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sprinkles08
sprinkles08, ASE Certified Technician
Category: Mercedes
Satisfied Customers: 22132
Experience:  ASE Master and Advanced level certified. Factory trained with 15 years dealership experience
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1998 S 320. Car sat months. Low power, would occasionally

Customer Question

1998 S 320. Car sat for 9 months. Low power, would occasionally cut out once at idle, about twice every 5 minutes, as if a cylinder missfired. Had a P325 B1 knock sensor circuit code. Added Seafoam can to 7 gallons of fuel and drove 75 ***** *****. Then I accelerated harder on hwy, and immediately got constant miss on one cylinder. Shut it down for 10 minutes, re-start and constant miss was gone, returned to running the way it was, with the occasional miss, but this time set off P0304. Also filled up with full tank of fuel. So replaced that coil with MB part from dealer. Ran great! No more intermittent miss at idle, and could rev at speed. After 20 ***** ***** decided to wash engine. Was pleasantly surprised that car continued to run strongly. Drove 10 ***** *****, parked overnight, started, but after 10 seconds poor idle, and poor accel, but much better over 3500 rpm. Now has P0300, 302, and 304. Please help!
JA: Thanks. Can you give me any more details about your issue?
Customer: Billy, I thought that was pretty detailed! What would you like to know?
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Submitted: 1 year ago.
Category: Mercedes
Expert:  sprinkles08 replied 1 year ago.

Hello and welcome to JustAnswer!

There are quite a few things that could be causing your misfire. It could be an ignition issue, a fuel issue, or a cylinder sealing/valvetrain issue. If it's intermittent or varies in intensity then odds are it isn't a valvetrain issue.

The most common cause of misfiring in this way would be spark plugs. Were the plugs replaced on the cylinders that are misfiring or just the one coil?

Fuel has a shelf life of about six months in ideal conditions. Has the old fuel been ran out of it now and the tank filled to see if it runs any better?

Customer: replied 1 year ago.
Forgot to mention I did replace ALL the spark plugs when I replaced the #4 coil, with Bosch. Looks like cylinders 4 and 2 run from the same coil, and WIRE, so I just ordered a new complete wire set, new ones will be Bosch. Wires definitely are old. About fuel, yes, I have run about 300 miles, so old fuel should be gone, or very diluted. Does water float or sink in gasoline? Thinking best to see how new spark plug wires work out. Will install them over the weekend, and let you know. If any other suggestions, please post. Just another idea: There does not seem to be a way to separate the 3 spark plug wire..they all fire right after each other. Has there been a problem with induction firing between the wires on these engines? Thanks.
Expert:  sprinkles08 replied 1 year ago.

Water would have a very hard time passing unless you used an additive with alcohol to allow it to bond to the gas.

Did you note any difference in condition of the plugs on the cylinders that are missing?

Customer: replied 1 year ago.
No, because at the time I changed them the car only had an intermittent miss, and light hesitation upon light acceleration. The incident when it went to a heavy miss after accelerating hard on the hwy, and set off the initial P0304, was short, and cleared up after cycling the ignition.
Expert:  sprinkles08 replied 1 year ago.

It may have shut the injector drivers down if it ran fine again after a key cycle.

it seems you're describing an ignition miss with the symptoms and intermittent nature. It's possible you could have injector issues but you'd need to swap the injectors to other cylinders and see if the miss moves. It could also be a cylinder sealing or valvetrain issue but that shouldn't be intermittent and would require compression tests. You can spray down the wires to see if they arc, you could test their resistance or try swapping them around to other cylinders, but if you already have a wire set I believe it would be best to go ahead and replaced them and re evaluate it.

Customer: replied 1 year ago.
Will do. Wires are on the way, and will replace them over the weekend. Will post results!
Expert:  sprinkles08 replied 1 year ago.

Great!