I have been searching for a tutorial for a compression check on my 99 E300D and can't find one. Anyone out there have any tips?
I have a compression test kit, but do I need a special adapter to perform the test at the injector?
Should I disconnect the fuel shutoff plug at the IP?
Cold engine or hot engine?
What numbers am I looking for?

I have 2 issues with this engine, one issue is 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. It only happens at the first start of the day and only at idle. This problem does not happen during the warmer months. This problem got a little worse this winter.

The other problem is after the engine has been running and up to temp, then shut off the engine, during the next start the engine will crank for 3-4 seconds and sputter before it starts, then it runs fine.

Thanks,

Mike
99 E300D 220K

This only goes up to 1995 but except for the shutoff the compression test should be similar.
http://w124-zone.com/downloads/MB%20CD/W124/w124CD1/Program/Engine/605_606/01-1200HA.pdf

Mercedes Benz Model 124 - OM606 Maintenance Manuals

You definately don't want Fuel getting injected into the Cylinders during a compression test.

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84 300D, 82 Volvo 244Gl Diesel

Thanks Diesel 911!
That's a nice service manual, do you know where I can find one for the W210? I have an online manual subscription but its not as user friendly as the one you sent.

The Manual you see is parts of the Mercedes Service Manual on CD or DVD.
I don't have a W210 site in my notes but do a google search for: Free Mercedes W210 Service Manual and see what comes up.

This is for a W201 but it used to be you could go through startekinfo.com and access all of the service manuals for free. But that was a few years ago. Note that I don't know or have much info or notes on other vehicles past 1985.
https://www.startekinfo.com/StarTek/outside/11832/?requestedDocId=11832

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84 300D, 82 Volvo 244Gl Diesel

Sounds like you have air in the fuel. Compression, hard to start, lack of power etc. if I don't have leaking rings at 500k, I doubt you have a compression issue..

__________________
Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k

For the W210 you’ll need to get one of the WIS manual sets from eBay. The Startek info site only has free access for the 123, 124, 126, 201, and 107.

Find an old computer you don’t care about and put it on your router’s guest network to install these, since some of these disks may harbor viruses.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

You guys will think I'm nuts, but I'm going to take this in a whole 'nother direction. Don't bother doing a compression check; you'll likely find that you're barking up the wrong tree.

Years ago on my N/A 606, I experienced the same behavior: Only when quite cold (winter) and only on the first start of the day - the car starts fine, then after 2-3 minutes it starts running rough like it has fuel starvation/air infiltration. Then after it's fully warmed up, it's running like a sewing machine again. Weird. Really weird.

I tracked it down to a leaky / faulty fuel thermostat. It appears that as the thermostat transitions between the two phases (pre-heating vs. bypass) it allowed air to get sucked into the fuel loop. But you say it's not leaking? Remember, it's not experiencing pressurized fuel to cause it to leak out. The thermostat is under vacuum; the fuel is being drawn into it from the tank via suction.

This perhaps could also explain the second part of your issue, but this part is shear speculation on my part: Since the fuel thermostat is leaking, when the car is parked the (air) leak would allow air to enter the fuel loop, allowing the fuel to drain back into the tank (instead of holding it in the lines) on the T-stat end. The air entering the lines could also allow the fuel on the other side of the loop to act as a siphon, pulling more air into the loop on the filter & injection pump side.

This was a really tricky one to diagnose when I had the issue...

EDIT & P.S. - Please come back to this thread when you solve the problem. That could really help someone in the future from tearing their hair out of their head pursuing a ton of dead-ends trying to track it down.

__________________
Current rolling stock:
2001 E55 183,000+ Newest member of the fleet.
2002 E320 83,000 - The "cream-puff"!
1992 500E 217,000+
1995 E300D 412,000+
1998 E300D 155,000+
2001 E320 227,000+
2001 E320 Wagon, 177,000+

Prior MBZ’s:
1952 220 Cab A
1966 300SE
1971 280SE
1973 350SLC (euro)
1980 450SLC
1980 450SLC (#2)
1978 450SLC 5.0
1984 300D ~243,000 & fondly remembered
1993 500E - sorely missed.
1975 VW Scirocco w/ slightly de-tuned Super-Vee engine - Sold after 30+ years.

I agree that its not likely to be a compression problem. The rest sounds complelling too.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Yes I totally agree with the others. The OM606 is a plumber’s nightmare on the low pressure fuel side. There are many opportunities for leaks that will cause issues with the engine running smoothly.

There are 6 fuel hoses with o-rings on the connnectors. They are supposed to be almost transparent when new. If yours are old enough they are opaque replace them. Collectively these hoses are about $100.

Note there is one connection to the back of the IP (the rack return connection) that is still made with an old school banjo bolt with crush washers.

