Rebuilt turbo, new manifold gasket, 8 lbs of boost. Not any noticeable power increase - PeachParts Mercedes-Benz Forum

gregp1962 · #1 03-17-2019, 11:40 PM

1984 300CD, automatic, US

I recently replaced the manifold gasket and while I had the turbo off, I rebuilt it. The turbo wasn't in bad shape inside. The intake manifold was so loose you could wiggle it. Somehow it measured 5 lbs of boost under load. Now, it's much quieter and tight. It now measures 8 lbs of boost which is noticeably better. But, I can't really feel an improvement in power while accelerating. One problem is the my kickdown switch isn't working. But, even manually downshifting it isn't noticeably better. What could improve acceleration?

Diesel911 · #2 03-17-2019, 11:59 PM

Look up threads on adjusting the Waste Gate. I believe the max is 12 psi of Boost.

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There is also a procedure for adjusting the ADLA once the turbo boost is OK.

tyl604 · #3 03-18-2019, 08:20 AM

Check your switchover valve; if it is clogged, you will get no power. Or if a vac hose has dropped off.

oldsinner111 · #4 03-18-2019, 08:49 AM

I ran 15 pounds of boost.Had enough fuel,with monark nozzles. removed stupid alda.

vwnate1 · #5 03-18-2019, 09:53 AM

Depending on how well your wastegate popoff valve seals and the total amount of boost (should be 12 PSI, easy enough to adjust on the car) you may not feel much boost until the engine passes 2,500 RPM .

The wastegate valve is easy to hand lap and this should be done every time the turbo is off the engine and flow tested with alcohol , gasoline or other very thin liquid as even a small weep will cause serious turbo lag until it's really spooled up and the engine has higher RPM .

Add a cheapo boost gauge and watch it ~ you should begin to get boost by 1,500 RPM, it should pass 10# boost by 2,000 RPM but remember : when you're tootling down the highway @ 60 MPH you'll only have a few (like 5) # of boost ~ it only makes boost when you feed it more fuel .

It may not be a rocket-ship but your Coupe is no slouch either....

I ass-you-me that you've recently adjusted the valves ? unless you can hear them clicking like a sewing machine, they're too tight and loosing you power and economy .

Diesel911 · #6 03-18-2019, 03:22 PM

Quote:

Originally Posted by tyl604

Check your switchover valve; if it is clogged, you will get no power. Or if a vac hose has dropped off.

And the Banjo Bolt at the rear of the Intake Manifold that attaches the switch over valve line.

gregp1962 · #7 03-18-2019, 04:49 PM

Before I try to diagnose, I better make sure my lines are correct. The banjo line attached to the rear of the intake manifold is cleaned when I had the manifold off. I just found a disconnected vacuum line that I can't find a place for. It goes from the Y near the oil filter and crosses behind the engine and is currently not connected to anything. Where does it go? Are there any definitive diagrams for both the ALDA and other lines associated with the switchover valve?

http://www.peachparts.com/shopforum/members/gregp1962-albums-repairs-picture6047-extra-vacuum-line.html

tyl604 · #8 03-18-2019, 08:42 PM

Top has two nipples. Vertical nipple leave open. Horizontal nipple - line goes to a nipple on back of valve cover.

Do not remember where the line on the bottom goes but most likely to the ALDA.

Can someone else chime in?

Alec300SD · #9 03-18-2019, 10:26 PM

Quote:

Originally Posted by gregp1962

Before I try to diagnose, I better make sure my lines are correct. The banjo line attached to the rear of the intake manifold is cleaned when I had the manifold off. I just found a disconnected vacuum line that I can't find a place for. It goes from the Y near the oil filter and crosses behind the engine and is currently not connected to anything. Where does it go? Are there any definitive diagrams for both the ALDA and other lines associated with the switchover valve?

http://www.peachparts.com/shopforum/members/gregp1962-albums-repairs-picture6047-extra-vacuum-line.html

Loose vacuum line probaly goes to the modulator on the transmission.

Labeled photo of the switchover valve and functional diagram are in the attached pdf.
http://handbook.w116.org/Engine/617/09-425.pdf

tyl604 · #10 03-19-2019, 08:52 AM

Boy, I must be way off. Need to go down to the garage and look at mine.

gregp1962 · #11 03-19-2019, 11:04 PM

I'm getting boost while accelerating starting around 1500 RPM. Full boost at about 2000. But, full boost for me is 8 lbs at this point. I'm thinking maybe the wastegate needs to be tightened a bit to increase it to 11 lbs. Do you all find it difficult to adjust wastegate while on the car? (Garrett)

ROLLGUY · #12 03-20-2019, 12:06 AM

It really does not matter how much boost you have if you are not adding fuel along with that air. Make sure you have the proper boost signal to the ALDA. The way I check it is to (1) remove the banjo bolt at the ALDA (2) with a finger sealing one side of the banjo fitting (the hose going to the fitting on the manifold) (3) while holding the engine at a steady RPM (about 2,000) (4) press the open end against where it would be if the bolt was holding the fitting against the ALDA. If the engine RPM increases, you have a good boost signal. If no noticeable increase in RPM, search for a restriction in the usual places. I personally delete the switchover valve, and provide the ALDA with a full unrestricted signal.

gregp1962 · #13 03-20-2019, 11:50 AM

So, if you delete the switchover valve, are you running rich most of time?

vwnate1 · #14 03-20-2019, 12:55 PM

No because the ALDA controls the fuel mixture .

That valve is for preventuing too much boost pressure from reaching the ALDA as the ALDA can develop leaks after too much pressure .

Yes, the waste gate can be adjusted in situ, in my experience I found that using two thin 8MM ATF nuts locked on the adjuster shaft, made the adjustment dead simple , it's important to lap the wastegate valve when the turbo is off the engine but if it's too late for that just remove the soiral spring holding the cover on and the adjuster is right there .

Getting the ding dang spring back in, is a lesson in patience ~ I discovered that allowing my fingernails to grow out for two weeks in advance, makes holding the inner end of the spring in it's grove, far easier .

When you *think* the cover is in place, grasp it firmly and yank ~ if it pops off, be glad it did as it would have popped off when driving and lost the spiral spring .

Maxbumpo · #15 03-20-2019, 01:41 PM

How fast does the car accelerate from 0 to 60 mph? Should be around 12 seconds I think.

Does the transmission shift at the correct points (about 5000 RPM with wide open throttle (WOT))? There are little tick marks around the perimeter of the speedometer which correspond to the WOT shift points.

Another point: The seals in the ALDA dry up over time, and performance is reduced because the ALDA leaks off the pressure without increasing fuel from the injection pump to match the increased air from the turbo. On the OM60x engines, the ALDA can be taken apart and new o-rings installed. Not sure if that is possible on the older engines, but it wouldn't surprise me.