Lose of Power 560 SEL - PeachParts Mercedes-Benz Forum

waylifeshouldbe · #1 11-15-2003, 06:45 PM

Hi All - Following months of reading this forum, I recently purchased an 88 560 SEL for the winter (Maine). Car has 102K. She looks real good and besides needing rear suspension accummalators (sp?) runs nice. I have however experienced on two occassions a sudden lose of power followed by resumption to normal. The car hesitated, I looked at rpm and noticed a wild fluctuation (600-2000), depressed the accelerator and car smoothed out. I am hopeful that I have been descriptive enough for someone to point me in some direction to find remedy. Love the car and love this forum. Thanks to all for your contributions!

waylifeshouldbe · #2 11-16-2003, 04:25 PM

Thanks Ellington -
Today I spray the cap, wires, and coil as suggested. Car ran fine with no change in its' smooth idle. I took the cap off to inspect. There appeared a fair amount of "carbon" soiling the copper. I gently sanded the area. The rotor also exhibited some deterioration. I cleaned it also. Put back together. Runs great (the same). I would gues these components to be original. Anyway of telling? Would it be prudent to replace after 102K. If this cap and rotor was from my 72 Chevelle ($40.00), i wouldn't even think twice. Again do not know yet as to whether I've done anything to "fix". I'll continue to drive and see. BTW, car has new plugs.

MikeTangas · #3 11-16-2003, 07:42 PM

If you've got carbon tracing inside the cap, now is probably a good time to replace it. Usually these distributer caps and rotors are nearly indestructable, but sometimes things happen. The cap part # is 000-158-52-02, dealer price is $179.00 while the rotor is # 000-158-40-31 and $40.50. FastLane has the rotor for $33 or so, but the cap is not available.

Don't get the aftermarket cap and rotor, you wont be happy with them and you'll only save about $80, insist on the Bosch parts.

waylifeshouldbe · #4 11-18-2003, 07:22 PM

I had driven the 88 560 sel for about 50 miles with no issues. Last night the vehicle "missed" on three separate occassions. No rhymn or reason. Today car ran great. I have not changed the cap and rotor and will do so as they would appear to be original (102K). Should I consider the coil also? I hate just throwing parts at this annoying intermittant problem but it is the only thing that is keeping me from loving this car. I have installed new plugs, injector cleaner, cleaned cap/rotor (still quite pitted), air filter. What's next? Thanks in advance!

#5 11-18-2003, 08:24 PM

I recall reading similiar probs and the culprit was the fuel pump.

Specifically fuel pump or fuel pump relay?

There's a ton of info here if you do a search. I'm sure more opinions will follow.

mhingram · #6 11-18-2003, 08:42 PM

I would seriously consider the ignition system. I had the a similar problem but it consistantly stumbled on acceleration from start. I rebuilt my fuel system injectors, seals, idle potentiometer, all the rubber, throttle switch, O2 sensor and OVP. However, it was not until I did the coil that my stall on acceleration was fixed. It was a good experience and my rubber needed replacing as did the injectors. But, it was pretty frustrating doing the fuel, which is alot more expensive and labour intensive for me as I was learning along the way, than the ignition with the exception of the EZL.
m

pentoman · #7 11-19-2003, 07:56 AM

If you say the car is 'missing' - i.e. jolts and has sudden on/off power characteristics, that would indicate an ignition related problem.

A fuel flow problem would be somewhat less sudden, and feel softer.

If you like, you can often say an electrics/ignition problem would feel electric, a liquid problem would feel liquid.....

So, particularly if you have missing and do not know the plug wires on the car - replace them.

First port of call for a misfire usually, even if they seem fine.

A '98 VW Polo I am currently using had misfiring which couldn't be cured for ages. Turns out someone installed cheapo 'universal' plug wires, which would short out to the radio shield around the distributor, even though the wires were quite new.

Remember, fit original parts!!

Q · #8 11-19-2003, 10:09 AM

Something relatively simple that you can do to eliminate one of the possibilities is to resolder the couple of large pins on the fuel pump relay. This is a common fault area for the W126 cars. If you own a soldering iron, it doesn't cost you anything.

#9 11-19-2003, 01:46 PM

BTW, the 560 has two fuel pumps, correct?

#10 11-19-2003, 01:48 PM

Yep--

And Q specifically hit the point I was grasping for. I recall many posts over the years describing similiar symptoms and the relays were the cause.

waylifeshouldbe · #11 11-19-2003, 03:39 PM

Thanks for the tip! Could you describe the procedure exactly. Also where exactly are these relays? I'll do this first think tomorrow. Also what is the known issue reference the W126 cars and their fuel pump relays - simply curious.

Q · #12 11-19-2003, 03:48 PM

I have documented my experience here in the forum.

Engine cuts out, but will start right back up

Here are more links

http://www.peachparts.com/shopforum/search.php?action=showresults&searchid=629607&sortby=lastpost&sortorder=descending

downeyjc · #13 11-19-2003, 07:13 PM

This doesn't sound like a fuel pump relay problem to me. Normally, when the relay fails, it does so when you are trying to start the car--even in cases where the relay is intermittent. I've not seen a case where a failing fuel pump relay would induce an engine miss under load, but I guess it's possible.

I would look closely at the ignition system, especially the spark plug wires and the coil. Had a coil go bad recently on my 560 engine--it's not a cheap item.

pentoman · #14 11-19-2003, 08:24 PM

I agree - fuel pump relay is very unlikely for these exact symptoms.

But it's good to know they can be a problem if you ever get random vehicle no-go.

Q · #15 11-19-2003, 08:37 PM

Mine would cut out when I lifted the throttle. It happened in phases. I would have 2-3 days of the problem and then nothing for weeks. This went on for 3-4 months. I would always start right back up until the last time when it wouldn't.

The car's are notorious for bad fuel pump relay solder joints. It's worth a look and it doesn't cost anything if you own soldering equipment.