I see. Hmm, absent computing the mileage on the pump, anybtips on determining its the fuel pump or jet pump, if a visual inspection doesnt show anything?

Jet pump / transfer pump troubleshooting
 

The only way would be measure the pressure on the return line to the jet pump. I think supposed to be 15-20 psi but that's fuzzy memory. It's easier to open the tank and disconnect the hose and activate the pump. (Hose pointing into the tank). It should spray like Fire hose.

On second thought: pull outlet hose and hook directly to a pressure gauge. I don’t know what the psi is supposed to be but significantly more than 50. 60? 70?

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Thanks for the suggestions Andrew!

Not been in the mood to fiddle with it lately, but will update when I do get around to it.

The first thing I would do is prop up the left side sender with a couple of sticks and have a look to see if there is any fuel spraying out of the jet pump feed.

After that if you can prop up the pump on the other side far enough to see if there is fuel flowing from the relief valve (on end of the third hose going back to the fuel pump well) that should give you an idea of weather or not the pump is providing enough flow for the jets.

Have a rag handy. The spray out the o-ring went right into my phone camera as i was taking a video to show people that exact diagnostic.

That is the best way to see if the o-ring has failed though. Not difficult and instantly know.

If it's not spraying, there could be blockage in the jet pump and bypass the bump though the pressure relief valve.

That all said if your pump is old that's the prime suspect.

Old pump will push less and less force over time, the FPR hides this detail from you until the jet pump doesn't get enough flow to siphon from left to right and you get identical symptoms of jet pump failure.


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Thank you gents, for the additional info!

Hope to get around to this soon.

Well, I got the courage to test drive and observe things.

I put in half a tank and now fuel levels are ok both sides, enough to drive around. But that's to be expected.

What I did notice is it is definitely low on power. I noticed it was a bit low previously but a lot more pronounced now. Flooring it you get big time hesitation and it does not really want to go. Easing into throttle you dont get that, but still down on power.

Not a fuel supply to pump issue as when this was happening the OBC was showing fuel supply on both sides of pump and there was a lot at the fuel pump side at the time this was happening.

Does this look like the fuel pump @andrewynn?

I've honestly never had a pump soft fail on me, it always was a totally dead pump.

andrewwynn - E53 fuel pump / siphon fix

Looked it up for ya! I'll need the info next month. I plan to install a new fuel pump after installing a hitch and rear wheel bearings.

Siphon jet is not an issue above flood stage (≈ 27 L). Siphon jet will also not work properly when electric pump is weak.

Anybody that has had a pump fully fail most likely had a soft failing pump for most of a year. They very rarely just quit. Brushed motors almost always lose torque slowly as their brushes wear out.

The FPR will mask a soft failing fuel pump. The signal will be when the siphon jet doesn't get enough excess fuel back from the FPR but the symptom is exactly the same as leaking siphon jet.

Testing fuel pressure at the rail while performing the throttle moves you described can help confirm fuel pump is the issue. PSI should be extremely stable only a full jab of throttle should exhibit a tiny dip in the psi.


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Got it guys, thanks for the links and additional comments!

Spoke to my indy, we worked out how to hook up his fuel pressure gauge setup so will set up a date to start diagnostics.

Hope to get it running at 100% soon!