Engine misfires following heater hose leak - Mercedes-Benz Forum
 
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#1 (permalink) Old 10-10-2009, 03:11 PM
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Engine misfires following heater hose leak

I had the plastic heater hose flange crack high on the driver's side firewall (see photo for location of leak). This covered the engine in radiator fluid. I replaced the flange (thanks to another post on this site) but now the engine is misfiring. There were 3 codes: misfire on cylinder 5, misfire on cylinder 6, misfire on multiple cylinders.
There were not any puddles of coolant around the ignition wires or coils when I pulled the cover but I wonder if the steam could have shorted something out - especially since the problem seems to be the last two cylinders close to where the leak was. Any thoughts on what might have been damaged from the drenching?
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#2 (permalink) Old 10-10-2009, 03:56 PM
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Do those two cylinders share the same coil? If so, maybe that is the issue.

You caught things fast enough and the car didn't overheat when the hose burst, right?
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#3 (permalink) Old 10-10-2009, 04:32 PM
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take the plugs out, check to see how they look. also check the wires and the coil packs for the missing cylinders.
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#4 (permalink) Old 10-10-2009, 11:25 PM
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I checked the ignition wires and coils - they seemed fine and there was no signs of their getting soaked. Still, I wonder if the steam was enough to short the coils and damage them. Just trying to get other informed suggestions before I start replacing coils. The two cylinders do not share the same coil, but they do attach to the two rearmost coils. Is there anything else on the driver's side of the engine block that could be damaged by the coolant/steam that would cause misfires?
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#5 (permalink) Old 10-11-2009, 01:26 AM
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your wiring harness to the coil packs runs right under there, if the insulation is punky getting soaked with antifreeze could cause your problem...

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#6 (permalink) Old 10-11-2009, 11:51 AM
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There are six small electrical plugs along the driver's side of the engine that are exposed and would certainly have gotten wet. Any idea what their function is?
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#7 (permalink) Old 10-11-2009, 07:04 PM
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Just to update - I swapped the rear and front coils and the misfire code moved from the rear to the front as well. Thanks to liquidusculade for this suggestion in another thread. I will go ahead and replace all of the coils, ignition wires and plugs at once just to make sure nothing else was potentially damaged.
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#8 (permalink) Old 10-14-2009, 06:51 AM
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...and of course, right under that broken plastic heater flange is the cable running to the crankshaft angle sensor. Make sure the cable and sensor connector are dried of coolant...
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#9 (permalink) Old 12-13-2009, 08:46 PM
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I swapped out all three coils just to have them all the same and the problem disappeared. Given the location of the leak the steam must have shorted the rearmost two coils - one of those quirky things. Anyway, I could not have done it without the help of this site. Thanks to all who contribute!
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