whilst someone was cranking the motor and it fired straight up.

[Spiky 37]

ok,

 

my car primes for around 3 seconds.

 

just to give you an idea of the time scales you are looking for,

 

if you want to send it down to test on my car, drop me a pm and i'll give you my address

[gti-si 0]

Cheers for the tip on the corroded connections, I'll have a look at them tomorrow. If not I'll send it down to Spiky to check if it works

[jonnie205 1]

so do the fuel pumps prime for a certain amount of time or what? i did a gti6 conversion once where the fuel pump stayed running with ignition on and did not cut off after 3 seconds, never found the problem so aborted conversion, every other one i have ever done has been fine

[Spiky 37]

so do the fuel pumps prime for a certain amount of time or what? i did a gti6 conversion once where the fuel pump stayed running with ignition on and did not cut off after 3 seconds, never found the problem so aborted conversion, every other one i have ever done has been fine

 

 

interesting mine primed for 3 seconds then stopped,

 

the i run one pump to empty the swirl pot, then run again, and it run for 10 ish seconds

 

n rossi car it runs about 15 seconds

 

very weird

 

both cars run fine

[gti-si 0]

Right, checked the connections and there all in good nick. Im gonna send it down to Spiky tomorrow, meanwhile I might nip to the sprappy and get another relay...The guy won't want alot for them atall, found there on Berlingo and expert vans and 406's aswell, so it's quite a common relay, no doubt i'll find one.

 

The only other thing I can think of is the crankshaft sensor or ECU. I really hope the ECU is fine though, and don't see why it shouldn't be...

 

With regards to pump priming, is there anyone who knows the purpose of the prime and can shed light on it? What makes the pump stop priming?

 

The relay isn't timed, it doesnt stop feeding the pump after a few seconds and I doubt the pump has a timer because it recieves the same 12v when running as it does when is the ignition on...So how would it run constantly when the engines running? If you think about it logically, the only reason the pump stops running is because it is up to pressure....once the fuel begins to inject, the pressure drops and the pump starts and maintains the pressure with help from the regulator...

 

I must have a completly kanckered regulator...Or I'm barking mad...and have got this completly wrong! haha...Still, point remains, either the relay, crankshaft sensor or ECU is knakcered...otherwise i'd have a spark...

[smighall 1]

The pump primes to expell any air that might have built up in the injectors.

 

The relay should have a switched live to pin 14 IIRC whilst cranking. The ECU then earths the other side of the relay to make the connection and provide power to coils/injectors and fuel pump.

[gti-si 0]

Not getting at you simghall, but quite a few people have posted up about Pin 14 and the wiring...

 

The loom IS wired correctly...it DOES have a switched live to Pin 14 and the relay does activate and feeds the pump on ignition.

 

However, when you say the ECU earths the otherside of the relay, is this the two earths on the head of the engine? They are earthed if so

 

Edit: Not knocking your post atall mate...cannot moan at free advice! Just making the point that i've got the switched lives sorted and it's wired up as it should be

Edited May 21, 2008 by gti-si

[smighall 1]

No, pin 7 out of the relay goes to the ecu and the ecu switches this when it wants to prime/run.

 

I know you say you have 12v with ignition, but have you checked that you still have 12v whilst cranking? As long as it's priming the relay itself should be fine. So the only other things it can be is:

 

1) No power on cranking

2) CPS not giving signal

3) Shagged ECU

[gti-si 0]

Right i'm with you, so the ECU does control the prime/run function? I've not actually checked that I have 12v whikst cranking. If the ECU were to be shagged, is it possible it's stuck in the run position? Hence why the pump runs continuously?

 

If I have no power on cranking...What would you think would be the problem? 2 or 3?

[smighall 1]

No power on cranking would mean that the 12v source you've used isn't live whilst cranking, for example - Stereo live 12v.

 

If it just constantly primes i'm not too sure, either 2 or 3 are viable problems.

 

In fact i'm pretty sure it will be the 12v. If it's priming constantly then it should still be giving power to the pump whilst cranking, and it clearly isn't. So that's definitly where i'd start first.

Edited May 21, 2008 by smighall

[welshpug 1,622]

unplug the ECU and see if it still primes.