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Hi All,

I've done my due diligence and searched the forum before asking these questions, but most answers are old and dated. I want to be sure I have the most current thoughts.
My 1986 560sel starts right up, and when I go I get a hesitation/stumbling, until I get up a little speed, then all is fine. High speed, highway, pedal to the metal, no problem. Just on initial take off, and sometimes when traveling and lightly accelerating. I've looked up all the info and I have run 3 gas tanks of Sea Foam, with minimal help. Sometimes it gets better while driving, sometimes it gets worse. Stopping and restarting sometimes helps, sometimes not lol.
Next recommendation is a tune up. That's where I need some advice....
(1) Best spark plug wires, and where to purchase them.
(2) Best Spark plugs recommended ( I know there are individual preferences but I'm trying to get an idea as to the 2 or 3 top preferred) and where to purchase.
(3) What else for a full tune up... Cap ? Rotor? Condenser (is there one?!?)? Air and/or gas Filters? Anything else for standard tune up/maintenance recommended?

Also, my heat works intermittently. I've read all the info on replacing the mono valve, but Bosch is NLA, so what is the brand most recommended, and best place to purchase? And can someone tell me exactly where it is located under the hood?

I've been sorting out the car (and using it) since we purchased it later last year. Info from you all has been extremely helpful along the way. I don't want to waste time having the same questions answered that can found in a forum search, but I just feel what I've found on these subjects has been somewhat incomplete, and dated.

Once again, thank you to all here on the forum, I would have been totally lost and probably spent big bucks to accomplish what I've been able to do so far. I like fiddling with the MB along with my Triumphs, so all advice is a great help!

Rand
 

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due to age of car, your issues could be any number of things. If I were you, I'd get a smoke check done (to detect vacuum leaks that you most likely have at this age) and a fuel pressure test/fuel leakdown test. Odds of your fuel system being 100% perfect, are slim to none.
 

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Hi All,

I've done my due diligence and searched the forum before asking these questions, but most answers are old and dated. I want to be sure I have the most current thoughts.
My 1986 560sel starts right up, and when I go I get a hesitation/stumbling, until I get up a little speed, then all is fine. High speed, highway, pedal to the metal, no problem. Just on initial take off, and sometimes when traveling and lightly accelerating. I've looked up all the info and I have run 3 gas tanks of Sea Foam, with minimal help. Sometimes it gets better while driving, sometimes it gets worse. Stopping and restarting sometimes helps, sometimes not lol.
Next recommendation is a tune up. That's where I need some advice....
(1) Best spark plug wires, and where to purchase them.
(2) Best Spark plugs recommended ( I know there are individual preferences but I'm trying to get an idea as to the 2 or 3 top preferred) and where to purchase.
(3) What else for a full tune up... Cap ? Rotor? Condenser (is there one?!?)? Air and/or gas Filters? Anything else for standard tune up/maintenance recommended?

Also, my heat works intermittently. I've read all the info on replacing the mono valve, but Bosch is NLA, so what is the brand most recommended, and best place to purchase? And can someone tell me exactly where it is located under the hood?

I've been sorting out the car (and using it) since we purchased it later last year. Info from you all has been extremely helpful along the way. I don't want to waste time having the same questions answered that can found in a forum search, but I just feel what I've found on these subjects has been somewhat incomplete, and dated.

Once again, thank you to all here on the forum, I would have been totally lost and probably spent big bucks to accomplish what I've been able to do so far. I like fiddling with the MB along with my Triumphs, so all advice is a great help!

Rand
Hello Rand,

In the above post, lesguy is spot on with probable vacuum leakage affecting mixture & driveability.

That said, I had the exact same driveability symptoms with my 560SEC in late 2003 - early 2004, then again with my 500SEC a year ago. It drove me nuts 'till I found the corrosion up inside the metal plug connectors where they push onto each spark plug. In both cases, it wasn't every plug being affected, but it sure ruined an otherwise smooth running experience.

Plugs & a wire set was the way to go.. & on the 500SEC I used a dab of dielectric grease at the wire end of each spark plug too. Trouble-free since.

I don't know if MB still sells the BQ 4 15 0028 wire set I bought years ago.. It had BERU brand metal spark plug connectors so I might go with the BERU wire set next time around.

Cap & rotor would be Bosch and I'd definitely put a dab of anti-seize on each of the 3 retaining screws as they can tend to seize in place depending on where you are in the country.

Intermittent heat, dollars to donuts, indicates a probable monovalve insert failure. It seems to be the most common issue with them over the years. You have read up on the subject and no doubt and seen others aggravation after 'replacing the monovalve'..

Please resist the temptation to purchase anything less than a true Mercedes-Benz replacement part. The others [for short money] just do not work. Eg: MTC, Uro, unbranded... Period.

