Jet pump / transfer pump troubleshooting
 

So I stalled at a light today in the 4.6is. Felt like a fuel issue. Gauge a bit below 1/4.

Checked OBC and 0 fuel at the right side and about 14 liters on the left. Called a friend to bring me a couple of gallons of gas and ended with about 7 liters on the right. X started instantly.

Drove straight home to change cars while watching the OBC. Fuel level on the right was varying especially when going up the parking ramps but didnt drive long enough to verify jet pump operation.

Any tips on troubleahooting thia problem? Jet pump was replaced maybe 5 years ago.

You just did all the necessary diagnostics. Jet pump is not working.

You can’t have zero right with anything in the left side when the pump is working.

More than likely just the o-ring has failed and with it being so young, your can likely fix it by just open, put the same o-ring back in and prop it with a zip tie to prevent it from opening back up.

I’ve done a few of these it’s always exactly the same. Look for my thread on the topic.

Search awr-fix in the title to find it.

There’s a small chance you aren’t getting enough pressure/volume from the main pump which can bring the same symptoms.

On e10 gas, life expectancy is 5000 hours. Multiply your avg mpg by 5000 and compare to your odometer. Eg: 14*5000=70,000 since the last fuel pump. If it's close or over that'll be far more likely candidate.

It's a little tedious but not terrible to pull the fuel sender from the left tank to confirm our deny early failure but the design has a fatal flaw that will kill every one.

Our 2001s both had this failure like clockwork.

The full diagnostic is: add a little more fuel and watch the right side. Or should settle to ≈ 1.4L on level ground steady state.

It should stay exactly the same until the left hits zero.

If the right starts to drop and especially gets below 1.0 jet pump is not pumping.

When it first starts, this might happen at 5-10L because the depth helps the pump.

Full failure, no pumping at all is about 27L.

It takes quite a lot of fuel flow going in circles from right to FPR back to left then to right to keep the jet pump happy so the electric pump failing will cause the same symptoms but it's much harder to diagnose and I've never found a spec of how much head the pump will make when blocked off or what the zero back pressure volume should be to test.

The usual test for electric pump failure is: pull the jet pump test for leaky o-ring, if that's good, check psi at the rail and confirm it's 50.0 no wavering.

While jet pump disconnected, you can turn the key on (pr start car if had start assist so no prime at key on) and watch the flow rate back from the FPR. It should be crazy pressure like a fire hose its supposed to be like 15 psi.

If that returning pressure is not strong and o-ring looks ok on the jet, it's usually the electric pump. The fuel filter can last 400,000 miles it's gigantic. FPR failure will usually lose pressure to the engine increasing the jet pump volume but there's a tiny chance it can fail where it will just close off to the pump itself and reduce the return flow but that's pretty theoretical I've never seen a mention of it actually happening.


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Thanks, Andrew, for that comprehensive reply!

One thing I think can cross off that list is the FPR and filter. Had a long crank problem and after putting on a check valve to no effect, put in a new OE fuel filter/FPR assy and replaced the rotted FPR hose. That cured the long crank to start problem. Was done less than 500 miles/2 months ago.

Interesting. My '01 X (M54) started to stumble, but not stall, on sharp turns, after I replaced the dead fuel pump last fall. Even with a full tank, and 50psi on a gauge.

I was going to replace the fuel filter/FPR assy and the FPR hose, as well as try a cheapo Amazon pump (just to see if the new Hella pump is the culprit), but I've been having health problems that keep me from going under the X. I think I might be able in a week or so.

My X never had a start problem, before or after the Hella pump install, nor the stumble. The old pump was OEM, as is the filter (both at 212k miles), and it ran great until it died while being inspected. The left side sender hasn't been touched.

So, I'm wondering if our similar fuel delivery problems might be solved the same way. Following....



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It's worth a try workingonit, since you have the filter on hand already.

I did want to properly diagnose my long crank before putting on a check valve and filter, but the fuel pressure gauge I had access to didnt have an adapter that fit the M62 fuel rail, so I went parts cannon on it based on posts here.

I may have to scrounge up a fuel pressure gauge adapter so I can do the tests Andrew is suggesting.

Hope your feeling better and that the filter fixes the problem with your X.

Or keep fuel level > 1/4 at all time and never worry about the O-ring issue...

I'm betting the real problem was the fuel pump.

Weak fuel pump wasn't pushing hard enough to push the jet pump up do its job


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27/90=0.3 1/3 of a tank. 450 mile range is now 300. Not a great option.

Once a year drive with test six running to confirm jet pump is working. It's silly to set up the next guy for failure. Wife did that to me. She always kept over 1/4 because she " ran out of gas" at 1/4 tank but never told me. I ran out of gas with DTE 90 miles because of the issue.

1/4 tank isn't a suggestion but a requirement until it's fixed but it's not a hard enough fix to warrant 50% more gas station stops.


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Could be, but since replacing the filter/fpr have gone to 1/4 and below a few times. Problem only started when I started this thread.

When it first starts to fail you can get to near empty. It probably takes a couple years to work from 1/20th of a tank to 1/3 of a tank just that most often people catch it about 1/4.


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