Mercedes-Benz Forum banner

21 - 40 of 40 Posts

·
Registered
1990 560SEC 334K miles as of 5/19, 1990 500SL (Euro Build) 67K miles as of 5/19 1985 380SL 130K
Joined
·
150 Posts
Discussion Starter #21
Check the green wire going to the ignition control module as well as the ICM itself. Is the wire stout and not falling apart? Is the ICM the Huco module or the giant resistor one?
Mr. Beast, I saw your input regarding fuel pressure damper on another thread. Can you give me your thoughts please?
 

·
Registered
1984 380SL
Joined
·
2,343 Posts
Mr. Beast, I saw your input regarding fuel pressure damper on another thread. Can you give me your thoughts please?
Sure, the green wire is apart of a safety feature of the fuel delivery system.

It sends a pulse to the ICM which is registered when a spark plug fires.

If the wire is corroded or failing, the pulse doesn't go to the ICM which won't let the FPR keep sending fuel.

It's green and runs from the fender ICM to the distributor . Do a search for it and the problems associated with it.
 

·
Registered
1990 560SEC 334K miles as of 5/19, 1990 500SL (Euro Build) 67K miles as of 5/19 1985 380SL 130K
Joined
·
150 Posts
Discussion Starter #23
Thank you. If I have no control pressure on the WUR the green wire isn't the cause as I have jumpered the FPR. Would it be a fuel pressure damper issue?
 

·
Registered
1984 380SL
Joined
·
2,343 Posts
Thank you. If I have no control pressure on the WUR the green wire isn't the cause as I have jumpered the FPR. Would it be a fuel pressure damper issue?
Woah really? You're not getting any fuel pressure?

Definitely not the green wire in this case.

I think you have a serious fuel clogging issue in the engine bay. Are you getting any fuel into the WUR?

Be careful jumping the fuel pump relay, you've pressurized the fuel system without a way for the gas to escape.

Check the system pressure regulator that lives in the back of the fuel distributor. This allows fuel to enter into the delivery system.


That's it, use the part number to shop around and find other articles on the forum about it.
 

·
Registered
1990 560SEC 334K miles as of 5/19, 1990 500SL (Euro Build) 67K miles as of 5/19 1985 380SL 130K
Joined
·
150 Posts
Discussion Starter #25
Woah really? You're not getting any fuel pressure?

Definitely not the green wire in this case.

I think you have a serious fuel clogging issue in the engine bay. Are you getting any fuel into the WUR?

Be careful jumping the fuel pump relay, you've pressurized the fuel system without a way for the gas to escape.

Check the system pressure regulator that lives in the back of the fuel distributor. This allows fuel to enter into the delivery system.


That's it, use the part number to shop around and find other articles on the forum about it.
Thank you for that. That's what I think is the culprit. I have a pressure gauge with ball valve. Reads 5. bar system pressure, but when I open the valce to read control pressure goes to 0. So where is the fuel going when i open the valve? The valve is on the WUR side of the gauge as it needs to be. It must be diverted back to the tank via one of the side valves on the damper, or thru a broken internal diaphram. It's not giving me any control presure.
 

Attachments

·
Registered
1990 560SEC 334K miles as of 5/19, 1990 500SL (Euro Build) 67K miles as of 5/19 1985 380SL 130K
Joined
·
150 Posts
Discussion Starter #26
Woah really? You're not getting any fuel pressure?

Definitely not the green wire in this case.

I think you have a serious fuel clogging issue in the engine bay. Are you getting any fuel into the WUR?

Be careful jumping the fuel pump relay, you've pressurized the fuel system without a way for the gas to escape.

Check the system pressure regulator that lives in the back of the fuel distributor. This allows fuel to enter into the delivery system.


That's it, use the part number to shop around and find other articles on the forum about it.
No, not the fuel distributor the damper. https://www.pelicanparts.com/catalog/SuperCat/3419/MBZ_3419_FULFUL_pg2.htm#item4
 

Attachments

·
Registered
1984 380SL
Joined
·
63 Posts
James,

If you are still having trouble with this, check the wires to the WUC. I had a no-start issue and found that one of the wires in the connector to the WUR had come out of the socket. Don't know if this will fix your problem, but it fixed mine.

