Fuel System enquiry

MULLEY · Post by **MULLEY** » Wed May 14, 2008 6:53 pm

To the techies out there,

where the fuel pump & filter are located on my 1990 Gti there is another device that is connected to the fuel supply, does anyone know what this is called?

I thought it might be the fuel pressure regulator???

Can anyone explain what it does in laymans terms please?

Many thanks

CitroXim · Post by **CitroXim** » Wed May 14, 2008 10:14 pm

Does it look like a small round canister attached to the end of the fuel rail with one pipe going to the inlet manifold and another going off to the fuel return line?

If so, that is your fuel pressure regulator and it's function is to keep the fuel presssure constant with respect to inlet manifold depression (Vacuum). If it were not there, the absolute fuel injection pressure would vary according to the manifold vacuum and fuelling would never be accurate. It also has a secondary function in keeping the fuel pressure steady against rising and falling battery voltage which would make the pump spin faster or slower depending on battery voltage and alternator output.

Accurate fuel injection is critically dependant upon the fuel pressure at the injectors being held within quite fine limits.

MULLEY · Post by **MULLEY** » Wed May 14, 2008 11:21 pm

Not 100% sure, i'll have to get under the car to double check. If it is the said part & is leaking fuel, can it be fixed? or is it a replacement only job??

If it was bypassed, could this cause any damage?

MULLEY · Post by **MULLEY** » Wed May 14, 2008 11:52 pm

I've had a look at the Haynes manual & i dont think what i'm on about is the fuel pressure regulator, as my car is a motronic mp3.1 which means that the regulator is in the engine bay.

I wonder if its the fuel pulsation damper that was leaking? Trouble is there are no pics of that part in Haynes so i cant be sure. I'll see if i can take a piccy tomorrow & post it to see if anyone knows what it is....

Cheers for the mo

Way2go · Post by **Way2go** » Thu May 15, 2008 12:16 am

Mulley, you and Jim are in 2 different areas. Jim is in the engine bay and you are at the back offside of the car. The fuel filter on the GTi is separate to the pump and possibly this is what you are referring to? It is a cannister type of thing near the pump. The whole cannister thing is available as a replacement.

MULLEY · Post by **MULLEY** » Thu May 15, 2008 12:30 am

Yes, it would seem we are at opposite ends of the car

Its not the fuel filter or the pump that was leaking, its another device which is connected to the fuel line further away from those 2 parts....

Thats the part i'm unsure as to what it is, except what haynes refers to which i've mentioned....

I'll take a piccy before wasting anyone else's time on this....

Post by **docchevron** » Thu May 15, 2008 2:43 am

MULLEY wrote: I wonder if its the fuel pulsation damper that was leaking?

It is indeed the fuel pulse damper.
And they can and do leak.
I know several people that have by-passed it altogether and apparentley they report no ill effects but personally I wouldn't run the car without it.

they are available from the main stealer for a few beer tokens.

If not any halfway decent fuel injection specialist should be able to get one of they dont have one already.

I know Tom Day in Keynsham keeps them on the shelf.

Vanny · Post by **Vanny** » Thu May 15, 2008 7:36 am

all it does is put load on the fuel pump so thatt it works rather than free spins, makes the pump last longer. It does go some way to absorbing pulses of fuel from the pump, but with such a huge distance and several rubber pipes to the fueal rail, it does nothing for damping the pulses at the rail (as they never get there).

If you by pass the pulse damper then you might reduce the fuel pumps life by a day or two (out of about 8,000,000 days), but chanign the unit needs the subframe dropping off, so not wortht he effort.

I don't run one.

Ian_Fearn · Post by **Ian_Fearn** » Thu May 15, 2008 4:34 pm

I've had 2 go. Replaced one but it was a waste of time as it did sod all.

MULLEY · Post by **MULLEY** » Thu May 15, 2008 5:29 pm

Many thanks for that handy info chaps, its been bypassed so all is well

Post by **docchevron** » Fri May 16, 2008 2:39 am

Vanny wrote: If you by pass the pulse damper then you might reduce the fuel pumps life by a day or two (out of about 8,000,000 days), but chanign the unit needs the subframe dropping off, so not wortht he effort.

I don't run one.

You'll probably lose more than a day from the pump.

And you definitley do not have to drop the subframe to replace it.

MULLEY · Post by **MULLEY** » Fri May 16, 2008 8:55 pm

I've got a brand spanking new pump incase it does go kaput, so no worries there....

Vanny · Post by **Vanny** » Sat May 17, 2008 1:15 am

docchevron1472 wrote:
Vanny wrote: If you by pass the pulse damper then you might reduce the fuel pumps life by a day or two (out of about 8,000,000 days), but chanign the unit needs the subframe dropping off, so not wortht he effort.

I don't run one.
You'll probably lose more than a day from the pump.

And you definitley do not have to drop the subframe to replace it.

Just need to have incredibly slender lady like hands then?

Post by **docchevron** » Sat May 17, 2008 2:37 am

What you saying like!

I've never had any problems, and my hands aren't that slender and lady like.... I hope...

AndersDK · Post by **AndersDK** » Sun May 18, 2008 9:56 pm

The pulsation damper lives at different locations according to exact model. On my Meteor (hatchback) it resides on top of the rear subframe RHS leg.
Only a quick glance - and then I instantly decided to cut the hoses and bypass the leaking thing.

On my 19TRIbeak it is fitted on a separate bracket near the pump/filter canister, and its located the same place on my 16RIbreak.

In all cases the pulsation damper was well and truly rusted away. The moment the hosestuds were touched they crumbled.
I have not had problems so far bypassing it - saving the approx £50 my local DK dealer wants for the part.