S280 engine/gearbox troubles (W140)

[black_camel]

Hello,

I seem to be having a bit of grief with my 1997 S280 (i-6). Basically cold starts (catalyst warm up), cold ambient temperature idling and tip-outs are very 'lumpy' with occasional missfires (from 1 or 2 cylinders).

When the engine warms up, it improves a little, but top end power is seriously restricted. Max speed is around 120mph - not the usual 155mph [i have access to a private test track].

It should be noted that the spark plugs were changed, the originals having no real indication of foulling or carbon deposits etc... The MAF sensor was also cleaned during the spark plug service. The engine no longer appears to be misfiring, though it tends to shake a little during idle and at certain rpms - indicating that are instabilites in the combustion. However, i cant seem to pinpoint the exact cause of the power loss. Can anyone help?

I have recently had the car serviced (merc A service) with the rear discs and pads having been changed. The new discs and pads are not sticking - no smell of burnt pads even after a 30min aggressive drive, but they have bedded in ok. So i don't expect this to be a cause of the driveability issues.

Another problem I have noted over the last month has been the degradation in shift quality. Gear shifts are now becoming more and more noticeable and abrubt torque jumps during up and downshifts are a regular event. The transimission fluid was replaced at 70k (mileage now at 83k). The transmission fluid service was carried out by a non-mercedes car dealer - so i suspect they did not use the correct grade of fluid. Has anyone else experienced similar problems?

Any help on these matters would be really appreciated.

 

[Blobcat]

Hi & Welcome,

It does not sound as if it is a MAS fault, however how was the MAS cleaned? once contaminated replacement is the cure.
If you ever had 155 out of a 280 you are doing well 141 was the listed top speed.
As for the gearbox, it looks as if the service has made it a lot worse. You are correct in that ATF to MB specification should be used. I would in the first instance change the ATF and filter.

 

[television]

Cleaning the MAF is no guarantee that it will work like new and at times they have to be replaced, your problems all look MAF related to me, even the gearbox will miss behave when the power output is incorrect from the engine.

Malcolm

 

[jberks]

I'd agree with Malcolm. Most of the issues you describe are typical for a duff MAS.

 

[black_camel]

Thanks for your quick response. Is there anywhere you would recommend buying a new MAF sensor from? Since replacement is quite an easy job.

Also, if I take the car into a mercedes specialist, what sort of money should I be looking at for a gearbox fluid/filter change?

 

[Blobcat]

Also, if I take the car into a mercedes specialist, what sort of money should I be looking at for a gearbox fluid/filter change?

£100-£200, I paid £150 at dealer, however because the torque converter drain plug was deleted post '99 they could only replace 4 out of the 7 ltrs in my gearbox. Still better than no change at all.
MAS do come up on ebay quite regularly

 

[black_camel]

Ok, I will try the MAF sensor first, then i will probably take it to the dealer to get the ATF changed.

Many thanks again!

 

[television]

Thanks for your quick response. Is there anywhere you would recommend buying a new MAF sensor from? Since replacement is quite an easy job.

Also, if I take the car into a mercedes specialist, what sort of money should I be looking at for a gearbox fluid/filter change?

You can buy a MAF on ebay, they are easy to fit, and not expensive, you should not need the gearbox oil change again when your engine is back to full power.

Malcolm

 

[kth286]

black_camel

The very first thing you got to do is take the car to an independent Merc specialist that has good diagnostic experience and get your codes read. No great expense.

There are a multitude of items that could be wrong and there is a list of some 40/50 codes available to highlight various sensor problems.

For instance one of the coils could be breaking down or even the wiring to the coils, which is a problem on your 104 engine type.

Perhaps the oxygen sensor in the exhaust pipe has gone open or closed circuit, or even the heater element within it has broken.

Just get the codes read first thing, and go from there. It is the proper way.

Regards

 

[black_camel]

Ok, so here is an update on the problem.

1. The MAF sensor has been replaced - no resolution.
2. The spark plugs have all been changed, even though the originals were all fine - no resolution.
3. The HT leads have been replaced - no resolution.
4. Distributor coil on cyls 3 and 4 has been replaced - some improvement but problems still remain.

Whilst on my way home from Sweden, I stopped off at a merc dealership in North Germany to get them to run some diagnostics on the car.

They could only figure out that cylinders 3 and 4 were missfiring, and recommended the change of HT leads. Which I did, but it didn;t solve the problem.

Cylinders 3 and 4 share the same distributor coil (using the 'wasted spark method'), so my guess was the next component to change is the distributor coil on 3 and 4. This seems to have made a slight improvement in the idle speed control, it returns to 600 rpm and remains stable. However, the engine still missfires a little under low speed acceleration, and hot starting has the same issue of missfires and lumpy idle control.

My local specialists guess was that part of wiring loom that connects into the distributor coils from the ECU has been slightly baked, and would need replacing. This slight baking of these wires could have occured several months back when the AC fans were not working due to a leak in the AC system - thus not supplying extra cooling to the radiator and causing the engine to overheat to and indicated 105 deg C. He doesn't recommend ordering a new loom from Merc; and at a cost of $600 - I am in a mind to trust him on this one.

So, my question is this:

Have any of you experienced this problem before on the 97 model year inline 6 cylinder engines - and do you agree with the specialists diagnosis? I am aware that the 'biodegradable' wiring looms were only an issue with pre 96 models.

I am sure it wouldn't hurt to replace the wires, but then it is a huge pain in the rear end to do it. Plus I will need to source some wiring that can withstand the high temperatures in the engine bay.

Any help would be hugely appreciated at this time.

Many thanks in advance.

 

[big x]

Ok, so here is an update on the problem.

1. The MAF sensor has been replaced - no resolution.
2. The spark plugs have all been changed, even though the originals were all fine - no resolution.
3. The HT leads have been replaced - no resolution.
4. Distributor coil on cyls 3 and 4 has been replaced - some improvement but problems still remain.

Whilst on my way home from Sweden, I stopped off at a merc dealership in North Germany to get them to run some diagnostics on the car.

They could only figure out that cylinders 3 and 4 were missfiring, and recommended the change of HT leads. Which I did, but it didn;t solve the problem.

Cylinders 3 and 4 share the same distributor coil (using the 'wasted spark method'), so my guess was the next component to change is the distributor coil on 3 and 4. This seems to have made a slight improvement in the idle speed control, it returns to 600 rpm and remains stable. However, the engine still missfires a little under low speed acceleration, and hot starting has the same issue of missfires and lumpy idle control.

My local specialists guess was that part of wiring loom that connects into the distributor coils from the ECU has been slightly baked, and would need replacing. This slight baking of these wires could have occured several months back when the AC fans were not working due to a leak in the AC system - thus not supplying extra cooling to the radiator and causing the engine to overheat to and indicated 105 deg C. He doesn't recommend ordering a new loom from Merc; and at a cost of $600 - I am in a mind to trust him on this one.

So, my question is this:

Have any of you experienced this problem before on the 97 model year inline 6 cylinder engines - and do you agree with the specialists diagnosis? I am aware that the 'biodegradable' wiring looms were only an issue with pre 96 models.

I am sure it wouldn't hurt to replace the wires, but then it is a huge pain in the rear end to do it. Plus I will need to source some wiring that can withstand the high temperatures in the engine bay.

Any help would be hugely appreciated at this time.

Many thanks in advance.

Have the obvious things like the crank sensor and O2 sensor been checked ?
Also check that the throttle body is not full of oil under the flap.The excess heat may have cracked one of the breather hoses or even damaged the head gasket.

adam