Mercedes-Benz Forum banner

Excess Blowby-1985 190D

12K views 43 replies 5 participants last post by  Compustar 
#1 · (Edited)
Hi Folks
Have a 1985 190D which had more problems than what actually worked. Solved most of them but the MOST critical one remains unsolved. I must have read what seems like thousands (slightly exaggerated) blowby problems forum discussions on the topic but nothing seems to be exactly my problem or else I too dumb to recognize it.

Here tis the situation (1985 190D, California version, 5 speed stick shift):
1. Extreme blowby-If I plug the PCV valve with my finger, the engine will die within a few seconds. So much pressure that I had to bypass the oil distribution hose on the Intake manufold and run a plastic line from the PC Valve to the rear of the car - mounting the plastic tube just under the end of the tail pipe.
2. Very little if any smoke from the exhaust pipe at any speed but the makeshift plastic blowby pipe looks like a jet engine spewing out oil and oil vaper at any speed.
2. Engine has great power
3. On a round trip of roughly 130 miles, the car throws out almost a GALLON of oil. I think most or all of it is expelled from the PCV thru to the end of the makeshift plastic tube.
4. Had to wire down the oil dipstick because the blowby will blow the stick almost out of the dipstick tube.
5, No apparent loss of antifreeze.
6. Get real good fuel milage (lots of power for a non-turbo 4 cylinder-so I wouldn't think I have a ring(s) problem.

Now, I understand that the engine breather assembly in the Valve cover which helps in reducing crank case pressure. Is there any way to test the breather system to see if maybe the diaphram failed? Or what do you think are some possibilities?

Oh, by the way, I don't know if PVC valve is the correct terminology or not but it looks like one

Thanks in advance for any help you can give me.
George
 
See less See more
#2 ·
First, I suggest learning more about how the exhaust gas recirculation system works. This may be causing some confusion. Study the Mercedes pdf manual / OM601 engine / intake manifold, exhaust manifold, emission control.

I have heard that some people like to disable the 190D OM601 EGR system, by simply lifting pin 3 of microswitch 134/I (double wire, normally closed position).
 
#4 ·
Hi,
Thanks for your help.
Been trying to borrow a compression tester for over a week now that's capable of a higher psi range (mine is of good quality but does not handle diesel ranges). Advanced Auto Parts is the only outfit that's within walking range (can't use my Mercedes - have the dash apart replacing the heater core). I do have a high volume air compressor that I can use for a leak down test - will have to read up on the procedure but guess that will also require a 400 plus psi compression tester. No other car to get anywhere. But will overcome these pesky little obstacles.

One thing that Vishvamata said aabout pulling the #1 pin on switch 134/1 brought back memories of other forums where they placed a small bearing in the vacuum line of the egr valve and also placing a metal plate somewhere in the EGR valve cutting the valve completely out of the system.

Could a defective EGR system play that much havoc on the the engine blowing that much oil thu the PVC & having such a high block pressure?
Thanks,
George
 
#6 ·
Thanks for the link - I've been afraid of that.This car has only 168K mile on it but have no idea how it was treated by the previous owner*s). .
I rebuild a 1967 Mercedes 200D engine back in the mid 70s (except replacing the pistens) for just a couple hundred dollars. But that was an easy engine to work on and at atime in life when parts were a whole lot cheaper. But it ram wll for 300K plus miles before I sold her.
This engine and living on Social Security (retired a couple years ago) will have to remain as is. Will still do a compression test.
Again, thanks alot for you help.
George
 
#7 · (Edited)
No problem.

Keep in mind the problem could be as small as one broken ring on one of the pistons, to fix that problem (without doing a complete rebuild) you may need as little as $200 parts - and that includes a new head gasket !

If you can do the work yourself then it is definitely worth doing

W201 diesels hold their value and depending on the car's overall condition, you can get your money back or even be ahead.

good luck.


- and 190D motor is no more complicated than the the 200D you rebuilt in the past, just few more EGR vacuum lines.
Once you have the motor out it is straightforward and simple.
 
#8 ·
In a California model, the EGR system does affect diesel blow-by, vented from the crankcase through the cylinder head cover, through a pressure control valve, and then to the intake manifold. The pressure control valve is balanced with the intake manifold pressure which is throttled by the EGR. Federal models do not have a pressure control valve.

The original poster said that the engine will immediately shut down if they cover the valve/hose with their finger. Intake air will be mostly choked by blocking the 1-to-4 output hose of the cylinder head cover.

The engine will shutdown if there is:
1. no intake air;
2. no injected fuel;
3. injector pump disabled by vacuum hose, normally by shutdown relay.

