1983 300D with 190K on it.

When warm, this car runs fast and strong. Far faster and stronger than any other 300D I have ever driven (about 10 different ones, back when I was looking to buy). The reason I bring this up is because I have no idea how this car was tuned before I bought it.

The issue is when the car is first started in the morning or after work, (I live in Southern California so its never really cold), at slower speeds, when you stomp on the accelerator, the car acts as if it is fuel starved like a bucking bronco. As soon as I take my foot off the accelerator, the bucking stops and if I am gentle on the accelerator pedal, the car accelerates nicely (although not quickly). I think the problem occurs when the turbo kicks in, but not sure. As the engine/fuel warms up in about 10 minutes, this problem disappears.

Work I have done so far:
• Fuel Tank has been removed and boiled and later washed out after algae bloom. New tank screen added was checked 2 weeks ago and was finally virtually spotless.
• The first small fuel filter (which is a clear hengst one) shows no sign of debris. Last month, I was changing it out twice a week to make sure I got all the algae out.
• Change the primary filter as well twice in a month.
• Cleaned the banjo connector and clear lines of the Alda circuit at the exhaust manifold. Also at the junction box and at the Alda itself.
• Molly Purged the injectors according to Diesel Giant page.
• Cleaned out all banjo connectors and clear fuel lines to and from primary filter, IP, lifter pumper with brake cleaner.
• Replaced all fuel and return lines with Viton.
• New Cigar hose.
• Blew air and Brake cleaner through hard return lines.
• Tried driving with gas cap off. Vent line seems clear.
• Checked and cleaned the oil blower hose (the one back to the air cleaner)
• Air cleaner changed 6 months ago and looks clean.
•*Valve adjustment was done 6 months ago. Had the timing chain checked and was told it was very tight and needed no adjustment. Must have been changed before I bought the car.

Egr, and Alda switch all in tact. I would prefer not to lose these but an open to suggestions. Could a clogged egr or flex tube cause this?

Now I know I am being greedy. This car runs amazing. Perhaps the best solution is just not to stomp on the accelerator for about 10 minutes until the engine comes up to operating temp (or its the fuel gets up to a certain temp.) But if anybody has any suggestions that I have not tried, please let me know.

Thanks
Doug

P.S. I don't want to confuse the issue, but I do run b100 for the most part in the car. Right now is about B50 (I just put 1/2 bio 1/2 dino it it) and have run the car only on dino, and it exhibits these same symptoms.

Bump, no suggestions?

Two things I noticed. You have not changed the secondary fuel filter. Although it may not be the problem it would be wise to change it. The effects created by this filter have been suprising with many people. I of course do not know if it is the problem. Yet it has to be eliminated in my opinion.

I noticed when you had the timing chain checked they stated it was tight. That is not your current problem but even a bad chain will be tight as that is a function of the tensioner. A good or marginal timing chain is determined by first checking the refferance timing marks. Check how to do this in the archives. It is easy.

Your actual problem just might be air. Have a look in your clear primary filter for air bubbles transiting the filter in a stream. Another cheap manageable check is to clamp off your return line and see how it drives when cold. It does no harm to do this.

I'm not sure I understand your statement. The return fuel is under a good amount of pressure and there is quite a bit of fuel traveling through the return system. If you clamp it off you are bound to blow off one of the injector return lines and end up with a mess.

It's normal for these cars to be a bit slow when cold. Ignition of the fuel isn't as complete and things aren't running as efficiently when everything is cold causing them to be a bit underpowered when cold.

How is the cold start up? I ask because if you have a glow plug out or weak glow plugs you could have less than optimal performance when cold but once things heat up that goes away.

What weight oil are you running. If you've got really thick oil it would slow things down some until warm.

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The relief valve may be sub standard or not regulating when cold. Clamping off the relief valve output does no harm. It makes whatever output from the lift pump available to eliminate the relief valve as an issue.

His car as I understand it is not slow but has a throttle pulsation effect if I understand his post . Unless he babies it. The normal presure entering the return circuit should be about 15 pounds. Clamped off the lift pump usually will not push harder than 30 to thirty five pounds deadheaded.

Barry, missed your last suggestion. I will give clamping off the return line a try.

1) Oil - 10W-40. 0-30. I don't recall.
2) Cold startup no problem at all.

Other fixes I have done:
1) Swapped out the primary filter. (the big one)
2) Keep replacing pre-filter.
3) Took the Overboost valve out of the loop. (The device on the firewall between the exhaust manifold and the Alda. I just joined the two plastic hoses with some vacuum hose.) This was advice from a mercedes expert who explained that when cold, that valve is closed and will not open until things warm up. Is this right? (I know about the safety issue, but functionally?) What are the wires running to overboost switch? Temp or pressure? This mechanic is a top expert in Los Angeles, but as I write this, now I have doubts about the explanation's accuracy.