The 000 835 06 44 repair insert can be had for less than $125 currently and totally worth it. Here's a link to an ad I found earlier. It's from an MB dealer, but how they offer lifetime warranty is beyond me.. Free shipping.

Ebay ad intentional: https://www.ebay.com/itm/New-Genuine-Mercedes-Benz-Lifting-Magnet-0008350644-OEM-/292897326443?_trksid=p2349526.m4383.l4275.c1#viTabs_0

The monovalve is located just to the right of the battery, is held in place with 4 screws, and has the electrical connection too. Depressurize the cooling system before taking out the screws and just a 'couple of drops' of coolant will be sacrificed during the change.

Good luck,

MBL
Screen Shot 2019-08-29 at 7.48.55 AM.png
 

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Discussion Starter #4
Hello Rand,

In the above post, lesguy is spot on with probable vacuum leakage affecting mixture & driveability.

That said, I had the exact same driveability symptoms with my 560SEC in late 2003 - early 2004, then again with my 500SEC a year ago. It drove me nuts 'till I found the corrosion up inside the metal plug connectors where they push onto each spark plug. In both cases, it wasn't every plug being affected, but it sure ruined an otherwise smooth running experience.

Plugs & a wire set was the way to go.. & on the 500SEC I used a dab of dielectric grease at the wire end of each spark plug too. Trouble-free since.

I don't know if MB still sells the BQ 4 15 0028 wire set I bought years ago.. It had BERU brand metal spark plug connectors so I might go with the BERU wire set next time around.

Cap & rotor would be Bosch and I'd definitely put a dab of anti-seize on each of the 3 retaining screws as they can tend to seize in place depending on where you are in the country.

Intermittent heat, dollars to donuts, indicates a probable monovalve insert failure. It seems to be the most common issue with them over the years. You have read up on the subject and no doubt and seen others aggravation after 'replacing the monovalve'..

Please resist the temptation to purchase anything less than a true Mercedes-Benz replacement part. The others [for short money] just do not work. Eg: MTC, Uro, unbranded... Period.

The 000 835 06 44 repair insert can be had for less than $125 currently and totally worth it. Here's a link to an ad I found earlier. It's from an MB dealer, but how they offer lifetime warranty is beyond me.. Free shipping.

Ebay ad intentional: https://www.ebay.com/itm/New-Genuine-Mercedes-Benz-Lifting-Magnet-0008350644-OEM-/292897326443?_trksid=p2349526.m4383.l4275.c1#viTabs_0
MBL, Thanks for the detailed info. I will stay with the mono valve from MB for sure having read about the others not being up to par. I appreciate the info on the wires, cap and rotor as well. I will follow your directions and make sure to use the dielectric grease... on the spark plug end I assume? I will follow up on your Ebay link, thanks for that.

I still wonder though which spark plugs are the most recommended. I did some research again last night and it appears one by NGK and one by Champion are favored the most. I don't have the numbers handy ( I am not at home right now), there were 2 different recommended for each plug as I recall, but I don't know which would be considered the better one for us.

Lesguy, thank you as well. I will follow up with that vacuum leak test. I had that happen years ago with one of my Triumphs and it was a long hard fought battle to finally pinpoint and correct the problem!
 

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Do not, repeat, do not use resistor plugs. Here you have some options....

Plugs:


Wires:


Good luck.
 

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My hunch is it's more vacuum leaks and/or something off in the fuel injection. Back when I got started on my SEC, I blew through several parts chasing high idle and some other issues. Injectors seemed to make a noticeable difference, but what made the biggest leap was making an internal adjustment to the EHA and fine-tuning the duty cycle. On the vacuum side of things, it's not a bad idea to replace all the idle air lines and the boot on the bottom of the air flow sensor assembly if they haven't been done (not cheap either). You can spend a weekend removing the intake manifold to get at all the potential air leak points, or you might end up dealing with problem after problem that crops up as the pieces fail one by one. Again, this is assuming they haven't been replaced (if they aren't pliable and/or are cracking, they should be replaced).

The fuel injection side of it can be a constant struggle, at least if "good enough" isn't good enough for you. Both my cars start right up and run out pretty well, but I can't quite get a glass-smooth idle on the SEL, and it takes a lot of cranking on hot start sometimes. Anyway, the place to start on that is the duty cycle adjustment. There are several threads and how-to's on it, but it has a big effect on low-speed operation, and it can signal other problems. In my case, I found that when I set the duty cycle at 2500 RPM as directed, the idle duty cycle would be 20-30% off (should be within 10). If that's the case, the EHA adjustment is likely necessary. Even starting with a brand new EHA and rebuilt fuel distributor didn't have me in the ballpark – new parts don't mean the problem is eliminated here.

