300sd stumper - PeachParts Mercedes-Benz Forum

luvmy84300sd · #1 06-28-2002, 09:37 PM

Hi Gentlemen,
This is my first attempt so please bare with me. I have a 1984 300sd that I purchased close to 3 years ago. The car is in exceptional shape (my mechanic said "either you buy it or I will" after looking at it for 3 hours). Our issue is a slight hesitation, noticeable smoke, and a clanking noise coming from the engine compartment when starting from an immediate stop. At any other time the car runs perfectly as it did when I bought it. We completed a typical 30k mile check up, replaced glow plugs, and the little primer pump. Has anyone encountered this before or have an idea? My mechanics last suggestion is the fuel pump but I disagree b/c it runs so well after the initial take off. Thanks for the forum!

luvmy84300sd · #2 06-29-2002, 08:43 AM

Thanks for the welcome TXBill! Our check up did include replacing all injectors (we knew that the #1 was about gone so we decided to do them all at once and we did replace the fuel filter. We are going to try and install a different filter hoping something may be wrong with the one we originally purchased. Do you happen to agree with my rationale' about it not being the fuel pump itself since the car performs wonderfully at all other times? Again, I'm not the mechanic but it seems if it were a pump problem I would notice it at all times that I try to accelerate, not just from dead stops.

Palangi · #3 06-29-2002, 09:27 AM

I assume that both the main filter and pre filter were replaced?

Is the throttle linkage all free (no binding) and properly lubricated?

Are the engine mounts OK? (Does the engine sit in the right position and not move excessivly when throttle is first applied?)

Fuel hoses OK, no leaks? All the way back to the tank?

Could the hesitation be transmission? I believe this one probably starts in second gear normally.

Could it be a tank full of bad fuel?

If everything else checks out, I believe i would get it checked for chain stretch and injection timing.

luvmy84300sd · #4 06-29-2002, 12:56 PM

Thanks P! I will definitely pass this on to my mechanic (as some of the things your bring up I am not aware of ie. the pre-filter?) and see what he says. I did try using gas from a different station than where I normall fuel and it still does it even this morning. The fuel injection timing has me curious...I'll keep you posted. Thanks again!

#5 06-29-2002, 07:50 PM

It almost sounds like the Injection Pump Rack could be sticking. The engine (not the motor but the engine [another plug for peh]) is momentarily starving for fuel; this would explain hesitation and knock, not sure about smoke. As Rack is released hesitation ceases as does knocking.

With all the service that has been performed on this car, the symptoms and probabilities seem to point toward the Injection Pump.

luvmy84300sd · #6 06-29-2002, 09:46 PM

Thanks for the reply mccann. Can you tell me this (keeping in mind my ignorance at this point about the mechanics...but I'm learning), is the pump you speak about the actual fuel pump? I know that hasn't been replaced but if what you refer to is what I call the small "primer" we did replace that.

P.E.Haiges · #7 06-30-2002, 11:46 AM

Luvmy 84300SD

I think I found your problem. You put gas in it instead of Diesel fuel, at least that's what you said.

P E H

luvmy84300sd · #8 06-30-2002, 07:36 PM

OOOOPPSSS! Boy I really said that wrong didn't I. Don't worry, I haven't made that mistake (not yet at least). To clarify I have only run diesel fuel in the car

Speaking of...can anyone tell me the benefits of running 45 cetane as opposed to 40? My manual doesn't reference 45 but the station I fill up (with diesel) only has 45 while all the other pumps in town run 40.

MVK · #9 06-30-2002, 08:42 PM

Higher the cetane number better is the diesel quality.
Cetane is for diesel what octane is for Gas. Higher those number better is the quality.

If the car had been sitting with fuel in it for too long, I have heard from people, that engine acts wierd during idle dont quote me on that I have just heard this from a truck guy once. Just to be on the safer side get the old fuel out and put the fresh one in. Also try one of the quality diesel additive in it. This way you get the bad fuel theory out of your mind while troubleshooting. Timing chain suggestion is good.
Welcome to our little family.

