Still trying to make progress on my W114 250 - Mercedes-Benz Forum

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post #1 of 6 (permalink) Old 07-02-2016, 04:27 PM Thread Starter
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Date registered: Jul 2014
Vehicle: 1972 Mercedes-Benz 250/8
Location: Canada
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Still trying to make progress on my W114 250

Hi guys, I'm still trying to get my 250 in a reliable state. There are zero people in my city that have experience with these cars so I'm really on my own here.

I've managed to get a lot done myself but Im stuck at these issues
  • The car sputters and feels like it wants to stall when I press the gas sometimes.
    (Could the fuel strainer be causing this?)
  • I also have to feather the brake when I stop for red lights because If I apply the brake normally the car feels like its going to stall by the time it stops.

I managed to speak to a retired mechanic who worked on my exact car in the past and was told the modulator valve needed to be replaced several years ago.

So I went out and bought a vacuum pump to see if the modulator valve holds vacuum but I have no idea where the modulator valve is, could someone point me in the right direction?

I also tried to replace the temperature switch as it is broken on my car (see pictures) what symptoms will this cause?

I ordered a replacement based on what the EPC told me was the correct part (0035452224) but the part I received uses a different connection than the one that's on my car.

Whats going on here?

Any help at all will be greatly appreciated.

Thanks so much
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post #2 of 6 (permalink) Old 07-02-2016, 04:32 PM Thread Starter
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I should mention the car has the 130.923 engine and my car shifts hard sometimes, that's what reminded the retired mechanic of the modulator valve needing to be replaced..
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post #3 of 6 (permalink) Old 07-03-2016, 05:11 AM
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The vacuum modulator is located on the lower transmission housing. Follow the vacuum piping from the intake manifold.

Which temperature switch are you attempting to replace? I believe the 1972 models use a manual gauge for the temperature gauge. The other senders are for choke, timing advance and a 100C cooling fan relay.

Easy test for the cooling fan. With the ignition in the "run" position, ground the wire from the connector to the engine. The electric fan should engage. This connector is usually a "bullet" style connector.

The sending unit you are showing is the "bayonet" style which is more commonly used for the choke/timing/idle relays. If there are numbers imprinted on the new sender such as 100C, 65C, etc., then it is for activation of a circuit and not a variable resistance type of sending unit used in temperature gauges.
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Last edited by Mike D; 07-03-2016 at 05:37 AM.
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post #4 of 6 (permalink) Old 07-03-2016, 02:41 PM
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Check the vacuum line to the brake booster for a leak also. Could also be a failing booster.

Replacing the fuel filters would be good advice, or your carburetors could be warped causing air leaks. sprays around the carb with carb cleaner and see if the engine speed changes.

what is the first picture showing? where does that braided hose go?
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post #5 of 6 (permalink) Old 07-04-2016, 12:20 PM
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I also have a 130923 in a '71 250C. If your engine runs fine when driving and is bad at idle only the first thing you have to do is ensure that you have no vacuum leaks. Vacuum leaks will cause a rough idle and hard shifting. Shifting like it kinda bangs into gear. Check the fitting at the top rear of the intake manifold. replace the rubber couplings with new, then trace the hard plastic lines along the firewall that goes into the firewall for your HVAC flapper doors.

Replace with new rubber every fitting you can find. Don't forget the line(s) going to the Distributor from your carb(s). Make sure that your Carbs are snugged down tight and that you have no leaks at the carb bases where they bolt to the intake. You can eliminate basically everything but the carbs by plugging the main vacuum port on the intake manifold. This isolates everything except intake manifold, carbs and distributor. The Vacuum modulator is mounted to the right side of your transmission. Leave that for now. It is probably not bad. Eliminate all of the easy stuff first.

I struggled with poor idle and running too warm for years. Three things cured my problems. First: NO vacuum leaks anywhere. Second. Replace the Viscous damper on your Fan if the car is running warmer than it should. I don't care how it feels. Replace it. Third: Replace the Points in your distributor with a solid state system of your choice. The temp sender that you show mounts at top right front of the engine by the engine thermostat. It is to turn on the aux fan for the AC when the water temp gets too hot. There are two locations for temp senders on the left side of the motor. The one near the front is a manual one piece sending unit for the instrument. panel gauge. by one piece I mean the sensor on the engine end and the actual temp gauge is attached to the other end. the tube connecting the two ends is filled with ether. Always treat this one gently.

If you have to completely remove the instrument cluster, the sending unit must be removed from the block and pulled through the firewall and kept as one piece with the instrument cluster. The sender near the rear of the block is connected to the emissions crap on the right fender well and is used to advance/retard timing depending on engine conditions. I disconnected and removed all that crap on my car. Unless you are a purist or need your car to pass smog requirements ignore it. I know this may not fix your car but it should help steer you in the right direction. Good Luck.
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post #6 of 6 (permalink) Old 07-05-2016, 02:34 PM
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Thanks to everyone for their useful and substantive contributions in this thread. I took the liberty of deleting some off-topic posts and I hope no one is offended by that. It's just that we have some great material here and I didn't want it waylaid by irrelevant back-and-forth. Carry on please!
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