1987 300D 12 seconds 0-60 -- what else to check? - PeachParts Mercedes-Benz Forum

renaissanceman · #1 08-06-2015, 02:37 PM

I finally checked the 0-60 time on my 1987 300D after all the work I've done to it, and found it was unchanged at around 12 seconds.

This run was done at 90 degrees ambient, with A/C off, but headlights and fogs on. The other run was done at 35 degrees ambient during the daytime. So theoretically, it may be slightly faster...but nowhere near the 9 seconds 0-60 I have read of.

I recently ran diesel purge though the injection system. The EGR is removed, and the ARV is disabled. I have cleaned out the line from the manifold to ALDA (it was clogged, but did not seem to make a difference). Fuel and air filters are new.

At full throttle shift points are near 5000 rpm. The engine starts to pull very hard just over 2000 rpm.

The manifold is still quite clogged with carbon, I just haven't gotten around to cleaning it yet. I'm wondering about the cat and whether it is restricted/clogged. It has had the recall done, at least the portion that replaced the trap ox with a cat. I don't know whether the turbo was replaced. I'm thinking about calling my Mercedes dealer to see if they have records of when the recall was done, and how much of it was done. I pretty consistently get 28-30 mpg, although on my last trip I got 26 or so with the A/C going full tilt through 110 degree heat.

Any ideas what to check next? I'd like this thing to scream.

tjts1 · #2 08-06-2015, 03:05 PM

Quote:

Originally Posted by renaissanceman

I finally checked the 0-60 time on my 1987 300D after all the work I've done to it, and found it was unchanged at around 12 seconds.

This run was done at 90 degrees ambient, with A/C off, but headlights and fogs on. The other run was done at 35 degrees ambient during the daytime. So theoretically, it may be slightly faster...but nowhere near the 9 seconds 0-60 I have read of.

I recently ran diesel purge though the injection system. The EGR is removed, and the ARV is disabled. I have cleaned out the line from the manifold to ALDA (it was clogged, but did not seem to make a difference). Fuel and air filters are new.

At full throttle shift points are near 5000 rpm. The engine starts to pull very hard just over 2000 rpm.

The manifold is still quite clogged with carbon, I just haven't gotten around to cleaning it yet. I'm wondering about the cat and whether it is restricted/clogged. It has had the recall done, at least the portion that replaced the trap ox with a cat. I don't know whether the turbo was replaced. I'm thinking about calling my Mercedes dealer to see if they have records of when the recall was done, and how much of it was done. I pretty consistently get 28-30 mpg, although on my last trip I got 26 or so with the A/C going full tilt through 110 degree heat.

Any ideas what to check next? I'd like this thing to scream.

Whoever told you 9 sec is wrong.

http://oudemercedesbrochures.nl/W124_Vorteile300TurboD_1187duits.html

Clean out the manifold asap, it makes more power earlier and helps smooth idle.

I can guarantee the trap ox is clogged. Chizzle it out.

Hook up a boost gauge. You should see 13psi by 2400rpm at WOT. But even if you see the correct pressure, with a clogged intake the airflow is restricted. There are tweaks you can do to get more pressure earlier like a simple electronic boost controller to prevent wastegate creep but cleaning the intake should be done first.

renaissanceman · #3 08-06-2015, 03:16 PM

Trap Ox is gone, and has been replaced by the under car cat.

I'm planning on cleaning the manifold in the next few weeks when I replace the glows. I do get a decent cloud of smoke at 4k+ rpm and WOT, indicating to me an air supply problem. Darn EGRs...

Maxbumpo · #4 08-06-2015, 03:25 PM

You may get a little better by advancing the injection pump timing a degree or two. Make sure the timing chain stretch isn't too bad (less than 5 degrees) or replace it to get the timing (valve and IP) back to spec. Note: replace chain before messing with the injection pump timing.

After that, you would probably want to get the pump re-calibrated or modified for more fuel deliver, add an intercooler, get a shorter differential, etc ($$$).

Other's may have some ideas, but your car is meeting the factory spec for 0-60, so I'd be happy with that and the fuel consumption. I only get 25-26 around town and just a little better on the highway.

Mxfrank · #5 08-06-2015, 05:05 PM

You cleaned out the Alda line...good. This line leads to a switchover valve on the left inner fender, if memory serves. Check the action of the switchover valve. If the line was clogged, the valve may be as well.

renaissanceman · #6 08-06-2015, 06:55 PM

I don't want to modify it, I just want to get it running up to spec. Sounds like I'm close to being there, I thought I was 3 seconds off. I'll check the switchover valve, clean the carbon out of the intake. Should I gut the cat?

