OM 606 Compression Check - Page 2 - PeachParts Mercedes-Benz Forum

208benz · #16 04-14-2018, 09:05 PM

This problem has definitely gotten worse this past winter so I am paying much closer attention to how the engine is running. I noticed that the engine runs rough around 2400 RPM with the transmission in park. There are more air bubbles running through the clear lines at this RPM especially the 2 lines on top of the fuel shut-off valve. While driving and keeping the RPM around 2400 and can feel a slight droning type vibration as well.

Also now that it’s getting warmer outside the engine takes longer to start when warm. This doesn’t happen all the time, but definitely getting worse.

So I decided to replace all of the clear fuel lines and the 2 black fuel hoses that go to the tank because they are old and showing dry rotting. Every hose I removed I inspected the o-rings and bore that it goes to for any evidence that could cause an air leak. I found 2 things that caught my attention. The green o-ring that goes on the bolt for the banjo fitting on the clear line that goes to the back of the IP was cut. The other thing I found was after removing the electrical connector to the fuel shut-off valve there was fuel inside of the connector, but not leaking out of the connector because there is an o-ring holding the fuel in the connector. I was hoping I had found the problem so I replaced the fuel shutoff valve in addition to all the fuel lines previously mentioned. I ran the engine with the IM removed and the air bubbles are still running through the lines but much less and the engine still runs rough at 2400 rpm.

Now I decide to do a compression check on a cold engine. The gauge I have is 350 psi max so when it reaches 350 I stop cranking. Here are the results:
#1 – 280 - took 10 seconds of cranking to reach this
#2 – 350 – took 10 seconds of cranking to reach this
#3 – 350 – took 7 seconds of cranking to reach this
#4 – 350 – took 7 seconds of cranking to reach this
#5 – 350 – took 7 seconds of cranking to reach this
#6 – 350 – took 7 seconds of cranking to reach this

According to the numbers Diesel911 sent me it appears all cylinders are within limits but the difference between cylinders fails.
Note: the procedure he sent me calls for a hot engine not a cold engine

Another thing I noticed is lots of oil in the 3” intake pipe that connects to the IM. I have always noticed this and never paid much attention, but it seems more than usual.

At this point I’m going to put the IM back on and drive the car for a while hoping for improvement but expecting the same. I know there are still some air bubble in the fuel system but that #1 cylinder concerns me.

ROLLGUY · #17 04-15-2018, 12:18 PM

Quote:

when the engine is cold during the winter months it starts fine then approximately 3 minutes later it idles very rough then goes away after a minute or 2.

This may be a long-shot-
I don't think anyone has mentioned anything about the GP relay or afterglow, but this may be part of the problem. The rough idling after 3 minutes could be the GP's cooled after the afterglow cycle. This would also explain why it gets better as the weather gets warmer. If the car was driven shortly after it is started (before the 3 minutes), would any rough running be noticed?

208benz · #18 04-15-2018, 03:41 PM

Quote:

Originally Posted by ROLLGUY

This may be a long-shot-
I don't think anyone has mentioned anything about the GP relay or afterglow, but this may be part of the problem. The rough idling after 3 minutes could be the GP's cooled after the afterglow cycle. This would also explain why it gets better as the weather gets warmer.

The afterglow shuts off 90 seconds after the engine is started. I'm not sure how long this should stay on for.

Quote:

Originally Posted by ROLLGUY

If the car was driven shortly after it is started (before the 3 minutes), would any rough running be noticed?

Sometimes I will get a single skip of the engine about 5 seconds after the engine is started. Then it will idle smoothly, then another single skip of the engine, then smooth again, then 3-4 minutes later it will run rough for about a minute or so then smooth again. This doesn't always happen.

Last night it was cold so I took the car for a ride this morning after doing all that work yesterday and have the same exact problem. After driving the car I popped the hood to check for leaks with the engine running and I'm still seeing quite a bit of air bubbles at higher RPM's but no air bubbles at idle. I don't know if this is normal or if I have a leak. Is there anyone out there with a 99 E300D that has nice clear lines? Can you start the engine and look at the lines around the fuel shutoff valve and see if there are any air bubbles when you increase the accelerator?

Diseasel300 · #19 04-15-2018, 03:59 PM

You should have NO bubbles in the fuel system, ever. Bubbles indicate air ingress, and air ingress means running problems.

There was a thread on this forum within the last year where the OP was tracking down a mystery air leak that turned out to be the fuel heat exchanger was cracked just enough to leak air but not fuel.

ROLLGUY · #20 04-15-2018, 04:03 PM

You could maybe try a piece of clear hose between the hard line supply from the tank to the fuel heater. If bubbles are present, air is getting in near the tank (or at least before the clear hose). If no bubbles before the heater, and bubbles after, you have narrowed it down a bit.