Derek
 

·
Registered
1990 560SEC 334K miles as of 5/19, 1990 500SL (Euro Build) 67K miles as of 5/19 1985 380SL 130K
Joined
·
150 Posts
Discussion Starter #28
Thanks for the heads up. I will do that. My big question is about pressure testing for control pressures. With no electric I get no control pressure. With electric get pressure but they are to high. Videos and info are directing me to test for a baseline with no electric. Then add electric to get values. If no control pressure at baseline(no electric) does that mean the fuel pressure regulator is faulty?
 

·
Registered
1984 380SL
Joined
·
2,343 Posts
James,

If you are still having trouble with this, check the wires to the WUC. I had a no-start issue and found that one of the wires in the connector to the WUR had come out of the socket. Don't know if this will fix your problem, but it fixed mine.

Derek
That wire is only used for applying 12v of heat to the WUR in order to lean out the mixture during a cold start. If it's left unplugged or is non-operational, the car would end up having abysmal fuel economy until the WUR was heat soaked from engine heat to get the proper mixture pressure set.


I know we're darting back and forth here. Apologies as I had to re-read your symptoms and clear my head of assumptions. More importantly, I needed to brush up on my KJet basics.

Given your symptoms and what the fuel pressure damper actually does, I don't believe the fuel pressure damper is your problem.
This picture gives a functional over view of how the CIS system works:
2614270


The fuel pressure damper is only used to prevent a water (fuel?) hammer effect when fuel demands are changed by the driver. This can damage the sensitive diaphragms within the WUR and the fuel distributor.

The pressure dampener is like a tiny fuel accumulator. It has a diaphragm and a spring inside. Since your pressure tester gets pressure between the WUR and Fuel Distributor, but it loses it, this means that fuel is in fact passing through the dampener.

His failure mode is simply to leak out the rear. If you notice, there's a vacuum line that runs to the intake manifold. If it leaks, the line will vent the gas into the intake, preventing forest fires.

If you want to alleviate your concerns regarding this part, the FSM gives permission to "update" him with what is essentially a larger fuel hose. Or, if you have the right fittings, use your fuel pressure tester to "delete" the part and examine the pressure. It will most likely stay at 5.0 bar.

See this article here: https://www.startekinfo.com/StarTek/outside/11883/PROGRAM/Engine/107/M116_38/07.3-001.pdf

2614271



From page 20 of article 07.3-120. If you can find the tecalan element or better yet create a high pressure vacuum hose to bypass temporarily, you can remove this from your list.

Since you have system pressure, but lose it post WUR, it would make more sense to re-examine the WUR and the system pressure regulator. I would especially give extra attention to the WUR. His job is to lean the mixture out by lowering the fuel pressure into the fuel distributor.

If the WUR is set incorrectly, he'll clamp up forcing more pressure into the system pressure regulator and thusly the mixture will not be correct to operate the car.

These articles will explain how to test and remedy it.


Thanks for the heads up. I will do that. My big question is about pressure testing for control pressures. With no electric I get no control pressure. With electric get pressure but they are to high. Videos and info are directing me to test for a baseline with no electric. Then add electric to get values. If no control pressure at baseline(no electric) does that mean the fuel pressure regulator is faulty?
It can, it can also mean your WUR is faulty. Both the WUR and the system pressure regulator determine the end mixture which is what gets the engine running.

I know that you said the WUR was recently rebuilt. However, it is very possible to have rebuilt parts not be re-built correctly or have the wrong ones sent. Our fellow user Nobby had a Porsche WUR installed on his 280SL which was causing all sorts of nonsense.

Check to make sure that the part number on the WUR is correct for your car. The FSM article I linked to above will tell you this.

If it's not, there's part of your problem. If it is correct, I would follow the FSM articles above to determine operation of both the WUR and the system pressure regulator. Personally, I would renew the system pressure regulator on principle to get a renewed baseline since these components are now 30 years old.

Let us know your findings.

Good luck!
 

·
Registered
1990 560SEC 334K miles as of 5/19, 1990 500SL (Euro Build) 67K miles as of 5/19 1985 380SL 130K
Joined
·
150 Posts
Discussion Starter #30
Wow that's alot to digest thanks. Check this short video outhttps://youtu.be/65-03E4UXWg he uses power, no power to achieve settings. It's porshe but the same system. This car has a 068 WUR on it which calls for a cold setting of 1.8-2.2 bar. But with no power attached as he specifies, I get no control pressure.
 

