nickf109

Ok guys, so I'm having an issue that my mech can't seem to figure out. It all started a couple weeks ago when my gas light came on late at night and I stopped for gas. I just about filled my tank up when my CEL came on and the engine started shaking bad. Found out that cylinders 5-1-8 were misfiring. Mech told me to change out the spark plugs so I did to Denso long life iridium. About a week later after I filled up again from E a diag said that 5-1-8 were misfiring again and had a random misfire a few times. I'm going to change the coil packs for 5-1-8 but I'm afraid it'll happen again when I go to put gas in again. Could it be a fuel pump or injector issue? Maybe head gasket bc it's 2 adjacent cylinders constantly misfiring? luckily I have extended warranty but worried that MB or my mech might just blow it off as a coil or spark plug issue like they have been.

thanks guys! any and all help is needed!

BLKROKT

What are the codes

nickf109

The codes I remember were
P0305
P0301
P0308

I'm not sure what the random fire code was honestly. :/

Alex.currie44

When this is happening are you seeing any evidence of significant amounts of steam - i.e. much greater than on cold start up or what is normally seen on a cold day?
From a couple of experiences when a head gasket goes and coolant leaks down into the cylinders thermodynamics usually occur and the water is converted to steam under pressure which just billows out in the exhaust.
Those codes are misfire in the cylinders you are seeing the misfires in.

realjones88

Take the car in and tell them to fix it...isn't that the whole point of the warranty?

Common reason for misfires does seem to be dead coil packs.

Alex.currie44

Must admit I too wondered what the extended warranty was doing for him if he was not pressing down on the problem with the dealer and they told HIM to change plugs.

BLKROKT

Bad gas

nickf109

There does seem to be a little more exhaust fumes than usual.....but as for the warranty, not even MB wants to start fixing anything until they know for certain what the problem is, that's why I'm looking around. I've brought it in to them twice and they told me to change the spark plugs.....the MB by me has the worst customer care sadly. So hence why I'm in this pickle here.

Alex.currie44

I would suggest it is not. Bad gas would cause not only 5-1-8 to misfire but the other 5 as well.

SuperFastYo

Try swapping coils to see if the issue follows the "problem" coil. If it doesn't pull spark plugs, inspect their health and check the gaps on them. If neither drop the car off at the MB dealer, get a loaner and tell them you're not coming back till its fixed.

Also you can probably contact big boy Merc and inform them of the the terrible service you're receiving as they will not address the problem and keep attempting to sidestep you. If its a sparkplug issue then they better prove its a sparkplug issue.

C1Forged

Run some injector cleaner in your next fill up and try again. Bad gas would do more damage, or conflict more cylinders. I doubt its a spark issue since it only happens when you start from a full fill up. A spark issue would be more consistent of a problem, and less situational.

ItalianJoe1

Does it only misfire the first time it starts?

Have you tried not running the car totally out of gas? Fill up when it reaches a 1/2 tank and see if it still does it.

nickf109

It'll misfire whenever I go to put gas in. When I filled up, the misfiring happened as the car was idling at the gas station. After going back and forth to Benz and my mech the misfires stopped at around half a tank. Thinking it was just a fluke, I drove it to E again but only filled up to half and same thing, as soon as I started pumping then the misfires happened again. I started it up today and it's not misfiring, only the CEL is on and there was no lagging or loss of power or shaking. That's what makes me think it's a fuel pump or injector problem.

ItalianJoe1

Are you filling up with the engine running?

It sounds like you have a faulty purge valve, sticking open and allowing the engine to flood with fuel vapors during refueling. Proper diagnosis is needed though.

It's also possible, you've got some crud in the bottom of your fuel tank that is stirred up by you pouring in new fuel. Try filling up without the engine running (you are supposed to do that anyway). See if it still acts up.