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  #1  
Old 05-03-2008, 05:14 PM
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Location: Sierras, CA
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380SL Hard Start & Poor Mileage

I wanted to start out by thanking the forum and all of the contributors. What an unbelievable wealth of knowledge!

I have searched and read until my eyes are blurry…

I have a 1982 380SL with 31,000 documented miles. The car is in excellent condition and runs beautifully with the following exceptions;

1) It has a hard time starting when warm, unless you apply the accelerator petal.
2) The gas mileage is poor. I’m getting approx. 10 to 11 MPG. I do live at 4000 feet elevation and I know that does play a role, but from several previous MB’s I expected better mileage. I do not treat/drive this car like my GT. It’s more like my baby! I have read quite a few post indicating that the mileage should be better.

After searching/reading previous posts it appears that it may be one of several items;

1) Accumulator
2) Cold Start Valve
3) Warm Up Regulator

Quite a few of the posts referencing hard starts after the engine is warm indicate that the problem was rectified after replacing the accumulator, but I did not find those same posts indicating poor fuel mileage. I have checked for vacuum leaks and all appears tight. While the cost of the accumulator is relatively inexpensive, the other suspects carry pretty hefty price tags. Has anyone else experienced hard starts and poor fuel mileage?

As always, I’m very grateful for any assistance and guidance!

Tim
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  #2  
Old 05-03-2008, 07:18 PM
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Join Date: Oct 2007
Location: Greater Metropolitan Beaverdam VA
Posts: 642
hard start

If your car starts o.k. when cold, look for a temperature related problem. I suggest you check out the engine temperature sensor that inputs to your fuel injection computer. I believe your car has three temperature sensors; one for your temp gauge, one for your aux fan and the one I suggest above. On my 560SL, that sensor is located at the front top of the engine easily accessible by removing the air claner housing. It is the sensor with two wires. Yours may be the same.

The sensor is relatively inexpensive (I think I recall about $40.00).

Last edited by rocky raccoon; 05-03-2008 at 07:20 PM. Reason: add information
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  #3  
Old 05-04-2008, 09:41 AM
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Want to spend 250$ to find out what's wrong and fix it? Get the WUR rebuilt. As a low milage car, it's not been run too often. Your WUR is most likely the cause for your problems. You can prove it with some diagnostics that require you to have a CIS compatable fuel pressure tester. Presuming you do your own work, that's a handy tool to have.

-CTH
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  #4  
Old 05-04-2008, 11:35 AM
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Location: Northern California
Posts: 31
That's exactly how my 84 380sl acted when I needed a new O2 sensor. The
O2 sensor will only start working when the exhaust gasses have heated it up, so it is inactive on a cold engine. When hot, it would send a wrong signal to the computer which started "dumping" fuel......12 mpg. For a 380 that is way off.
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  #5  
Old 05-04-2008, 12:26 PM
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Possible Bad WUR

This car does not have a computer for the fuel injection and there is no temp sensor on your car which could cause this problem. There is a controller box which uses the O2 sensor to control the "lambda valve". This valve looks like an injector with two hoses on it. The lambda controller is a very dumb bit of analog circuits. The job of the labmda valve is to tweak the air mixture slightly richer or leaner for emissions control. The lambda vave can only move the air/fuel mixture a few percent and a failure in the O2 sensor/lambda system can NOT this cannot cause the engine to run rich enough to get 11MPG.

DO NOT drive the car running this rich. The engine block in your car uses a silicon/aluminum allow which wears out very quickly (a few hundred miles) if the mixture is rich enough to wash down the oil film from the cylinder walls. That happens at about an AFR of 11:1. A mixture that rich would explain 10MPG.

You have to check your control pressure. This is very easy to do with a simple tool. Email me at the office (support@unwiredtools.com) and I would be happy to lend you one at no charge. It takes less than 5 minutes to check control pressure. If the control pressure is less than about 3.2bar when the car is warmed up then your Warmup-Regulator is bad. A bad WUR is very easy to fix, if you fix it before it destroys your engine.

A bad fuel accumulator can cause a WUR to go bad by allowing pressure pulses to propagate through the fuel system. These pressure pulses cause calibrations shifts and metal fatigue failures in the little brass parts inside the WUR. That's generally why rebuilt WURs are not a good option.

The control pressure test I mentioned will also diagnose a bad accumulator.
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1982 380SLC
1994 E320TE
1998 E300DT
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  #6  
Old 05-04-2008, 03:38 PM
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Wow!

Thank you all for the responses! The car will be parked until I get to the bottom of this!

Steve, I have sent you an e-mail.

Again, a big Thank you to the "community"!!!

