CDI glow plug replacement- Buckle up, your'e in for a fun ride! - PeachParts Mercedes-Benz Forum

ROLLGUY · #1 06-20-2020, 03:29 PM

My niece owns the CDI that got me introduced to the W211 platform years ago. I bought the car from a dealer in Ohio for cheap (at the time) because it had the "Black Death". I repaired it (thread here somewhere), but there was also a broken glow plug causing a CEL. I got the CEL to go out by faking out the computer with the installation of a glow plug screwed into a nut welded on a tube, and bolted to the intake manifold. That satisfied the system for years, until January when another glow plug went bad. I decided to just replace them all, and deal with whatever it took to get them out. She ordered the parts, and then the COVID-19 thing prevented her from getting the job done until this week. She had a week off, so she scheduled the job.

I ordered a broken plug removal kit CDI broken glow plug removal tool- how does it work? and watched a few videos.

Ready or not, here we go!
I first removed the covers, and then the fuel rail. I did not remove any of return hoses, there was enough slack to get the rail out of the way. I covered all the fuel nipples with tape, and later with some caps when the tape came off. Of the six plugs, one needed the complete treatment using most of the tools in the kit. One came completely out without issue, the other four came out from the threads, but were stuck with carbon on the shaft.
With the four plugs out as far as possible, I filled the wells (area around the glow plugs) with PB Blaster. I applied more a couple times while I worked on other plugs.

The photos may be a little mixed up, but the entire job will be explained, even if the explanation does not match the photos.

ROLLGUY · #2 06-20-2020, 03:53 PM

With the plugs soaking, I worked on the worst one first. The kit came with a guide that is supposed to fit in the well of the head. I inserted the guide, and it was so tight, I worked for several minutes to get it out. Once I got it out, I decided to grind it down a bit so it would fit snug, but still able to remove it by hand. The next problem was with the step drill. The slot in the drill was not deep enough for the set screw in the tool holder to go in far enough, so I ground the slot in the bit deeper. I had to use a longer screw, then cut it off and grind it smooth. This tool holder gets chucked into a drill, and is guided by the outer guide inserted in the well of the head. This one was the most scary one, as the drill had to be close enough to just barely graze the head surface, leaving behind a coil of steel thread. Drilling just a little at a time, and removing the guide so I could see how far in the drill was going, I got past the threaded area of the plug. I could see just a sliver of thread in the aluminum head. Using a strong magnetic pick-up tool each time, I retrieved as much of the metal chips as possible. I then drilled the shaft with a drill bit that works with an M6 tap (not provided in the kit), and tapped it with the M6 tap I had. I don't know why the M6 tools are not provided in the kit, as the threads on the puller are M6. The kit has a 1/4-28 tap, but that was of no use. With the drilling and tapping complete, I screwed in the puller, and tightened the large nut, thereby pulling the glow plug shaft from the head. Success! The only thing remaining (and the hardest part), was to remove the steel threads from the head.

ROLLGUY · #3 06-20-2020, 05:51 PM

There are a couple parts of the kit that are for drilling out the center electrode. The tube fits into the smallest hole drilled by the step drill, and the smaller drill bit is supposed to drill out the electrode guided by the tube. It did not work. The problem was that the electrode material was harder than the drill bit, so it was useless. Also, by the time the hole is deep enough to accept the tube, the drill chuck hits the head (drill bit too short).

Using the M6 tap, the old plug comes out easy with the puller. The last plug that was soaking in PB was just pulled out with pliers. I suppose if I had waited longer, and gave the others a little more PB, they would have came out without drilling, tapping and using the puller.
After pulling the plugs or parts thereof, I used a small brush on a drill. I also used my shop vac to vacuum out the holes.

ROLLGUY · #4 06-20-2020, 06:34 PM

Some photos of the hole after brushing, the hex part of the plug drilled out, ready to drill and tap, a piece of the thread after drilling, and a complete plug pulled out with the puller.

engatwork · #5 06-20-2020, 06:43 PM

Good pics and write up. I don't know if you know this but if you are drilling or tapping a hole out and want to capture the shavings put a liberal amount of grease on the bit or tap to capture the bits. Then clean/replace grease until bits are out.

ROLLGUY · #6 06-20-2020, 06:50 PM

The one plug that I had to drill out, I was able to peel out the steel threads and run the tap provided in the kit to clean the threads. After successfully getting all the parts of all the plugs out, I vacuumed all the wells and plug bores and then inspected them. I applied anti-seize to the threads and the shaft of the new plugs, and torqued them down. The fuel rail and hard lines were then installed. I had to crank it over for a few cycles before fuel arrived to each of the injectors. It did stumble and run a little rough at first, but smoothed out nicely after a bit. The last thing to do was to clear the codes using my Icarsoft MB II.

ROLLGUY · #7 06-20-2020, 06:53 PM

Quote:

Originally Posted by engatwork

Good pics and write up. I don't know if you know this but if you are drilling or tapping a hole out and want to capture the shavings put a liberal amount of grease on the bit or tap to capture the bits. Then clean/replace grease until bits are out.

Yes that is a good tip, and have used it many times.