Super Slow 1987 300D - PeachParts Mercedes-Benz Forum

noquarter1 · #1 07-10-2019, 01:41 PM

Tl;DR version: I’m trying to get input on my action plan for fixing my slow 1987 300D with 255k miles (20-25 second 0-60 time). I have a tentative plan which I’d like input on.

Long version: I recently inherited a 1987 300D with 255k miles from the original owner, my uncle. It wasn’t running, so I had it towed to my house where I swapped the battery and it fired right up. It had a super rough idle that shook the entire car, so I took it to a local indie Mercedes mechanic to diagnosis. He changed the oil, replaced the injection return hoses, said he “repaired fuel injection” (as per the invoice, need to get clarification from him on what that means), and replaced the overload fuse. When I got the car back and the car idled as normal, so I put new tires on it since the old ones were dry rotted. After driving it for the first time, I found it’s extremely slow. I didn’t think anything of it at first (being the former owner of a 1989 Land Cruiser, which is basically a glorified tractor), but I’ve since seen many sources say that the car is capable of a sub 13 second 0-60 time.

I tested the 0-60 time on a slight decline, and it was in the mid 20’s. This is probably partially due to the car being reluctant to upshift until the RPM's are high (and it feels like a kick in the pants when it does, but that’s another issue for another day, thinking it might be the transmission modulator). It has decent off the line to 10-15 mph (seat of my pants observation), but no guts after that. I’ve only had naturally aspirated cars, so I’m not absolutely sure, but I don’t think the turbo is spooling, or at least I can’t tell any difference. After a few hours of internet research, I came up with a tentative plan. Before I dive in, I’d love to utilize the collective wisdom of this board to make sure I'm on the right track, and hopefully provide a plan of action for others who might need direction.

Current Plan (In Order of Escalation):
-Put fresh diesel in tank (current fuel is a few years old)
-replace fuel filters
-Open air intake; replace air filter if necessary; make sure it’s clear all the way to the turbo. Check to make sure airflow sensor is clear
-Remove the line going from the intake manifold to the switchover valve; clean nipple, ensure hose isn’t cracked and is clear
---repeat for the line going from the switchover valve to the ALDA
-run line from intake manifold directly to ALDA; if performance improves, replace switchover valve (haven’t been able to find a part number for this yet)
-remove ALDA; if performance improves or black smoke shows upon acceleration, reinstall and adjust via shims or screw on top
-check wastegate on turbo to make sure it works. If not, replace with aftermarket wastegate for 602 from atpturbo (haven’t been able to find a 603 wastegate)
-make sure turbo spins freely, doesn’t have excess play. If it does, service or replace
-remove/cap EGR (I’ll eventually do this regardless of whether or not the issue is fixed by this step, as my car is exempt from emissions)
-drop fuel tank, clean screen
-cut out catalytic converter (or whatever it is that Mercedes put in when they replaced the trap) in case it’s blocked. Replace with straight pipe.
-rebuild/replace injection pump
-take car out back behind the shed; put it out of its misery

Do you think I’m missing any steps, have any errors, or should rearrange the order? I’m going to start at the beginning tonight. Any input and/or feedback is appreciated, and I’ll update the thread with my progress to hopefully help others with this issue.

Diseasel300 · #2 07-10-2019, 02:01 PM

Sounds like lack of turbo boost or a restricted exhaust. Trace the hoses from the intake manifold to the ALDA, the switchover valve on the firewall is often connected incorrectly or clogged internally. Manifold line goes to the bottom nipple. Middle nipple goes to the ALDA. Top nipple is open to atmosphere. Open up the downpipe and see if you suddenly have power, if the cat is clogged, it'll kill your performance, diesels need a free flowing exhaust.

The transmission issues are probably related to the lack of power. The transmission is tuned to shift with an expected power input, if the power isn't there, you get a late/rough shift. Fix the power problem before worrying about the trans.

Maxbumpo · #3 07-10-2019, 02:57 PM

X2, what Diseasel said. Classic symptoms of no turbo boost, usually due to a plugged overboost valve (aka switch-over valve). Could also be due to failed turbo (can you spin by hand, access via front air intake accordion plenum), broken or disconnected boost line, busted ALDA.

Other possible causes you've got in your list (air filter, plugged fuel filters / tank screen, plugged exhaust system).

Make sure the brakes aren't dragging.

EGR failed wide open causes a massive power loss, accompanied by lots of smoke.

