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Old 06-04-2021, 01:02 AM
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andrewwynn andrewwynn is offline
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Join Date: Jun 2015
Location: Racine, WI
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Last Friday night while attempting to drive 1/2 mile, car stalls, refusing to restart.

Pull out foxwell and command the pump on; I hear noises but definitely not normal.

Fortunately I had a spare pump, less fortunately, it was 75 miles away.

Back to fortunately; my best friend happened to have the spare in his garage and was free the next day to drive it to me.

Had only one complication swapping the pump; the center seat belt was locked and I couldn't figure out how to release it and my "always with" socket set under the passenger seat was out because I used it to remove the stiffening plate.

So: utility knife to the *rescue*.

Replacement genuine but used pump worked great and back in action, I also took the opportunity to fix my left sender unit which only went down to 7.8L so the car would never go below 30 miles to empty.

So that issue resolved.

However; today driving about 40 minutes to job site, car stalls exactly same symptoms from 5 days earlier! WTF.

Scan showed typical errors from gas related stall but the more interesting part; pressing on gas test point valve pin and air comes out like venting a tire! Lots and lots of air!

I pull up test six and it shows 40L which is way higher than the isthmus between the tanks and the right side was reading zero.

(That is physically impossible without something broken).

I figured I must have pulled the discharge hose from the right tank when I fixed the level sensor on left tank so I open the right side first since it's a much better view of the siphon jet outlets.

Crap; they are ok, but I did visually confirm the right side was bone dry, not 4oz of fuel at the bottom. 4 paper towels would have made it dry.

So: off to the left side to solve this mystery;

Pulling out the sender unit the problem becomes instantly apparent;.



Holy what the fug!

Somehow I managed to get the "foot" of the sender unit between the two hoses from the aft siphon jet! The float arm was caught at apparently 40L or so.

The silver lining;

I figured out how to remove the resistor unit from the sender unit to repair it without removing the sender unit (it's non trivial to unclip that thing and not mess up the seals, one that is plastic on plastic).

So after refurbishing the resistive unit and testing the full sweep with test six, I put the thing back in and put the sender unit back in non moronically this time!

Drive to gas station with 2g of gas a brother delivered to me, I just finished fixing the issues when he arrived

After repair the left side read 1.4 which is a bizarre coincidence being what the right side will read at flood stage.

Minor quibble; 1.4 extra liters vs. 7.8 won't throw my DTE off

The real bonus is the only way to really test your siphon jet is to drive the tank dry which nobody should ever do on purpose.

The result; siphon jets working perfectly! There was not 300ml total both sides of the tank!

I'm a moron for a day for not watching test six after fuel pump replacement! Rookie mistake!

I would have immediately noticed left tank not dropping and especially when the right tank gets below 1.4L. (that's reserve fuel only).

When operating correctly, when right tank says 1.4 you actually have 5.0, starts dropping below that, it's time to immediately get gas and confirm your siphon jets are working.

On the 2g trip, the right side measured 0.7 to 0.9L even though we put in 7.6!

So only five liters fits in the right side untill the left fills enough to flood over the isthmus, so all things equal any amount over 5L should get you a reading of 1.4L, however since there is a lot of fuel pumping around in circles, and into the left side to get siphoned to the right, the right side will read lower while all gas is depleted.

As long as test six will show any value in the right tank, you should be able to drive ten miles.

A sheriff stopped to check on disabled car, he was a little surprised when I said I've already diagnosed the problem and should be fixed in 20 minutes (using only a crowbar and 10mm socket), and brother on the way to deliver gas.

So the moral of the story; always always check test six after anything fuel supply related; always!

And the silver lining; the only way to know for sure if siphon jet is fully operational is to drive to empty so mine passed.

(The far better way is to just monitor test six and drive until right tank reads 000). If there is any reading on left side there is a problem with level sensor or siphon jet o-rings. Until you refurbish your siphon jet o-rings you should do that test twice a year.

When the o-ring fails, the right side will drop with left side reading 15-20L

Miraculously I had only half load of tools so back seat was up!

Learn to read test six and when needed fix your o-rings.
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2012 E70 • N63 (wife)
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