·
Registered
1984 380SL
Joined
·
2,343 Posts
Wow that's alot to digest thanks. Check this short video out
he uses power, no power to achieve settings. It's porshe but the same system. This car has a 068 WUR on it which calls for a cold setting of 1.8-2.2 bar. But with no power attached as he specifies, I get no control pressure.

I've seen that video before. Notice how when he plugs in the heating element and the pressure changes? That takes a good minute or two to happen. You should see the pressures change slowly.

The thing is, your car should still be able to start and run with 5.0 bar out of the WUR. Even if it drops to 0, you should have a running car and then have it stop running after a certain amount of time.

Have you had a chance to investigate intake and vacuum system leaks? A gross intake system leak will also lead to no start issues.
 

·
Registered
1990 560SEC 334K miles as of 5/19, 1990 500SL (Euro Build) 67K miles as of 5/19 1985 380SL 130K
Joined
·
150 Posts
Discussion Starter #32
Yup, I've seen that video before. Notice how when he plugs in the heating element and the pressure changes? That takes a good minute or two to happen.

You need to check the system pressure regulator and ensure that this is at the appropriate pressure setting. Once you have that then move onto the WUR.

My gut is on the WUR, though my assumptions tend to be wrong these days so follow the FSM!

Also worth noting that your intake system also affects enrichment. Make sure your hoses are correctly attached once you get the car working.
Thank you. When you watch the video you will see he gets a reading with no power more significant than my number. When I plug the WUR up to power after a few minutes I get a peak of 3.5 bar. When no power, it goes to .5 bar. I'm thinking this warm up regulator is not calibrated properly.
 

·
Registered
Joined
·
1 Posts
I have a 1985 380SL, in a no start condition. I have checked fuses, OVP. I have replaced the fuel pump and jumped the relay. New wires, rotor and cap . I'm getting power at the pump. I'm also getting power at the cylinders. I get spark at cylinder. Thoughts? Solution?
Thanks in advance.
Unfortunately those models have a single row chain. If it has been up dated it will have a double row. However, the single row may have jumped time. If so it more than likely bent some valves. You will need to remove the valve covers to check cam timing.
 

·
Registered
1984 380SL
Joined
·
2,343 Posts
Unfortunately those models have a single row chain. If it has been up dated it will have a double row. However, the single row may have jumped time. If so it more than likely bent some valves. You will need to remove the valve covers to check cam timing.
Only 1981-1983. Model years 1984 and 1985 came double from the factory.

Thank you. When you watch the video you will see he gets a reading with no power more significant than my number. When I plug the WUR up to power after a few minutes I get a peak of 3.5 bar. When no power, it goes to .5 bar. I'm thinking this warm up regulator is not calibrated properly.
You're definitely onto something. Keep us posted on your troubleshooting quest!
 

·
Registered
1995 E420, 1998 E300TD, 2002 CL230K 6spd, 2002 CL230K auto, 2002 C280VRT VR6 Project, 2001 A6 2.7T
Joined
·
7 Posts
Thank you. When you watch the video you will see he gets a reading with no power more significant than my number. When I plug the WUR up to power after a few minutes I get a peak of 3.5 bar. When no power, it goes to .5 bar. I'm thinking this warm up regulator is not calibrated properly.
If you have not already determined the root cause of the "No Start" I would suggest that you get back to basics as follows:
Carefully spray flammable carburetor cleaner or brake cleaner or gasoline into the airflow sensor plate venturie, press the accelerator pedal to the floor, and try to start the engine, Note: Should take less than one fluid ounce of gasoline to get the engine to start up temporarily, if the engine does not start or "pop off" even if momentarily, AND, you have verified sufficient spark at the spark plugs, then you may have fouled out the spark plugs, Note: A visual examination of the plugs could reveal gasoline fouling by having a black appearance and/or liquid fuel present on the tips of the plugs, also be aware that a fouled spark plug may produce a spark as tested when remove from the engine but fail to produce an adequate spark when installed and under the forces of heat and compression.
Inspect and or replace the spark plugs as a set if found to be suspected of fouling.
A few more notes: The fuel pump must be supplied with 12+ volts and adequate amperage during volume and pressure tests!
The fuel pressure readings you have reported suggest several possibilities
1) The engine should at least "pop off" and run poorly with 5 bars of pressure as with the test gauge valve closed
2) The fact that your pressure drops to zero when opening the test gauge valve suggests that you may not have adequate fuel volume from the fuel tank, Perform a fuel volume test.
Many folks are unaware of the difference between volume and pressure, when you open the test gauge valve you are allowing the fuel to pass into the calibrated orfice of the WUR and then, after the fuel passes through the WUR, it pass into the non restricted "Return fuel passage", so, you may have pressure but without volume the pressure will fall off to zero even with a good WUR.
Some possible reasons for low fuel volume are as follows:
Restriction in fuel pump supply hose in bottom of fuel tank. There is a screen or strainer in the bottom of the tank where the big supply hose attaches.
Inadequate fuel pump performance: Assuming voltage and amperage supply is adequate and all electrical connection are clean and tight and pump is of OEM quality.
Fuel pump check valve malfunction: "binding in closed position"
Fuel accumulator malfunction: Internal diaphragm substantially damaged, allowing larger quantity of fuel to return to the fuel tank via vent hose. Pinching off the vent hose as a test will reveal this problem as will "Cautiously" removing the accumulator vent line and verify fuel flowing out of vent port when system is pressurized.
There are other possibilities for your no start condition but this is a good starting point.
Additionally: Double row timing chain engines are not immune to jumping timing due to broken guide rails or breaking high mileage chains. All of the above advice assumes that you have verified the compression of the engine and your readings are within specifications. An engine with a compression problem would exhibit a speeding up and slowing down of RPM`s when cranking, and if the timing jumps more than one tooth it will experience piston to valve contact. This condition would/could prevent the engine from starting.
 

