300SDL Rough Idle and Smoke on Start up - Page 4 - PeachParts Mercedes-Benz Forum

Diseasel300 · #46 03-23-2021, 12:12 PM

Quote:

Originally Posted by Deutscheauto

I tried to look for the orifice at the intake manifold. Unfortunately, I could not locate one. Can you describe the exact location? I will look for it.

Follow the vacuum line that goes from the manifold to the switchover valve on the firewall. The nipple on the manifold that vacuum line connects to clogs. Poke it clear. You need a long wire or nail, it's a deep fitting.

Maxbumpo · #47 03-23-2021, 02:42 PM

Quote:

Originally Posted by Deutscheauto

I used to notice air pressure in the gas tank on every fill-up. It used to make a whoosh sound each time I opened the gas cap. I knew there was an air ingress from somewhere. I have been chasing it for the longest.

I'll bet that "whoosh" sound was not air escaping from the tank, it was air rushing INTO the tank. A very common problem is that the fuel tank vent will get plugged up and then as you drive the car and consume the fuel, a vacuum build up in the tank as the fuel comes out but no air can go in. Usually there is no change in engine power or performance, but eventually your fuel tank will collapse with the vacuum, and then you'll have a smaller / lower capacity fuel tank.

Fuel tank vent is visible below the rear of the car, it's just a rubber hose hanging down with a little plastic bell-like thing at the end. Sometimes an insect will build a nest inside and plug it up.

Diseasel300 · #48 03-23-2021, 02:45 PM

Quote:

Originally Posted by Maxbumpo

I'll bet that "whoosh" sound was not air escaping from the tank, it was air rushing INTO the tank. A very common problem is that the fuel tank vent will get plugged up and then as you drive the car and consume the fuel, a vacuum build up in the tank as the fuel comes out but no air can go in. Usually there is no change in engine power or performance, but eventually your fuel tank will collapse with the vacuum, and then you'll have a smaller / lower capacity fuel tank.

Fuel tank vent is visible below the rear of the car, it's just a rubber hose hanging down with a little plastic bell-like thing at the end. Sometimes an insect will build a nest inside and plug it up.

That "bell" looking fitting is actually a control valve. It allows zero vacuum in the tank, but will allow 1-2PSI to build up inside the tank. 1-2PSI is enough to cause the positive pressure "whoosh" when you open the tank cap. It's normal behavior.

Maxbumpo · #49 03-23-2021, 02:52 PM

If you are still getting smoke at start up, and the injector pressure is below 135 psi, that would be a good thing to fix next.

Also I don't see that you've ever checked the stretch (wear) of the timing chain. If that is 4 degrees or more off, it will affect engine performance and should be corrected (new timing chain).

If you still have smoke after that, I have to ask if you practice "good engine hygiene"? What I mean by that is practicing good habits that prevent carbon build up in the pre-chambers.

(1) Never allow the car to sit and idle with a cold engine to "warm it up". After a cold start, once the oil pressure is good and the engine is running mostly stable, drive off gently (1/3 to 1/2 pedal only and keep the RPMs down to 2000 or 2500 or less) until the engine is fully warmed up. Fully warmed up = coolant at or above 80 Deg C and the oil pressure drops to about 1.5 BAR at idle.

(2) Drive it hard once she is warmed up, and try to get at least one "Italian" tune-up each time you drive it.

Under full throttle acceleration with a fully warmed up engine, there should be no visible smoke. If you get more smoke when you mash the accelerator, you've got carbon build up that needs to be burned out. See (1) and (2) above. Multiple Italian tune-ups may be needed, or several months of hard driving (drive it like you stole it).

Maxbumpo · #50 03-23-2021, 02:55 PM

Quote:

Originally Posted by Maxbumpo

Under full throttle acceleration with a fully warmed up engine, there should be no visible smoke.

I'm assuming that your ALDA is original and unmolested, and has not be adjusted to enrich fuel under boost.

Weak engine performance, on the other hand, could indicate your ALDA needs attention, but first chase down the possible leaks / plugged orifice that Diseasel300 has indicated. Have to get a good manifold boost signal first.

Deutscheauto · #51 03-24-2021, 11:25 AM

Quote:

Originally Posted by Diseasel300

Follow the vacuum line that goes from the manifold to the switchover valve on the firewall. The nipple on the manifold that vacuum line connects to clogs. oke it clear. You need a long wire or nail, it's a deep fitting.

I cleaned the orifice, which is located just below the over-boost pressure switch. It was dirty but not plugged. There is no change in performance.

Deutscheauto · #52 03-24-2021, 11:41 AM

Quote:

Originally Posted by Maxbumpo

If you are still getting smoke at start up, and the injector pressure is below 135 psi, that would be a good thing to fix next.

Also I don't see that you've ever checked the stretch (wear) of the timing chain. If that is 4 degrees or more off, it will affect engine performance and should be corrected (new timing chain).

If you still have smoke after that, I have to ask if you practice "good engine hygiene"? What I mean by that is practicing good habits that prevent carbon build up in the pre-chambers.

(1) Never allow the car to sit and idle with a cold engine to "warm it up". After a cold start, once the oil pressure is good and the engine is running mostly stable, drive off gently (1/3 to 1/2 pedal only and keep the RPMs down to 2000 or 2500 or less) until the engine is fully warmed up. Fully warmed up = coolant at or above 80 Deg C and the oil pressure drops to about 1.5 BAR at idle.