Maxbumpo · #4 07-10-2019, 02:58 PM

May also be a really stretched timing chain causing the injection pump timing to be way late. If the car got regular oil changes, not likely, hopefully you have maintenance records you can check.

dieselworks · #5 07-10-2019, 08:07 PM

I'd check the condition of the small hoses. If they are in poor condition you could be loosing a pressure signal and that wouldn't allow for extra fuel to accommodate boost. Especially if the car sat outside. But do check to see if the turbo spins. If it doesn't then a kit is in order. It does sound like you're not getting boost.
I had a boost hose that came from the intake manifold to a connection that went to the alda that slipped off and no boost. Could be something simple like that.
Roddy

Sent from my SM-G900I using Tapatalk

noquarter1 · #6 07-10-2019, 11:25 PM

Thanks everyone for the quick replies.

I didn't have time to do much tonight, but I did look at the hoses running from the intake to the overboost/switchover, and the hose running to the ALDA (see attached pic, green arrow is from intake, red arrow is to ALDA). It was all hooked up correctly. Is the cap supposed to be on top of the valve covering the top most nipple?

I then disconnected the hose from the intake to the switchover valve, removed the nipple from the intake manifold, and cleaned it with brake cleaner. I also then put a new hose running directly from the intake nipple to the ALDA, do see if the switchover valve is bad. A quick spin around the block and a quick 0-40 (traffic) showed that nothing changed, so it's not the switchover valve. I didn't replace the hose going from the switchover to the ALDA, but I doubt that's the root.

Tomorrow I'll check out the turbo to see if it spins freely, and this weekend I'll see about removing the Cat from the exhaust. Fuel filters are ordered, so I'll install those when they arrive.

Thanks everyone, and, once again, if you have advice or feedback, please let me know.

R.Diesel · #7 07-11-2019, 12:25 AM

Instead of trying “fixes” I would suggest you accurately diagnose the problem. Start by attaching a T-fitting to the pressure line between the ALDA and the intake manifold. Gages are cheap at harbor freight. Once you are sure that you have a boost issue you can start testing the various elements starting with a vacuum test on the ALDA. After that ensure that you’re have proper vacuum in the system and replace as necessary. Finally test wastegate actuator, transducers and switchover valves.

noquarter1 · #8 07-11-2019, 01:14 AM

Quote:

Originally Posted by R.Diesel

Instead of trying “fixes” I would suggest you accurately diagnose the problem. Start by attaching a T-fitting to the pressure line between the ALDA and the intake manifold. Gages are cheap at harbor freight. Once you are sure that you have a boost issue you can start testing the various elements starting with a vacuum test on the ALDA. After that ensure that you’re have proper vacuum in the system and replace as necessary. Finally test wastegate actuator, transducers and switchover valves.

Good call, I'll pick some gauges up and test. I'll search for the info as well, but do you, by chance, know the proper psi I should be looking for?

It's true that I'm sort of throwing a lot of stuff against a wall and hoping something sticks, but since the car has been neglected for years, I don't think anything I do is wasted effort. Anything I look or replace today is something I don't have to do tomorrow, though potentially the scattershot approach is delaying the ability to merge onto the interstate without saying a few hail mary's first.

R.Diesel · #9 07-11-2019, 03:53 PM

Two different issues here: pressure and vacuum.

The mechanism that meters fueling is called the ALDA. A pressure hose goes from the intake manifold to the ALDA. If pressure doesn't reach the ALDA actuator due to a clogged nipple, deteriorated hose, or leaky ALDA your engine will not get sufficient fuel, there will be a loss of power and harshly shifting transmission as a result of mismatched power to clutch pressure ratio.

The mechanism that meters boost is the wastegate actuator. A vacuum line is feeding pressure from a switchover valve and vacuum transducer to the actuator. At idle you should have Vacuum pressure equal or near system values ~25MMhg I believe.

Double check this number elsewhere but I believe our cars run around 1 bar or 14psi at WOT or thereabouts. T a vacuum/pressure gage to the intake/ALDA line run a hose to the interior, hook up the gage and go for a drive. Note the pressures at idle partial, and full throttle. Once that is done we can troubleshoot from there.

This will show both pressure and vacuum.

https://www.harborfreight.com/automotive/diagnostic-testing-scanning/fuel-pump-and-vacuum-tester-62637.html

get enough of this

https://www.pelicanparts.com/More_Info/0079976182.htm?pn=007-997-61-82-M22

and two of these

https://www.pelicanparts.com/More_Info/1162760929.htm?pn=116-276-09-29-M22

and one of these

https://www.pelicanparts.com/cgi-bin/ksearch/PEL_search_2016.cgi?command=DWsearch&description=1170780145

Check for veracity but it should get you started...

Diseasel300 · #10 07-11-2019, 04:21 PM

Quote:

Originally Posted by R.Diesel

The mechanism that meters boost is the wastegate actuator. A vacuum line is feeding pressure from a switchover valve and vacuum transducer to the actuator. At idle you should have Vacuum pressure equal or near system values ~25MMhg I believe.

