Dirty valves and poor compression- can I improve it with hard running/cleaning? - PeachParts Mercedes-Benz Forum

mtbguy · #1 07-12-2009, 11:36 PM

I recently bought a 1991 300D 2.5T with 140,000 actual miles on it in very good shape. It was a one owner car and pretty well maintained.

I ran a carfax on it and the miles appear legit, but it was owned by an elderly woman and only driven about 2200 miles in the last four years (almost all low speed city miles). The first 100,000 miles were put on it pretty quickly from 1991 to 1996 when the husband was a traveling sales person and after that the miles have been added very slowly and the car was mostly driven around town in last ten years. It runs well but is a bit sluggish and I have tightened up some slack linkage, changed the fuel filters, done a diesel purge and cleaned the ALDA valve. I also loosened the ALDA valve screw counterclockwise about 2/3 of a turn (which did seem to help quite a bit). Once the turbo kicks in it does okay, but the mechanic said the engine compression seemed low to him, and that I should be getting better MPGs. Its been getting about 28 in mixed driving so far.

I took it in to a Mercedes shop for the pre-purchase inspection and paid them to look over it, give me a list of things needed, and check the timing and timing chain for stretch. They said the timing was fine and the chain was stretched about 1.5 degrees, and should be fine for another 100k probably. Only area of real concern was replacing flex discs which I am doing this week. They also recommended preventative maintenance replacement of injection pump ( I'm also doing myself this week) and new fan clutch- which it does need for sure.

My question is the shop owner told me that the car was still sluggish and when they turned the engine over by hand the car seemed to not have that much compression. He said you could "feel" if they had good versus low compression without even formally testing it. He thinks the valves are dirty/carboned up from all of the low speed driving (and lack of driving).
He recommended more diesel purge and lots of higher speed highway trips to burn all the junk off. (I also added Startron algae enzyme treatment to the tank to help). The car starts right up with no hesitation from a cold engine and idles well with no smoke/vibration etc. The original fuel filters DID have what looked like algae/fungus in them to me and I have heard good things about the Starbrite startron.

Does this guys theory make sense? Can you actually tell that the engine is slightly low on compression just by turning it over by hand like that during the timing check?

Its a very highly respected shop that has been around for 16 years and they seemed to know what they were doing. They also charged a very fair price for the work done on the car so I don't think they are trying to scam me into a bunch of unnecessary work.

The injectors are original except one was replaced about a year ago. Car is getting about 28 mpg in the mixed driving I have done so far.

Thanks for any ideas on this!

compress ignite · #2 07-12-2009, 11:52 PM

Edit:
28 MPG in mixed driving Ain't so bad... Original figures touted 25 city/35Hwy.

Redline's 85 PLUS Fuel additive product will help you DeCarbonize the Combustion Chambers (AND help clean Injectors)

A HIGH Quality Synthetic Motor Oil will help clean the internally lubricated
moving parts. (Redline,Royal Purple,Mobil 1 Truck and Turbodiesel)

Your Intake system is contaminated by a combination of Soot from the EGR
mixed with Oil Mist from the Valve Cover Breather Hose that's plumbed into the Intake between the Air Filter and the Turbocharger.
(You're gonna have to manually clean the aluminum Intake)
BUT GSXR's "Trash Elimination" modifications will Keep it clean
(AND add other benefits):
Wastegate actuator swap for OM602.962?

Brian Carlton · #3 07-13-2009, 12:16 AM

Quote:

Originally Posted by mtbguy

Does this guys theory make sense? Can you actually tell that the engine is slightly low on compression just by turning it over by hand like that during the timing check?

Its a very highly respected shop that has been around for 16 years and they seemed to know what they were doing. They also charged a very fair price for the work done on the car so I don't think they are trying to scam me into a bunch of unnecessary work.

I suppose that it's possible for a highly skilled technician to get a feel for the compression in a given engine when he rotates it manually via the crankshaft. Although it's highly inaccurate for a quantitative measure, it may be possible from a qualitative standpoint.

If the engine has suffered from valve deposits due to quite a bit of low speed running, you've got nothing to lose by putting about 4K on it at higher rpms to see if the conditions improve. From my limited experience with one 617, the valves appear to lose the capability of a perfect seal at 150K miles or so and the compression is going to suffer slightly. A proper valve job, while relatively inexpensive if the labor is performed by the owner, restores the engine to an excellent condition with instantaneous starts in very cold weather and some good off the line performance.

Take the low cost approach first........drive it for 4K miles and see how she does........

compress ignite · #4 07-13-2009, 12:37 AM

mtbguy,

"They also recommended preventative maintenance replacement of injection pump ( I'm also doing myself this week) and new fan clutch- which it does need for sure."

I've gotta ask if maybe you meant your Lift Pump[Fuel Pump]
(on the side of the Injection Pump)

Skippy · #5 07-13-2009, 12:52 AM

Can work wonders for these cars. Fun to do also.

#6 07-13-2009, 08:07 AM

I find some of the things that this shop told you to be disturbing.

To begin with, making a compression test by turning the engine by hand is about as unscientific and unproffessional as anything that a shop could do. It takes a compression gauge to do a compression test.

It also bothers me that they recommend a "preventive maintenance change of the injection pump." The IP is either working correctly or it's not. Changing it on a PM basis is ridiculous IMHO.

