W123 troubles

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Lance
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Posts: 369
Joined: Thu 06 Mar, 2014 9:33 pm
Model you own: w114
Location: Altona Meadows, Melbourne

W123 troubles

Post by Lance » Tue 19 Dec, 2017 9:57 pm

Hello all,
Having troubles with my W123. Have had to press the W114 into daily driving duties.
When I accelerate hard it misfires and carries on and won't rev past 4200. When accelerating gently it runs smoothly without problems. I accelerated hard then the engine died so I pulled over. When I turned the ignition on I heard the pump run, then it would fire but would promptly die. After a few goes it ran and I drove it home.
The other day it wouldn't start so had to take the wifes car to work. When I got home it started after a few tries. I put a timing light on the ignition cable but it was firing. After another couple of tries it fired and ran fine. I replaced the fuel pump relay.
One other thing, since I have had the car the tacho occasionally reads too high, not sure if this is related. I replaced the coil with a new one but this made no difference.
Any suggestions?
Tomorrow I will check the basics and go through the manual to carry out all the checks.
Regards,
Lance Smart

W114 280E 5 speed manual
W123 280E

mathuisella
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Joined: Sun 08 Jun, 2014 7:03 am
Model you own: w123
Location: Brisbane, North side.

Re: W123 troubles

Post by mathuisella » Wed 20 Dec, 2017 8:28 am

I take it you have a petrol car ( w123 ) ?

if the car will not rev quickly under load, i would dare say that you have bad spark or Fuel delivery bottleneck, possibly a partially clogged filter. But also check your spark plugs and clean them when you take them out either way, and change fuel filters. Including the one in the fuel tank as that clogs up over time and may still be uncleaned since the car was new 30+ years ago as it was on one of mine.


this is the in tank fuel filter in one of my w123's before i cleaned it, and yes the car still ran like this, albeit was a bit low on power and wouldn't rev as quickly under load as it was a fuel delivery bottleneck, which went away once cleaned.
25578844_10212881024673188_1490166275_o.jpg
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User avatar
Lance
Adenauer
Posts: 369
Joined: Thu 06 Mar, 2014 9:33 pm
Model you own: w114
Location: Altona Meadows, Melbourne

Re: W123 troubles

Post by Lance » Wed 20 Dec, 2017 1:48 pm

Yes, very good suggestions but I have had a thought after reading the description of operation of the fuel pump relay from the manual. When I took it for a test drive it died on me. Then when I tried to start it it would fire then die. At starting the relay gets it signal to run from terminal 50, then once the engine starts it gets it from the terminal TD. Does this mean that my tacho signal is faulty (as explained above the tacho has been reading high and jumping about since I have had the car) or is it in the ignition box?
Regards,
Lance Smart

W114 280E 5 speed manual
W123 280E

mathuisella
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Model you own: w123
Location: Brisbane, North side.

Re: W123 troubles

Post by mathuisella » Wed 20 Dec, 2017 4:46 pm

i typed some stuff, but then lost it :/

just do the filters please. Save some time and narrow down the issue with the most likely cause and also the cheapest.


the tank filter can be cleaned with some kerosene and a toothbrush. the prefilter in the engine bay is $5 and there should be a third filter, but i really don't think it would block that if you have the other 2 in the system.

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Lance
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Posts: 369
Joined: Thu 06 Mar, 2014 9:33 pm
Model you own: w114
Location: Altona Meadows, Melbourne

Re: W123 troubles

Post by Lance » Wed 20 Dec, 2017 5:17 pm

Will do this, but just did the ignition test recommended in the manual and it is telling me that the distributor is faulty.
Regards,
Lance Smart

W114 280E 5 speed manual
W123 280E

User avatar
Lance
Adenauer
Posts: 369
Joined: Thu 06 Mar, 2014 9:33 pm
Model you own: w114
Location: Altona Meadows, Melbourne

Re: W123 troubles

Post by Lance » Wed 20 Dec, 2017 8:00 pm

Finally worked out how to do the ignition test, seems to check out OK, so need to look at fuel system as next cause. How do you pull that filter out from the tank, a big socket I would assume?
The fuel pump and filter were replaced shortly before I bought the car and I replaced the little filter in the fuel distributor after I bought it.
Regards,
Lance Smart

W114 280E 5 speed manual
W123 280E

mathuisella
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Joined: Sun 08 Jun, 2014 7:03 am
Model you own: w123
Location: Brisbane, North side.

