Fuel pressure problems helllp

Hi guys so I have had a cutting out issue on my mk1 gti cab it's 1985 (b reg) 1.8 I have changed pretty much everything I possible can in the fuel system but am still having the problem

I have put a fuel pressure tester on and it idles happily at 5 bar then when it get hot it starts to stutter down to 4 and when it drops to 3 bar it cuts out

Leave it for a little while and it's starts again
Can anyone help me with why it's dropping in pressure after running for a while

Thanks


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Bad pump as is it whining? or bad fuel pump relay, quite common on the CIS that as the pumps are running the relay heats up and gets cold solder joints at the relay inside the relay box.

It is so common over here in that CIS folks either carry a spare horn relay, or Fuel Pump Relay in the glove box. or Jumper it out.

I would install the horn relay in its place as a test to see that the pressures stay up and the pump runs, be warned that the pump will run as long as the ignition is on instead of getting it's on/off signal from the Coil.

Use as a Test or a Limp home thing.

Not all fuel pump relays are the same read more about it at www.cabby-info.com.

Hi briano
The pump isn't whining and I have replaced both pumps (underside and intank) I have been told it may be the relay but on inspection there is no relay in the fuse board for the fuel pump so my guess is someone has had a fiddle with it in the past

The pump doesn't run constant however I put a solid live from the battery to it and it did constantly run and still cut out which is even more confusing


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There was a TSB can't remember it but they relocated the Fuel pump relay from one spot on the fuse panel to another.  Cabby-info.com has the TSB I think.

If you Jumpered the battery live to the pump and it cuts out, then I would think.

1. Your new pump is junk.
2. Bad grounds to both your pumps.

Pumps that die after a bit are usually fouled or bad.  They can overheat internally and flat stop.
Usual indication is that the main pump will start to whine prior to stopping from over heating.  I would also suspect that the intank pump is also having similar issues as the Grounds for both pumps are at the same tie point.  

So you have to make sure that the in-tank pump is functional as if it is bad it can cause the primary pump to fuel starve…over heat and die.  As I stated it usually whines about overworking….but then again it could just up and quit.  As the flow of fuel diminishes so does the cooling of the motor, as the fuel is used as an internal coolant…

Another look for is the pump getting hotter than a firecracker as that is a sign of overheating as well.

Since the fuel pumps are Vane Pumps, clearances matter and a hot pump can easily bind.

Hi briano
The pump isn't whining and I have replaced both pumps (underside and intank) I have been told it may be the relay but on inspection there is no relay in the fuse board for the fuel pump so my guess is someone has had a fiddle with it in the past

The pump doesn't run constant however I put a solid live from the battery to it and it did constantly run and still cut out which is even more confusing


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Ok thanks I will check the earthing first then the pump would you know where I would find the ground and I take it you don't know where the relay would have been put by any chance


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IIRC it was moved from the location to a spare relay position above the fuse panel but I thought it was for earlier models as in early 80's.  83 and up it should be in the number 2 space on the panel

If some one moved it or jumpered it out, as you would see a different relay or jumper wire in the number 2 position… I hate POS (previous owners screwups or servicemen).

Most of the issues I ever had with my Cabbies was POS related.  Once I got them all de-bugged I usually had a worry free car…The hardest thing was OEMing the POS repairs…..



 

Ok thanks I will check the earthing first then the pump would you know where I would find the ground and I take it you don't know where the relay would have been put by any chance


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Also I haven't changed the fuel accumulator I cleaned out out but didn't change could this have an effect on fuel pressure


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If there is fuel that comes out of the screw then it is bad, other than that I don't know CIS well at all as I am Diesel/Digi knowledgable…. I do know that CIS when it is properly adjust is very dependable, but from what I have read over the years, "CIS Cause It's Satanic" is the most common theme.  

While I understand the MK1 frame, and owning a Diesel for 20 years, and now have been rocking Digi for 15 or so… I am more familiar with those….Oh and Carbed US and British Cars…. I was trained early on in Knowing that Lucas was the Lord of Darkness, and the wires in a Bug-eye/MG protected the fuses constantly….Where Lucas was the Lord, Bosch is his Prince.    All in Fun.



 

Hi, as i understand you are cheking system (line) control pressure?

Hi yes I am putting a pressure gauge before the filter at the end of the fuel line


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its not clear what you are cheking than to perform fuel pressure test you must to install gauge between the control pressure regulator and the center fitting on fuel distributor.

By putting it where I have I am checking the pressure of the fuel coming through from the pump


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1 If pressure is too low, check fuel pump output. Disconnect fuel return line from fuel distributor and run a hose from fuel distributor to container.
2 Operate fuel pump via jump wire in relay panel with engine not running, and measure output after 30 seconds. See Fuel Pump Output Specifications table. 30 Sec. Flow Rate 1000 cc. If not as specified, check fuel lines, filter, fuel accumulator, and fuel pump.