Slight miss on my 560SEC

[Dieselman]

Get the car booked in for a RR tuneup session. Nearly all faults can be found as the engine is running under load in a controlled enviroment.

It can only be one of three things, compression leakage, ignition fault, fuel fault. You just need to find which it is.

One thought is that it could be running too lean at particular revs.

 

[jgevers]

Hi,

Glad to hear that the smoking problem has been solved and that your garage has exceeded your expectations.

I can't remember the exact layout on the 560, but if I guess correctly, the car is fitted with Bosch KE Jectronic. If the replacement ECU does not solve the problem,have a look at the side of the fuel distributor. There should be a black unit bolted to the side of it. This is the fuel pressure regulator. If you unbolt this,you'll find a copper screw at the back of it. Behind the screw there should be an allen screw that adjusts the fuel control pressure.

I would expect that your car will be a bit lean at when it's missfiring due to general change of vacuum due to different cams, compression ratio etc.

If you hook up the K Jet pressure gauges, try to change the pressure by about 0.2 bar and see if the missfire changes. The gas analyser should be able to confirm whether you are going the correct direction. Pay particular attention to the oxygen and carbon dioxide readings rather than carbon monoxide and hydrocarbons.

Let me know if these ramblings make any sense.

Cheers

Job

 

[KLP 92]

Hi,

Glad to hear that the smoking problem has been solved and that your garage has exceeded your expectations.

I can't remember the exact layout on the 560, but if I guess correctly, the car is fitted with Bosch KE Jectronic. If the replacement ECU does not solve the problem,have a look at the side of the fuel distributor. There should be a black unit bolted to the side of it. This is the fuel pressure regulator. If you unbolt this,you'll find a copper screw at the back of it. Behind the screw there should be an allen screw that adjusts the fuel control pressure.

I would expect that your car will be a bit lean at when it's missfiring due to general change of vacuum due to different cams, compression ratio etc.

If you hook up the K Jet pressure gauges, try to change the pressure by about 0.2 bar and see if the missfire changes. The gas analyser should be able to confirm whether you are going the correct direction. Pay particular attention to the oxygen and carbon dioxide readings rather than carbon monoxide and hydrocarbons.

Let me know if these ramblings make any sense.

Cheers

Job

The black unit at the side of the fuel distributor was changed at the same time the fuel distributor was changed. It came with the new distributor.

I'll print off the post off and run it down to George's tomorrow, i'm pretty sure he's said he's tested the fuel pressure side of things but i'll have it rechecked.

 

[stats007]

Could it be related to a specific engine vibration at that rpm - an oscillation causing a fuel or air trap?

 

[jgevers]

I would expect that the engine has slightly different fuel requirements that the standard settings. Adjusting the fuel pressure regulator is a way to increase or decrease fuelling under load.

The KE Jectronic systems still rely on engine vacuum to change the pressure differential in the metering head. This means that a change in vacuum due to cams or compression ratio change, will affect vacuum. The most vulnerable area is part throttle, at low revs and low load. Most early fuel injected engines are running quite lean already in this area, so a slight reducton in fuelling will result in a missfire. You might find that your engine will need a slight increase in fuelling compared to standard setings.

Adjusting the fuel pressure is an accepted way to do this on a K(E) Jectronic system, as fuelling is regulated by pressure differential anyway (rather than injector duration on more modern inection systems).

Cheers

 

[jgevers]

If you don't want to b#gger about with the fuelling, try to increase the plug gap by about 0.2mm. The increased spark KV might be able to burn the air fuel mixture a bit better.

Good luck

 

[jaymanek]

Have you tried going to a Bosch Specialist Centre? They can usually sus anything out to do with the KE Jetronic..

 

[Vips]

Sadly, the workings of the 560SEC is beyond me so I cannot even guess at what the problem may be. However, I'm pretty sure you / GF will get to the bottom of this, just like your smoking habit!! Good luck.

 

[jgevers]

Have you tried going to a Bosch Specialist Centre? They can usually sus anything out to do with the KE Jetronic..

Not as simple as that anymore. Bosch, in their wisdom, have changed their Bosch Service Agent requirements. It is now called Bosch Car Service.

The Bosch Service Agent was build on technical competence and correct tooling. The Service Agent of old would have a Bosch System Technician who has had all the relevant training as well as all the relevant tools.

The Bosch Car Service requirements are much lower. So a Bosch Car Service that was not a Bosch Service Agent previously might not have the correct skills and equipment to deal with the older K and KE Jectronic systems.

If you have a look in a Yellow Pages of a few years old, you'll find the guys that were Service Agents.

Cheers

 

[jaymanek]

Typical!!!

Well ive always used a mobile tuner from coventry for stuff that I cant figure out myself... He cures a miss on my SL and had all the correct equipment to diagnose the fault. V knowledgable on the KE Jetronic too...

Mastertune if anyone in the area wants to use him. In the yellow pages..

 

[KLP 92]

If you don't want to b#gger about with the fuelling, try to increase the plug gap by about 0.2mm. The increased spark KV might be able to burn the air fuel mixture a bit better.

Good luck

the gap on the plugs has already been increased. On the old 560s, the run better anyway with the gap increased by 1mm. Made no difference.

 

[KLP 92]

Could it be related to a specific engine vibration at that rpm - an oscillation causing a fuel or air trap?

There is some "play" in one of the accelerator damper rods that run across the engine. It has crossed my mind that it could be this so i've ordered a new accelerator linkage rod (it has a small damper in it which is shot to bits in mine!), but its a rare part and is oput of stock even in MB Germany! Should be here hopefully soon.

 

[KLP 92]

Fingers crossed but i think its fixed!!:bannana: :bannana:

Changed the CIS KE control module today and so far the car's revving fine! No miss or stuttering as it did previously. Haven't taken it for a road test as there is alot of things that need to be put back together, about a days work!

Will let you know tomorrow how its got on.

 

[jgevers]

Result!

 

[KLP 92]

Result!

Hope so, best bit is that the CIS ke module cost £30! Bought it from a guy breaking a 560 on ebay, normally retails at £900 from MB!

 

[C43AMG]

Will you be bringing it to the GTG on Sunday ? It woud be great to see it being a ex 560 SEC person.

 

[KLP 92]

Will you be bringing it to the GTG on Sunday ? It woud be great to see it being a ex 560 SEC person.

I'm hoping to get the car all done by Thursday, which gives me 3 days just in case! 99% positive i will be in the SEC.

 

[stats007]

Nav you should do a breakdown of exactly what processes you went through for a 'How To..' if you have time.

 

[GregE240]

lol, with pictures!!

Nice one KLP...

 

[KLP 92]

Nav you should do a breakdown of exactly what processes you went through for a 'How To..' if you have time.

Well i would need alot of time!! Its been one of those projects that i would not want to ever have to do again. Its been one nightmare to another and there are still afew minor probs which i'm trying to iron out before the GTG.

I could do a 'HOW NOT TO DO' which would probably be more appropiate!

I'll work on a 'HOW TO' in my free time but i'll give you a taster: "buy a cheap car with plently of probs, throw a shedload of money at it and end up with an expensive car with fewer problems!" Forgot to mention the stress, headache, endless amount of hours.....no days....maybe months of hard work that went with it!!