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  #1  
Old 08-15-2012, 05:52 PM
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Help, local MB mechanics can't figure out my car

93 300D, 2.5T W124 diesel.

History: I've had this car for 5 yrs and 75K. It never has seemed to have the advertized power that I read on here (0-60 in 12.8secs). Ok, fine, it's a 20 year old car but my 0-60 is probably 30 secs. Finally, recently I totally lost all power, engine idles and takes off just fine but had no boost (boost guage installed awhile ago, turbo had been working as the OEM set up, vacuum wastegate style). Always felt like maybe not enough fuel. Then a couple weeks back, no boost, no power just a real dog worse than it ever has been. Never sounded like it was going to die, just a dog. I could only get 62 mph up hill on the freeway locally (modest grade here in central NC). Runs like mad on the level or downhill of course.

So, I did the gsxr wastegate mod, switched over to the pressure wastegate, boost on default set up. I now have boost, up to ~13 psi at max RPM's but still major lack of power. Car has zero smoke under hard acceleration.

Fuel filters changed, no change in performance. So I gave up and took to the local MB shop (ABW in Chapel Hill, NC). I told them when i dropped it off the mod i had done to the turbo.

Oh boy, I get a call today from a mechanic (had a bit of an attitude) saying all my vac lines are buggered up and I can pay him $95 and hour to hook back up. I say no, no, no, you don't understand. So I try to explain this is now like the W123 style. He still doesn't follow me. Says I have no boost to trigger the aneroid sensor (I assume that is the alda??). I mention, look at the boost gauge on the dash, it should say around 12 psi when winding up! Then says my vac is bad, well I have one of those gauges too, reading 22 mm hg. At this point I am thinking uh oh, I am in trouble with this guy. He says he blocked the EGR port and no change (well duh, that is unhooked now that Ihave the pressure wastegate set up. I just left the vac line there for looks for inspection. I guess he never noticed the other end is off, just there for looks for the NC stateinspection).

So I told him - just stop what he's doing. Please don't work further on my car.

So I am on my own (and this forum). Now what, please help!!! I am looking for what to do next for diagnosis to find my problem. I really feel it's a fuel supply issue. When i changed the filters, fuel just ran out of the supply line freely, didn't seem plugged but not sure what it should look like. things on my mind are the following.

Do the ALDA's screw up ever?? How do I tell?
Does the lift pump ever fail?
Anywhere else to look and how to check things out.
I've done some searching here but not exactly clear on how to proceed. I am a moderate DIYer and can usually think through things but want some advice from the guru's here. Thanks!

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  #2  
Old 08-15-2012, 06:14 PM
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Quote:
Originally Posted by benmack1 View Post
Does the lift pump ever fail?
Does it have moving parts?

Anything with moving parts can fail. I had a 617 that was a dog until I overhauled the fuel pump.
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  #3  
Old 08-15-2012, 06:22 PM
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Quote:
Originally Posted by benmack1 View Post
93 300D, 2.5T W124 diesel.


Do the ALDA's screw up ever?? How do I tell?
Yeah the banjo fitting that screws into the intake gets filled with oil and soot. This blocks any pressure from reaching the ALDA at the IP and you get minimal fuel. Your lines can also leak away your signal, giving the same result.
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  #4  
Old 08-15-2012, 06:24 PM
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I am not familiar with your car, but I do know diesels. Lack of power is usually traced to lack of fuel. It may be that your fuel pressure is low. You might want to put a fuel pressure gauge on your supply line and check the pressure, especially when the engine is running.

Check to ensure that you don't have a blockage from somewhere else, like the tank strainer (I don't know if a W124 has one) or filter.

I would look at possibly running the car on an auxiliary fuel supply (like a small can of known good diesel with the supply and return lines running into it) to ensure you don't have a problem there.

Good luck.

PE
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Old 08-15-2012, 07:21 PM
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If I'm not mistaken, the ALDA on the 602 does not have a banjo fitting....so you don't have the same issues that you do with the older cars.

Why not remove the ALDA just for grins and see what happens?
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  #6  
Old 08-15-2012, 07:49 PM
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which end of chapel hill are you on? I'm a bit of a drive, but Mt Holly/charlotte is not far, and I can test your fuel pressure, and trace out the lack therof...
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  #7  
Old 08-15-2012, 08:22 PM
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Quote:
Originally Posted by vstech View Post
which end of chapel hill are you on? I'm a bit of a drive, but Mt Holly/charlotte is not far, and I can test your fuel pressure, and trace out the lack therof...
Man, that is an awesome offer and very kind of you. I may take you up on that. I will try a couple of the simple suggestions before I burden you with my issue. If I get no where I'll be trying to get back to you on this. I have read alot of your posts over the past few years so really appreciate the offer from an expert. I live actually out near Burlington so not that far from Charlotte. Heck the car cruises on the flat just great so should make it to Charlotte fine if needed.

