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Abrupt K-jet wierdness and what should k-jet fuel pump pressure be?

Started by raueda1, 24 June 2022, 12:33 PM

raueda1

Finally I'm back to this problem.  I had wanted to drive the car on a beautiful California road trip but it wasn't to happen.  But it was a blessing in disguise.  I just got the fuel line off and did an autopsy on the hose.  See pix below.

The first (hose 2) is the hose itself.  It was indeed just 4 years old.  Ovviously it's now curved, but nothing severe at all.  It appears to be fine.  No obvious cracks, splits, et.  But.....

The next (hose 1) is the hose bent by the banjo fitting.  Note the bubble-looking blob.  That's the hose cover separated from the rest of the construction.  That should never happen.

Finally there's the hose 3 autopsy pic.  I cut off the delaminated section and sliced it open.  Note the large cracks.  There were also lots of microcracks that aren't visible.  This kind of degradation should occur over decades, not years.  The hose construction is neoprene jacket over nitrile (NBR, Buna-N etc) liner.  Reinforcement is polyester I expect, but not sure.  Anyway, this is what you see after prolonged aging under extreme conditions.  Fuel contact doesn't do much to NBR and there's little direct oxygen exposure.  It's almost as if the NBR was compounded without the appropriate stabilizer package.  Or maybe it's the ethanol in the fuel?  Whatever the case, I find it pretty damn scary.

The new hose looks identical.  I'm going to keep a very close watch on it.  You probably should too.  I'll report back when it's all back together (assuming that this is the root cause of my pressure issues).  Cheers,
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

raueda1

Another quick thought -

Gasoline isn't very oxidatively stable.  It literally sucks up oxygen from the air.  This forms peroxides, which are deadly to rubber (among other things).  There were car fires back in the '70s as EFI systems were widely introduced and epichlorohydrin rubber was used in fuel systems.  Fuel oxidation caused epichlorohydrin (the fuel hose liner) to revert to bubble gum.  Seriously.  The result was adoption of nylon-lined fuel hoses.

Anyway, many of us store our cars for long periods.  This is a perfect storm.  I add fuel stabilizer in the fall, but who knows how effective it really is?  I shall study further....
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0