Tim
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  #7  
Old 05-06-2008, 09:51 AM
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Dissent

Trouble is, when WUR's go bad, the result is high control pressure, which, while it makes for hard cold starts, also causes poor acceleration and poor cold running. Gas mileage might improve because the mixture is lean.

I would bet on a leaky cold start valve, a worn-out oxygen sensor, or maybe even a damaged o-ring in the fuel distributor plunger.
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'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #8  
Old 05-06-2008, 01:16 PM
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Location: Sierras, CA
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Chuck,

Thank you for the response!

The O2 sensor is brand new. I have carefully checked for vacuum leaks visually and with carb cleaner. I have visually inspected the engine compartment as well as the fuel pump, filter, and accumulator area and see no leaks. I have also visually checked every electrical connection in the engine compartment.

During the pre purchase inspection, the "mechanic" had played with the mixture and really messed things up, as well as caused quite a few of the injectors to leak because he was too lazy to pull the rail to replace the gaskets on the covers. I put the car on a trailer and hauled it 6 hours round trip to a gentleman that specializes in vintage Mercedes. I told him I did not care what the cost, I wanted everything perfect. When I picked the car up, it ran very smoothly. My only complaints were as noted above.
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  #9  
Old 05-06-2008, 02:30 PM
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Does the length of time the car sits affect the time it takes to start? The classic accumulator or other leak-down is that the longer it sits, the longer you have to crank, to give the system enough time to build enough pressure to open the injectors.

If the time to start is independent of the time it sits, then I would suspect the CSV or o-ring. Either could cause an excessive amount of fuel at start which you are offsetting by opening the throttle and giving the poor thing some air.

BTW, this does not have a "fuel rail." It has eight individual lines from the fuel distributor. So I am not sure what gaskets you are talking about. You don't need to mess with the injectors to get the valve covers off.

It would help to know what on-off ratio you are getting (lots of posts), as well as the control pressure, and how long it holds pressure after you shut the engine off.

Another thing that occurs to me is that the altitude/less oxygen in the air may be causing the O2 sensor to send a low voltage signal, which would cause the lambda controller to richen the mix. I'm not sure how you would compensate for that in early K-Jet. Another reason to see what the on/off ratio is doing.
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'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

Last edited by ctaylor738; 05-06-2008 at 02:44 PM.
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  #10  
Old 05-07-2008, 12:36 PM
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Chuck,

Again, Thank you for responding.

When the car is completely cold it starts immediately. The difficulty in restarting is when the engine is warm. The longer it sits, the easier it is to start.

The poor mileage occurs even at lower elevations (100 to 400 feet) so I'm not sure it would be the O2 sensor.

I will do a search to learn about the on-off ratio.

Thank you again!

Tim
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  #11  
Old 05-10-2008, 03:25 PM
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Update:

Steve at www.unwiredtools.com was gracious enough to offer me the use of a pressure gauge to check the control pressure.

The pressure gauge arrived as promised and I performed the following;

1) Loosened and moved air filter assembly out of the way.
2) Removed inlet side of fuel line. The car has been sitting (unstarted) since first posting on the forum. Interestingly, there was no fuel leaking from fitting at time of removal as described in the instructions provided with the gauge by www.unwiredtools.com.
3) The outside temp at the time of the test was 62.4 F
4) Reassembled inlet side of fuel line with gauge installed as per instructions.
5) Car started immediately with a "turn of the key." Within 30 to 45 seconds after car started pressure rose immediately to 40+ PSI.
6) Approximately 2 to 3 minutes into test, pressure had risen to 54 PSI.
7) Approximately 4 to 5 minutes into test, cars idle lowered, and pressure held at 52 PSI.
8) I did notice that car was not idling as smooth as it has previously. Not what I would describe as "rough," but not as smooth as it has idled in the past.

I can’t say “Thank You” to Steve at www.unwiredtools.com too many times! I literally live over two hours each way from the closet metropolitan area that might even have the necessary gauge to do this test! I have posted pictures in the hope that this might help someone else. I have benefited greatly from the members on this site and welcome the opportunity to “Pay it forward”!

Tim
Attached Thumbnails
380SL Hard Start & Poor Mileage-pressure-test-001.jpg   380SL Hard Start & Poor Mileage-pressure-test-002.jpg   380SL Hard Start & Poor Mileage-pressure-test-004.jpg   380SL Hard Start & Poor Mileage-pressure-test-005.jpg   380SL Hard Start & Poor Mileage-pressure-test-010.jpg  

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  #12  
Old 05-11-2008, 01:34 PM
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Control pressure problem

Those are very interesting test results. From your earlier description it seemed that the mixture was too rich. Now it looks like it's too lean and you WUR isn't pushing into cold start at all.

