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1983 380-SEL, '67 220D (sold), '65 200D (sold), '75 L-206D (sold)
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291 Posts
Not sure if your model has this, but check the integrity of the cable from the Ignition Control Unit to the middle backside of the distributor. I think I damaged mine by removing the distributor cap a few too many times. The locking hook is very near the cable input. Both sides of this 3 foot green cable were crumbling end caps and there was exposed wire. Sealing this cable up seem to solve the cold start for me. More details in the last month or so of this forum post:

http://www.benzworld.org/forums/w126-s-se-sec-sel-sd/2049481-91-w126-420sel-no-spark-issue.html?highlight=

Hope that helps.
 

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1991 560sec. 1969 280SL
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989 Posts
Discussion Starter #62
The fuel pump check valves made no difference to the starting problem. Thought I should check ignition system, needs plugs, upon trying to remove the three dist. cap screws discovered one was rusted solid, had sprayed penetrant a couple of days ago but still would not budge even after tapping on it with screw driver in head. The blasted head broke off :eek, anyway removed the cap and discovered the cap was broken away from said screw and the break looked fresh, oh well. Ordered the parts needed and will be replacing with Bosch original. The spark plugs NGK BP6ES are on order also tested resistance of rotor that was fine. I have a brand new set of OE wires. This is not going to fix the starting problem but needs to be done.

I have a feeling the starting problem is related to the air flow sensor plate. Though after switching engine off I'm able to push plate down all the way and watch it return to rest position, same is not true with cold engine.

I suppose I should wait until I receive my ignition parts to be certain I have to remove the AFS housing.
Thoughts as always appreciated.
Thanks.
 

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Outstanding Contributor
1988 300CE
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1,424 Posts
The fuel pump check valves made no difference to the starting problem ...
That’s why I only replace parts if tests suggest to do so.

What you know (from the holding pressure test) is that there’s a leak in the fuel system. Tests you’ve done so far suggest that there is no external leak and no leak in the accumulator or in the pressure regulator. The old check valves were possibly good too ... another holding pressure test would tell us more.

What has not been tested yet is the leak tightness of the
- axial seal ring for the CP
- CSV
- injectors

Leakage from the CP can, of course, be related to the AFM plate. See what I said about that in posts 22 & 38.

And don’t forget what I said about the ECU & EHA in posts 25, 48 and 50.

H.D.
 

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1991 560sec. 1969 280SL
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989 Posts
Discussion Starter #64
Update

Thought I should update all concerned. Removed and cleaned the AFM housing, cleaned throttle and reinstalled. Did not replace any ignition parts as I did not suspect anything with that. After checking every last component in the fuel system and finding no problem, there was only one thing left as far as fuel holding pressure and that was the injectors. Replaced the injectors and seals with brass Bosch ones. The car still had originals. Any way problem solved. Special thanks to HD for guiding me through the steps and, and everyone else who took part in the thread. Great bunch of guys. This forum puts every other to shame.

Thanks a million.
Dave S.:smile
 

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1991 560sec. 1969 280SL
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989 Posts
Discussion Starter #67
Thank you both. I'm happier than an Arab on a camel running to the virgins. :devil
 

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1990 560SEC 334K miles as of 5/19, 1990 500SL (Euro Build) 67K miles as of 5/19
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126 Posts
Residual pressure could also be lost in the pressure regulator, via CSV, via (at least one of the) injectors, or because of a problem with the axial seal ring for the fuel distributor’s control plunger (worn, or not reached by the control plunger with the engine switched off, for instance because the Lambda adjustment screw has been turned too far cw. Or there could be an external leakage somewhere between the pumps and the pressure regulator, which would come along with a smell of fuel though.


If the fuel pressure loss is related to the control plunger seal ring, cycling the ignition switch might even be counterproductive. … But there could also be other reasons for the starting problem. There could be deposits on the backside of the intake valves and in the last part of intake ports. In that case the first injected fuel is (partly) absorbed by these (in the morning dry) deposits, resulting in a poorly atomized air/fuel mixture. … Both cases could be a possible reason why waiting five minutes seems to help.

