Posted this on benzworld...but think there are more actual mechanics here...

Bought a 2002 clk55 high miles. Ran pretty well. Over last month or so, it started to lose acceleration. Finally seem very slow. Would hesitate a good deal at lower rpm...would start to accelerate a bit once revs were up.

Mechanic friend and I started troubleshooting. Have a code scanner. Was getting slow signal from 02, but this was cleared and has not come back. Had run some regular fuel. Some premium fuel added made maybe a slight difference. Fuel filter, spark plugs, no change. Seafoamed it and slight difference.

When changing fuel filter mechanic said fuel pump was a bit noisy. So one was ordered.

Guess I made a bit of mistake changing the fuel pump...as gas was lost from engine to fuel pump. Does not want to prime.

More details...the old fuel pump ran fine and started fine...just did not accelerate as it should have and did in the past.

After I put in new pump...car did start...I drove car a short bit and it was acting like air in fuel lines...major stumbles if you gave it some gas. Worse than before. Parked car and let it idle to warm up the engine and perhaps clear air in lines. After a bit it died.

Could not restart...though it did attempt to start a bit.

Was impossible to hook fuel pump up wrong. Wires were sized big and small so could not put them on backwards.

Decided maybe it was a bad replacement pump...so I put original one back on...but no change.

When I put on original pump...there was pressure on the fuel filter side of the fuel pump. I had no problem with fuel running out of the engine side of the lines this second time...though I was careful not to lower then fuel line so the fuel could run out.

Throttle position sensor was replaced before I bought it. Hooked up to scanner could watch lot of data from the car...everything seemed to be fine...but no idea what range the data should fall in.

Opened valve on fuel rail and some fuel came out...perhaps need a second person to open valve while trying to start car to purge fuel lines.

I know purging should not be needed...but probably a couple pints of fuel came out.

Had high hopes that fuel pump was the problem...and still have hope...once get fuel flowing again. Even tried some starting fluid. Would run...for a short bit...but did not prime the lines. Tried turning the key on and off many times without attempt to start to prime lines...but did not help. Opened fuel cap to try to help relieve vacuum to help it prime...but also did not help.

Ideas welcome



Tried cleaning maf...

Thought it might be throttle position...but that was replaced before I bought it...and live data from code reader looked good.

Going to try to get it to prime...somehow...any suggestions? Real mystery is original issue.

Still sounds like fuel pressure ISSUE.

Have you or tech checked the fuel pressure? should be 55psi measured at injector rail.

The fuel filter is the pressure regulator, possibly the new one is the problem.

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Trying to remember if it is possible to install the filter backwards on this model?? Should have a flow arrow on it, check it out.

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