560 SEL idles very rough - PeachParts Mercedes-Benz Forum

David Kingsbury · #1 08-13-2003, 02:26 PM

My 88 560 SEL idles very rough. It does not stall or run poorly. It just idles rough. The car will also not come close to passing my state's emission test. My mechanic says the fuel meter is bad. This is not a cheap part new or rebuilt. Anyone have experience with this? I would be willing to put one in and try it if I could locate a used unit for under $100.00. I believe the 420 and 560 use the same part. I am just not sure about the year range.

I should probably mention that when I got the car it had a very bad case of valve seal leak to the point that half the sparkplugs were caked with carbon and oil. Is it possible that the fuel injectors are also clogged or caked causing the problem?

joe p · #2 08-13-2003, 04:54 PM

Ok, whats the base CO reading. (duty cycle, fully warmed up, pin#3 in the diag connector to hot on your meter, ground the other end) It should be in the 50% range, if not, set it to about 50% and see how it idles.

If the co wont get in line, time to look at sticking EGR valve pintles, the o-rings joining the halves of the intake or injector seats leaking air. Unless the car skips at idle and it can be traced to one hole which is unchecged after swapping injectors from hole to hole, odds are the fuel head is fine.

Joe

#3 08-13-2003, 05:13 PM

Trying to check CO without knowing if the engine is in fuel control is one way of going about it, but...

MB references suggest for an 88 560SEL with rough idle, in order of importance:
1. Check Lambda control
2.Injectors
3.Ignition system
4.Individual cylinder fuel quantity delivery

Good luck

#4 08-13-2003, 05:15 PM

Oh yeah, what are your emissions test results?

David Kingsbury · #5 08-13-2003, 06:04 PM

Thank you for the input.

I will dig up my EM test and post the numbers. I will also start with the injectors because it seems like something I might be able to get some quick results from.

#6 08-13-2003, 06:21 PM

perhaps dump some inj. cleaner in and take a drive tonight?

I'll be in office all day tomorrow and will see what I can find if you respond back.

Thomaspin · #7 08-14-2003, 11:15 AM

I did and the work required to fix the idle and failed smog test appears here.

Your mechanic can pump white smoke into the engine to detect these.

David Kingsbury · #8 08-14-2003, 12:04 PM

Attached are my EM text results.

My mechanic said he can tweak it to get to pass and then set it back, however I am not going for it. Even for a guy whose daily driver has a 5.6-liter and whose wife’s SUV has an 8.1-liter engine… this is bad for the environment.

Injector cleaner into the fuel tank did not work. I am going to use the weekend to do some serious diagnostics.
HC (PPM)
MAX AVE MEAS
198 35 335
183 14 350
CO (%)
MAX AVE MEAS
0.81 0.15 5.02
0.71 0.06 5.36

sbourg · #9 08-14-2003, 01:11 PM

High CO and HC generally means running way too rich - probably beyond the ability of lambda control to correct. Maybe a leaking fuel distributor - probably what the tech was referring to. Pooling raw gas under the airflow sensor plate seems to be reported a lot as a symptom.

Steve

#10 08-14-2003, 01:54 PM

David,
I cant make sense of your test results as they seem to be different from ours, which reading of the MAX,AVE,MEAS is the final reading based on that determines pass/fail?

What is allowed standard?

David Kingsbury · #11 08-14-2003, 02:09 PM

This is perfect example of how great this group is. Your response is leaning toward what my Mechanic is saying.

Second and third opinions are great.

If it is a leaking fuel distributor can I rebuild it? As an experienced mechanic, but not with the Mercedes fuel distributor I would think of just taking it apart and changing out some o-rings and gaskets.

I did not probe my mechanic too much for information on the problem. It is his job to make money of his knowledge and experience as a mechanic. However, I am driving a 1988 and not 2003 model Mercedes, so I am trying to be thrifty and still have the pleasure of driving a Mercedes.

#12 08-14-2003, 02:27 PM

I dare say if your problem was a leaky fuel anything, you would have start/ drivability issues, not just slightly high emissions.

Good Luck

David Kingsbury · #13 08-14-2003, 02:55 PM

This is a passing grade for my vehicle.
HC (PPM)
MAX AVE MEAS
198 35 66
183 14 122

CO (%)
MAX AVE MEAS
0.81 0.15 0.13
0.71 0.06 0.18

Thomaspin · #14 08-14-2003, 03:29 PM

Are you sure your cat con is OK?

In my case the indy probed the exhaust upstream of the main cat con at the oxygen sensor location (420ppm HC) then at the tail pipe (320ppm HC) which told us the cat con was defective.

After replacing the (smashed) cat con, tailpipe reading came down to 11ppm! We did replace one of the two pre-cats (this was a 1981 M116 380SLC - your M117 560SEL s/b similar) as it came attached to the main cat, but it's the latter that does most of the work.

That was after I did all the work on the induction system which fixed the rough idle. After all that the idle was dead smooth but you could smell the gas at the tailpipe - didn't even have to consult my dog on that one....

I do like your thinking - UT is so pristine, especially around Bryce and Zion, that every bit helps.

David Kingsbury · #15 08-14-2003, 03:49 PM

Thanks for the suggestion on the cat. I believe the test that is done in Utah is checking the temp before and after the cat to see if it is clogged. It is something I am going to have to confirm.

Utah is great. Thanks you mentioning it. I have traveled the world several times on business to return to what I consider one of the most beautiful spots there is. We are lucky enough to have a home that is right at the base of the Wasatch mountain range. 11,000 feet of Rocky Mountains in your front yard is hard to beat.

Your website is fantastic. I have used it many times and I feel I owe you something in return. If you need anything let me know. I will be in Tokyo and Seoul in a few weeks.