Correct me if I am wrong: the switchover valve should be open with the engine off, correct? The pressure switch should be open with no boost.

What's the best way to clean the switchover valve?

winmutt · #7 08-06-2015, 07:25 PM

Quote:

Originally Posted by renaissanceman

I don't want to modify it, I just want to get it running up to spec. Sounds like I'm close to being there, I thought I was 3 seconds off. I'll check the switchover valve, clean the carbon out of the intake. Should I gut the cat?

Correct me if I am wrong: the switchover valve should be open with the engine off, correct? The pressure switch should be open with no boost.

What's the best way to clean the switchover valve?

The ALDA is a fuel cut off device, starting in the cut off position. As pressure is applied, it increases fuel. When ~16psi or something is reached, the switch vents the pressured air into the atmosphere, cutting fuel and slowing down. When it's in operation the car will oscillate very consistently in power. It could be leaking air, as the ALDA can as well. For starters, just by pass the the valve, take it for a 0-60 spin and see if its any faster. If it is, find a new one. They are about $50 online or $3 at jy found on almost any benz made into the late 80s and on.

The ALDA is adjustable, if it still has the black cap on it, I would back it out 1/2 a turn, unless you live in a state where they do an inspection of such things.

If you don't have emissions, I would see if you can stick a piece of rebar through the cat. If you cant push it through, then keep pushing harder. When you can push the rebar all the way through, you should be turning 168hp.

Drago · #8 08-06-2015, 08:30 PM

0-60 in 12 was the best I could do. removing the ALDA and making sure the vacuum lines seem to improve the acceleration. I don't think I can get it to go any faster unless I do some serious modifications. my mpg dropped to 27

Wodnek · #9 08-06-2015, 08:56 PM

Mine was 10 seconds when i bought it with 170,000 miles. I ran home brew bio in it for 70,000 miles, and today it has 265,000 miles. it is now 11 seconds 0-60. With age and wear these run slower. Figure injector wear, turbo wear, etc. Probably normal. It seems like it is in an acceptable range.

Mxfrank · #10 08-06-2015, 11:57 PM

Quote:

Originally Posted by renaissanceman

I don't want to modify it, I just want to get it running up to spec. Sounds like I'm close to being there, I thought I was 3 seconds off. I'll check the switchover valve, clean the carbon out of the intake. Should I gut the cat?

Correct me if I am wrong: the switchover valve should be open with the engine off, correct? The pressure switch should be open with no boost.

What's the best way to clean the switchover valve?

The switchover valve has an NO and an NC connection. If I recall correctly, the NC connection is permanently capped off. So it should pass air or vacuum when not powered. If it's plugged, you can temporarily bypass it. I've never had much luck with cleaning one that's really jammed with tar, so just replace it.

Leave the cat alone. it'll regenerate itself at highway speed.

tjts1 · #11 08-07-2015, 01:39 AM

Quote:

Originally Posted by renaissanceman

Trap Ox is gone, and has been replaced by the under car cat.

I'm planning on cleaning the manifold in the next few weeks when I replace the glows. I do get a decent cloud of smoke at 4k+ rpm and WOT, indicating to me an air supply problem. Darn EGRs...

The cat under the car is a trap oxydizer. It was installed during the recall when they removed the one before the turbo. Its now clogged.

renaissanceman · #12 08-07-2015, 01:32 PM

Interesting. Lots of varied opinions on this topic. I'll work on cleaning the air intake before thinking about the cat, I suppose.

Mxfrank · #13 08-07-2015, 02:12 PM

There's a procedure for measuring exhaust gas pressure on 603 engines. Before you start poking broomsticks through your cat, at least make sure you have a problem.

renaissanceman · #14 08-07-2015, 02:21 PM

Would you happen to know what that procedure is?

OM617YOTA · #15 08-07-2015, 03:12 PM

On gassers, I'd drill a small hole ahead of and after the cat. Start the vehicle, have someone rev it while feeling the exhaust coming out of both holes. Significant difference in flow felt(very scientific) and I'd replace, remove, or punch out the cat. The holes can then be plugged with self tapping machine screws.

There are also ways to test that involve tapping a copper or steel line into the pipe ahead of and behind the cat and hooking it up to a pressure gauge, with certain amounts of pressure differential allowable. I never got that scientific, was usually pretty easy to feel a large difference.