[W126 Coupe] idles rough when properly lean

[Shayegan, Richard]

I'm gonna do a Usenet style mid-post reply, hopefully it will keep my formatting.

________________________________

From: mbcoupes-bounces at mbcoupes.com on behalf of Dick Spellman
Sent: Fri 3/4/2005 9:09 PM
To: Mercedes Coupes Mailing Lists
Subject: Re: [W126 Coupe] idles rough when properly lean



Hello Richard:

To help narrow the possibilities, try answering these questions one by one.

>What is the mileage on the MB?


number of miles or MPG? Number of miles is 140900. Last MPG numbers I have are 17.6MPG highway (driving btwn 75 and 120 averaging about 85mph). Like I said though, when I brought it in for a ball joint and asked them why my plugs are fouled they said it was running really rich, and that leaning it to make it proper made the idle rough. I haven't driven enough since they set the mixture midway between proper and really rich to give you any MPG numbers for the current mixture setting.

>How many miles since the following were replaced? (electrics)
>ignition wires
>O2 sensor

both of these were done 30k ago, also mechanic checked O2 sensor and said it was good and also said my ignition system was good.

>sparky plugs

just replaced them


>cap and rotor

30k miles ago


>Have you checked for a 'fat' spark on the coil wire?
>Have you checked for a 'fat' spark on each of the plug wires?
>Do you need to know how to do this???


No, no, and yes respectively, though the mechanic did say my iginition system is good so maybe the answer to the 3rd question should be it doesn't matter.


>How many miles since the following were replaced? (fuel)
>injectors

14k miles ago, along with the air idle tubes or whatever those rubber hoses running along each bank of injectors is called, and injector holders/seals.


>fuel filter

22k miles ago


>accumulator

Don't think it's ever been done. If it has, it wasn't within the last 7 years and even that is doubtful (I have the records computerized, but some of the really old stuff might have been done and not computerized. I do have the paper records, but if it goes bad after 7 years it's gone bad again so it's a moot point).


>Any major work been done on the fuel system like replacement of fuel
>distributor, other stuff?  Describe and how many miles since R&R?

Yes, it had a rebuilt fuel distributor (CIS flowtech was the rebuilder) put into it 8000 miles ago. Since it was a rebuilt part I had my mechanic put it in. He noted when he gave me back the car that he had to set it real rich to get the car idling smooth, but that the distributor checks out. Two days later I brought it back because it was having trouble starting (turned out to be the battery, but neither I nor the mechanic noticed it had leaked out 1 cell entirely so we both assumed distrbutor), and my mechanic checked it, said it's ok but he wanted it overnight and the next day said it's still ok.

>Does the fuel pump deliver the needed pressure?
>What is the pressure?

Don't know the answer to number two, but the mechanic checked number 1 and said yes.


>Does the fuel pump make any noise at idle or hum on cold days, has it ever
>been replaced?

Never been replaced, but it has hummed on cold days for as long as I can remember (so figure on at least the last 14 years) so I don't think that's the problem.


>Do you smell any gas fumes around the fuel distributor and are there any
>signs of fuel (wet area) in and around the EHA valve?

I used to smell gas when I floored it and when idling with the heater on so I replaced the injectors/seals/holders and that took care of that, so I never checked the EHA valve. Never figured out where it is either.

>Are you running this engine on Premium only?
>Or are you occasionally or always dropping the fuel grade and what grade to
>you use?

Always premium 93 octane.


>Have you dumped one can of BG-44 in the fuel tank with the prescribed
>Premium and volume of gas and given the injection system a good gutting of
>the crud build-up?

I did before replacing the fuel distributor hoping it would help (both Pat Goss and my mechanic told me it wouldn't but it couldn't hurt so why not). Incidentily, when I called Pat Goss about trying BG 44K I also won a free can on his show. I have it in the garage. Should I use it? I'm reluctant to since the injectors and distributor are fairly new, but I'm starting to figure couldn't hurt might help. If your response is I should use it, I should wait until I'll be doing city driving right (i.e. not putting it in now since I'll be driving back to college Sunday)?

>I think we would all be interested in your reply to help us narrow this
>issue down.


I should not it doesn't idle rough all the time, but like 95% of the time. I'm trying to find a rhyme or reason but so far I can't.

Thanks,
Richard

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