·
Registered
1990 560SEC 334K miles as of 5/19, 1990 500SL (Euro Build) 67K miles as of 5/19 1985 380SL 130K
Joined
·
150 Posts
Discussion Starter #36
If you have not already determined the root cause of the "No Start" I would suggest that you get back to basics as follows:
Carefully spray flammable carburetor cleaner or brake cleaner or gasoline into the airflow sensor plate venturie, press the accelerator pedal to the floor, and try to start the engine, Note: Should take less than one fluid ounce of gasoline to get the engine to start up temporarily, if the engine does not start or "pop off" even if momentarily, AND, you have verified sufficient spark at the spark plugs, then you may have fouled out the spark plugs, Note: A visual examination of the plugs could reveal gasoline fouling by having a black appearance and/or liquid fuel present on the tips of the plugs, also be aware that a fouled spark plug may produce a spark as tested when remove from the engine but fail to produce an adequate spark when installed and under the forces of heat and compression.
Inspect and or replace the spark plugs as a set if found to be suspected of fouling.
A few more notes: The fuel pump must be supplied with 12+ volts and adequate amperage during volume and pressure tests!
The fuel pressure readings you have reported suggest several possibilities
1) The engine should at least "pop off" and run poorly with 5 bars of pressure as with the test gauge valve closed
2) The fact that your pressure drops to zero when opening the test gauge valve suggests that you may not have adequate fuel volume from the fuel tank, Perform a fuel volume test.
Many folks are unaware of the difference between volume and pressure, when you open the test gauge valve you are allowing the fuel to pass into the calibrated orfice of the WUR and then, after the fuel passes through the WUR, it pass into the non restricted "Return fuel passage", so, you may have pressure but without volume the pressure will fall off to zero even with a good WUR.
Some possible reasons for low fuel volume are as follows:
Restriction in fuel pump supply hose in bottom of fuel tank. There is a screen or strainer in the bottom of the tank where the big supply hose attaches.
Inadequate fuel pump performance: Assuming voltage and amperage supply is adequate and all electrical connection are clean and tight and pump is of OEM quality.
Fuel pump check valve malfunction: "binding in closed position"
Fuel accumulator malfunction: Internal diaphragm substantially damaged, allowing larger quantity of fuel to return to the fuel tank via vent hose. Pinching off the vent hose as a test will reveal this problem as will "Cautiously" removing the accumulator vent line and verify fuel flowing out of vent port when system is pressurized.
There are other possibilities for your no start condition but this is a good starting point.
Additionally: Double row timing chain engines are not immune to jumping timing due to broken guide rails or breaking high mileage chains. All of the above advice assumes that you have verified the compression of the engine and your readings are within specifications. An engine with a compression problem would exhibit a speeding up and slowing down of RPM`s when cranking, and if the timing jumps more than one tooth it will experience piston to valve contact. This condition would/could prevent the engine from starting.
I have a new fuel pump, new accumulator and new fuel filter. I have a clean screen in the tank. I went ahead and jumpered the FPR and cracked a 12mm fuel line at the FD. I turned the mixture tower clockwise until the fuel flowed and then just back enough that it stopped. It started. So I am oit of the no start. I replaced the FPR to make sure that relay wasn't involved. I put it on the scope and had a duty cycle of %50 acieved, then it went to %75 and has stayed there. I hear a "buzz" from the frequency valve at idle. When I try to adjust the mixture at the tower to lean it out, it will stall without lowering the duty cycle. The O2 sensor is new and properly gounded. Thoughts of why the duty cycle is high?
 