This car is almost 20 years old. The dealerships don't get very enthused about working on a car that is 10 years old, much less 20. In addition, the dealers don't do very much diesel work any more. When they do, it is on a modern, common rail engine. It is entirely possible that there is no one in the service department of that organization that has ever done much early diesel work.

If I were you I would start searching for an experienced independent shop.

In the mean time, take that car and run lots of Techron in the fuel, give it some extra frequent, HOT oil and filter changes and drive it like you stole it!

moon161 · #7 07-13-2009, 08:23 AM

I've got a head where the a couple valves have a preferred seating position. Rotate it 1/2, 1/4 turn and you can hear it stop leaking with air in the piston.

I've also had a friend recommend just rotating the closed valve in place to break up carbon deposits, italian tune up would probably do the same.

mtbguy · #8 07-13-2009, 11:11 AM

Quote:

Originally Posted by compress ignite

mtbguy,

"They also recommended preventative maintenance replacement of injection pump ( I'm also doing myself this week) and new fan clutch- which it does need for sure."

I've gotta ask if maybe you meant your Lift Pump[Fuel Pump]
(on the side of the Injection Pump)

Thanks for the good advice. I bought a new vacuum pump made by pierburg for the car because I read some threads where the older style ones broke apart and fed shrapnel into the timing chain area- trying to avoid that and I think many of them are tired/worn by about 150k.

I switched the oil to Delvac last week and will probably go to the Mobil One Turbo Diesel synthetic 5/40 after the next change, and stick with it.

So far I've driven it about 600 miles, and it does seem to be getting more energetic the more I drive it. I am no longer afraid of pulling off of our street and onto the main road near our home. I just bought some of the redline additive yesterday- so will try it and the Italian tuneup quite a bit for the next few thousand miles!

mtbguy · #9 07-13-2009, 11:17 AM

Quote:

Originally Posted by LarryBible

I find some of the things that this shop told you to be disturbing.

To begin with, making a compression test by turning the engine by hand is about as unscientific as anything that a shop could do. It takes a compression gauge to do a compression test.

It is entirely possible that there is no one in the service department of that organization that has ever done much early diesel work.

In the mean time, take that car and run lots of Techron in the fuel, give it some extra frequent, HOT oil and filter changes and drive it like you stole it!

Thanks- I think you are correct in saying they don't do much diesel work and I kind of thought that doing the compression test without a gauge was very unscientific.

I already bought and unboxed the new vacuum pump and am changing the fan clutch today so will just go ahead and put it on at the same time since I am "in there".

I have a few bottles of Techron- I'll use that too! My car is going to be using ALOT of fuel additives in the next few months.....

patbob · #10 07-14-2009, 01:47 PM

When I adjusted my valves, I could feel the compression in each cylinder as I hand-rotated the engine. IIRC last time I had it tested #1 - #4 had compresison in the mid 300's with #5 being a bit lower. That's not great compression, and yeah, you can feel it, but its subtle. There's a lot of variables with that technique, so having your mechanic make an observation like that might justify a compression test, but that's about all you can really conclude from it.

moon161 · #11 07-14-2009, 02:31 PM

You can feel a valve that's not closing or seating pretty easy, you roll the crank around and the cylinder will build little or no pressure. Take a lawn mower, pull the starter slowly. Ok, pull the spark wire, loosen the spark plug a touch, repeat. You can feel the build and decay of resisting torque through a wrench handle, or on the main pulley if the accesories are disconnected. An absolute indication may be hard to reach, but if #1,3 and 2 feel strong and 4 feels soft, that's a good reason to look at #4, isn't it? I'm sure you could tell a decent amount the valves from the hisses and farts that the engine makes as you roll it through the firing order. I know my engine sounded significantly different after I adjusted the valve clearance.

BTW, how do you know it's not just a tight valve? Anyone pull the valve cover and stick feelers in there? I'd bet a dollar it's a tight exhaust valve. Mario can't fix that with the skinny pedal, but he could burn it if he tried hard. That's a pickle.

tombance · #12 07-14-2009, 02:36 PM

He has an OM602 engine with hydraulic valve adjustment, so a tight valve is pretty unlikely!

moon161 · #13 07-14-2009, 03:08 PM

Who gets my dollar?

mtbguy · #14 07-17-2009, 12:29 PM

Thanks for the responses everyone. I have run several tanks of fuel through the car now and backed off the ALDA screw one turn CCW and the car seems to be driving better all the time. With each fill up of the tank I have been adding about 2 oz of the Starbrite algae eater enzyme and a dose of the Redline 85 diesel catalyst.

I know you cant associate lower compression with bad fuel, but the engine seems to be getting stronger the more I drive it fast on the highway. Even my wife noticed a difference in its pep as a passenger. The only real problem now is that sometimes when I stomp on the gas pedal between 1000-2000 RPM it downshifts and accelerates well, other times it doesn't do anything and takes forever to accelerate. Once it gets to around 2500rpm the turbo kicks in and all is well. I am thinking this has something to do with the computer controlled wastegate perhaps?

Next thing to do in about 500 miles is change the oil from dino Delvac to Synthetic Mobil One Turbodiesel 5W/40.

jltcasper3 · #15 07-17-2009, 10:25 PM

If it's fast sometimes and then it gets slow, i suspect it's a boost issue, these engines use vacume to operate the wasegate. If theres a bad vacume transducer valve u will have no vacume to turbo witch means no boost. I strongley reccomend the pressure operated wastgate mod and egr delete.

Wastegate actuator swap for OM602.962?