Author Topic: After engine stalls, fuel backflows from return line thru IP to filter (& tank?)  (Read 667 times)

Reply #15April 10, 2021, 01:04:25 am

Otis2

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Right, that sound like a great idea, thanks. 

I wasn't keen to leave it completely open, although if VW did it stock originally, I guess it works OK.

I expect that you're talking about something like this:


Reply #16April 10, 2021, 11:08:58 pm

ORCoaster

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    Restoring a Caddy as time and weather allows
That filter is also perfect to put between the coolant reservoir and the line from the radiator to monitor coolant crud.  Kudos go to Libby for that one.

Also in lieu of clear lines, you can pop one of them in the line to the IP from the filter for observational purposes/ monitoring for air bubbles. 
Rabbit repairs to body damage need attention before trying to sell it in the spring

Reply #17April 11, 2021, 12:56:15 am

sgnimj96

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I use the old 300d pre-filter on the fuel line before the spin-on filter.   Shows if crud is coming out of the tank.
Sometimes RockAtuo has them for <$2. 
https://www.ecstuning.com/b-mtc-parts/in-line-fuel-filter-priced-each/0014777901~mtc/
If a lot of crud is coming out of the tank you can spray it out backwards and re-use.
Most of them are 50-70 micron
81 Scirocco 1.6D (conversion)    86 Gofl 1.6D      2003 Golf Tdi   1985 300TD

Reply #18April 11, 2021, 03:48:27 am

fatmobile

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 Right that's what I'm using.
 I keep picturing a bug crawling up that line and dying.
Or a wasp plugging it up.
 I've had and heard of several fuel tanks collapse when this vent is clogged.
Tornado red, '91 Golf 4 door,
with a re-ringed, '84 quantum, turbo diesel, MD block

Reply #19April 15, 2021, 02:44:02 am

Otis2

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Thanks again all, I am really grateful this forum still exists, and that so many of the old school players are still here.

On your recommendations, I bought three cheap Fram fuel filters for the project. 

Then I pulled out the T fitting for the hoses leading from the vapour tanks to the charcoal cannister, and popped a fuel filter into each of the two lines leading to the vapour tanks.  Charcoal cannister is now redundant, and I will pull it out when I get time.

I chopped one nipple end of two the Fram filters off, and then drilled them out to 3/16", to better match the I.D. of the hose from the vapour tank.

So, job done. (Well that, plus the new fuel tank, which is a b!tch of a job with getting the crossover tube and hoses into place in a 2wd Vanagon, I can assure you.  Probably had that thing up and down six times, with trial and error running the crossover and vent hoses.)

So, with a new Bosch spin on fuel filter filled up with fresh diesel, and about 15 litres in the new tank, I did a test start.

The engine flashed right up, and ran for a few seconds until the diesel in the fuel filter was exhausted, then it sputtered out to a stall.

Finally, I pulled off the aftermarket check valve, that was plumbed right before the filter. 

I replaced that check valve with the third of my Fram filters, tried to start it again, and all was perfect.

On testing the check valve on the bench, it was clearly blocked.

So I think that check valve was the key cause of my initial shut-down, air bubbles in the feed, the milkshake in the return line, and the odd suction reversing from the tank up the return line into the injection pump. 

I notice that the new Fram filter drains about half way a few minutes after engine shut down.  I guess this was the symptom that caused the previous owner to install the check valve in the first place.

Not sure whether it's worth installing another check valve, or whether I should just live with a little air in the lines on cold start.

Thoughts?

Reply #20April 15, 2021, 10:56:39 pm

fatmobile

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 Start it and drive it awhile.
  A week or so.
 Then look for air in the lines.
It can take awhile to get air out of the whole system.
 It likes to get trapped in the filter since air doesn't go through a diesel soaked piece of paper easily.
Especially a new filter since there is almost no pressure drop across it.
Tornado red, '91 Golf 4 door,
with a re-ringed, '84 quantum, turbo diesel, MD block

Reply #21April 18, 2021, 02:49:20 pm

libbydiesel

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No check valve is necessary.  The only time a check valve would be beneficial is as a band aid against a leak at the engine or against excessive vacuum on the tank side of the filter.
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