There are some things I'd do automatically if I was starting on a new-to-me car, like putting in new non-resistor plugs (my SEC had Bosch platinum +4s when I got it – not a bad plug itself, but bad for these cars). NGK BP9ES plugs seem to be the only commonly available non-resistor choice. New air and fuel filters are up there too, along with fuel system cleaner like you've been doing (I put a bottle of Techron through now and then). Unfortunately, it seems to take some tinkering on the fuel injection to get most cars running perfectly, even after all the other common culprits (vacuum system, ignition system, failed electrical components like O2 sensor) have been run down. I found the learning curve fairly steep: I treat the system almost as much like a carburetor as EFI. Digging through the service manuals and reading up on the basic function of the car's systems (especially Continuous Injection System), then tinkering with the car itself were how I learned what I've gathered so far. I'd say it's one place where even a committed DIYer would find it worth digging up a CIS guru, but even your local "import experts" are likely to throw parts at it and do little better than you.
 

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Discussion Starter #7
Do not, repeat, do not use resistor plugs. Here you have some options....
".........................."
Good luck.
Riiiight! I saw that suggestion almost everywhere, no resistor plugs! Thank you for the links and suggestions. I looked at quite a few options over the past few nights, and there were lots of different suggestions, so it became a bit confusing trying to determine which way to go. The choices offered by you really helps. I have no previous experience with a Merc and I want to be sure I am using what most of you on the forum are likely to suggest/use. I will order parts today and hopefully get this "mini project" underway by next week.
Thanks again!
 

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Discussion Starter #8
My hunch is it's more vacuum leaks and/or something off in the fuel injection.....
If the tune up doesn't do it, my next step will be to follow what you and Lesguy are suggesting could be wrong, and try that course of action.

The fuel injection side of it can be a constant struggle...... – new parts don't mean the problem is eliminated here.

Yep, new parts are pretty but I've certainly found, like you say, they don't always fix the problem. It sure is nice when you get things right tho!
There are some things I'd do automatically if I was starting on a new-to-me car ...... I'd say it's one place where even a committed DIYer would find it worth digging up a CIS guru, but even your local "import experts" are likely to throw parts at it and do little better than you.
I have found that I know my limitations. When I get to that point, I will bring it to 1 of 3 independent MB mechanics in my area, all very experienced and very good. I would rather fix it myself, but I also learned when its time to 'give'.

As a point of reference, when I bought this car last December it was very clean, with less than 63K miles. The owner was a collector and sold this one because he bought the same exact year and model, but with only 32K miles! It was well treated when he bought it, and hardly used. There were lots of little issues that I have been working on since owning, and the list is shrinking, so I'm making progress. I will say I would never have gotten this far without the suggestions, links, and help from this forum. I am on here a lot and read but I don't offer much in the way of suggestions as I have no experience with these except what I am learning from you all!
 

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Discussion Starter #9
One more question... both front seats are really horrible... springy, very soft, non supportive, and make for an uncomfortable ride. I see where MercedesSource.com (Kent Bergsma) has a kit he sells to beef up the springs. Is that a decent buy? Is there a better, easier way that would work? It seems like a reasonable price to pay for a higher level of comfort ( I hope!), but I don't know if the kit is as helpful as he suggests.
 

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Discussion Starter #10
One more question... both front seats are really horrible... springy, very soft, non supportive, and make for an uncomfortable ride. I see where MercedesSource.com (Kent Bergsma) has a kit he sells to beef up the springs. Is that a decent buy? Is there a better, easier way that would work? It seems like a reasonable price to pay for a higher level of comfort ( I hope!), but I don't know if the kit is as helpful as he suggests.
Upon further research (hours lol!) and viewing lots of answers, I found this thread which details the kit from Mercedessource.com:

In that thread i found an excellent couple of sources to do the same job with DIY'er product availability.. this is the route I am going to take:
It looks like this company will work with you to make exactly what you need, and there are other products on this page that can be used to firm up the padding and anything else needed.

In the meantime I am ordering plugs, wires, cap, rotor, mono valve replacement (Bosch), and going to get on it ASAP! Thanks again everyone... very, very helpful info as always!
Rand
 

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Discussion Starter #12
Just a bit of factual data from NGK re: spark plugs

Ive had no issues with these:
https://www.fcpeuro.com/products/bosch-spark-plug-wr9dc-plus-bosch-7911

Which actually matches the same part #'s that the MB dealership provided to me over the phone.

I also realize resistor vs non resistor is kinda like oil brand topics. Can be very heated.

It's whatever works best for a persons own car.
Interesting info Lesguy, thanks for this. Everywhere I searched on this forum in regards to Spark Plugs reiterates that we should not use resistor plugs. I wonder why after reading this.....??
 

