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Landrover Discovery V8 1998 - Fuel rest pressure question - Fixed #

Posted by Joe McGeoghan on August 7, 2013, 3:56 pm

Year of Manufacture *: 1998
Engine Size and Code *: 3.9
( Optional ) ECU Type: 14CUX

This Disco is intermittently hard to start. Fuel pressure is ok, but drops immediately when engine is turned off.

Can somebody tell be how rest pressure is maintained on this engine. Is it controlled by the fuel pressure regulator on the rail, or is there another non-return valve somewhere? Cannot see anything obvious. Nothing shown on RAVE.

This car has an LPG conversion, so pump not readily accessible.

Thanks in advance.

Re: 1998 Discovery V8 Fuel rest pressure question.

Posted by Mark Carter <iframe src='https://members5.boardhost.com/ukautotalk4/info/user=UKAT1428' width='330' height='300' border=0 style='border:none;'> on August 7, 2013, 5:48 pm, in reply to "1998 Discovery V8 Fuel rest pressure question."
Mark Carter

I would have thought that there will be a non return valve on the outlet of the pump.

But I have not looked at one myself.

Mark

Modern cars, Its all wizardry and witchcraft

Re: 1998 Discovery V8 Fuel rest pressure question.

Posted by Simon Kefford <iframe src='https://members5.boardhost.com/ukautotalk4/info/user=ukat3159' width='330' height='300' border=0 style='border:none;'> on August 7, 2013, 6:34 pm, in reply to "1998 Discovery V8 Fuel rest pressure question."
Simon Kefford

If this has got the cat flap air flow meter, then the fuel pump doesn't run until it has air flowing through the flap. ie on cranking the flap opens and signals fuel pump to run. There is no non return valve.

The pump maybe tired, regulator a fault, engine vacuum or signal for pump to run missing intermittently.

Maybe some help...

Simon

Re: 1998 Discovery V8 Fuel rest pressure question.

Posted by Joe McGeoghan <iframe src='https://members5.boardhost.com/ukautotalk4/info/user=UKAT5290' width='330' height='300' border=0 style='border:none;'> on August 7, 2013, 7:08 pm, in reply to "Re: 1998 Discovery V8 Fuel rest pressure question."

Customer renewed pump (new, genuine) a few months ago. Hot wire, not cat-flap AFM.

Pump works fine, as and when it should (circa 2.5 bar). My problem is that system is not holding pressure when engine is stopped. Shouldn't drop more than approx 0.7 bar in a minute. This drops to zero immediately.

Thanks, guys.

Re: 1998 Discovery V8 Fuel rest pressure question.

Posted by Mark Carter <iframe src='https://members5.boardhost.com/ukautotalk4/info/user=UKAT1428' width='330' height='300' border=0 style='border:none;'> on August 7, 2013, 7:46 pm, in reply to "Re: 1998 Discovery V8 Fuel rest pressure question."
Mark Carter

Has this vehicle got a return?

What's the problem with the vehicle, hot start?

Mark

Modern cars, Its all wizardry and witchcraft

Re: 1998 Discovery V8 Fuel rest pressure question.

Posted by Joe McGeoghan <iframe src='https://members5.boardhost.com/ukautotalk4/info/user=UKAT5290' width='330' height='300' border=0 style='border:none;'> on August 7, 2013, 9:28 pm, in reply to "Re: 1998 Discovery V8 Fuel rest pressure question."

Straight-forward feed and return MPI. Return governed by vacuum controlled pressure regulator. Regulator holds vacuum and varies pressure when actuated with Mityvac.

Problem is that vehicle is sometimes difficult to start. ECU only actuates pump for (roughly) three seconds, so you only have one bike of the cherry. Cycling the ignition builds pressure and allows the engine to fire readily.

The problem is lack of rest pressure.

Re: 1998 Discovery V8 Fuel rest pressure question.

Posted by Mark Carter <iframe src='https://members5.boardhost.com/ukautotalk4/info/user=UKAT1428' width='330' height='300' border=0 style='border:none;'> on August 8, 2013, 7:27 am, in reply to "Re: 1998 Discovery V8 Fuel rest pressure question."
Mark Carter

>>> The problem is lack of rest pressure <<<

Or lack of flow?

Mark

Modern cars, Its all wizardry and witchcraft

Re: 1998 Discovery V8 Fuel rest pressure question.

Posted by Joe McGeoghan on August 8, 2013, 7:40 am, in reply to "Re: 1998 Discovery V8 Fuel rest pressure question."
Edited by board administrator August 12, 2013, 1:32 pm

No!! Rest pressure!!

Re: 1998 Discovery V8 Fuel rest pressure question.

Posted by Mark Carter <iframe src='https://members5.boardhost.com/ukautotalk4/info/user=UKAT1428' width='330' height='300' border=0 style='border:none;'> on August 8, 2013, 9:39 pm, in reply to "Re: 1998 Discovery V8 Fuel rest pressure question."

Sorry to have upset you, hope you sort it out. Goodbye.

Regards
Mark

Modern cars, Its all wizardry and witchcraft

Re: 1998 Discovery V8 Fuel rest pressure question.

Posted by Kim Doerr <iframe src='https://members5.boardhost.com/ukautotalk4/info/user=UKAT5116' width='330' height='300' border=0 style='border:none;'> on August 19, 2013, 11:20 pm, in reply to "Re: 1998 Discovery V8 Fuel rest pressure question."

I would of thought Mark may have been on the right track with a faulty non return valve on the pump, easy to check though! Gauge in line and clamp before gauge and then after gauge immediately after engine cut, if it holds pressure you know where the prob is.
This lack of pressure causes boiling of fuel and bad hot start.
Hope this helps, all the best, Kim

Re: 1998 Discovery V8 Fuel rest pressure question.

Posted by Ed Kaps <iframe src='https://members5.boardhost.com/ukautotalk4/info/user=UKAT5536' width='330' height='300' border=0 style='border:none;'> on August 22, 2013, 5:04 pm, in reply to "Re: 1998 Discovery V8 Fuel rest pressure question."
Edward Kaps

Fit an inline n/r valve after the pump.

Fixed #

Posted by Joe McGeoghan on August 27, 2013, 3:56 pm, in reply to "Re: 1998 Discovery V8 Fuel rest pressure question."
Edited by board administrator August 30, 2013, 1:58 pm

Just back from holidays to have another look at this.

Non-return valve from Ebay for £5 has done the trick. Thanks, Guys.

Joe

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