Also replace the o-ring on the back of the fuel shutoff valve (remove the 2 screws and pull the valve out of the IP).

And while you have it all apart replace your primary and secondary filters, be sure to replace the o-ring on the primary filter, and fill your secondary filter with clean fuel or diesel purge when you reinstall it.

In short rule out all causes of low side air in fuel before going down the compression test road. These engines are quite tough and compression issues are rare with these.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Fortunately for me this problem has been a nuisance rather than a real problem such as engine won't start, loss of power, always runs rough, excessive smoke, etc. So I just deal with it and go through the motions of replacing what makes sense when I have the spare time and without spending too much money.

I think last winter I replaced all of the clear fuel lines with viton o-rings attached from the OEM. Also replaced the o-ring on the shutoff valve. It didn't fix the problems. By the way this is inexpensive and easy to do for anyone not familiar with the job, and this should be considered preventative maintenance in my opinion.

I replace the fuel filter, pre-filter, and air filter every other oil change. I change oil (Mobil 1) & filter every 10K miles and consistently need to add 1 pint of oil after 5K miles. That's not bad.

Last spring I decided to have the injectors rebuilt because I consider this preventative maintenance (car has 220K) and mostly was hoping the problem would go away, but it did not go away as I expected.

The fuel tank screen was replaced 5 or 6 years ago, I'm thinking about replacing that again for preventative maintenance, but again I don't expect that to fix the problem.

I replaced the crankshaft sensor 2 years ago. Someone had a theory that this sensor could cause a delayed start if the sensor was heat soaked, and I agree with that theory because I have seen heat soaked components cause issues, so I tried that but it didn't work. And of course the connector was so dried out that it broke when I removed it so I had to replace that harness. That was a fun time.

I tracked it down to a leaky / faulty fuel thermostat. It appears that as the thermostat transitions between the two phases (pre-heating vs. bypass) it allowed air to get sucked into the fuel loop. But you say it's not leaking? Remember, it's not experiencing pressurized fuel to cause it to leak out. The thermostat is under vacuum; the fuel is being drawn into it from the tank via suction.

Sorry, this was a post from RunningTooHot (I accidentally hit send on my last post):

"I tracked it down to a leaky / faulty fuel thermostat. It appears that as the thermostat transitions between the two phases (pre-heating vs. bypass) it allowed air to get sucked into the fuel loop. But you say it's not leaking? Remember, it's not experiencing pressurized fuel to cause it to leak out. The thermostat is under vacuum; the fuel is being drawn into it from the tank via suction."


I'm thinking about trying this. I haven't pulled the IM in a while and I like to see how things are looking in there. Maybe I can verify a leak on the fuel thermostat.

I will keep you posted and sorry again for the paste error.

Mike

Just like for you, this was a minor annoyance - not a significant obstacle to normal operation. Although it would act fuel starved for about 30-45 seconds if driving while it hit that magical transition temperature. It was more of a curiosity to figure it out than a need to fix it.

Keep in mind that you may not necessarily see a fuel leak at the fuel thermostat since that part of the fuel loop is under suction; it may be a "one way" leak - pulling air in, but not leaking fuel out externally.

Instead of throwing money at it speculatively, try to simply bypass it temporarily. When I changed out my clear lines, I kept the old ones to butcher them for an easy way to run an occasional can of diesel purge. So if by chance you have your old lines, just cut the two appropriate ones and clamp a piece of fuel hose on them for a bypass. Pop those on the car, and I'll bet you'll find the problem has disappeared.

__________________
Current rolling stock:
2001 E55 183,000+ Newest member of the fleet.
2002 E320 83,000 - The "cream-puff"!
1992 500E 217,000+
1995 E300D 412,000+
1998 E300D 155,000+
2001 E320 227,000+
2001 E320 Wagon, 177,000+

Prior MBZ’s:
1952 220 Cab A
1966 300SE
1971 280SE
1973 350SLC (euro)
1980 450SLC
1980 450SLC (#2)
1978 450SLC 5.0
1984 300D ~243,000 & fondly remembered
1993 500E - sorely missed.
1975 VW Scirocco w/ slightly de-tuned Super-Vee engine - Sold after 30+ years.

Here is a picture of the fuel thermostat bypassed. I have a good video with the engine running in this configuration (rags removed) but the forum is rejecting it for some reason. I will run the engine tomorrow morning and hope its cold enough to reproduce the problem. If not cold enough I would like to put the IM back on and drive the car for a while with the fuel thermostat in bypass. Is it ok to run the car like this?

I think you're on the right track with the O-rings. Your air leak will likely be somewhere near where you see the bubbles show up when you're revving the engine. Air in the system will definitely cause rough starting, especially when the engine sits and all the air accumulates in the filter and hard lines.

The forum doesn't allow video attachments. You can upload to a hosting site like YouTube and paste the link back in this thread.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]

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