Over fuelling on starting

[AdrianC]

there is no fuel going back on the return pipe T junction

What, ever?

Then the fuel pressure regulator is where I'd start to look. Fuel should be going around all the time - the pump delivers far more than the injectors ever use. It's not like the pump on something older with a carb, pumping against the needle valve and just "running light" when the valve closes. The fuel circulates all the time, and on idle the vast vast majority should go back. The FPR should be closed - preventing fuel going back to the tank - when the pressure in the rail is below the intended pressure (3bar, IIRC), then open against spring pressure to let excess pressure out when it rises above that.

The injectors are on the "outside" of the inlet valve, so fuel/air mix will only get into the combustion chamber when the valve is open. But if the FPR is failing to let excess fuel out of the rail back to the return, and the pressure's too high in the rail, more fuel will be injected whenever the injectors open...

[wizwilson]

Yes it maybe " What Ever "

but i can tell you now that the fuel pump has NO wires on it, it is NOT running, but engine is, and if i clamp the pipe before the filter the engine will not run, i also clamped the return pipe and removed the pipe from its T peace in engine bay, with the engine running and NO fuel pump connections on but engine running no fuel coming out of T peace, this is what is so confusing, it shouldn't run without fuel pressure BUT IT DOSE !!

i would also like to point out i have been Mechanic / Auto Electrician for 40 years, so im not stupid around vehicles, but this is the first time ive come across this scenario, but felt sure that somebody on this forum might have a more in depth Knowledge of this system than me

[AdrianC]

it shouldn't run without fuel pressure BUT IT DOSE !!

There isn't another fuel pump somewhere in the line...?

Does it start, run and stay running until you turn it off, no matter how long?

Have you removed the blanking bolt from the rail T-union, see what residual pressure you've got in there?

[wizwilson]

No other pump, yes it will run till i turn off, it will rev up but only if you do it slowly, no haven't taken blank out yet but will try tonight, my guess is that no pressure just whats sitting in the pipe, have removed filler cap so there is no pressure in tank.

for anybody else reading and think this is a load of rubbish, i can assure you that this is no trick, and im as flummoxed as the next man, it shouldn't run but it dose.

im wondering if the injectors will stay open if the ECU is missing a feed or an earth ?

and am trying to find information on when you switch ignition on will the pump prime then shut off ?

should the stabilization valve work all the time or only when engine is cranking then started ?

[AdrianC]

and am trying to find information on when you switch ignition on will the pump prime then shut off ?

Yes.

Whether the injectors stay open or not is irrelevant if there's no pressure in the rail...

[wizwilson]

Hi,
so is the yes to this question or both ?

and am trying to find information on when you switch ignition on will the pump prime then shut off ?

and this ?

and am trying to find information on when you switch ignition on will the pump prime then shut off ?

if so then there is an issue here as they will both run continuously with ignition on and engine not running.

and yes i would guess that the injector would be closed till triggered, and with pressured fuel behind them would spray.

but as i have said this is not a normal scenario there is no obvious fuel pressure, yet the engine runs, so it must be getting fuel some how, so the other possibility is 1 injector is broken open, and there is no fuel pressure build up when pump connected as it is all flowing into one cylinder ?

[AdrianC]

The pump should be fired up for a few seconds on first turning the key, to prime the rail. After that, it should work all the time the engine's running, and not if it isn't. This is partly a fire-safety thing, to prevent the pump adding the entire contents of the tank to a fire...

You don't yet know what the pressure in the rail's doing, right? Take the blanking plug out, turn the key, and see what happens. Can you beg/borrow/steal a pressure gauge?

[mark]

the digijet fuel pump relay powers up on the turn of the key for a couple of seconds, mine primes the system twice then it earths at the ecu if the key is not turned to the cranking position. so the pump is switched off by the ecu running to ground. with this cycle being so short you will struggle to get a reading at the injector under normal circumstances, if your system is open then you will have a reading at the injectors and fuel pumping through the system.
so were back to cleaning and checking all the contacts at the ecu and making sure that it is sound.

mark

[wizwilson]

Ok update on issue, after extensive testing of circuits by myself and good friend ( also auto electrician ) the verdict is the ECU is at fault, if every thing is connected correctly, when you switch the ignition on, the fuel pump runs continuously and the injectors stay open, causing massive over fuelling hence non-start, if you disconnect the pump there is enough suck in cylinders to pull fuel down through injectors to allow it to run, as all the injectors open together this helps with this particular fault.

am now going to look round to see if i can find somebody to test it to see whats blown, have had apart cannot see anything burnt or dry solder joint so must be a component, defiantly one for the books though who would have thought you could get a fault that would allow the fuel pump to run continuasly and hold injectors open, but if the pump had become disconnected then engine would still run simply by induction vacuum sucking fuel through injectors.

anybody know where you can get these tested and repaired ????

[mark]

I don't know of anyone who tests and repairs.........if you find someone come back and let us know......best place for a s/h replacement is the wanted pages
or £250ish http://www.gowesty.com/ec_view_details.php?id=3859" onclick="window.open(this.href);return false; for a rebuilt

mark

[wizwilson]

Found a place in Staffordshire ATP Electronics 01543427900, who can test for £45 and repair for approx £200, but luckily found second hand unit on ebay for £50, so am going that route, might work out if not then its a repair job.
also found another company in Colchester that might be able to repair ACTronics 01206849920, will ring them tomorrow.

[wizwilson]

The inside of the ECU looks brand new, VW were ahead of there time in sealing things up.

[wizwilson]

Anybody know where to get the seals for the injectors into head ??

[wizwilson]

There are 2 rubber seals that position injectors in head, anybody know where i can get them ????

[AdrianC]

There are 2 rubber seals that position injectors in head, anybody know where i can get them ????

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