Slight miss on my 560SEC

[KLP 92]

I'm having a small prob on the 560 SEC. The car has a very fine "miss", just around the 1500 rev mark, where its the most noticable. Its hard to notice, but its definately there! Its been there since i purchased the car, hoped it would have gone by now!!

So far i've changed:

Fuel pump
Fuel pump relay
Fuel filter
Fuel distributor
Fuel injectors
Throttle body
Ignition Control Module (EZL)
Ignition Coil
Ignition leads
New spark plugs (changed twice)
Distributor Cap + complete distributor assembly
Rotor Arm
Crankshaft position sensor & lead
Idles speed control relay
ECU (swapped with another 560 which ran perfect)
OVP relay
4 pole temp sensor (controls the EZL and CIS KE)
Engine compression checked etc - no probs at all
All vacuum pipes pressure checked-ok


I've probably changed more but its still there!!!

The car is at GF, he's stumped as to what else it could be. The only other fault on the car is the ASR is faulty. George is currenctly looking into the ASR fault, thinks it may have something to do with the miss. Not convinced though, as the later M119 engines can have the ASR bypassed with no effect on the engine.

Is there something else i'm missing? Am getting really fed up at the mo with the car!!!

On a good note, it doesn't smoke blue anymore!! It was a top end prob which was rectified by GF very professionally. He even changed my oil pump FOC as a goodwill gesture!


Other parts changed on the car:

Full engine build (new tappets, springs, lifters etc)
New oil pump
New timing chain & tensioner
Rebuilt G/box
Rebuilt LSD diff
New radiator
New water pump
New viscous fan
New electric cooling fan

Not to mention all new suspension/rubbers/mounts/bodywork etc etc!!

 

[aka$h]

Ive got a quick fix - "Autotrader", and the words, "£1000's spent"..........

 

[grober]

Most obscure misfire problem I can think of

KLP92
Since you have covered all the bases the most obscure fault I could recall on cars of that time with a similar problem was caused by a faulty tachometer. The test was to disconnect it and if the fault disappeared then replace the tacho. Thats my contribution to the "obscure faults" archive. Glad you've given up "smoking" you know it makes sense.

 

[KLP 92]

KLP92
Since you have covered all the bases the most obscure fault I could recall on cars of that time with a similar problem was caused by a faulty tachometer. The test was to disconnect it and if the fault disappeared then replace the tacho. Thats my contribution to the "obscure faults" archive. Glad you've given up "smoking" you know it makes sense.

Normally i would laugh if someone had suggested that to me first! But having changed everything else, its worth a long shot! I'll give it a try today.

 

[Vlad]

KLP.....on two of my recent 300E's I have suffered from a slight misfire around the same rev's as yours and also from a slightly lumpy idle (how's your idle?)

On both occasions its has turned out to be faulty fuel distributors (yours has the same kind, albeit for an 8 cylinder).

Apparently its quite a common problem due to a gradual silting up of the fuel distributor which get worse if you use injector cleaner as it tends to clean the fuel lines of crud which then gets stuck in the fuel distributor......its one of the most common items purchased from breakers yards !!

Its only a suggestion and for all I know you may have already have checked into this.

 

[KLP 92]

KLP.....on two of my recent 300E's I have suffered from a slight misfire around the same rev's as yours and also from a slightly lumpy idle (how's your idle?)

On both occasions its has turned out to be faulty fuel distributors (yours has the same kind, albeit for an 8 cylinder).

Apparently its quite a common problem due to a gradual silting up of the fuel distributor which get worse if you use injector cleaner as it tends to clean the fuel lines of crud which then gets stuck in the fuel distributor......its one of the most common items purchased from breakers yards !!

Its only a suggestion and for all I know you may have already have checked into this.

The car idles fine. I've had a new fuel distributor fitted, no joy!

 

[KLP 92]

I have been led to believe it may be my CIS ECU, located in the passenger footwell. Found one on ebay for £30, will hopefully arrive on Saturday! MB want £900 for it so i hope this is the right one!!

 

[imadoofus]

Cis?

 

[Asif Kazani]

KLP 92, just a thought, what color were the injectors that you had installed and where were they made in? I used to have a lot of problems with my M 110 engine with Bosch K-Jetronic Injection system. There are both, gold colored and silver colored injectors available. The gold ones did not cause slight misfires that the silver ones did. Also, these need be from Bosch Germany and not any other plant that Bosch has. Since you have already replaced the Fuel Distributor, I could not think of anything except the Fuel Pressure regulator or plug wires which shall be made by Beru and not Bosch since Beru were better.

