K-Jet fuel pressure test part 2

Earlier in the week I attempted to run a fuel pressure test on my 1979 280SE.    On further examination, I was pretty sure I had it connected up wrong.   The instructions call for the pressure gauge to be attached to the larger fitting on the warm up regulator.  The warm up regulator is hidden down to the side of the engine on the M110.   The bigger fitting is actually a banjo bolt on this WUR, so this time I hooked it up (hopefully) correctly.  My goal was to test cold control pressure.

testing cold control pressureThe readings made more sense this time.   System pressure seemed within specification.    Control pressure on the other hand was too high.    The warm up regulator also did not behave as it should.    The control pressure stayed high, and when the electrical connection was plugged in, it just got higher as the engine warmed up.    Once the engine was at operating temperature, removing the vacuum line stalled the engine. Noisy Pump

I’m not going to bother posting the readings here, as I plan to re-do all these tests.    After I stalled the engine with the vacuum line test, I noticed how noisy the fuel pump had become.   The longer I ran the tests, the noisier the pump became.   In addition, as well as getting noisier, the pressure started to fluctuate and the engine started to run roughly.

Previously, I ran the fuel volume test.   The test passed, but I still think the pump is on its way out.   The more I go over this car, the more I think it has sat for a while, and these things just don’t like sitting.  I wish I had heard this before I changed the hose and filter, would have been so much simpler to do it at the same time.

I don’t think changing the pump is going to be the fix for my issues.    It looks like I have a high control pressure issue even with a dying pump. The tests still failed when the pump wasn’t noisy and was passing the volume test.  The gauge was also pretty steady at that time.  However, It seems silly to go and spend a lot of money on a rebuilt WUR before fixing the obvious stuff and running the tests again.

I have a couple of spare fuel pumps from my 420SEL parts car.   According the previous owner, they were replaced just before the car went off the road.   I’ll try one of these and re-test.

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