(2) Drive it hard once she is warmed up, and try to get at least one "Italian" tune-up each time you drive it.

Under full throttle acceleration with a fully warmed up engine, there should be no visible smoke. If you get more smoke when you mash the accelerator, you've got carbon build up that needs to be burned out. See (1) and (2) above. Multiple Italian tune-ups may be needed, or several months of hard driving (drive it like you stole it).

Last summer, I checked the timing. The crank and the cam perfectly align at 0 degrees.
Whenever I find a clear road, I do the Italian tune-up. It throws a cloud of smoke, and it would gain power for a day or so. Then it goes back to power loss mode.

Diseasel300 · #53 03-24-2021, 12:36 PM

Quote:

Originally Posted by Deutscheauto

Last summer, I checked the timing. The crank and the cam perfectly align at 0 degrees.
Whenever I find a clear road, I do the Italian tune-up. It throws a cloud of smoke, and it would gain power for a day or so. Then it goes back to power loss mode.

Things to check:

1: Is your turbo free to spin? Pull the intake boot off and see if the turbo turns easily with your fingers. Start the engine and let it idle. The turbo should be spinning. It won't make boost at idle, but it should be rotating if the bearings are good and the wastegate is closed (which it should be).

2: Confirm you don't have an overboost protection fault or a clog in the switchover valve. Join the 2 vacuum lines together that connect to the switchover valve on the firewall. If your problems disappear, that valve is clogged or there's a fault in the overboost protection circuit. You can prove the latter by reconnecting the vacuum lines to the valve and unplugging the electrical connector. If the problem remains, the valve is stuck. If it goes away like when you joined the 2 lines together, the overboost circuit has a problem, likely the sensor on the intake manifold (which you can test by unplugging it and plugging the switchover valve back in).

3: Are you certain you don't have EGR problems? I had a vacuum transducer leaking on my 350SD and it caused all sorts of power delivery issues. You can kill vacuum to the EGR valve by pulling the vacuum line off and inserting a golf tee.

4: Lastly, does this car have the "Trap oxidizer" or the later "Oxidation Catalyst" in the exhaust stream? They can clog and cause power loss and lack of boost.

filp · #54 03-24-2021, 02:30 PM

Quote:

Originally Posted by Diseasel300

Stick clear tubing on the return line from the filter to the hard line on the firewall. You'll see it full of air in the morning with the 5/16" hose. Believe me, I tried 4 different brands and 3 different types of hose clamps after everyone on this forum was ADAMANT that 5/16 is fine. It simply isn't and several other people here have had the exact same experience I have. It'll work for a few days to a couple weeks, but it *WILL* leak air. Perhaps on the 61x cars it's fine, but NOT on a 60x car.

So I did replace the "firewall to lift pump with prefilter" with 7.5mm and then the "lift pump to fuel filter" one as well. The latter used to have a transparent tubing that cracked, I removed the old tubing from threads, now the 7.5mm hose seems to be a bit loose, so I clamped it hard.

Overall no change in engine loudness. Is the second fuel line I've replaced (the one with banjos) meant to be even smaller than 7.5mm?
Edit: found somewhere on this forum that 1/4 inch ID is more appropriate for formed hoses, will try this in the evening.

Maxbumpo · #55 03-25-2021, 10:57 AM

Quote:

Originally Posted by Deutscheauto

Whenever I find a clear road, I do the Italian tune-up. It throws a cloud of smoke, and it would gain power for a day or so. Then it goes back to power loss mode.

Well there you go, you have a severely carboned up engine, and so you need to start driving it good and hard, "like you stole it" until you no longer get smoke.

May have carbon fouling of the rings too, so I'd recommend Mobil 1 oil (diesel rated) for the rest of your ownership. However, watch the oil consumption. If it goes up and stays up with M1, you will probably want to go back to dino.

Deutscheauto · #56 03-25-2021, 10:58 AM

Quote:

Originally Posted by Diseasel300

Things to check:

1: Is your turbo free to spin? Pull the intake boot off and see if the turbo turns easily with your fingers. Start the engine and let it idle. The turbo should be spinning. It won't make boost at idle, but it should be rotating if the bearings are good and the wastegate is closed (which it should be).

2: Confirm you don't have an overboost protection fault or a clog in the switchover valve. Join the 2 vacuum lines together that connect to the switchover valve on the firewall. If your problems disappear, that valve is clogged or there's a fault in the overboost protection circuit. You can prove the latter by reconnecting the vacuum lines to the valve and unplugging the electrical connector. If the problem remains, the valve is stuck. If it goes away like when you joined the 2 lines together, the overboost circuit has a problem, likely the sensor on the intake manifold (which you can test by unplugging it and plugging the switchover valve back in).

3: Are you certain you don't have EGR problems? I had a vacuum transducer leaking on my 350SD and it caused all sorts of power delivery issues. You can kill vacuum to the EGR valve by pulling the vacuum line off and inserting a golf tee.

4: Lastly, does this car have the "Trap oxidizer" or the later "Oxidation Catalyst" in the exhaust stream? They can clog and cause power loss and lack of boost.

1. The turbo moves freely. I hooked up a long vacuum hose and tested it while driving. The turbo boost was at 10 PSI.
2. I replaced the switchover valve no too long ago. But, I will try step 2 and post the result.
3. I have done plugging the EGR lines with golf tees, but no change in power.
4. This car does not have a "Trap Oxidizer".