W126 distributor cap, plug wires info - PeachParts Mercedes-Benz Forum

unkl300d · #1 03-01-2009, 10:55 PM

Hello,
my 1989 300SE has intermittant stumbles during idle. Like explosive burps.
(gas mileage seems to have dropped a bit)

My Beru silicone wires have 36K miles on them as does the distributor and rotor since brand new.
Should the wires, plugs and cap/rotor last longer?

Does the dist. cap come off with a 5mm hex? What tool is best used to manage the final third hex nut at the cramped bottom?

What is the best way to pull off the plug boots from the spark plugs?

I've researched the past archives and have a general idea on some stuff but seek some more updated detail.

Thanks car has 136K miles on odometer

pawoSD · #2 03-01-2009, 11:07 PM

Might be dirty/plugged injectors....tried running some injector cleaner? Redline SI-1 and Chevron Techron are good.

Our 300E has run smoother and smoother and mileage gotten better and better after running a few tanks with Redline SI-1 in it. It idles so smooth you can't even tell its running! As an experiment I have now switched to using V-Power gas instead of running Redline....to see if its just as good.

porkface · #3 03-02-2009, 01:22 PM

i'd have someone check it out before throwing parts at it. yes, cap, rotor and/or wires can cause what you describe. and yes, 36k would be a short life. the coil can act up, along with any fuel problem the car have might to cause the same thing. good luck, chuck.

unkl300d · #4 03-02-2009, 01:51 PM

Hey thanks so far for the opinions.

I did use chevron techron fuel treatment recently.

I also observed the engine running in the dark in order to spot any insulation gaps (sparks) at the boot ends attached to plugs.
none.

What's the best tool/strategy for the lower hex bolt on the dist. cap?

THX

pawoSD · #5 03-02-2009, 03:04 PM

Quote:

Originally Posted by unkl300d

What's the best tool/strategy for the lower hex bolt on the dist. cap?

THX

An allen key? Thats what I used.

Did you pull and inspect the spark plugs? How old are they? Might have a dirty one (or more).

unkl300d · #6 03-02-2009, 03:10 PM

Hey thanks.

I plan to pull the plugs and dist cap to inspect.

You are right it may just be a plug. But the plug boots look like they need a gimmick to pull off w/o damaging them. I have a basic plug boot puller 'plier' cheapo but it really does not fit toward bottom for a good grip...

Dist cap: I did a dry run with a 5mm allen wrench but the lower hex nut is in a position where the allen wrench can not rest inside without the handle being avaivalble to torque it counterclockwise. It rest up onto the cap bottom or nothing.

slk230red · #7 03-02-2009, 03:54 PM

Quote:

Originally Posted by unkl300d

Hey thanks.

I plan to pull the plugs and dist cap to inspect.

You are right it may just be a plug. But the plug boots look like they need a gimmick to pull off w/o damaging them. I have a basic plug boot puller 'plier' cheapo but it really does not fit toward bottom for a good grip...

Dist cap: I did a dry run with a 5mm allen wrench but the lower hex nut is in a position where the allen wrench can not rest inside without the handle being avaivalble to torque it counterclockwise. It rest up onto the cap bottom or nothing.

To pull off the plug wires, I made a puller out of a wire coat hanger. I bent it into a U shape, then put a curl in the ends so I could reach end and put the curled ends on the metal tabs/ears and pull the connector off.

pawoSD · #8 03-02-2009, 06:35 PM

I use a craftsman "spark plug boot puller" $6 made in USA at your local sears.

Works fine, it grabs right above the metal part of the boot with two rubber fingers....doesn't damage it at all. I've pulled ours several times with it and it works great.

porkface · #9 03-02-2009, 07:27 PM

i forgot to mention the plugs. if they are platinum, they will cause the same problem, even after 5k or so. if you need plugs get bosch or ngk copper non-resistor plugs. the oe design plugs do MUCH better than the platinums sold as an "improvement". good luck, chuck.

unkl300d · #10 03-03-2009, 02:41 PM

Hey guys great ideas.

I will consider the tool options.

Also you all are right about platinum plugs. I've read how they are funky.

I need to figure out the botom dist cap hex nut access...

pawoSD · #11 03-03-2009, 04:06 PM

I am using standard NGK RESISTOR plugs in our 300E and it runs great with them. The key is not to use platinum plugs. Pretty much all Bosch/NGK resistor plugs will work ok. I've gotten the best performance and mileage running NGK standard resistor plugs.

Cal Learner · #12 03-04-2009, 09:15 AM

Quote:

Originally Posted by pawoSD

I am using standard NGK RESISTOR plugs in our 300E and it runs great with them. The key is not to use platinum plugs. Pretty much all Bosch/NGK resistor plugs will work ok. I've gotten the best performance and mileage running NGK standard resistor plugs.

Even better than running NGK standard non-resistor plugs?

amgraves · #13 03-04-2009, 09:14 PM

I have had an even better experience with a properly matched set of Autolite non-resistor racing plug in my 300E. Very easy to find and the car runs better than ever. I found that with ANY resistor plug, the distributor cap and rotor were out in no time!

Aaron

Aardvark · #14 03-05-2009, 04:10 AM

A quick note on finding those arching electrical nuisances.
Sometimes they can not be seen under the hood, even at night. A trick I've learned when checking for plug wire arch, is a plant misting bottle, with good ole H2O. Spray the wires in the dark, and watch the light show begin. You will be shocked at how many electrical arches happen.

Aardvark

unkl300d · #15 03-12-2009, 12:26 AM

OK here is some more specific info for the archive.

I bought the Craftsman spark plug pliers (#947315) and a spark indicator # 19380, a pen that has a fuse that lights up and pulses with the current after placing the pen body over the plug wire. Neat.

Pliers and hand combined worked to remove the plug boots. I was told by a former 1989 420SEL owner that the boots need to be turned first then pulled out. Contrary to a forum poster that claimed rotating the boot does nothing...

I can not so far ascertain this point.

How to remove the distributor cap.

Remove the black plastic cover held by side tabs. Pull up and the thing comes off. It has tracks in the back side also that have to be fitted when replacing.

(allen wrench = allen key)

The dist. cap has three hex nuts. The two top ones are readily accessible and come off with a 5 mm allen wrench. (hex wrench).

The third one is located below and over the serpentine belt pullet etc.

Use a long armed allen wrench. Insert the longest arm's end into the hex bolt from the fan vantage point.
The radiator fan has one blade which is spaced farther apart than the rest. This area allows space to work within.

Use a 6 inch crescent wrench to grip the allen wrench arm from above.
Use the crescent wrench to turn the allen wrench and remove the lower hex bolt. Reverse for installation.

You must snap off loose the plastic plug wire cover plate (that sits on the valve cover) in order to allow the wires slack. This way you can pull off the dist. cap without having to disconnect any wires. Unclip the coil wire from the wire holder on engine body also.

Check cap contacts. Use sandpaper and an arced motion to lightly sand carbon from contacts. Contacs are concave so don't sand flat side to side.

Don't sand the carbon brush at the cap's center.

Do lightly sand the rotor's contact. It also has a curved surface.
Reassemble. Hand tighten the hex bolts. 'Torque' down the top two first then the bottom one last.

Cleaning the cap helped my problem a bit. It was not very dirty.
Now I need to remove all plugs. The pen helped me suspect the two plugs nearest the firewall.

I'll try atomizing water over the boots first.

my car has NGK plugs installed right now. 36K miles on 'em.