H.D.
I have a '90 560SEC, testing with a cold engine. New pumps. Rebuilt fuel distributor. Pressure gauge in cold start port on FD and service port. jumped FPR to active pumps. I get 92psi/6.4 bar. Then i stop power to the pumps it drops to 2.2 bar pressure, but I can hear what i thought was fuel leaking, only to hear the sound is coming from the FPR. The "vacuum" line on the back side of the FPR doesn't leak fuel and I can feel a diaphram when I pull and puff on it. Are these signs of the FPR being kaputt? Total failure? Next steps? Tests? Otherwise it can't be revived to my knowledge.....new or used? Does this part fail from gas being in contact with rubber for many years? Its got a spring mechansim in it, but the vacuum diaphram seemed intact unless there is anotrher main one. So buying a low mileage used one is not any better? So go new?
Thanks! Update..recapping, the pressure peaked at 6.4 bar. I then stopped jumping them to power. Then energized the pumps again, the pressure had dropped down to 2.2 bar. I left it to investigate online why the pressure was not going back up to the 6.4 bar when pumps are on. I left it for the day/overnight at 2.2 bar. When I checked it today it fell to 1.6 bar in the time frame of overnight with the same pressure lines and gauge attached. Today I clamped the return flow of gas to the gas tank via the FPR, energized the pump pressure remained at 1.6 bar. I have not tried clamping the return flow of gas to the tank from the Accumulator to see what effect that will have. Open to ideas. If it is accumulator or FPR or both.
Thanks!
 

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1988 300CE
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If, when you jumper the FPR, the fuel pressure at the CSV port does not rise at all and stays at 1.6 bar, as you report, then there is:
1) either a problem with the pressure gauge or its connection to the CSV port
2) or no fuel in the tank
3) or a blockage between fuel tank and pressure regulator (via pumps - filter - FD)
4) or a problem with the fuel pumps or their wires to the FPR socket or to ground
5) or a problem with the pressure regulator

If you can hear the fuel pumps run when the FPR is jumpered, open the fuel return line at the pressure regulator and check if, when you jumper the FPR for 5 seconds, at least 125cc of fuel come out.

If that is the case, and there is no problem with the pressure gauge or its connection to the CSV port, then there is a problem with the pressure regulator. In that case, replace it … for instance, with a good used one if you can find one.

If that is not the case, take a closer look at the above mentioned items 2, 3 & 4.

I happened to receive an email notification about your post in this thread James560SEC. ... I receive such notifications from Benzworld only sporadically and without this notification I would not have noticed your post in this more than two and a half years old thread. So if I don’t react on posts it has usually to do either with lack of time or missing email notifications. :rolleyes:

H.D.
 

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1990 560SEC 334K miles as of 5/19, 1990 500SL (Euro Build) 67K miles as of 5/19
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HD, here is how it all worked out. I had original pumps on my car, I noticed corrision on one of the pumps connection and lound sounds from the. I cleaned the connection but the pumps failed. No pressure. I replaced both pumps. I jumpered the pumps. Pressure peaked ar 6.4 bar and went down from there. Still no pressure to speak of. I did as you suggested and attached a clear line to the return line of the FPR. Jumpered the pump for 5 seconds. Fuel continued to flow after the power ceased. I waited until the flow stopped, I cleared the line into the bucket and measured. 250cc, So I surmise that my car had been operating on failing fuel pumps. The fuel pressure that did get to the FPR was not diverted back to the tank, as it was low already so all of it went to running the engine (poorly i might add). So when I put new pumps on the newly rebuilt FD, the FPR got correct pressure and then failed catastrophically. However, only you FD gave me the test to isolate the FPR as the cause, and I have scoured the boards for a test like the 125cc test.. I discovred the potentiometer problem doing duty cycle static tests. I have installed the Bosch Poteniometer part I will update when the new Bosch FPR is installed. Thank you!
 

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1990 560SEC 334K miles as of 5/19, 1990 500SL (Euro Build) 67K miles as of 5/19
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126 Posts
HD, I decided to go with a new one. It looks like the latest model of vehicle they put this part on were 1993 Bentley's and Rolls. So I wasn't going to spend $100 on a used one from a 560SEL that has 116k miles on it. Miles aren't the issue. It's the length of time that it has been in contact with gasoline. Now I read that the ethanol used in our 90/10 gas is eating gaslines at a higher rate of speed than plain gas was, and that PTFE lined hoses are needed. I don't think they were/are using rubber diaphrams lined with PTFE. If not, then the parts that are reliant on functioning rubber diaphrams will be degrade faster. I can get a new Bosch FPR for $290 tax in/delivered from RockAuto. Done!
 

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1988 300CE
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… only you FD gave me the test to isolate the FPR as the cause … … Thank you! …
Assuming that ^this “FD“ means “H.D.“ :D … you‘re welcome James560SEC.

... Now I read that the ethanol used in our 90/10 gas is eating gaslines at a higher rate of speed than plain gas was, and that PTFE lined hoses are needed. I don't think they were/are using rubber diaphrams lined with PTFE. If not, then the parts that are reliant on functioning rubber diaphrams will be degrade faster. ...
Ethanol can cause problems with certain rubber materials, but these are not used on the KE-Jetronic. However, ethanol can cause the system‘s alumin(i)um parts to corrode with the time. There are good additives that can prevent that and also stop already existing corrosion. Another problem with ethanol is increased formation of deposits (intake valves, combustion chamber, injectors, …). Good additives can also counteract that … which in case of E10 I generally recommend to use !