·
Registered
1984 380SL
Joined
·
2,343 Posts
I have a new fuel pump, new accumulator and new fuel filter. I have a clean screen in the tank. I went ahead and jumpered the FPR and cracked a 12mm fuel line at the FD. I turned the mixture tower clockwise until the fuel flowed and then just back enough that it stopped. It started. So I am oit of the no start. I replaced the FPR to make sure that relay wasn't involved. I put it on the scope and had a duty cycle of %50 acieved, then it went to %75 and has stayed there. I hear a "buzz" from the frequency valve at idle. When I try to adjust the mixture at the tower to lean it out, it will stall without lowering the duty cycle. The O2 sensor is new and properly gounded. Thoughts of why the duty cycle is high?
First of all, great news. It's been awhile since my days with this system so apologies for shooting all over the place. Junkyarddawg's advice was sound.

To properly set the air flow meter screw, you'll first need to plug the hose coming off of the charcoal canister. Next, get the engine up to 80*C operating temperature. Make sure the engine is hot.

Take the reading then. I'm assuming you have a proper o-scope and not a simple duty cycle meter. If you have a duty cycle/volt meter, you'll need to pull the data from the fuel ECU. This thread will have clear instructions on how to do that as well as explain why we can't use the diagnostic port.
https://www.benzworld.org/threads/k-jetronic-with-lambda-overview-and-adjustment.2182425/

Basically, you make very fine adjustments - 1/64ths of a turn. Rev the engine to 3500 rpm and then take a reading again. Keep adjusting until you get the reading as close to 50/50 as possible.

The duty cycle mixture presupposes a fully sealed intake system and operating fuel pressure system. If you have an intake leak, the fuel trim will default to rich. At that point, you'll have to replace intake parts with a smoke test to reveal the culprits.

Good luck!
 

·
Registered
1990 560SEC 334K miles as of 5/19, 1990 500SL (Euro Build) 67K miles as of 5/19 1985 380SL 130K
Joined
·
150 Posts
Discussion Starter #38
Doesn't lean out. It will stall. It's either the oil temperature telling the lamba to keep it rich, or the OVP or the setting of the WUR keeping it rich. The frequency switch is buzzing. The WUR is under warranty so I'll swap it out as the cold control pressure is. 5 bar only should be 1.8-2-2bar for a 068 type WUR. When I unplugged the oil temperature connector there was no change. So WUR or OVP is my belief at this point. Unless the frequency valve is buzzing and not performing properly.
 

·
Registered
1984 380SL
Joined
·
2,343 Posts
Doesn't lean out. It will stall. It's either the oil temperature telling the lamba to keep it rich, or the OVP or the setting of the WUR keeping it rich. The frequency switch is buzzing. The WUR is under warranty so I'll swap it out as the cold control pressure is. 5 bar only should be 1.8-2-2bar for a 068 type WUR. When I unplugged the oil temperature connector there was no change. So WUR or OVP is my belief at this point. Unless the frequency valve is buzzing and not performing properly.
When my OVP relay and oil temperature sensor were bad, I was still able to set the duty cycle to 50/50. However, my fuel economy was still abysmal.

I chased my tail until I eventually replaced both of those parts.

If you can't lean it out, investigate your fuel pressures and vacuum system health. A problem in either will lead to this issue. Your hunch on the WUR might definitely be it.
 

·
Registered
1990 560SEC 334K miles as of 5/19, 1990 500SL (Euro Build) 67K miles as of 5/19 1985 380SL 130K
Joined
·
150 Posts
Discussion Starter #40
I'm sending out the WUR under warranty to correct the cold control pressure setting. I will update here when it's back and working and see what the mixture does. Thanks for the heads up on the oil temp sensor and OVP. The problem is the WUR pressures keeping it rich. Imo
 
21 - 40 of 40 Posts
Top