1986/87 cars are a PRESSURE operated waste gate, the hose to the waste gate actuator should connect to the manifold side of the turbo. The vacuum operated one didn't come along until later. If there is a vacuum anything on the turbo it is the ARV and can be safely disconnected (federal W126 cars with the same engine didn't have it).

R.Diesel · #11 07-11-2019, 04:56 PM

Quote:

Originally Posted by Diseasel300

1986/87 cars are a PRESSURE operated waste gate, the hose to the waste gate actuator should connect to the manifold side of the turbo. The vacuum operated one didn't come along until later. If there is a vacuum anything on the turbo it is the ARV and can be safely disconnected (federal W126 cars with the same engine didn't have it).

OP heed this. There are several different layouts and I referenced a newer design. The procedure is the same. Make sure you familiarize yourself with your diagram and understand what does what. Thanks for clarifying diseasel.

noquarter1 · #12 07-11-2019, 10:39 PM

Thanks for the help. Please excuse my ignorance, I'm clearly new to this, despite having tried to do my research, which is why I confused the intake manifold to ALDA as being a vacuum, when it is pressure line.

I attached a pic that I drew on to show what I did. I ran a line (red in the pic) from the intake manifold nipple directly to the 'Y' connector which is also connected to the ALDA and goes on to something else (transmission related, I think). In that line from the intake manifold nipple to the 'Y' connector, I inserted a 'T' connector, with that line running to the Harbor Freight pressure gauge (represented in green). I then ran it inside the car, and, once warmed up, floored it to see how much pressure I'm getting (measured clockwise on the gauge).

At idle, it registered flatly at 0. The needle didn't move.

I then did a 0-60 run with the accelerator firmly against the floor. The highest psi it registered was 3.

So, this would suggest there's no boost at all, is that correct? I wasn't able to get to the turbo tonight to see if it spins or if the wastegate opens. Could a clogged cat converter also be a culprit?

Thanks so much.

dieselworks · #13 07-13-2019, 02:26 AM

If the turbo is spoiling and you get 3 psi then it's starting to sound like the problem is related to a clogged exhaust. What I would do is disconnect the downpipe and lay it to the side. Use some wire to temporarily hold it in place. Take the car out. Yeah it'll be a little loud. And check the turbo pressure and see if you get anywhere near 14 psi. If the boost responds the problem is a restriction somewhere downstream of the turbo. This is pretty much a no cost check and will definitely point you in the right direction.
Be sure to let everyone know the results of your little experiment.
Roddy

Sent from my SM-G900I using Tapatalk

R.Diesel · #14 07-13-2019, 05:11 AM

Quote:

Originally Posted by noquarter1

Thanks for the help. Please excuse my ignorance, I'm clearly new to this, despite having tried to do my research, which is why I confused the intake manifold to ALDA as being a vacuum, when it is pressure line.

I attached a pic that I drew on to show what I did. I ran a line (red in the pic) from the intake manifold nipple directly to the 'Y' connector which is also connected to the ALDA and goes on to something else (transmission related, I think). In that line from the intake manifold nipple to the 'Y' connector, I inserted a 'T' connector, with that line running to the Harbor Freight pressure gauge (represented in green). I then ran it inside the car, and, once warmed up, floored it to see how much pressure I'm getting (measured clockwise on the gauge).

At idle, it registered flatly at 0. The needle didn't move.

I then did a 0-60 run with the accelerator firmly against the floor. The highest psi it registered was 3.

So, this would suggest there's no boost at all, is that correct? I wasn't able to get to the turbo tonight to see if it spins or if the wastegate opens. Could a clogged cat converter also be a culprit?

Thanks so much.

It could be a lot of things. Have you purchased a handheld pump like the mityvac? I should have added it to the list as you haven't really tinkered with Mercedes vacuum systems before.

https://www.harborfreight.com/mityvac-vacuum-pump-39522.html

You'll need it to diagnose leaks around your system. That or a good cigar

Id start with the easy stuff first. 138 sends pressure to 103. The more pressure the more fuel and consequently more boost. Check that 138 isn't clogged (doesn't hold even slight vacuum) and that 103 doesn't leak that pressure (does hold at least partial vacuum)

Maxbumpo · #15 07-13-2019, 07:53 AM

Quote:

Originally Posted by R.Diesel

Id start with the easy stuff first. 138 sends pressure to 103. The more pressure the more fuel and consequently more boost. Check that 138 isn't clogged (doesn't hold even slight vacuum) and that 103 doesn't leak that pressure (does hold at least partial vacuum)

This diagram appears to be for the vacuum-operated waste gate? I think it is wrong for the OP's car. The OP has already done the first check, and now performed a different test and determined that boost is way too low. Your second check may be worth a try after we get the boost fixed.