SL/R129: Misfire/Water Pump
Thread Starter
Junior Member
Joined: Aug 2017
Posts: 30
Likes: 1
From: Los Angeles
1997 SL500 AMG
Misfire/Water Pump
I bought this 1997 two weeks ago knowing it had a misfire in cylinder 8. I pulled the spark plugs and found the one in cylinder 8 to be cleaner than the others (the other 7 were really fouled), whIch I understand is the result of coolant in the cylinder--but bracket that for a moment.
I replaced the spark plugs with the recommended Bosch copper non-resistors, cleared the code, but the CEL light came back on. I was going to replace coil #8 next but am I wasting my time with coils when the suspected coolant in the cylinder is probably causing the misfire?
the car has a visibly leaky water pump so I lose coolant (I have distilled water in the cooling system no antifreeze--fearing a bad head gasket I didn't want to spew coolant into the head).
there doesn't appear to be water in the oil.
the expansion tank is pressurized after the engine runs.
i suppose pressure testing the block should be next. or should I replace the water pump first? Do I need to replace the fan clutch too?
Any advice would be appreciated.
I replaced the spark plugs with the recommended Bosch copper non-resistors, cleared the code, but the CEL light came back on. I was going to replace coil #8 next but am I wasting my time with coils when the suspected coolant in the cylinder is probably causing the misfire?
the car has a visibly leaky water pump so I lose coolant (I have distilled water in the cooling system no antifreeze--fearing a bad head gasket I didn't want to spew coolant into the head).
there doesn't appear to be water in the oil.
the expansion tank is pressurized after the engine runs.
i suppose pressure testing the block should be next. or should I replace the water pump first? Do I need to replace the fan clutch too?
Any advice would be appreciated.
Member
Joined: Oct 2007
Posts: 109
Likes: 6
From: Seattle
2002 G500, 1961 190b, 2001 SL500 Sport
A bad water pump wouldn't affect the cylinders other than causing the damage in the first place. Before you buy a new water pump, pressure test the motor. Get an air compressor and a hose to put air into a spark plug hole from a leak down tester or compression tester. Pump up the bad cylinder to 50 psi with the plugs out. See if bubbles come out of the radiator tank or air comes out of the other spark plug holes.
Thread Starter
Junior Member
Joined: Aug 2017
Posts: 30
Likes: 1
From: Los Angeles
1997 SL500 AMG
I don't have a compressor so I will have it pressure tested. If I want to drive it anywhere, the water pump has to be replaced. Is it unadvisable to do an induction cleaning if the engine is misfiring ? Thanks for your time.
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