The result is that each one of things did seem to lessen the pulsing (killing of power when pulling away from a stop or slow speed) but the problem still persists.

Barry, where is the relief valve?

Relief valve is connected to the return line at the injection pump. In your case after some reflection I do not think it is an issue really. Even if it were I would not expect pulsing.

Several things to do if you are interested. Make sure there is a cigar hose in the fuel return circuit and that someone has not replaced it with a piece of hose.

Take something like a good hairblower and heat the injection pump up for quite a long time when the engine is dead cold. Moderate heat for a longer time is prefferable to lots of heat for a short interval. The heating is to warm the fuel inside the injection pump not just the pump casing. The engine itself is to be left cold.

You want to find out if the higher viscosity of the cold fuel is doing or aiding some malfunction in the injection pump. Specifically in the rack/govenor area. As soon as the injection pump is good and warm take the car for a drive. Pulsing effect gone post it on site and I can make a suggestion of what to do.

This simple test with a little luck will hopefully eliminate the injection pump or condem it for the pulsing effect. Your problem is not a common one with these cars so somewhat seemingly uncommon methods are reasonable to attempt to locate the cause. I really have never liked guessing at things or changing parts. Usually a test of some sort can be engineered to at least indicate something.

Another thing I was somewhat aprehensive to mention. If when the engine is cold. Loosen the oil filler cap. Start the engine. If the oil cap just sits there or rattles around a little is fine. Pull the throttle linkage to increase the rpm. Is the oil cap still sitting there? Do the same test with the cap screwed down. Is the pulsing back? I have heard of cases of really excessive or greater engine blowby when these engines are cold mentioned by observers..

Excess blowby pressure will shut the engine down by turning off the fuel supply. If this drops the blowby pressure the fuel will turn back on. If the cycle where to repeat the symptom might feel like a pulsing.

There has never been a case of pulsing reported before from this problem .There have been reports of some engines not being able to start or shutting down though a few times from the excess blowby effect. Some also have reported that blowby was much heavier when their engine was cold reducing as the engine warmed up.

Both these suggestions are somewhat long shots. Yet they are both easy to do tests that may indicate something.

If the engine is "fuel starved", the vehicle will simply accelerate very slowly............or not at all. There is no relevance between fuel starvation and "bucking bronco". This is not a gasoline engine.

Therefore, I do believe that you're off on a wild good chase regarding fuel simply because the description "bucking bronco" is somewhat inaccurate when seeking assistance.

My suggestion is to further clarify your situation with additional detail and description of the symptom.

As long as your Timing Chain Tensioner and the Tensioner Rail are OK the Timing Chain is going to be tight because it compensates for the stretch in the Chain.

The above is not the same as your Camshaft Timing being off due to X degrees of Timing Chain Stretch.

If the EGR is momentarily sticking open that could cause your symptoms.
Deactivate the EGR by pulling and plugging off the Vacuum Hose that goes to it and see what happens.

Is your idle speed within spec when the Engine is running but cold?

An Air leak in the Fuel inlet?

Fuel Supply Pump or Pressure Relief/Overflow Valve issue?

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84 300D, 82 Volvo 244Gl Diesel

All the EGR would cause is an increase in exhaust gas and a decrease in oxygen in the cylinders.

I fail to see how this would manifest itself into a "bucking bronco"?????

I have the same lower power problem on a cold engine but I also have a low idle at 500 rpm cold when warm 700. How can the idle change with engine temp. Is this also Doug 183s problem.

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1984 300SD turbo 126
"My true love"

God made me an atheist and who am I to question His wisdom

If the governor is functioning properly and the engine is operating correctly, it cannot.

However, the idle speed governor has a limited range. If enough load is placed on the engine, the governor cannot open the rack to compensate.

Either there is something that is pushing the governor to the rail and it cannot compensate.............or the governor, itself, is not operating properly.

My 300TD also has an intermittent cold miss. It seems to only happen until the boost comes on, and disappears once the engine warms up. I've been thinking I should do a valve adjustment to see if that helps. The funny thing is it starts instantly, and doesn't smoke at idle, even cold; it really doesn't act like it has low compression.

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1981 Mercedes 300TD, 1994 Honda Civic Del Sol
http://mefi.us/images/fuelly/smallsig-us/67195.pnghttp://mefi.us/images/fuelly/smallsig-us/103885.png

Decrease in O2 = decrease in combustion.

Also the intake port closest to the EGR is going to get the most decrease in O2; at least at low speeds.
So the Cylinders up front will not carry as much of the load as the Cylinders to the rear since they will not burn the Fuel as well.

So the Cylinders to the rear will push harder and take load and the front Cylinders may just be going along for the ride. And, that cause uneven rpms and surging.

If that can equal Bucking I do not know because that might mean something different to the Original Poster then it does to me.

I actually believe it is more likely he has an Air Leak.

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84 300D, 82 Volvo 244Gl Diesel

By design, the EGR does not actuate when the engine is cold.