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  #1  
Old 09-04-2023, 10:36 AM
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Unhappy Loss of power / Fuel pump issues?

Hi all,

did a nice 2000 mile trip around Europe in the last month with the family in the 4.8is. Overall it went very well and the car performed great.... except on the last 50 miles on the way back home.

On the motorway, cruising at about 70mph, i notice the motor hesitate/ splutter once or twice but then cleared up. No lights on the dash. Short while later, lose all power and had to pull over to the hard shoulder (or rather just lane 1 as this was on the M25, a new fangled "smart" motorway without an emergency lane).

Engine cuts out as soon as the car comes to a stop. Won't restart. 1/4 tank of fuel in the car still and have literally just driven about 800miles or so over the last 24hrs so fresh fuel too. Still no warning lights on the dash.

The police kindly tow us off the motorway. They tried starting the car again too. Nothing. Tow truck comes a while later, still won't start so they recover us to the nearest petrol/service station. Here another recovery patrol joins us. Its about 2hrs now since the initial breakdown.

Recovery mechanic plugs into OBD. No errors. Tries starting it... coughs and splutters a bit which is more than what we had before. I get him to try again and a few attempts later it does actually start. Runs rough for a short while before settling back into normal idle. Couple of misfires on two cylinders on the OBD readout now but no further errors.

They towed us back home anyway and I have since used it for a short 1 or 2 mile trip locally and it seems to be running fine.... Not sure I'd want to trust it for another long trip like this though.

Any ideas as to what might actually need doing? Recovery mechanic suggested fuel pump.
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  #2  
Old 09-04-2023, 10:46 AM
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Siphon jet is screwed and so it's not transferring fuel over the drive hump leaving 1/4 tank showing.

Look up Andrew's fuel pump o-ring/siphon jet fix.

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Old 09-04-2023, 10:50 AM
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I've not added any fuel. Is it normal for it to start working again?

They did pull the car up onto a flatbed which tilted it at a good 30deg or so and I wondered if that had anything with getting it working again.
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Old 09-04-2023, 11:31 AM
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The flatbed could definitely get some fuel to crossover. Fill it up (full) and see if the liters match with what it it says on the gauge.

Hidden menu (high cluster) will also show fuel amounts in both sides.

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Old 09-04-2023, 11:50 AM
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thanks. I've been doing seem reading and it certainly sounds like it could have been that.

I had a very similar incident in January this year too as we were descending an alpine pass. Same problem with power but since we were on such a steep and long decline I managed to keep the car running and by the time we got to the bottom it seemed to sort itself out enough to fill up and has been fine since then till last week. That was also at about 1/4 tank level but with the car on a steep decline.

I have regularly run to below 1/4 tank since then too.

Will fill it up and keep it topped up and see how things go. If that seems to cure it will just fix/replace the siphon pump I guess.
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Old 09-04-2023, 04:21 PM
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Almost certainly siphon jet. Search for awr-fix in title and look for the fuel supply thread that includes how to fix the Siphon jet.

Did you never drop below 1/4 tank? Once the Siphon jet fails you won't be able to use fuel below 1/4 tank. As it gets worse 3/8 tank.

There's a design defect that will eventually allow the o-ring to push out of the groove.
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Old 09-04-2023, 04:28 PM
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You can confirm siphon jet by monitoring the hidden menu #6.

The right tank liters will drop to about 1.4 L about when left tank will read about 27L.

That's about the point where the two sides of the "saddle" will be separate.

After this point, the right should stay the same while the left drops to zero.

If the right drops below "1.4" the siphon is not working properly.

When not working properly, the electric pump will push fuel to the left side faster than the siphon will push to the right side.

When siphon not working the right side will slowly drop from 1.4 to zero. If you see it get below 1, get some fuel ASAP. There's about 3.6L of fuel remaining once you get to 000 on the dash.
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Old 09-05-2023, 04:27 AM
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Hi Andrew, thanks for your input. I've been reading your thread about the fix!

So here's the thing, I do drop below 1/4 tank and fairly regularly at that. Especially if my wife has been driving as she won't fill up till its running on fumes! Several times on this trip in fact it would have dropped below 1/4 tank as otherwise we'd just be stopping for fuel 100miles sooner and making more fuel stops. In the last month we have filled up with the yellow light on and the OBC showing 20 miles range or less at least twice.

In this case then perhaps its just a dodgy fuel pump or filter? When we got it running on the tow truck the fuel filter did make the odd noise. Car has done 85k miles so barely run in compared to some of the Xs on here
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Old 09-06-2023, 08:37 AM
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The fuel filter on e53 is "lifetime" but the FPR integrated has an o-ring with about 15-18 year life expectancy.


I replaced my wife's filter and FPR when she had symptoms that led to FPR. During the post mortem discovered the 29 o-ring was at fault not the $70 filter/FPR.

Check the fuel pressure while engine is off. It should maintain some pressure overnight.

If the pressure holds, almost certainly the electric pump.

Do the hidden menu six to confirm Siphon jet is working properly.

What's the miles? The fuel pump has a life expectancy of 5000 hours. Look at your average speed (mine is typically ≈27) and multiply.

Eg: 27*5000=135000

On our two e53, they both failed about 133000 miles.

The FPR will mask pump failure. It gets weak at EOL and will get enough pressure to the engine but not enough to also siphon from the left side so it can be tricky to find the problem.

Ideally putting a T into the supply fuel line and the return is the proper diagnosis.
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Old 09-06-2023, 09:34 AM
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The car is on 85k miles but only the last 5k or so in my ownership. Not sure what the average speed/ fuel consumption would have been. Its been a city car most of its life though so its quite possible the fuel pump has done over 5000 hours. 20mph average speed over its life probably would be about right so its over 5k hours.

I'm happy enough to throw parts/money at this... but the harder thing is having confidence that its fixed because the car is working fine again right now.

How do I to hidden test 6? Can't seem to find the instructions for that. Do I need something to plug into the OBD?
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