Re: W123 troubles

Post by mathuisella » Sat 23 Dec, 2017 8:18 pm

under the car, beneath where you fill the tank in the middle between the wheels you'll see the outlet for the tank, drain the tank of all it's fuel and use a 46mm socket to undo the large filter :) it will drop out nicely and you'll see how clogged it has become over 30+ years.

give it a good clean and reassemble.


note: around the 46mm socket/nut/plug there's some insulation that may or may not interfere with the socket fitting. use a stanley knife to cut away the excess.

also, the tip of your socket, so it gets good grip on the nut area make sure it's flush.

there's only about 2mm of depth on the nut for the socket to grip, so having a standard flanged socket will not work well, see the pictures
d2ovq.jpeg

d5ja5.jpeg
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mathuisella
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Model you own: w123
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Re: W123 troubles

Post by mathuisella » Thu 15 Feb, 2018 12:31 am

How did you go with all this ?

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Lance
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Model you own: w114
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Re: W123 troubles

Post by Lance » Thu 15 Feb, 2018 8:17 pm

I was planning to update this as there is good info for others.
Your suggestion to check the filter was a good one. Although the filter was fine, when I was disconnecting the hose a stream of fuel spurted out the side. Replacing this fixed most problems. But it still died at 4200. That turned out to be a dud relay (non genuine) as I fitted a second hand relay and the problem went away but it would still die on me occasionally and was hard to re-start.
Ever since I had the car the tacho has been erratic and this had become worse. I suspected the ignition trigger unit as the cause. I removed the relay, wired in a switch to turn the fuel pump on and off and connected a voltmeter to the two center sockets and mounted that on my dash. I drove like this for a couple of weeks and finally saw the tacho and voltmeter drop to zero and recover. This made sense as the car would sometimes die momentarily then recover. So I organised a secondhand ignition trigger unit and fitted that with a new genuine relay about two weeks ago and the car has been fine since and the tacho is now fine.
So if your car dies briefly, cuts out but can be re-started (or is difficult to re-start) or if the tacho is erratic then the ignition unit is the problem.
In fact, my W114 occasionally cuts out in the same way so that must be developing the same problem but I have a secondhand unit that I will install and try.
Regards,
Lance Smart

W114 280E 5 speed manual
W123 280E

mathuisella
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Posts: 401
Joined: Sun 08 Jun, 2014 7:03 am
Model you own: w123
Location: Brisbane, North side.

Re: W123 troubles

Post by mathuisella » Thu 15 Feb, 2018 11:41 pm

Just a tip, when relays and other electrical units are failing/failed, try resoldering all the bits on the pcb ( printed circuit board) of the relay.

over time, the solder joints become " dry" and develop cracks, this happens especially in manufactured stuff that uses lead free solder. Solution: resolder every joint with leaded solder and enjoy driving for another 30 years or more.

https://www.youtube.com/watch?v=fQcDUHotThE

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Lance
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Posts: 369
Joined: Thu 06 Mar, 2014 9:33 pm
Model you own: w114
Location: Altona Meadows, Melbourne

Re: W123 troubles

Post by Lance » Fri 16 Feb, 2018 7:17 pm

Yeah, did that but still had troubles, that's when I hooked up the voltmeter to find out the real cause. The relay was original so was happy to replace it with new.
Regards,
Lance Smart

W114 280E 5 speed manual
W123 280E

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