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Mercedes-Benz 1998 E320 - 160,000 Miles Strong
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Discussion Starter #1
Is this diagram correct?

I got a p0304 error I wanna know which coil pack to replace. Thanks
 

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'01-E320 & 02-ST2
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That is a correct diagram.

However, don't REPLACE the coil pack. Rather, start by swapping the coil from 5 to 4. If the misfire moves, it's the coil. If not, it's probably an ignition wire, though there are other possibilities.

Also, note that despite the specificity of the code, it may not be that cylinder; I had a pending 303 code that actually turned out to be a bad ignition wire on cylinder 4.

Good luck.
 

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Discussion Starter #5
That is a correct diagram.

However, don't REPLACE the coil pack. Rather, start by swapping the coil from 5 to 4. If the misfire moves, it's the coil. If not, it's probably an ignition wire, though there are other possibilities.

Also, note that despite the specificity of the code, it may not be that cylinder; I had a pending 303 code that actually turned out to be a bad ignition wire on cylinder 4.

Good luck.
I moved the coil pack and ignition wires from 4 to 1 and 4 still had problems what does that mean?? Thanks
 

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I moved the coil pack and ignition wires from 4 to 1 and 4 still had problems what does that mean?? Thanks
It means of course you'd still have problems, since you had them to start with. ;)

It's not whether you still have problems.

The question is whether the code moved. If you swapped the wires and coils between 1 and 4, reset codes, and still have the same code coming back, then it's clearly NOT the coil or the wires, true?
 

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Discussion Starter #7
It means of course you'd still have problems, since you had them to start with. ;)

It's not whether you still have problems.

The question is whether the code moved. If you swapped the wires and coils between 1 and 4, reset codes, and still have the same code coming back, then it's clearly NOT the coil or the wires, true?
Correct I swapped everything from 1 to 4 except the spark plugs and I also cleared the code. Right away I got the p0304 error whats it all mean?
 

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Correct I swapped everything from 1 to 4 except the spark plugs and I also cleared the code. Right away I got the p0304 error whats it all mean?
That means either you have a bad plug in that cylinder* (at least they're easy to access!!) or that the problem is not in ignition. If it's not ignition, then you could have a bad connection at the injector, or the injector itself could be failing. Unless you're 100% certain that both plugs are fine, I'd pull them next.

Oh, and be sure you have the a wire plugged into the a plug and b to b, as that will cause misfires as well.

Personally, I like to start cheap and work my way up, so I'd probably start by testing all of the ignition leads. Just do them one at a time; that takes longer but then you don't end up maybe creating more confusion.



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* We're both also also assuming that on your car your P304 code is really cylinder 4. As noted I had a P303 code that turned out to be a problem on a different cylinder, which I found only by testing each of the wires before going on to other things. If your car is reporting the miss on 4 but it's actually on 3 or 2 or 5, swapping stuff on other cylinders won't affect that. I'm hopeful that my car is an aberration, because otherwise what's the point of single-cylinder misfire codes?
 

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Discussion Starter #9
That means either you have a bad plug in that cylinder* (at least they're easy to access!!) or that the problem is not in ignition. If it's not ignition, then you could have a bad connection at the injector, or the injector itself could be failing. Unless you're 100% certain that both plugs are fine, I'd pull them next.

Oh, and be sure you have the a wire plugged into the a plug and b to b, as that will cause misfires as well.

Personally, I like to start cheap and work my way up, so I'd probably start by testing all of the ignition leads. Just do them one at a time; that takes longer but then you don't end up maybe creating more confusion.



____________________________
* We're both also also assuming that on your car your P304 code is really cylinder 4. As noted I had a P303 code that turned out to be a problem on a different cylinder, which I found only by testing each of the wires before going on to other things. If your car is reporting the miss on 4 but it's actually on 3 or 2 or 5, swapping stuff on other cylinders won't affect that. I'm hopeful that my car is an aberration, because otherwise what's the point of single-cylinder misfire codes?
Is it possible that my MAS is the culprit here? I now have the dreaded P0170 & P0173 codes as well.
 

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Is it possible that my MAS is the culprit here? I now have the dreaded P0170 & P0173 codes as well.
That's possible, but it seems more likely you have a couple of things wrong. Failing maf can trigger ther codes, but never heard of it triggering a misfire code in a single cylinder.
 

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Discussion Starter #11
Whats the correct range and setting to test the injector on a multimeter? I changed plugs and wires, then changed to new plugs problem remains at cylinder 4. Thanks
 

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Nominal injector resistance is 14-18 ohms. Set meter to lowest scale. If it shows out of range click it up a notch.
 

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Once again, thanks to Witek.

If the injector itself checks out, it may be the connector. Connector repair kits are inexpensive and widely available, which suggests failure is not an isolated event. That said, I don't recall anyone posting that as a fix, but too often folks don't follow up and report back.

Good luck.
 

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Discussion Starter #14
Well the issue is that in the mornings my engine runs rough then i get a CEL/CEE light I pull out my ODBII scanner and it shows P0304 then I run it a couple of times during the day and it disappears. I think its an injector but I needed to know what range to set the scanner on. I assume I can test the injector without having to pull it out of the rail? I'm so close to getting my smog check I only have 2 more sensors I need to fill the CAT and the SEC AIR.
 

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Well the issue is that in the mornings my engine runs rough then i get a CEL/CEE light I pull out my ODBII scanner and it shows P0304 then I run it a couple of times during the day and it disappears. I think its an injector but I needed to know what range to set the scanner on. I assume I can test the injector without having to pull it out of the rail? I'm so close to getting my smog check I only have 2 more sensors I need to fill the CAT and the SEC AIR.
You can check injector resistance by removing connector and measuring across two male pins. Check it both cold before you start it and then again after it runs normal.

You had manifold off of this engine. Have you checked for vacuum leaks near #4 intake port?
 
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