All of the sudden it seems I'm losing fuel pressure when sitting for more than an hour or so and here's what I know:

Cranks for a solid 15-20 seconds and doesn't fire up until the second turn of the key. (this 2nd turn may be a clue).
One time I cranked it for only 5 seconds or so and it still required additional excessive cranking before it started.
It will restart immediately when hot, or immediately after "getting it started", without issue. If it sits for an hour plus will not restart easily.
Lately I can smell fuel near the filler door at times, so for all those reasons I think this is fuel pressure related.

Additional info:
It runs completely normally, no codes, pending or otherwise, for over 100 miles and 6 or 7 restart sessions.
PO replaced the fuel pump about 15k ago.
I haven't found any fuel stains under the truck.
I peeked my head under there at the filler tube and nothing appeared blatantly wet.

Does not seem flooded when it starts so I think that rules out leaky injector(s) bleeding off pressure, plus the lack of codes indicating misfires from fouled plugs. Not sure if O2 sensors would come online in time to detect a rich condition but I think there would be misfires for sure. Due to the location of the port on the rail I haven't verified actual pressures but my gut tells me that's what this is looking like. The fuel smell is a bit of a "smoking gun" as well. Are there any other components to the fuel system which could cause this scenario? Any thoughts on what I should look at first? I have a parts truck that ran when parked so I think I have adequate spares, I just don't know where to begin and would rather not blindly replace things that aren't likely candidates. I'm hoping some of you more wiser folks have some thoughts. Thanks.

 

since there is no return line, and you think the front end of fuel supply is OK,,,it's possible that there is leakdown at the fuel pump fitting..or the pump....or maybe something else...it's a pain , but checking line pressure /leakdown would be helpful....

 

Yeah, could be a leaking pressure relief valve which is in the tank. Not sure it is worth changing, you can turn the key to the run position and the fuel pump runs for 20 sec to prime the lines. Then turn it off and turn it on again for another 20 sec prime and then hit start.

 

I've never heard the pump run under key only, and conflicting reports abound here on the forum. Is that verified? I'd think you two would know so I'm guessing I'm wasting my breath asking. In my automotive experience the ECU waits to see the crank spin before the relay powers the fuel pump but I'm not familiar with how LR does it.

 

Every car that I have worked on, I can always hear the fuel pump run when ignition is on before engine start. Granted I've only really worked on a few different models and not very extensively but yeah, it should prime before you start cranking. Never confirmed it on a disco but you can test by doing what was recommended and see if it works.

Maybe the fuel pump is out and the only reason it is starting after excessive cranking is because the vacuum is pulling enough? Not entirely sure if that's possible but just some ideas.

 

I haven't heard the fuel pump running on either of my Discos. Can't hear it on my VW Golf, haven't heard it on any of my wife's Accords or the CR-V. I did hear it on my Audi. Depends on the type of pump, where it's located, and how well it's insulated. But if the key is on, the pump should be running.

 

I think it also depends on the type of fuel injection, CIS, D-Jet, L-Jet, Motronic, etc, since the ECU controls the ground path to the fuel pump relay in some of these scenarios. Motronic below 1.3 definitely needs to see the crank spin before it will provide ground to the relay. I also don't understand the purpose of the "priming" phase if there's a check valve in the system to prevent depressurization. I have a mechanical fuel gauge in my M5 and it reads 3 Bar whether the engine is running or not. There's no priming that's occurring (or needs to occur) when I turn the ignition on.

I just read through the BOSCH Motronic 5.2.1 Engine Management System manual and found the following statement:

"The ECM energizes the fuel pump relay when the ignition is first turned to position II. It also energises it during engine cranking and when the engine is running." (interesting that they spelled "energizes" two different ways in the same sentence).

To me this confirms that the the fuel pump is powered when the key is on. I did not see anything about the ECU removing power for any reason other than key off.

It was dead quiet at 9pm last night so I went outside to try Extinct's recommendation of leaving the key powered for 20 seconds to see if that restored pressure in the rail before cranking. I went around back but could not hear a thing out of the fuel pump, it must be a super quiet pump. Anyway, I hit the key after 20 seconds and it started right up. Ever the pessimist I now wondered if maybe the rail had somehow retained pressure from my 5pm "excessive cranking episode", which could invalidate the 20 second test. Because this has been so repeatable for the last two weeks I figured I would just wait until morning and give it 5 seconds of cranking to confirm the condition, and THEN try the 20 second test. Well, of course it started up immediately this morning. First time in 2 weeks, WTF.

Now my theory is a failing fuel pump relay. I'm thinking maybe it isn't (wasn't) pulling in on the the first crank attempt, but then cycling the key for the second attempt woke it up. The smell of fuel at the back of the truck is a pretty gaping hole in this theory however. I think pulling up the carpet and a quick check of the pump connections is next. Get a meter on the power connector to see what's happening when as well as look for leaks.

 

After two weeks of dealing with the problem and making sure I had enough background info into the problem before posting this thread, I unfortunately now have to report that it has vanished. Since my last post I have waited longer and longer between start attempts to ensure adequate time for the rail to depressurize. My plan of attack was to turn it over for a couple seconds to confirm that it was a no-start scenario, and then turn the key to position II to allow the pump to pressurize the rail, per Extinct's suggestion. For the last 4 attempts the damn thing started right up on the first turn of the key. The last time was a 24hr waiting period. I'd say that maybe I was losing my mind but I distinctly remember being at the grocery store last week and after sitting for a half hour, the truck just cranked away without starting for about 20 seconds, which at the time caused to to think that the problem was worsening. Oh well. Good news I guess. For now...

If anything else comes of this (which it probably will), I'll be back.

 

You might have had a piece of trash in the PRV holding it open slightly, or maybe it just wasn't seating correctly. Take the win.

 

I have exactly thesame problem. I replace MAP and fuel pump because I detect that my tracks fuel pressure. Problem still thesame, untill one morning it stalled and I need to have it towed into my garage.. what i did is replaced the crankshaft sensor and it solved the issue... it is now running perfectly with no issue at all. I hope this can help solve yours