Fuel pressure drops to zero after shutoff, hard to start warm. - Land Rovers Only

atikovi · 04-04-2007, 02:18 PM

I just got this '96 Discovery 5-speed with 166K and I starting to work on the bugs. It's hard to start when warm, as in, I crank a few seconds, stop, crank again, stop, and crank again and usually it starts the third time. I hooked up a fuel pressure gauge and noted the pressure at idle was 30 psi. but when I shut the engine off the pressure dropped to 0 within 10 seconds. Thats the problem. What should I check as the cause? I replaced the filter and I don't think it's leaking injectors.

Disco Mike · 04-04-2007, 03:04 PM

There is a valve in the fuel pump that should maintain the pressure, sounds like yours has failed. I believe you have to replace the pump to correct the problem.
Mike

Elemental · 04-05-2007, 05:18 AM

Why do you not think it's injectors?

atikovi · 04-05-2007, 05:43 AM

The fuel pressure bleeds down to zero in 10 seconds. If the injectors were leaking that much I'm sure the engine would be running bad (rich) all the time which it isn't and would smoke a lot when starting up from all the fuel in the cylinders which it's not.

Elemental · 04-05-2007, 06:50 AM

That makes sense, but its a easy check to confirm. And, Injectors in your vintage do have a high failure rate.

wiseguy · 04-05-2007, 07:30 AM

Question-how does it drive out -and also is there rough ideling as if it s not getting enough fuel?

atikovi · 04-05-2007, 08:05 AM

It idles smooth and runs fine otherwise.

wiseguy · 04-05-2007, 12:02 PM

Atikovi- The reason im asking is because Ihave a 96 disco that does theeee exact 3 cranks and starts right up... drives fine (rough idle). So when Mike said it sounds like a pressure valve .Im not quite sure about that. Ijust put in anew fuel pump hoping that would cure all ,not exactly.So the delima still stands -Id swear threr is some lek of pressur when not in use I just dont know where(and no fuel escaping through pressurevalve near the throttle body . If you or anybody is or have had theses probs please help .ps no chek engine light so i wonder if it would even through a code. see ya. NOT SO WISE guy!

werldcup · 04-05-2007, 12:14 PM

Are you sure it isn't running rich? Have you pulled the plugs to confirm?

wiseguy · 04-05-2007, 12:57 PM

werld - Ichanged out the plugs before I put the pump in... now those plugs varied in decomp . Some where hevily carbed up but I was unsure really how old they where since its relatively new to the family! how do they look if it runs too rich.What would cause that. se ya!

werldcup · 04-05-2007, 01:20 PM

The plugs will be black and wet if your injectors are dumping excess fuel.

atikovi · 04-05-2007, 01:29 PM

Just installed a new fuel pump. Now after turning the engine off I still have over 25psi fuel pressure 30 minutes later. Problem solved.

wiseguy · 04-06-2007, 05:25 AM

Im very glad your pump solved you probs !!!! And to world cup-3of the new pluggs had reminants of fuel and turning dark,meaning injects are leaking some fuel that would explain loss of fuel pressure and gas smell DAH. I guess it takes a new perspective to make everything seem so obviuos (even a mechanic friend of mine didnt figure it out .I guess im looking for some injecters ...outstanding .

South_Island_Disco · 04-11-2007, 04:44 PM

Another cause of a drop in fuel pressure after shut off, is a split O ring on the fuel pressure regulator.
Unbolt the regulator from the fuel rail and check the condition of the O ring.
Mine was spilt in three places.
Take usual precautions when doing this, battery disconected, fuel rail depressurised and lots of rag under the regulator to catch the fuel that runs out.

atikovi · 04-11-2007, 05:07 PM

I spoke too soon when I said the problem was solved. While it does hold pressure now after shut-off and THAT problem is solved, when I took it for a test drive the engine started to miss during acceleration. I still had the fuel pressure gauge connected and saw that the pressure was dropping the more I pressed on the gas. I guess the new fuel pump is too strong for the old and weak pressure regulator to keep the fuel pressure up. I ordered a new regulator and will see what happens after installing it.

04-04-2007, 02:18 PM	#1 (permalink)
atikovi Member Join Date: Jan 2007 Posts: 13 Gallery: 0	Fuel pressure drops to zero after shutoff, hard to start warm. I just got this '96 Discovery 5-speed with 166K and I starting to work on the bugs. It's hard to start when warm, as in, I crank a few seconds, stop, crank again, stop, and crank again and usually it starts the third time. I hooked up a fuel pressure gauge and noted the pressure at idle was 30 psi. but when I shut the engine off the pressure dropped to 0 within 10 seconds. Thats the problem. What should I check as the cause? I replaced the filter and I don't think it's leaking injectors.

