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  #1  
Old 07-25-2020, 03:47 PM
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Hard to start wont idle cold 300SL W107 1988

Hello to you all. I wonder if you could point me in the right direction please. I have a 1988 300SL and it won't run properly when cold because it is too lean. It won't idle when cold or rev up it keeps coughing back through the inlet. You have to feather the throttle in order to rev it. Once warm it revs up fine.

Does this car have a warm-up regulator because I cannot find one? Fuel pressure is around 100psi

Any help greatly appreciated

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Hard to start wont idle cold 300SL W107 1988-img_20200725_113720.jpg   Hard to start wont idle cold 300SL W107 1988-img_20200725_113726.jpg   Hard to start wont idle cold 300SL W107 1988-img_20200725_105004.jpg  
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  #2  
Old 07-25-2020, 04:50 PM
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As a first step, ensure that the ignition system is in top condition. Correct spark plugs w/ correct gap, clean distributor cap (inside & out), clean rotor.

Then, note the notch in the left side of the fuel distributor; in the notch is a "tower", open to the top. That it is open is a clue; it was plugged when new. In the tower is an adjustment for the mixture. Insert a 3mm hex key, push down & turn slightly. You will feel the screw drop a bit farther and engage the actual adjusting screw. Clockwise is richer. No more than 1/8 of a turn at a time; keep track of turns. After each adjustment (with engine stopped) release the adjustment screw, and try a start.
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Old 07-25-2020, 05:12 PM
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Hello Frank, thank you for your reply. It has had new plugs and ignition leads. I have checked the CO mixture and it was lean (0.01%) I have adjusted it to 0.6%, is that too lean still? What richens the mixture when cold?

Many Thanks
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  #4  
Old 07-25-2020, 05:17 PM
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Anyone know what the EHA does? I bet the w124 forum would be a good place to get m103 info.

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Past mb: '73 450sl, '81 280slc stick, '71 250, '72 250c, '70 250c, '79 280sl, '73 450sl, parted: '75 240d stick, '69 280s, '73 450slc, '72 450sl,
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Old 07-25-2020, 05:38 PM
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[QUOTE=fonzi;4075439]Anyone know what the EHA does? I bet the w124 forum would be a good place to get m103 info.



I found this about the EHA https://www.youtube.com/watch?v=YjqgPTfKOG0
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  #6  
Old 07-26-2020, 03:20 PM
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1-stay away from the eha. it does have a function but NEVER fails other than leaking fuel out of the pins into the connector. never had 1 cause a running problem unless someone messed with it.

2-you have to have a fuel pressure tester and the ke-jet testing is different than k-jet. without knowing pressures, you can't diagnose the problem. iirc, upper and lower chambers are .4 bar apart when hot. if they are the same pressure upper and lower, it will run lean. i suggest you google mercedes ke-jet testing and look for the 124 or 201 manuals as they would have complete info for testing. being a gray car, the us specs will be ok for you, just not perfect. i doubt the difference will be a problem. getting gray specs is the problem i see.

3-you also need a volt meter or 2 as you need to watch amperage at the eha, easy to make special harness, and on the 10 pin connector to watch duty cycle. i use 3 so i can watch to o2 sensor, also. that testing is in the manuals.

i worked on 1 gray 103 engine 107 and it had a running problem but it was ignition, not fuel. not a lot of help there. i will say i enjoyed that car more than the heavy v8s we got to drive. much better feel. good luck, chuck.
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Old 07-26-2020, 04:02 PM
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[QUOTE

i worked on 1 gray 103 engine 107 and it had a running problem but it was ignition, not fuel. not a lot of help there. i will say i enjoyed that car more than the heavy v8s we got to drive. much better feel. good luck, chuck.[/QUOTE]

