Soft bottom end power om617 - PeachParts Mercedes-Benz Forum

rwd4evr · #1 12-02-2019, 08:46 PM

My 85 300sd has been feeling really sluggish on the bottom end and actually struggled to keep 60 miles an hour going up a long grade a couple times. I bypassed the overboost solenoid I suspected and it feels a bit better. So I hooked up a boost gauge at the alda to make sure it's getting boost, at the same time removing the line that goes this whatever the hell it is. My vacuum pump recently took a crap so I was thinking that it may be influenced by vacuum and pulling fuel. So now I've got decent power back but I'm only really getting boost to come in at like 2500rpm, so it still pretty soft off the line. On top of that, I'm showing like 16 psi at 4000 rpm. Granted this gauge could be off but it's not affecting when boost comes in. I should have full boost (10 psi?) Before 2000 rpm right? I'm guessing my alda is dying? Once in awhile it feels "spunky" just off idle like it normally did. So, I'm thinking about pulling the thing off. Could I be missing something besides the alda killing boost down low?

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rwd4evr · #2 12-02-2019, 09:34 PM

Side note, I just deleted the EGR with a plate while I was messing with it.

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Usaguy · #3 12-02-2019, 09:40 PM

Quote:

Originally Posted by rwd4evr

I'm showing like 16 psi at 4000 rpm.

fsm says you should have 0.7-0.8 bar (10-12 psi) at 4000 rpm at full load

graph shows 10psi at 2000rpm at full load

link to the boost graph on page 4:

https://www.startekinfo.com/StarTek/outside/12265/disc_2/program/Engine/617/09-450.pdf

rwd4evr · #4 12-02-2019, 10:07 PM

Just found the waste gate line was broken. Now have correct 10 psi at full tilt. Boost still is just starting to come up at like 2200. No full boost untill very close to 3000. I'm tempted to throw a little propane at it to see if it's a lack of fuel at low rpm causing the late boost. It pops up very quickly once it gets up to the higher range. If I roll in low gear at 2500 and whack it it jumps to about 8 and rolls up to 9.5-10 at 2900-3000. I don't hear any turbo crunchy sounds. I guess I should pull das boot and see if there is any loose or tightness in the turbine shaft. I'm fairly convinced in my head it's the alda. But really I've never had any issues with the running condition of a om617. Had the over boost solenoid go screwey on my 300td, unplugged it and never had another problem.

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rwd4evr · #5 12-02-2019, 10:13 PM

Quote:

Originally Posted by christuna

fsm says you should have 0.7-0.8 bar (10-12 psi) at 4000 rpm at full load

graph shows 10psi at 2000rpm at full load

link to the boost graph on page 4:

https://www.startekinfo.com/StarTek/outside/12265/disc_2/program/Engine/617/09-450.pdf

Nice!! Thank you, I was waiting for someone to say where and how much I should be seeing. That is perfect. I thought I remembered that reasonable boost should be in at 1500 and all of it shortly after. I've definitely got something going on.

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Diesel911 · #6 12-03-2019, 12:06 AM

Thanks for posting the Chart.

Poor acceleration is usually due to a fuel supply issue.

Restricted Tank Screen, Plastic filter and or spin-on Filter.
Then there is the Fuel Pressure Relief/Overflow Valve that controls the fuel supply pressure to the Elements inside of the Fuel Injection Pump.

If you have the type of Fuel Pressure Relief/Overflow Valve that can be taken apart there is a spring and ball bearing inside; the ball bearing is the valve. The Spring can be stretched to achieve a free length of 27mm.

Sometimes the issue is a plugged or restricted fuel tank vent.

Diesel911 · #7 12-03-2019, 12:08 AM

See if your ALDA will hold a vacuum. If it does not it could mean the metal capsule has a crack.

rwd4evr · #8 12-03-2019, 12:58 AM

Quote:

Originally Posted by Diesel911

See if your ALDA will hold a vacuum. If it does not it could mean the metal capsule has a crack.

That's a good idea. Have to try that tomorrow.

As far as a filter, I guess it's possible but the big filter is fresh. The little filter I actually removed and cleaned a few weeks ago when it started sputtering and dying. I'm pretty familiar with filter running issues. I have a new little one I am putting on to get it out of the equation but I don't see how it's bad down low and fine up top with a fuel restriction. Maybe lift pump? IDK.

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Diseasel300 · #9 12-03-2019, 08:36 AM

Quote:

Originally Posted by Diesel911

See if your ALDA will hold a vacuum. If it does not it could mean the metal capsule has a crack.

The capsule is extremely durable. Usually lack of holding vacuum is the rubber seals. There's a thread on here with the sizes. Replacing them makes a HUGE difference in how the car drives, and yes it's worth doing.

rwd4evr · #10 12-03-2019, 06:03 PM

So opening up the top square part and installing orings basically? Kent seems to say once it's opened it's done. What is the alda removal vs non removal crowd these days? Most threads I found were years old.

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Diseasel300 · #11 12-03-2019, 06:07 PM

Kent is full of it, he seems to thrive on spreading FUD. It's just a metal bellows housed in an aluminum case with 2 rubber O-ring seals in it. Having done several, I can assure you they are not "done" once opened. If the seals leak, you have to build that much more boost to overcome the leakage before the bellows collapse and lift the fuel enrichment plunger on the IP.

rwd4evr · #12 12-03-2019, 08:48 PM

I take most of what he says with a grain of salt but when I've never been in something I'm certainly more cautious. If I open the top while it's in place I'll essentially have it "removed" performance wise right? So I can see if it's smoky ECT.? Then put new seals in and see how it drives in comparison. I didn't even get to check it today.

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vwnate1 · #13 12-03-2019, 09:05 PM

Subscribed to see what you discover .

? Is the ALDA holding vacuum ? .

I've discovered sticky / leaky boost pop off valves, if you take the turbo off it's a simple thing to rake the valve out (it's just a BIG exhaust valve) and hand lap it until it seals properly again, this will increase the speed in which the boost pressure builds .

A -little- bit more boost is helpful too once you get it set right .

Diseasel300 · #14 12-03-2019, 09:06 PM

The ALDA has to come off the IP to open it. There are 4 screws on the bottom side that have to come out. A vice, hand-impact, and #3 phillips bit are your friends. If you want to run it without ALDA, you certainly can. If running without ALDA solves the power problem, you know that re-sealing it will fix the issue.

vwnate1 · #15 12-03-2019, 11:18 PM

Don't be in any hurry to open it up until you've tested it in situ and then checked / cleaned the boost sensing pipes, adjusted the valves (if they're quiet you know they need adjusting !) , removed and pop tested the injectors, so on and so forth ~ unless everything is in perfect order doing modifications will make things worse and simply piss you off .

BT, DT and spent 50 years working on engines that others had screwed up by ignoring the basics .