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1979 280CE
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Discussion Starter · #1 ·
1. Where is the fuel filter and strainer? Also how do you remove them?

2. When changing the spark plugs is it just a matter of pulling the wire of and takeing the old one out and putting a new one in, or do you have to reset something?

3. Should I replace the spark plug wires?

4. If I do put in new spark plug wires does it matter where they plug into the distributor cap.

5. Should I put in a distributor cap also?

6. What are the best spark plugs and wires if needed?

Thanks for your help. I've never changed out spark plugs on any car before so if the questons are stupid you know why.
 

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'84 300D/ dakota benz trk. Sold... miss it. "88 260E '91 190E 2.6 '89 Volvo 240DL "85 300D
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dude, i do not know about 123 gassers. but i DO know about small block chevys. if you are doing electrical service, change it all. new plugs,wires,cap, rotor, points if applicable. and YES it matters what wire goes where. you will need to know the following: firing order, it should be somewhere on the engine, may be on intake. you will need to know rotation of rotor, you will need to know where on the rotor is the #1 plug wire. you will need to know what the plug gap is. it should be very easy on this forum to find out all this info. i would bet that your fuel filter is at the rear axle right with the fuel pump like a 124.
 

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1979 280CE
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Discussion Starter · #3 ·
Thanks, I know the firing order. How do you change all those parts(cap,rotor,wires,fuel filter). Why do I need to know the plug gap? How do I know where the first plug should connect? I'm very new to this and I know very close to nothing about it so every bit of help I can get would be great. Thanks
 

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2007 S550
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1,165 Posts
The easiest way for someone to do a refit without the luxury of experience is to do one thing at a time. Take one wire off, measure it against the new ones and replace it with the correct length corresponding new wire, same thing with the plugs. The plug gap is the distance or gap between the wire at the bottom of the plug and the center. You place a feeler gauge of the correct thickness into this gap and tap it down so it is the correct gap on each plug... they will all be the same. I'm not real sure any of us on this forum would actually suggest you dive into a cap and rotor replace without a little more practical experience.... easy to mess up if done incorrectly. You should be fine with the plugs and wires, just take your time and take them off and on one at a time.
 

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'84 300D/ dakota benz trk. Sold... miss it. "88 260E '91 190E 2.6 '89 Volvo 240DL "85 300D
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well, like i said, i know nothing about 123 gassers. however, i will tell you like we are talking about a straight 6 chevy. your cylinders are: as you are facing the engine 123456 etc. toward the windshield. front to back per say. follow the #1 cylinder plug wire to your dist. cap. THAT is your #1 wire. label it, tag it , whatever. now look for screws, clips, whatever that is holding down you distr. cap to the distr. undo it, take it out of the way. have assistant bump engine over and see which direction rotor is turning. CW or CCW. THAT is your rotation. if you know firing order you will see that when the rotor passes #1 wire the next wire it goes by will be for the next cylinder of your firing order. you see? it is very simple just think about it. gap is important because it will determine what kind of spark quality you have. too big a gap and the spark may not be able to jump it. too close and it may not be hot enough. you would be safe gapping it at .035 i would say. again, i do not know gasser 123's. it should be on a data plate on your car.
 

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Several pointers on changing spark plugs:

1. pull the plug wire off the plug by the boot, never by the wire
2. Get a special rubber lined spark plug socket to remove and reinstall plugs with.
3. Coat the 3 or so lowest threads of the new plugs with neverseize compound before installing them.
4. Always start new plugs by hand and use ratchet or torque wrench only for final tightening.
5. Keep the rubber lined spark plug socket straight and tight on the plug during tightening. It is easy to crack the porcelain plug insulator otherwise,which will result in missing at low speeds.
 

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'84 300D/ dakota benz trk. Sold... miss it. "88 260E '91 190E 2.6 '89 Volvo 240DL "85 300D
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something else we do is use a little dielectric grease on the boot for future ease of removal of wire. i also use a little neverseez on the threads.
 

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1979 280CE
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Discussion Starter · #8 ·
So should just leave the cap and rotor alone? I'm pretty sure i can handle plugs and wires. Where can I get a feeler gauge to measure the gap for the plugs?
 

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'84 300D/ dakota benz trk. Sold... miss it. "88 260E '91 190E 2.6 '89 Volvo 240DL "85 300D
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no, change it all. all parts needed can be obtained at a parts store. the cap and rotor are the most no-brainers of the job. if 123 gassers are like other cars, the rotor and cap can only go on one way.
 

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1979 280CE
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Discussion Starter · #10 ·
Could you tell step-by-step on how you remove and reinstall the cap and rotor.
 

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'84 300D/ dakota benz trk. Sold... miss it. "88 260E '91 190E 2.6 '89 Volvo 240DL "85 300D
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i couldn't. i have yet to be able to say for 123 gassers " been there done that" so i will recluse myself from this one.
 

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1979 280CE
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Discussion Starter · #12 ·
Can anyone else with a gasser please help me:bowdown:
 

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1979 280CE
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Discussion Starter · #13 ·
if I bought a Haynes repair manuel, would that explain to my step by step in how to go about doing this job?
 

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79Mercy said:
if I bought a Haynes repair manuel, would that explain to my step by step in how to go about doing this job?
No. Manuel is not for sale. :D However, if you buy a Haynes manual, it probably would tell you the basic steps involved in replacement.

I can give you some general guidelines:

Distributor caps are retained to the distributor body in several ways. Most common is two spring clips on the side. Some vehicles have two Phillips screws. Unfortunately I do not know what your Mercedes has.

If you replace the distributor cap and rotor, do it as follows:
Pull on plug wire by the boot to get it off the plug, and then from the distributor cap. Place the new distributor cap close to the existing one (still on the distributor) and orient it in the same way. Then plug the loose plug wire in the corresponding socket. Do the same for all six plug wires.

Then get the wirefree old cap off and transfer the new one on and screw/clip in place.
 

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89 Mercedes 300E, 91 Mercedes 300CE, 71 BMW turbo 2002, 73 BMW 2002tii, 85 BMW 635csi
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1979 280CE
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Discussion Starter · #17 ·
Nutz, Please read my post over at the other site.
 

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89 Mercedes 300E, 91 Mercedes 300CE, 71 BMW turbo 2002, 73 BMW 2002tii, 85 BMW 635csi
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p100 said:
I must admit that the Haynes manual I have for diesel 123s is pretty useless.
I cannot find a Bentley manual for diesel 123 in your link.







Nah,try the Technical Companion maybe :confused: It covers the W123 models,but to what extent,I can't tell you!

 

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83 300d turbo, 79 c123 AMG
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Hey Nutz is Bentley that much better? I got a Haynes a few weeks ago, titled 280 w123's, and to my enjoyment, the engine diagram (with all the labled pieces) was a 250! What crap.
 
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