208benz · #21 04-15-2018, 04:42 PM

Quote:

Originally Posted by Diseasel300

You should have NO bubbles in the fuel system, ever. Bubbles indicate air ingress, and air ingress means running problems.

There was a thread on this forum within the last year where the OP was tracking down a mystery air leak that turned out to be the fuel heat exchanger was cracked just enough to leak air but not fuel.

I bypassed the fuel heat exchanger 2 weeks ago, same results.

Quote:

Originally Posted by ROLLGUY

You could maybe try a piece of clear hose between the hard line supply from the tank to the fuel heater. If bubbles are present, air is getting in near the tank (or at least before the clear hose). If no bubbles before the heater, and bubbles after, you have narrowed it down a bit.

I can see some bubbles going into the pre-filter, but very hard to see and not a lot of air bubbles. The 2 lines going in & out of the fuel pump (i think that's what it is). It's mounted on the lower left side of the injection pump. There is quite a bit of air in that area.

When I replaced the clear lines yesterday I also placed a small piece of blue paper towel in each bore and cleaned the inside of the bores with emery cloth to remove any corrosion, sharp edges, dirt, etc, got them nice and shiny, then of course removed the piece of paper towel and wiped out the bore with some clean diesel fuel on a blue paper towel.

208benz · #22 04-15-2018, 08:15 PM

https://www.youtube.com/watch?v=2cgpRt46fhs

Here is a link to a video I made, it's the first video I have made so it's not really great but good enough. I bypassed the fuel tank and rigid lines and used a small bottle as a gas tank, like doing a diesel purge. Still getting air bubbles, can be seen mostly on the lower line on the fuel pump. The car is smoking really bad, I'm thinking it has to do with the test I did. I have not put it back together to see if the smoke clears.

208benz · #23 04-17-2018, 10:49 AM

Here are some more things I tried.

With engine off I plugged the return line on my temporary fuel tank then pressurized the supply line with a syringe of fuel and locked it. There is not an air bubble anywhere in the fuel system at this point. My guess is I probably put less than 5 psi of pressure on the fuel system. I also disconnected the fuel shutoff valve electrical connector, there was fuel in this plug again, I cleaned it and dried it with compressed air.
2 things I noticed after letting it sit overnight pressurized:
- The #1 or #2 delivery valve has a slight weep. This was never noticeable because it easily evaporates.
- There are signs of fuel in the shutoff valve connector. I don’t know if this is residual from maintenance or if there is actually fuel leaking into the harness from inside the injection pump.

After putting everything back together I ran the engine to check for leaks and now noticing air bubbles in the fuel lines at idle. See attached fuel diagram:
- No air bubbles at line #1
- Air bubbles at lines #2,3, & 4.
- No air bubbles at lines #5, 6 & 8.

Is it possible the fuel filter housing has a crack or the bores where the fuel lines go in are worn causing the air leak? I’m thinking about replacing this housing, its $74 from the dealer.

The attached photo is after the engine is shut down. There is an air pocket in the supply line at the pre-filter inlet, I think this is normal but would like to confirm if anyone knows the answer.

208benz · #24 05-04-2018, 03:34 PM

I replaced the fuel filter housing and still having a problem with this engine. The problem has gotten worse over the last few weeks. I get numerous hard kicks of the engine at idle right after starting the engine. This goes away after a minute or so. I'm still seeing air bubbles in the fuel line coming out of the pre-filter. Take a look at the attached video.

https://www.youtube.com/watch?v=KmThj2W3ofw

The first fuel line in the video is the fuel supply, there are no bubbles in this line, the fuel then runs through the pre-filter then into the fuel line marked in red. If you look closely you can see small air bubbles especially if you look at the black fitting. I'm starting to think this is normal.

The are a lot more air bubbles in the fuel lines running in and out of the lift pump. This is not shown in the video.

I have a lift pump that I might replace, but seriously thinking the #1 cylinder is my issue. Here are the results from the compression check again. Does anyone think I have an issue with the #1 cylinder?

Compression check done on a cold engine. The gauge I have is 350 psi max so when it reaches 350 I stop cranking.
#1 – 280 - took 10 seconds of cranking to reach this
#2 – 350 – took 10 seconds of cranking to reach this
#3 – 350 – took 7 seconds of cranking to reach this
#4 – 350 – took 7 seconds of cranking to reach this
#5 – 350 – took 7 seconds of cranking to reach this
#6 – 350 – took 7 seconds of cranking to reach this

According to the numbers Diesel911 sent me it appears all cylinders are within limits but the difference between cylinders fails.
Note: the procedure he sent me calls for a hot engine not a cold engine