MVK

Palangi · #10 06-30-2002, 09:45 PM

The idea of a sticky rack is interesting. Could that possibly be caused by a misadjusted rack dampener pin? A sticky rack could certainly account for the hesitation.

#11 07-02-2002, 12:59 PM

The Injector Pump is the box on the driver's side of the engine with the fuel lines running to the nozzles on the head. In the rear of this box is a bolt with a 14mm lock nut and a 12 mm adjustment nut (Rack Damper Bolt). I would remove this bolt and be sure that the spring loaded pin at the end of the bolt is not sticking. The popular opinion seems to be that repalcing this bolt makes for better adjustment capabilities to the Rack.

#12 07-02-2002, 04:59 PM

I believe the vehicle came with a silver colored rack dampener bolt. The replacement is gold. I had a silver original and had tried to get the spring loaded pin to work. When I finally got around to picking up a gold replacement I found that I was able to get the idle to adjust. I noticed the replacement pin had a much stiffer spring than the old one.
The MB shop told me he was surprised that any of these were still out there with the old silver rack dampener bolt in them. They had more or less all been defective. Once replaced the idle improved substantially. I don't know if that would made the engine cranky at take off though. That sounds more like a motor mount problem.

psfred · #13 07-02-2002, 09:24 PM

Does this happen only after the car has been at speed, you stop momentarily, the immediately take off (as in a stop sign with no traffic), or does it happen every time you accelerate from a stop?

If it only happens after the engine has been at speed and only if you just stopped, you probably have a sticking injection timer (behind the vacuum pump). This presumes that you don't have the problem if you idle for a while, as in at a traffic light.

If it happens every time you take off, cold or hot, no matter how long you've been idling, your injection timing is fast. This can still be a stuck injection timer (completely stuck, not slow in returning to late timing), or the result of replacing a chain without checking and adjusting the injection timing.

MB diesels DO NOT snort and rattle like a Mack truck at low rpms!

Peter

luvmy84300sd · #14 07-02-2002, 10:59 PM

WOW Peter....what a lot of insight! Here is the big stumper about the whole problem. The problem is not consistent at any time. The only thing I can count on is that when I start my car in them morning (I have to back out of my driveway onto the street) she runs perfect. I wind through my subdivision slowing and speeding based on the curves and it still performs at it's best. I eventually come to a stop sign where I have to wait for oncoming traffic to cease so I can turn left. This turn is when the car will hesitate, make the clanking noinse, and spit out a lot of smoke. It seems as soon as the car changes into the next gear after take off, the problem goes away and I get a big boost of energy (the turbo I guess) and she runs great again.....until I hit the next area where I have to either slow up greatly or come to a complete stop. When I apply the initial pressure to the accelerator the car still doesn't jump on command and the smoke billows. I also would like to find out how much smoke is supposed to come from these cars. When I acquired it a few years ago it didn't seem that I saw smoke from the rear view mirror.....whereas now I am seeing smoke roll behind me from time to time with this issue.

Hope this helps to clarify your question a little.

psfred · #15 07-03-2002, 07:52 PM

Your EGR valve is stuck open! The huge clouds of inky black smoke and the funny rattle give it away -- too much exhaust in the intake and the fuel won't burn. You get lots of knock, but it sounds kinda muffled, enough smoke to stop traffic, and no power until you get the rpms up to where the exhaust gas ratio is right, and it takes off when the turbo comes up.

You can either replace the EGR or just pull the vacuum line and make a plate fit under the top of the EGR to cap it off -- when they stick they will sometimes also lift under exhaust pressure. Put the plate between the EGR and the manifold. You can make it out of scrap sheet metal (not aluminum).

My Volvo did exactly the same thing, huge pain in the butt on a long hill! I plated off the EGR, complete cure.

Sorry I didn't remember it at first!

Peter