H.D.
 

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1990 560SEC 334K miles as of 5/19, 1990 500SL (Euro Build) 67K miles as of 5/19
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126 Posts
Assuming that ^this “FD“ means “H.D.“ :D … you‘re welcome James560SEC.


Ethanol can cause problems with certain rubber materials, but these are not used on the KE-Jetronic. However, ethanol can cause the system‘s alumin(i)um parts to corrode with the time. There are good additives that can prevent that and also stop already existing corrosion. Another problem with ethanol is increased formation of deposits (intake valves, combustion chamber, injectors, …). Good additives can also counteract that … which in case of E10 I generally recommend to use !

H.D.
Yes, I meant HD, but had FD as in Fuel Distributor on my mind as I had just rebuilt mine. I am using StarTron enzyme fuel treatment to great improvement IMO, I don't know what effect it has otherwise on degradation of materials. I know it functionally decreases the size of the water molecule(or something to that effect) so it can be effectively passed with the "burn" off....as engines don't like water. But operationally I think its much better. You have suggestions/input on an additive? They approved E15 now??
Thanks again, HD
 

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1988 300CE
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... I am using StarTron enzyme fuel treatment to great improvement IMO, I don't know what effect it has otherwise on degradation of materials. I know it functionally decreases the size of the water molecule(or something to that effect) so it can be effectively passed with the "burn" off....as engines don't like water. But operationally I think its much better. You have suggestions/input on an additive? ...
I‘m not familiar enough with respective products in the US market to recommend a specific one, and I prefer not to talk much about things I don‘t know much about. … As a politician I‘d probably not be able to win any election. … ;)
 

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1990 560SEC 334K miles as of 5/19, 1990 500SL (Euro Build) 67K miles as of 5/19
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HD, can you tell me the proper way to set the potentiometer on the airflow housing? I replaced the FPR and now have pressures. Do I need to back out the adjusting screw on the meter flow plate all the way to the full lean position to begin with to close the flow plate? Then I set a voltmeter using the top 2 pins using volts and look for .7 +or - .1?? Reason being I am now in a no start situation with screw all the way lean. I can't get it to turn over to adjust it running. Can I set it with key in position 2? I turned the screw all the way lean. Whats a good position to get it started, as in how many turns rich from all the way lean once potentiomter is set.

Thanks in advance, as I can't find good detailed instructions anywhere on the boards.
 

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1988 300CE
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HD, can you tell me the proper way to set the potentiometer on the airflow housing? I replaced the FPR and now have pressures. Do I need to back out the adjusting screw on the meter flow plate all the way to the full lean position to begin with to close the flow plate? Then I set a voltmeter using the top 2 pins using volts and look for .7 +or - .1?? Reason being I am now in a no start situation with screw all the way lean. I can't get it to turn over to adjust it running. Can I set it with key in position 2? I turned the screw all the way lean. Whats a good position to get it started, as in how many turns rich from all the way lean once potentiomter is set.
Yes I can. But right now I don‘t have enough time for that. … And before you tackle the calibration of the AFM potentiometer, when you say “adjusting screw on the meter flow plate“, are you by any chance referring to the adjustment tower between AFM plate and FD ?
 

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1988 300CE
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Yes I am.
Okay James … you may not know this, but when your car left the MB factory about 30 years ago it did that with a difficult to remove plug in this adjustment tower. And it did that for a very good, but commonly way underestimated or even completely ignored, reason. This plug may not be in place in most CIS-E MB‘s anymore, but the reason for it still is. … At least post #39 of This Thread should make you aware of that. … ;)

H.D.
 

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1990 560SEC 334K miles as of 5/19, 1990 500SL (Euro Build) 67K miles as of 5/19
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Understood. How many turns clockwise from closed will get me back to the approxamte default or "previouly capped" setting please?
 

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1988 300CE
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Understood.
Very good! … So from now on you can explain CIS-E car owners why that adjustment tower was secured by a difficult to remove plug. ;)

How many turns clockwise from closed will get me back to the approxamte default or "previouly capped" setting please?
I don‘t know what you mean by “from closed“. … There is no specific number of turns from any position that will get the engine to start again, unless you remember how far in what direction you have turned it. ;)

James560SEL, I like to see and help to keep CIS-E MB‘s on the road. But I only help to keep them on the road in proper condition, not somehow. … And with “proper condition“ being the objective, after having fiddled around with the Lambda adjustment screw there are many things that have to be checked on your car now, as you probably realized when you read the thread I mentioned in post #78 … which you say you understood.

Proper assistance in checking all these things takes more time than I currently have. Maybe other forum members have time for that. Getting your car to start again is an easy task that other forum members should certainly be able to help you with. :)

H.D.
 
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