2001 ML320 Error Code 306... Need help - Mercedes-Benz Forum
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#1 (permalink) Old 04-06-2011, 05:58 PM
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2001 ML320 Error Code 306... Need help

2001 ML320 with 91K. I have had a very slight rough idle at times and been meaning to change the plugs / wires. Last Friday I was driving to work and had to accelerate to get on the freeway. Went up to 4500 rpms and the CE light came on. Read the code and it said 306 (mis fire cyl 6).

Ordered new (OEM) plug wires, plugs, and a coil pack for 6. Replaced all today and went for a drive. Same thing. Swapped new coil pack off 6 (cyl closest to drive) with 4 and same code (cyl 6 mis fire). What would cause this, it can't be a plugs, wires, or coil pack?

It only happens on hard acceleration and runs very rough until the code is cleared. Then it will run fine till hard acceleration again.

Any ideas? I am a little stumped.

Thanks,

Chris
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#2 (permalink) Old 04-06-2011, 10:08 PM
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Originally Posted by cmb1998 View Post
2001 ML320 with 91K. I have had a very slight rough idle at times and been meaning to change the plugs / wires. Last Friday I was driving to work and had to accelerate to get on the freeway. Went up to 4500 rpms and the CE light came on. Read the code and it said 306 (mis fire cyl 6).

Ordered new (OEM) plug wires, plugs, and a coil pack for 6. Replaced all today and went for a drive. Same thing. Swapped new coil pack off 6 (cyl closest to drive) with 4 and same code (cyl 6 mis fire). What would cause this, it can't be a plugs, wires, or coil pack?

It only happens on hard acceleration and runs very rough until the code is cleared. Then it will run fine till hard acceleration again.

Any ideas? I am a little stumped.

Thanks,

Chris
Planning on pulling the #6 injector and swapping with the #4 tomorrow to see if problems resolves.

If anyone has any other ideas would love to hear it.

Thanks

Chris
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#3 (permalink) Old 04-07-2011, 01:27 AM
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Injectors should leave a code even if the CEL is not on. What kind of scan tool can you get your hands on?
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#4 (permalink) Old 04-07-2011, 02:22 AM
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Switching the injectors would be the logical approach, but that same approach should have been used on the coil and wires.

Before you remove the injector rail, with the engine running, spray some Brake Cleaner around the #6 injector and on the intake manifold to check for air leaks.

Remember about the clip on the air intake pipe when removing it. Make sure you lubricate the O-rings prior to re-installation.
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File Type: pdf R&I Injectors.pdf (23.5 KB, 131 views)
File Type: pdf R&I Air Intake Pipe.pdf (33.4 KB, 108 views)
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#5 (permalink) Old 04-07-2011, 04:29 AM
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I should have been more specific. Dead injectors can leave a code. An small air leak
most likely will not. Follow 43's steps.
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#6 (permalink) Old 04-07-2011, 09:05 AM
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Switching the injectors would be the logical approach, but that same approach should have been used on the coil and wires.

Before you remove the injector rail, with the engine running, spray some Brake Cleaner around the #6 injector and on the intake manifold to check for air leaks.

Remember about the clip on the air intake pipe when removing it. Make sure you lubricate the O-rings prior to re-installation.
Thats for the suggestions, I will dig into it tonight. Only reason I didn't swap the coil pack before ordering was that I was heading out of town and wanted to have all the parts needed when I returned so I ordered an extra coil pack. It was just time to do the plugs / wires while I was torn into it. Your right though, I should have swapped the coil packs before ordering...

I am using a Launch Tech CReaderV. I bought it for my truck, but it's suposed to read all codes. Might be time to download the update and see if it pulls any other codes. The only one it was pulling initially was the 306.

Thanks,

Chris
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#7 (permalink) Old 04-07-2011, 09:14 PM
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Thats for the suggestions, I will dig into it tonight. Only reason I didn't swap the coil pack before ordering was that I was heading out of town and wanted to have all the parts needed when I returned so I ordered an extra coil pack. It was just time to do the plugs / wires while I was torn into it. Your right though, I should have swapped the coil packs before ordering...

I am using a Launch Tech CReaderV. I bought it for my truck, but it's suposed to read all codes. Might be time to download the update and see if it pulls any other codes. The only one it was pulling initially was the 306.

Thanks,

Chris
Pulled #4 and #6 injectors. Took all of about 15 mins to get them out. Cleaned both and put them back in (swapped). Spent 2 hours trying to get the little clips on the injectors. What a total pain in the ass.

Went to start and spit 1/2 gallon of gas all over the floor. Appears to be leaking at the #6 injector. Looks like another day tareing into the ML.

-Chris
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#8 (permalink) Old 04-07-2011, 09:22 PM
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I should have been more specific. Dead injectors can leave a code. An small air leak
most likely will not. Follow 43's steps.
Gas is leaking from the top of the #4, #5, and #6 injector. I must not have got the clips that hold the injector and the fuel rail back on right. And tips? I have it over the top of the wings on the fuel rail on all three.

Thanks,

Chris
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#9 (permalink) Old 04-08-2011, 05:18 AM
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Either injectors are no seated back in the rail or o-rings that seal them got damaged. Part number for o-rings 019 997 13 48 x12.

Don't use sharp objects to remove o-rings. Fingernails or plastic only. Lubricate with dab of vaseline.
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#10 (permalink) Old 04-08-2011, 05:24 AM
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Gas is leaking from the top of the #4, #5, and #6 injector. I must not have got the clips that hold the injector and the fuel rail back on right. And tips? I have it over the top of the wings on the fuel rail on all three.

Thanks,

Chris

Did you ignore reading/printing the instructions on R&I Injectors? There are precise instructions about placement/attachment of the clip .

Go to the dealer and purchase 12 O-rings and three new clips. DO NOT SUBSTITUTE ANY OTHER O-RING. Make sure you oil the O-rings before installing.
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