Good Luck.

 

[KLP 92]

KLP 92, just a thought, what color were the injectors that you had installed and where were they made in? I used to have a lot of problems with my M 110 engine with Bosch K-Jetronic Injection system. There are both, gold colored and silver colored injectors available. The gold ones did not cause slight misfires that the silver ones did. Also, these need be from Bosch Germany and not any other plant that Bosch has. Since you have already replaced the Fuel Distributor, I could not think of anything except the Fuel Pressure regulator or plug wires which shall be made by Beru and not Bosch since Beru were better.

Good Luck.

I think the fuel injectors are gold, purchased from MB.

Fuel pressure has been checked, and with use of a nice flash looking machine the fuel system was bypassed, but still no joy.

The plug leads were changed twice, no joy, am currently running magnecor leads.

 

[KLP 92]

Cis?

"The acronym CIS stands for "Continuous Injection System". This is a primarily MECHANICAL fuel injection system produced by Bosch and widely used on many European cars from the 70s and early 80s including VW, BMW, Volvo, Mercedes, Porsche, Ferrari and the list goes on. In a typical electronic fuel injection system (EFI) the fuel is pulsed at the injector by electrical signals from a computer brain box which gets it's info on fuel requirements through the use of a myriad of electronic engine sensors. In the Bosch CIS system, the injectors are continuously injecting fuel into the manifolds. Fuel requirements are metered by a simple and mechanical air flow box. The more air that's allowed into the engine, the more fuel that is flowed to the injectors through the use of a fuel metering block."

 

[Asif Kazani]

The more I think about it, 1500 RPM mark just about where the timing advance mechanism kicks in. May be need to have the weight inside the ignition distributor oiled and checked. Also, how about rechecking the Plugs after the oil consuming/smoking incident. Sometimes, just by virutue of these items, one or a couple of them is bad.

 

[KLP 92]

The more I think about it, 1500 RPM mark just about where the timing advance mechanism kicks in. May be need to have the weight inside the ignition distributor oiled and checked. Also, how about rechecking the Plugs after the oil consuming/smoking incident. Sometimes, just by virutue of these items, one or a couple of them is bad.

Had all 8 plugs replaced (about the 4th time now!). All are fine. I've had the whole distributor changed, still the same. The miss has been here since purchasing the car, before the oil smoking!

 

[Asif Kazani]

O.K. I know you've had enough with the guessing game. How about the green condensor wire that goes from the distributor to the ECU??

 

[KLP 92]

O.K. I know you've had enough with the guessing game. How about the green condensor wire that goes from the distributor to the ECU??

The green wire has been changed, but it goes to the ignition control module (EZL) on mine, or is this a different wire?

 

[mercmanuk]

i'm sure this might sound stupid but why not book it into a main dealer,get then to connect the computer up and just tell you whats causing the problem!if it costs 1hr labour it must be worth it to save the hassle of second guessing the fault

 

[Asif Kazani]

The green wire has been changed, but it goes to the ignition control module (EZL) on mine, or is this a different wire?

Sorry, I meant the EZL and not the ECU.

 

[KLP 92]

i'm sure this might sound stupid but why not book it into a main dealer,get then to connect the computer up and just tell you whats causing the problem!if it costs 1hr labour it must be worth it to save the hassle of second guessing the fault

Its spent a week at MB Finchley, no joy. Its an 1989 car, very primative and pre MB diagnostics. (Well there is some sort of diagnostic port but comes up with no faults)

Judging by the amount of money spent so far i would be jumping up and down in joy if 1 hour MB main dealer rates could isolate the fault.

The car is currently at George Fraser's Garage, they are stumped as to what it could be, and as a personal favour he sent the car to MB to see if their technicians could see something he couldn't.

Also i've had the head technician and electrical engineer from MB Edgware look at the car, still no joy.

 

[grober]

Steve Brothertons article on mercedesshop

Its spent a week at MB Finchley, no joy. Its an 1989 car, very primative and pre MB diagnostics. (Well there is some sort of diagnostic port but comes up with no faults)

Have you read this article. http://www.mercedesshop.com/Wikka/EngineControls

 

[graeme73s]

Speak to a guy called Chas he specialises in the SEC model and he's 15 minutes from Brands Hatch in a village called Kemsing. He might be able to shed some light on your problem. This is his number from memory 07973 553071, if i'm wrong send me a PM and I'll dig it out for you. cheers Graeme