90 300D Power loss - PeachParts Mercedes-Benz Forum

2.5Turbo · #1 12-25-2006, 03:46 AM

Well, I come back from school for Christmas and my car is slow again

My parents have been driving it occasionally while I was gone so it just doesn't sit and rust. Recently they drove it and it all of a sudden was really low on power, like the boost line to the ALDA was clogged. Really flat power band like a non turbo car. I removed the ALDA lines and fittings and blew them out and cleaned them, but same result. The switchover valve passes air fine. I even tried directly connecting the ALDA to the manifold with just vacuum fittings and a coupler. No dice.

Tried resetting the EDS by leaving the negative battery cable off overnight. Still slow. Don't have a boost gauge so there really is no way of testing the turbo, but I did pull the pipe to the turbo and check the compressor. It felt within spec and turned freely. I'm starting to suspect the fuel system. I didn't see any bubbles larger than normal in the pre-filter, and I haven't taken the spin on filter off yet as I don't have a replacement at the moment. It starts right up and doesn't hesitate like an engine with a leaky fuel system would do. Should I just change the filter and go from there? I did put a couple gallons of B99 in there about 1500 miles back, could gunk released by that be plugging my filters?

#2 12-25-2006, 04:19 AM

Filter is a good place to start.

fj bertrand · #3 12-25-2006, 07:15 PM

How's the air filter? also, when chaging the secondary spin on fuel filter, pour the contets of the filter into a glass jar and see what it has caught...

2.5Turbo · #4 01-17-2007, 11:19 PM

Changing the filters didn't help, so I took it to my indy mechanic. They read the trouble codes from the EDS and found one for the air flow sensor, fuel rack position sensor, and crank sensor. They cleared the codes. Checked the car and it still didn't have any power. They then drained the tank and cleaned out the strainer which was pretty gunked up. There was an improvement, but it still isn't like it used to be. Still kinda feels like it does when the ALDA is unplugged, however I have verified that the switchover valve, lines, and fittings are clear and passing air.

Any ideas? I still haven't figured it out. One scenario I can think of is that the mechanic drove the car right after he cleared the codes, and it set another when he was done driving it. What's the procedure for reading and clearing codes on the EDS? I seem to remember seeing somewhere that it involved a light bulb and bridging some pins on the socket up next to the battery.

2.5Turbo · #5 01-20-2007, 01:03 AM

Posted a reply on an older thread and didn't get any replies so I thould a new thread would get people's attention

Anyway, my 1990 300D 2.5T just started acting like the ALDA line was yanked off out of the blue one day. No warning signs, it just went back to its old ways of 18-19 second 0-60's. Ok, that's the sign of no boost. So I go to the ALDA and yank all the lines off the manifold and switchover valve, and blow them out. Nothing was blocking them, and the switchover valve was passing air. The fittings in the ALDA and manifold were clear too. I even bypassed the switchover valve and fed boost pressure directly to the ALDA. So the ALDA was getting pressure. Next thing I thought was filters. Had the air and both fuel filters replaced, no dice. At that point, I gave up

and brought it to the mechanic.

He had the car forever...he checked nearly everything. He read the codes, and it was throwing a few. One of them was a crank sensor, so he decided to try and replace that. He replaced it, and it still was slow. Reset the codes, and took it for a drive. Still slow. He hooked a boost gauge up, and saw that it was getting low and erratic boost. He decided to take a look at the tank strainer, and it was starting to get plugged with gunk. He drained the tank and cleaned the strainer. It got a little better, but it still was way under spec. I'm going to build a little EDS reader circuit so I can get any more codes it has set and clear them. Any further ideas from anyone? I'm certain that the fuel system from the tank to the IP is now squeaky-clean, and all filters are brand new.

I'm pretty stumped......

Monomer · #6 01-20-2007, 08:14 AM

a turbo problem?

did you check for play in the turbo?

Brian Carlton · #7 01-20-2007, 09:08 AM

Quote:

Originally Posted by 2.5Turbo

He hooked a boost gauge up, and saw that it was getting low and erratic boost.

Not entirely sure on how the boost is controlled on the 2.5, but, this is the place to begin. Does the turbo have sufficient output and what's controlling that output?

Doesn't that vehicle have a vacuum controlled wastegate? If so, the problem is almost certainly due to the vacuum control system. There's a vacuum leak somewhere or the wastegate itself is not functioning properly.

If the ALDA doesn't see boost, the vehicle will always be a dog.

nhdoc · #8 01-20-2007, 09:58 AM

It's obvious but often overlooked...fuel and air filters...how long has it been since they were changed? Fuel filters especially can seem to get plugged "overnight" and cause performance problems, especially with the new fuels (don't ask me how I know this

).

If the boost test was accurate then I would also look at the wastegate controls...that would be #2 on my list after making sure the filters were clear.

kerry · #9 01-20-2007, 11:02 AM

Filters were done.
I'm with Brian. Check the wastegate.

TMAllison · #10 01-20-2007, 11:24 AM

I did this on a 90 2.5 turbo ~8 years ago so do not remember exactly, but.....

Look at parts 707 on the diagram. As I recall was referred to as Y31/1 & 2 and one of them provided vacuum for the wastegate. They are located just behind the right headlight on the lower firewall.

http://www.detali.ru/cat/oem_mb2.asp?TP=1&F=124133%5F15S&M=603%2E960&GA=722%2E357&CT=M&cat=503&SID=14&SGR=135&SGN=08

pmari · #11 01-21-2007, 01:46 AM

2.5 Turbo Boost problem.

What codes are you throwing?

Brian Carlton · #12 01-21-2007, 08:23 AM

From the other thread, it's almost a certaintly that you don't have vacuum to the wastegate.

Test for this with a suitable vacuum gauge and T it into the wastegate vacuum line. Drive the vehicle and watch for vacuum on the gauge. Without it, you'll get no boost because the wastegate is stuck open.

2.5Turbo · #13 03-14-2007, 02:00 PM

Follow up and cry for help on my no boost 300D 2.5T:

Well we took it to the mechanic again and they ran some tests on the vacuum wastegate system and found it fully functional. Read the codes again and it was still giving air mass sensor, rack position sensor, and crank speed sensor codes. He recommends just letting it go, waiting until something breaks enough to render the car inoperable. He says the sensors and the labor required to get to them are too expensive for it to be worth it on this car. I'm going to build a code reader today and start tinkering. Any thing I can do to these sensors to fix them? Or could the codes be a result of a different problem? I'm really tired of 18+ second 0-60's.

For those not familiar with the problem, here's what we've done so far:

-Replaced fuel filters
-Cleaned tank screen
-Ran straight diesel purge...fuel system is squeaky clean now
-Checked injector nozzles, pop pressures, within spec
-Cleaned out ALDA lines and switchover valve, everything passes pressure
-Checked overboost switch and switchover valve, functional
-Oil/filter change

If this is going to cost thousands to get back on the road, I'm thinking about swapping wastegates to a pressure activated one like on the 87 300D. Is that possible on my turbo, or does the whole thing need to be replaced? As far as I know it's the EDS that is holding my wastegate open. Eliminating that link (and keeping the transducer with a golf tee in the line to the actuator) should fix the problem, even if it will go crazy with all these codes.

I'm at a loss here.....any help whatsoever will be greatly appreciated!

Dana B. · #14 03-14-2007, 04:21 PM

You're right: Without a turbo, car isn't worth driving. Check all vacuum lines. Mine gave me trouble for a year until I disconnected the overboost assy.

larry perkins · #15 03-14-2007, 04:29 PM

did you replace the air filter?
larry perkins

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