OP did not complain about failure to shutdown, so #3 is eliminated.
Engine runs, so #2 is eliminated.
If EGR intake is switched from fresh air to exhaust, that is normal idle condition and the EGR intake is throttled, then the engine is deprived of fresh air.

Compustar, What happens at idle when you first actuate both accelerator microswitches, then cover the vent hose with your finger?

Whether the 190D holds value is relative. My 1984 2.2L MT5 parts car cost $250, and it only had a broken timing chain (and interior was pretty beat up). You may want to shop around for a parts car, usually from somebody who cannot finish a full restoration project.
 
#9 ·
EGR (Exhaust Gas Recirculation) is a vacuum controlled process whereby some of the burnt exhaust gases are redirected from the exhaust manifold back into intake manifold to mix with fresh incoming air/fuel - All that to reduce emissions.

On california cars, some of the crankcase fumes are also added to the EGR, other models simply vent through cam cover tube into the intake manifold

The EGR vacuum valve is pretty much controlled by two micro switches on the throttle linkage and gets activated at open throttle .

The excess blow-by in this case has nothing to do with EGR system, it is simply high pressure escaping past piston rings.

Please read the linked article on excess diesel blow-by
 
#10 ·
Hi Vishvmata,

Actually never tried engaging the two microswitches at the same time holding shut the valve cover PCV tube. Right now I hav the air intake manifold off the engine (was waiting to see if I could find a diesel able compression tester). But now you've got my curiosity up and going to slap her back together and run the test taht you suggested.
Will be back with the results.
Thanks,
George
 
#11 ·
Hi NMBMBZ
Didn't see your last post until after I responded to Vishvmata.
I hope it's not th rings but am afraid that's the problem.
Going to test the microswitches really to se what happens. After whatever needs to be done I would like to close off the EGR system - understand from other forums that it increses horse power- though don't know if that advisable or not..
Thanks,
George
 
#12 ·
>The excess blow-by in this case has nothing to do with EGR system
I would agree that the CAUSE of excess blow-by is separate from the EGR system. But the OP's complaint that the engine stops at idle, by just covering the intake manifold blow-by tubes is CAUSED by the EGR system, and is not an EFFECT of excess blow-by. My suggested test helps the OP easily eliminate the pressure control valve as a defective part, which was one of his/her specific questions.

Compustar, in my opinion it is much more reliable to disable the EGR by removing one microswitch connector pin, and preventing the vacuum switches from turning on in the first place, than by plugging vacuum lines.
 
#13 ·
Hi Vishvmata and NMBMBZ,

I slapped her back together this after noon - took lomger tha anticpated cause 2 of the manifold bolts dropped underneath the fuel injector. Had to walk to Advanced Auto Parts to buy a decent flexible magnet to get the out. Slapped her back together and cranked her up.

Here are the results of the finger closing the PVC Valve and simultanelously cloosing the 134I switch (closed both the q34I and 134II switch).
Engine died in 2-3 second whether the switch was open or closed.
Still very little or no smoke from the exhaust pipe BUT light grey smoke and oil dropplets comes out of the PVC outlet with enough pressure to kill the engine if the PVC valve is held close. Engine runs smooth and has lots of power.

Guess I'll continue to try finding a diesel compression tester. If I'm lucky, it might be the head gasket leaking - doen't always have to be a leak in the coolant area - or maybe a leaky valve - but I never be that lucky.

If I may have to tear the engine apart, I hate to replace just the rings on the pisten with the bad ring(s) without doing a complete overhaul but can't afford to do anything else. Makes me wish that I didn't retire.

Thanks,

George
 
#15 ·
So let me get this straight -- you pull the output tube from the valve cover (1 to 4 intake manifold tubes) and when you plug the 1 tube, the engine stalls. And this is regardless of microswitch condition. What happens at > 3200 rpm (EGR is supposed to be disabled at high RPM).

Also consider testing static cylinder pressure, pdf manual page 01-015.

Glad I don't have a CA vehicle!
 
#16 ·
Shucks, I didn't try the test at 3200 rpms.

I tried the test several times at idle speeds (900-1100 rpm depending if the A/C was running or not) by closing off the valve cover output tube and closing the both of the microswitches BUT did not try the the test at 4300 rpm. Will do the high rpm test now and get back to you.

Thanks,
George

Thanks,
George
 
#17 · (Edited)
Ran out of fuel so wasn't able to perform the 3200 rpm test. Will pick some up tomorrow when my grandson takes me to Harbor freight (they have a leak-down tester with two pressure gauges (incoming and cylinder leak pressures) for $34.95 less 20% Discount=$27.99 total). Am sure it's a great Chinese thing and not very accurate and probably won't last long - but testers report relative pressures anyway. I'm sure I'll have to jury rig an adapter to use device in the glow plug holes.

