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2001 ML55 AMG
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15 Posts
Discussion Starter #1
Hi all,...been a while
picked up a very nice 2006 ML350 with a few issues..priced accordingly. In limp mode on pickup, the lady said her mechanic told her it was missing and would cost around 2K to fix; she did not have the bread to cover it so had to let it go.
Ran a scan on it and pulled up a lot old trivial background stuff.. however, after clearing the data it only kept bringing up P0304 consistently, occasionally P0306, P0305, P0306 & P0303.
Removed the plugs (Bosch) and saw some had the earth tapped over to get the gap correct (worn) Bought a new set and fitted, started up and only 304 came up...maybe a Coil pack swap with a known codeless one. Nup! repeated this for a number of times, noticed that #4 plug was coming out wet with no sign of combustion. The cycle was clear codes, wait, startup - ran smooth enough out of gear, then CEL started flashing at around 8-10 secs then on consistently.
Got under the car while running in driveway and Infra red gun on the rear of the cats both sides. Bank1 was 150C and bank2 was 40-60C. The cat would not be blocked as another ML I had was...throwing misfires on RHS bank and going int limp mode everytime a bit of throttle was used( cut the top off the cat, removed material and welded it back up..problem solved)the cat material had worn enough to turn 90degrees and block the outlet like a plug.
This one is only showing P0300 & P0304. The wet plug may have been a leak (and confirmed) by checking the rail pressure after shutoff and sitting for a bit..nothing!
Removed the injector and cleaned it, operated it with carb cleaner firing through it. It had decided that the heating of the Bank2 O2 rear sensor was not happening for a bit.. checked the resistance and the voltage, put it together...didn't come back.
That brings me to where I currently am. My query is- how does the loom supplying the voltage and signals to #4 coil get checked, as this is the only consistency I am rotating around. Has Plugs, has fuel; either the wiring to coil #4 may have some issue(of which I am not full bottle to check) or the cylinder pressure in #4 is below par, however I do not have a 12mm adapter to fit on my compression guage to check it..
Any input would be appreciated as the missus wants to drive it but only when sorted reliably!! (as one does!)

Cheers
Wintech
Perth
 

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Registered
2001 ML55 AMG
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15 Posts
Discussion Starter #3
Can’t you just check for spark using a spark tester or the visual method?
Actually, all the other coils have tested true; in running static, and under load. The only consistency is - that any coil tested on cyl #4 shows a P0304 code. Whereas; they run fine on any other cylinder...same goes for individual plugs.
 

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Registered
2001 ML55 AMG
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15 Posts
Discussion Starter #5
The CEL should be flashing. Is it?

Please read PDF.
Hi 43sqd,
the pattern is... clear codes; restart engine. 3-5secs of running then CEL flashes and then remains on solid. P0304, P0300 showing in DTC's
 

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Premium Member
02 ML320 06 ML500
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16,843 Posts
When the CEL flashes, it is telling you that your CATs can be compromised. Raw gas, without being burned is going through the exhaust manifold and then through the CAT.


Are you sure that there are no other code/s?
 

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Registered
2001 ML55 AMG
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15 Posts
Discussion Starter #7
43sqd-
no other codes consistently coming up at all regarding the misfire other than the P0300 and P0304.
I did a freeze frame on the warm-up and got (P0128) Component Y110 (Three-disk thermostat valve) jams in opened position. : Coolant temperature rises too slowly. I doubt that could be the main contributor, but will be looked at.
One thing I did notice is that the, temps taken on the outside of the front cats are dramatically different for a misfire of one plug. 4-6 bank measures 55DegC and the 1-3 bank 180DegC. I did have a W163 320 throwing misfires on 1-2-3 and going into limp mode. that was due to a front cat crumbling and turning 90deg to the airflow! removed the top of the cat, removed material and rewelded the muffler and problem solved! I have already checked this one for the same problem with a borescope through the O2 sensor and intact and clean.
Working my way through checking the resistance of the injectors and wiring atm. Hoping for something to become more apparent!

Cheers
wintech
 

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Premium Member
02 ML320 06 ML500
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16,843 Posts
Please read YELLOW in PDF. When the eng. is cold at start up, more fuel is injected until operating temp. is achieved. The ECM will reduce fuel in stages according to the coolant temp.

If the ECM continuously sees that the eng. is still cold it will continue to inject more fuel until too many misfires are recorded in one or more cylinders and then shut down those cylinders.

Replace the Thermostat, no aftermarket.
 

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