Please keep us posted on your repairs. If you get a replacement WUR please feel free to PM me on how to adjust the mixture adjustment screw on the air metering plate.

We're happy that the Control Pressure Gauge worked out for you. Using the gauge is much better than guessing at what the cause would be!
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1982 380SLC
1994 E320TE
1998 E300DT
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  #13  
Old 05-12-2008, 08:58 AM
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This sounds fairly normal to me. You don't say what the CP was when you started the car, but it should have been in the 21-28 psi range. So if it was at 40 in 30-45 seconds, that's about right. Your warm CP is right on at 52 psi = 3.6 bar.

Next up is a check of the duty cycle/on-off ratio.
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Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #14  
Old 05-12-2008, 11:57 AM
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Wur?

Tim this is a key point so make sure of you results or if needed repeat the test. There was no residual pressure when you started the car because you fitted the gauge. When you removed the fuel inlet fitting there was also no residual pressure. We'll come back to that.

When the gauge was on the car and you first started the engine it's normal for the fuel system to take a few seconds, perhaps 5 seconds, to pump up the control pressure. During this initial pressure rise did the pressure rise up to 40+ immediately (within a few seconds), or did it rise to 20+ PSI then rise slowly to its final value over a minute or two?

When the car was fully warm and you saw 52 PSI were the vacuum hoses connected? If the vacuum hoses are disconnected the control pressure should drop to about 40PSI. Does it?
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1982 380SLC
1994 E320TE
1998 E300DT
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  #15  
Old 07-25-2008, 01:37 PM
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Problem Resolved (I think)

I (think) I have finally resolved my issues and thought I would post a follow up for the benefit of all. Hopefully this will save someone time and frustration!

First of all, I owe a huge debt of gratitude to one of the Moderators on this site. They have for all these past weeks since my first post, painstakingly helped, advised, educated, and dealt with all of my questions, inexperience, frustrations, etc. You know who you are and I will never forget you!

As you can see from the original post, I was dealing with high fuel consumption (11 MPG) and very rich fuel mixture. No matter what I did (at the direction of an extremely helpful and knowledgeable Moderator) the duty cycle/on-off ratio would not change and was running between 75/80%. I won’t go into all the details because if I were to post all of the things that were tested, retested, etc. this post would be a small book.

After everything that was checked, replaced (including a new brain see attachment), and rechecked, it appeared that I still had a large vacuum leak. After several weeks of coming home after work and spending hours each night trying to find the leak, I had reached a new level of frustration. Out of desperation I drove the car to a shop 50 miles away that had a smoke machine. After $100.00 for the smoke test the leak was finally found! The problem was well hidden below the Mass Air Flow Sensor and Fuel Distributor (see attached PDF item #14) and caused by what the CD refers to as the Air Guide Housing. As you can see in the picture (attached) there are no less than 6 large cracks with the largest being approximately 2 ½ inches long. There is no way to see the cracks without the smoke machine. After questioning the previous owner, I feel these cracks have been in existence for well over 15 years! Keep in mind that this car was inspected before purchase, and also transported the car on a trailer to a specialist in classic Mercedes. The second person did find injectors that were leaking but no one has ever found the cracks in the Air Housing Guide. I now have what I believe to be normal vacuum, and I still need to replace the Accumulator and get my Duty Cycle adjusted but it appears that the cracks in the Air Guide Housing were creating the high fuel mixture and poor mileage. There may still be minor issues to deal with but I wanted to report back on the progress.

If you find this issue with your car it may be helpful to note that the first replacement Air Guide Housing did not properly fit into the newly designed plate. I had to remove the new Air Guide Housing and return it. The second new Air Guide Housing was not much better. I ended up placing it into the plate and applying clamps for a week before reinstalling it. To avoid doing this job a third time, I applied a small amount of super glue around the forward rounded edge (see photo) of the new plate to insure it sealed properly until it was bolted down.

In closing I wanted to again thank the above referenced Moderator whom I now refer to as the Master! Your kindness, patience, and goodwill will never be forgotten! I also wanted to recognize the fantastic members of this forum that take the time and effort to help out people that they have never even met! I very actively belong to no less than 11 forums pertaining to Heavy Equipment, Fishing, Boating, Mercedes Benz, Snow Removal, Welding and IT. This forum is by far the most helpful! I’m proud to be a member and hope that someday I will be knowledgeable enough to Pay It Forward!

Tim
Attached Thumbnails
380SL Hard Start & Poor Mileage-img_0344.jpg   380SL Hard Start & Poor Mileage-crackedhousingaltered-copy.jpg   380SL Hard Start & Poor Mileage-pict1140.jpg  
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Old 07-25-2008, 01:37 PM
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