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Interesting info Lesguy, thanks for this. Everywhere I searched on this forum in regards to Spark Plugs reiterates that we should not use resistor plugs. I wonder why after reading this.....??
Not sure. Bosch (cant find the link right now) says the same as NGK does in the link above: resistor has no affect at all on engine performance. Ive yet to see factual evidence stating otherwise.
 

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I just go to the dealer and no worries about the wrong plugs. They even have a slight difference as recommended between W126 V8 models and aren't expensive.

Resistance is in the leads so needs to be not in the plugs. However, if you have aftermarket leads, is this still true?
I think the idea is most likely not to put unnecessary stress on the EZL or anything like that.
 

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Resistor plugs were designed to reduce noise and interference to on board computers, it also makes the spark plug run hotter so it can produce the same spark intensity.

Our cars are before those times and don't need resistors, as Ian said, it messes up with the ezl.
 

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Do not, repeat, do not use resistor plugs. Here you have some options....

Plugs:


Wires:


Good luck.
+ 1 on Kingsborne wires. They are in San Marcos (near San Diego, SoCal).
Karlyn STI wiresets (same Co as Bremi) are not bad either. Like Kingsborne, they used to come with BERU booth's. BERU wiresets would have been on top of my list, but a few years ago they were taken over by a multinational conglomerate, and I heard took a hit in quality..

The non resistor copper core Bosch W9DCO (SoCal) supposedly haven't been produced in more than a decade. Not so, small batches are still made, but dealers try to sell them for more than platinum/iridium - at a kings ransom. I had the ceramic part come apart in India made Bosch, Spain, Poland, Czech etc is o.k. in my experience.
A good and inexpensive alternative are NGK copper core BP7ES. Usually autozone stocks only 4 or 6 sets, and you may have to go to 2 stores for a set of 8.
If I remember correctly, Bosch W9DCO (or DC = slightly thinner copper core), come gapped at .032. Some experts recommend regapping wider, up to .042, I usually go to .038.

Anything with R as in WR means resistor (sorry Malcolm).
Cheers
 

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Discussion Starter #18 (Edited)
I have had a dickens of a time trying to get spark plugs for my '86 560sel. No one locally has any of the choices you've all suggested (Champion NY11C; NGK BP5EFS, or 6 or 7 ; or Bosch). I ordered and received 8 plugs but found I ordered the NGK resistor plugs accidentally (BRP) so I had to return them. I finally found a seller on Amazon that had some N11YC's in stock, so I ordered 8 today and hopefully I'll have them in a few days. I did receive my other ordered parts (Bosch Dist. cap, rotor, and NGK wire set) and will wait for the plugs to do a full change at once. Hoping this will clear my 'stumble' issues. I did remove all the plugs in place and cleaned them. Then sprayed the inside cap of the wires with Carb cleaner, cleaned and replaced everything. I took it for a ride hoping that would help, but no luck there.
If the new parts get rid of it, I'll be very happy. If not, I'll look into a smoke test for a vacuum leak, and then go from there. Thanks all, I'll update along the way.
 

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I have had a dickens of a time trying to get spark plugs for my '86 560sel. No one locally has any of the choices you've all suggested (Champion NY11C; NGK BP5EFS, or 6 or 7 ; or Bosch). I ordered and received 8 plugs but found I ordered the NGK resistor plugs accidentally (BRP) so I had to return them. I finally found a seller on Amazon that had some N11YC's in stock, so I ordered 8 today and hopefully I'll have them in a few days. I did receive my other ordered parts (Bosch Dist. cap, rotor, and NGK wire set) and will wait for the plugs to do a full change at once. Hoping this will clear my 'stumble' issues. I did remove all the plugs in place and cleaned them. Then sprayed the inside cap of the wires with Carb cleaner, cleaned and replaced everything. I took it for a ride hoping that would help, but no luck there.
If the new parts get rid of it, I'll be very happy. If not, I'll look into a smoke test for a vacuum leak, and then go from there. Thanks all, I'll update along the way.
just curious..did you call your local dealer during your search for plugs?
 

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Discussion Starter #20
just curious..did you call your local dealer during your search for plugs?
Oh yeah, I spent a bit of time online and on the phone over the past few days. One call to a close by Auto Zone where the clerk assured me they didn't have any but the other store across town had 9. Well before I drove there I called, and they had 9....of the BPR5ES!! Nope...
2 additional calls to NAPA stores near me, and one auto parts dealer as well. No one had any of the proper NGK's, BP5, 6 or 7. same on the Champions N11YC. I knew they wouldn't have any Bosch plugs based on the more common ones I was requesting.... apparently they are not all that common!
I did read somewhere on the forum about Bosch plugs one could get directly from an MB dealer, the number was given as 003 159 12 03. It appears to be specific to our MB's, a Bosch, but no details as to what they are exactly. I was unsure so I opted for the ones that were recommended by several of you here.
 
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