Will let you know results.

George
 
#21 ·
That's the easiest way other than having someone else there holding it down for you.

As for testing compression, it's unlikely that your car has low compression given that you say it has good power and runs smoothly. In particular, I think it highly unlikely that one cylinder has loose or broken rings, because that will make most diesels run like absolute garbage.

To check for blow-by, simply remove the dipstick with the engine running, and feel for pressure coming out of the dipstick tube. If there isn't much, you don't have to worry about that.

The EGR system COULD have to do with your oil consumption, assuming your car has the pressure control valve which appears on CA cars and later-model 300D 2.5 Turbos or 350SDs. Said valve functions like a throttle, blocking off most of the intake air and causing the engine to actually pull a some vacuum. Such systems are now commonplace on diesels (at least the Fords I've worked on), but early ones were very troublesome.

If the car has a pressure control flap, I would disable it by putting a ball bearing into the line in some place it won't wind up sucked through. Disabling it electronically can make the car's stupid electronic brain very, very angry.

Anyhow, if that valve is closing, it may cause the engine to be pulling air through the breather system (it isn't really PCV on a diesel, it's really just an open crankcase ventilation system) to such an extent that it's sucking out the oil. That is to say, it isn't being blown out, but sucked out. No double entendre was intended there.

Good luck, PM me if you have further questions.
 
#22 · (Edited)
The OP has a CA 1985 190D, with the PCV as you describe. There is no ECU "brain" for that MY, hence my suggestion that opening one microswitch contact is more reliable than blocking two vacuum lines to disable EGR.

The EGR control unit behind the battery is fairly "dumb." Lifting the microswitch lead simply prevents the vacuum switches from actuating.
 
#23 ·
The OP has a CA 1985 190D, with the PCV as you describe. There is no ECU "brain" for that MY, hence my suggestion that opening one microswitch contact is more reliable than blocking two vacuum lines to disable EGR.
There is an EGR control unit behind the battery. It lacks the EDS system (in all of its irritating glory) that exists in later models, yes.

And I'd only block the ONE vacuum line, the one for the pressure control flap. Blocking the line for the EGR valve itself may cause some overheating at highway speeds in addition to eventually creating a pinhole leak in the EGR pipe from which horrible black foulness shall come forth.
 
#24 ·
Hi,
Thanks for your input.
Bought, today, from Harbor Freight a leak-down tester & a Deisel compression tester. Will soon find out if I have a cylinder/valve/head problem. With coupon codes both pieces of equipment cost around $50. I haave know idea how accurate they are but probably doesn't matter since we're dealing with relative numbers. the equipment looks like quality stuff but ofcourse doesn't mean it will wear any length of time.
Reference to a comment about blowby from the dipstick - I have to tie down the dipstick to keep it from blowing half way up the dipstick tube (to keep the oil in the engine instead of all over the hood of the car). So I suspect a problem in the cylinder.
Will let you all know the results. meantime I have to yank the tank out of the car and pressure clean it - found a lot of junk in the pre-filter after running out of fuel (while attempting the "plugging valve cover vent/disabling 134I&II test).
Thanks,
George
 
#28 ·
You can test the modification by simply actuating both microswitches, by hand.

There are 3 EGR valves on the CA version. The crankcase recirculation valve is passivly balanced with the intake manifold pressure/vacuum. If the exhaust recirculation valve is stuck open (allowing flow to air filter box), then you will get some exhaust in the intake airflow. If the air intake valve is stuck open, then you already have 1/2 of what you want -- fresh air.

You can easily see the air intake valve change position when actuating the microswitches. To verify the exhaust valve, you can remove the air filter, then put your finger near the exhaust inlet port and feel if there is any warm exhaust coming through.
 
#29 ·
Since 134II is hooked up and used only Auto Xmissions (mine is a stick shift), and 134I is for the EGR system, could I simply unplug and leave unplgged the dual electrical connector? Think that would b the same thing as pulling one of the pins from the 134I part of the connector.

Didn't get very far in removing the fuel tank - had to abandoned the project - couldn't get the jack high enough to craw underneath the car to ren=move the fuel lines. So I cleaned the tank and lines best I could.

I did remove the Fuel Sending unit WHICH WAS A BIG MISTAKE - not in the actual removal but where I laaid the unit afterwards. My neighbor has a great, wonderful dog bbut he's a tool thief. He was in the garage with me for awhile and I guess he took a fancy for my sending unit - cause it wasn't there when I was ready to reinstall the unit. Todate both my neighbor and I collectively have lost dozens of tools to the little hound. So far, we have never been able to recover any of them.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top