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04-04-2007, 03:04 PM	#2 (permalink)
Disco Mike Moderator Join Date: Aug 2004 Location: Parker, Colorado Posts: 5,131 Gallery: 0	There is a valve in the fuel pump that should maintain the pressure, sounds like yours has failed. I believe you have to replace the pump to correct the problem. Mike

04-05-2007, 05:18 AM	#3 (permalink)
Elemental Senior Member Join Date: Feb 2007 Posts: 3,017 Gallery: 0	Why do you not think it's injectors?

04-05-2007, 05:43 AM	#4 (permalink)
atikovi Member Join Date: Jan 2007 Posts: 13 Gallery: 0	The fuel pressure bleeds down to zero in 10 seconds. If the injectors were leaking that much I'm sure the engine would be running bad (rich) all the time which it isn't and would smoke a lot when starting up from all the fuel in the cylinders which it's not.

04-05-2007, 06:50 AM	#5 (permalink)
Elemental Senior Member Join Date: Feb 2007 Posts: 3,017 Gallery: 0	That makes sense, but its a easy check to confirm. And, Injectors in your vintage do have a high failure rate.

04-05-2007, 07:30 AM	#6 (permalink)
wiseguy "Former Left Coaster" Join Date: Mar 2007 Posts: 16 Gallery: 0	Question-how does it drive out -and also is there rough ideling as if it s not getting enough fuel?

04-05-2007, 08:05 AM	#7 (permalink)
atikovi Member Join Date: Jan 2007 Posts: 13 Gallery: 0	It idles smooth and runs fine otherwise.

04-05-2007, 12:02 PM	#8 (permalink)
wiseguy "Former Left Coaster" Join Date: Mar 2007 Posts: 16 Gallery: 0	Atikovi- The reason im asking is because Ihave a 96 disco that does theeee exact 3 cranks and starts right up... drives fine (rough idle). So when Mike said it sounds like a pressure valve .Im not quite sure about that. Ijust put in anew fuel pump hoping that would cure all ,not exactly.So the delima still stands -Id swear threr is some lek of pressur when not in use I just dont know where(and no fuel escaping through pressurevalve near the throttle body . If you or anybody is or have had theses probs please help .ps no chek engine light so i wonder if it would even through a code. see ya. NOT SO WISE guy!

04-05-2007, 12:14 PM	#9 (permalink)
werldcup Mean and Green Join Date: Mar 2006 Location: San Diego, CA Posts: 100 Gallery: 0	Are you sure it isn't running rich? Have you pulled the plugs to confirm?

04-05-2007, 12:57 PM	#10 (permalink)
wiseguy "Former Left Coaster" Join Date: Mar 2007 Posts: 16 Gallery: 0	werld - Ichanged out the plugs before I put the pump in... now those plugs varied in decomp . Some where hevily carbed up but I was unsure really how old they where since its relatively new to the family! how do they look if it runs too rich.What would cause that. se ya!

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04-05-2007, 01:20 PM	#11 (permalink)
werldcup Mean and Green Join Date: Mar 2006 Location: San Diego, CA Posts: 100 Gallery: 0	The plugs will be black and wet if your injectors are dumping excess fuel.

04-05-2007, 01:29 PM	#12 (permalink)
atikovi Member Join Date: Jan 2007 Posts: 13 Gallery: 0	Just installed a new fuel pump. Now after turning the engine off I still have over 25psi fuel pressure 30 minutes later. Problem solved.

04-06-2007, 05:25 AM	#13 (permalink)
wiseguy "Former Left Coaster" Join Date: Mar 2007 Posts: 16 Gallery: 0	Im very glad your pump solved you probs !!!! And to world cup-3of the new pluggs had reminants of fuel and turning dark,meaning injects are leaking some fuel that would explain loss of fuel pressure and gas smell DAH. I guess it takes a new perspective to make everything seem so obviuos (even a mechanic friend of mine didnt figure it out .I guess im looking for some injecters ...outstanding .

04-11-2007, 04:44 PM	#14 (permalink)
South_Island_Disco South_Island_Disco Join Date: Nov 2005 Location: Timaru, New Zealand Posts: 10 Gallery: 0	Another cause of a drop in fuel pressure after shut off, is a split O ring on the fuel pressure regulator. Unbolt the regulator from the fuel rail and check the condition of the O ring. Mine was spilt in three places. Take usual precautions when doing this, battery disconected, fuel rail depressurised and lots of rag under the regulator to catch the fuel that runs out.

04-11-2007, 05:07 PM	#15 (permalink)
atikovi Member Join Date: Jan 2007 Posts: 13 Gallery: 0	I spoke too soon when I said the problem was solved. While it does hold pressure now after shut-off and THAT problem is solved, when I took it for a test drive the engine started to miss during acceleration. I still had the fuel pressure gauge connected and saw that the pressure was dropping the more I pressed on the gas. I guess the new fuel pump is too strong for the old and weak pressure regulator to keep the fuel pressure up. I ordered a new regulator and will see what happens after installing it.