which reminds me....most of the issues i've had in the past with cold start in 102s and 103s are in the ignition. plugs and wires may not be enough as the cap, rotor and coil pays a price when simple maintenance is ignored. only bosch or ngk plugs, bremi or karlyn wires-not bosch, bosch or bremi cap and rotor only, and bosch or bremi coil, if you need 1. sold lotsa that design coil because they were done. look for a white spot around the metal bracket that is part of the coil. that's where the spark is escaping, looking for the path of least resistance. bosch gray silicone wires are terrible. i had 4 sets i went through on 3 cars many years ago. given your problems, you might have more than just lean fuel. and lean fuel is harder to fire than rich. takes more kv from the coil to fire. get a kv tester and see what the coil can do. if it's tired AND you're lean, the existing kv may not be enough to light the fuel. good luck, chuck.
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  #8  
Old 07-26-2020, 06:40 PM
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Quote:
Originally Posted by porkface View Post
1-stay away from the eha. it does have a function but NEVER fails other than leaking fuel out of the pins into the connector. never had 1 cause a running problem unless someone messed with it.

2-you have to have a fuel pressure tester and the ke-jet testing is different than k-jet. without knowing pressures, you can't diagnose the problem. iirc, upper and lower chambers are .4 bar apart when hot. if they are the same pressure upper and lower, it will run lean. i suggest you google mercedes ke-jet testing and look for the 124 or 201 manuals as they would have complete info for testing. being a gray car, the us specs will be ok for you, just not perfect. i doubt the difference will be a problem. getting gray specs is the problem i see.

3-you also need a volt meter or 2 as you need to watch amperage at the eha, easy to make special harness, and on the 10 pin connector to watch duty cycle. i use 3 so i can watch to o2 sensor, also. that testing is in the manuals.

i worked on 1 gray 103 engine 107 and it had a running problem but it was ignition, not fuel. not a lot of help there. i will say i enjoyed that car more than the heavy v8s we got to drive. much better feel. good luck, chuck.
Hey Chuck thanks for your message and the tips. I will rule out the EHA then unless someone has tried adjusting it? I have looked for a testing manual online but couldn't find one. DO you know of a website where I might find one?

Is the EHA controlled by an ECU, I'm guessing it is. Someone told me to check the unit behind the Glovebox (Black rectangle box with round pins) but I think this might just be the fuel pump relay as it clicks when the fuel pump goes on and off.
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  #9  
Old 07-27-2020, 12:34 AM
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P_uk:

Regarding the EHA (Electro-Hydraulic Actuator):
If the EHA is not functioning for any reason there will not be any mixture enrichment for starting, post-start, or warmup. There are a few obvious things that would cause the EHA to not function, or to not receive an enrichment signal.
1) Connection between EHA and ECU is unplugged, or broken.
2) ECU is not working.
3) An air or water temp sensor is sending a "hot" signal when cold.
4) The air-flow plate potentiometer is not sensing plate movement, or is not providing a signal to the ECU.
5) The throttle switch is disconnected, or not signaling correctly.
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  #10  
Old 07-27-2020, 04:52 PM
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You may find useful information here:

Benzworld: Warm-up regulator

Rob
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  #11  
Old 07-27-2020, 06:15 PM
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Quote:
Originally Posted by Rob Pruijt View Post
You may find useful information here:

Benzworld: Warm-up regulator

Rob
It would be useful if the system in question had a WUR; however it does not.
The system is KE-Jetronic.
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  #12  
Old 07-28-2020, 09:15 AM
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try here-

07 Mechanical/Electronic Injection - M103
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  #13  
Old 07-28-2020, 05:54 PM
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Thanks for the tips guys. I will investigate further and let you know how I get on.
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  #14  
Old 07-29-2020, 11:00 AM
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On USA models all the cold start enhancements are in the "E" part of the KE system, and the ECU receives power from Overvoltage Protection Relay. This also powers the ABS system, and if the OVP fails the ABS warning light on the IP illuminates.

I assume your M103 is a UK model, and I don't know if it's configured the same as emission controlled USA models.

Duke
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  #15  
Old 07-29-2020, 12:00 PM
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Ive had a friends eha fail on a e 300 coupe, it was hard to start and intermittently no acceleration, after much head scratching i replaced the eha and the car ran perfect

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