I will try a couple things first (no idea how to measure fuel pressure so will try the things I do think I can manage to do without making it worse). I like the 'run it on an accessory fuel tank' I have a diesel purge set up with a gatorade bottle I can use as a makeshift fuel tank for supply and return to eliminate the strainer/tank.

I will also remove the alda and see what happens. I've read about that and kind of wanted to see what that might do anyway. I'll report back on those results (may take a bit as I have a business trip next week to get out of the way).

Thanks a bunch guys!!! Great ideas and great folks that offer such help. I don't want to be a burden but really appreciate the help. That shop was such a disappointment today - Ugh. I'm kinda looking forward to this as a chance to learn though. Also happy to have my precious pile of junk back on my property in my possession. that mechanic makde me nuts with his incompetence. Good grief, I am just a half-way shadetree mechanic and felt I understood more than he does!
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Old 08-15-2012, 08:23 PM
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Quote:
Originally Posted by shertex View Post
If I'm not mistaken, the ALDA on the 602 does not have a banjo fitting....so you don't have the same issues that you do with the older cars.

Why not remove the ALDA just for grins and see what happens?
Woops, I was afraid of that, I couldn't remember, sorry if that caused confusion benmack.
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  #9  
Old 08-15-2012, 08:25 PM
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One little thing I might mention....I found trying to get the ALDA off with a 24mm wrench and channel locks (as gsxr suggests) a little unwieldy. Next time I do it I think I'll use two wrenches (24mm and 27mm) instead.
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  #10  
Old 08-15-2012, 08:28 PM
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Whatever kind of fitting it is can clog with manifold soot. The kind on your car takes a 12mm wrench. Don't overtighten or you'll be buying a new one. Make sure there's a clear path for air from the manifold to the ALDA. If a clear line doesn't restore power, remove the ALDA either to test or permanently.

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  #11  
Old 08-15-2012, 08:44 PM
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Originally Posted by sixto View Post
Whatever kind of fitting it is can clog with manifold soot. The kind on your car takes a 12mm wrench. Don't overtighten or you'll be buying a new one. Make sure there's a clear path for air from the manifold to the ALDA. If a clear line doesn't restore power, remove the ALDA either to test or permanently.

Sixto
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So what exactly needs to be done? Loosen that fitting then clean out things with a pipe cleaner or something?
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  #12  
Old 08-15-2012, 09:08 PM
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The 617s are not made like this and I am not sure which of the newer models are but the Fuel Pressure Relief/Over Flow Valve on the back Rear of the Fuel Injection Pump is said to have Plastic Parts inside that go bad. That would reduce the Fuel Pressure inside of the Fuel Injection Pump Housing.

More than a few people have rebuilt their Fuel Supply/Lift Pumps. There is 2 DIYs on the type you have on your Fuel Injection Pump.
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Old 08-15-2012, 09:09 PM
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I spritz brake parts cleaner through the whole chain. The overboost switchover valve doesn't seem to mind.

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  #14  
Old 08-16-2012, 09:47 AM
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I 2nd post 4 ,if fuel is being slowed by filters ,and the tank filter is the summertime wonder because of algea ,youll have this same issue.Start simple and work your way up.

Last edited by chasinthesun; 08-16-2012 at 11:25 AM.
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  #15  
Old 08-16-2012, 11:47 AM
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Quote:
Originally Posted by benmack1 View Post
I now have boost, up to ~13 psi at max RPM's but still major lack of power.
This is rather interesting.

If you measured the boost properly, and hopefully at the ALDA line, the ALDA will be seeing 13 psi boost. Therefore, there is no possiblity of clogged fittings or bad lines or any other issue other than an ALDA that doesn't respond to boost.

That being said, I find it very surprising that the turbo can actually make 13psi without the additional fuel provided by the ALDA. I would suspect that the 13 psi, if accurate, must occur very high in the rpm range............probably above 4000 rpm or more. This would indicate that you definitely are not getting the fuel from the ALDA although it does see the boost pressure from the turbo.

The fastest check you can possibly make is to simply remove the ALDA and take it for a drive. You may find that all issues disappear if the ALDA is the culprit.

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