E280 a misfire when a/c is ON

[Igorniko]

Hi! Has anybody dealt with this problem? During wintertime engine worked well but now it is not... At idle when I switch off a/c the angine works without any problem but once I push EC button and activate aircon the engine starts jiggleing. Also sometimes I see that there is a loss of power when accelerate at 2500rpm approx. What can it be??

[Tony From West Oz]

With the EC button out and the A/C on do you still get the misfire?
Most likely cause is a vacuum hose perished causing poor vacuum to one or more devices.

[Igorniko]

With the EC button out and the A/C on do you still get the misfire?
Most likely cause is a vacuum hose perished causing poor vacuum to one or more devices.

I've noticed today that I got misfire (once every 20 sec) when the A/C was off (at the intescection while waiting for traffic light).. But when I switched on the A/C the misfire (jiggling) appeared every 3-5 seconds.

Vacuum hoses look good but I still cannot see the full picture... Maybe it is coils or spark plugs?

[Ivanerrol]

This is you : :pray: :pray: :pray: :pray: The prayer man.

Hopefully it's not your wiring. You may have heard of the dreaded eco-wiring of the '92 - '96 model Benz's

Misfires are generally electrical - which includes coils, leads and plugs.

First step is to check your plugs. The plugs required are plain old copper $3.00 ones. Nothing fancy - no iridium, no platinum, no multi pronged or no resisitive types.
Second check your plug leads. make sure there are no cracks or any "hardness in the leads. Get a Multimeter - check the resistance end to end - it should be around 1100 ohms. The plug ends actually have the resistance value on them.
Thirdly - coils are generally sound. When they break down they give a constant misfire. One coil fires two cylinders. On your year E280 M104 you have 3 coils. They are mounted underneath the manifold.

Fourth do a goggle search of eco wiring '90's Benz's.

W124 series II M104's are great cars. I would have no hesitation on spending the dollars getting a repaired or new wiring harness as long as there are not too many other dollars required on other issues with the car.

[Igorniko]

This is you : :pray: :pray: :pray: :pray: The prayer man.

Hopefully it's not your wiring. You may have heard of the dreaded eco-wiring of the '92 - '96 model Benz's

Misfires are generally electrical - which includes coils, leads and plugs.

First step is to check your plugs. The plugs required are plain old copper $3.00 ones. Nothing fancy - no iridium, no platinum, no multi pronged or no resisitive types.
Second check your plug leads. make sure there are no cracks or any "hardness in the leads. Get a Multimeter - check the resistance end to end - it should be around 1100 ohms. The plug ends actually have the resistance value on them.
Thirdly - coils are generally sound. When they break down they give a constant misfire. One coil fires two cylinders. On your year E280 M104 you have 3 coils. They are mounted underneath the manifold.

Fourth do a goggle search of eco wiring '90's Benz's.

W124 series II M104's are great cars. I would have no hesitation on spending the dollars getting a repaired or new wiring harness as long as there are not too many other dollars required on other issues with the car.

Thanks a lot!!!

The engine harness was replaced 4 years ago (previous owner spent $4000 on it). So I believe that this is ok..

I've also read the fault codes - there is 085 code still in place (Model 124, 129 and 140: AIR pump switchover valve (Y32) and/or electromagnetic AIR pump clutch (Y33)) - I have NO air pump and NO air pump clutch on my car so this is also not the issue (I believe :pray: ).

I suspected plugs / high voltage wires or coils but was unsure.

Now I will start from step 1 - buy new plugs (the last change was 7 years (45K) ago). You've noticed that there should be basic ones.
Are these good ones: Bosch Super Spark Plug F8DC4??

[Ivanerrol]

The engine harness was replaced 4 years ago (previous owner spent $4000 on it). So I believe that this is ok..

I've also read the fault codes - there is 085 code still in place (Model 124, 129 and 140: AIR pump switchover valve (Y32) and/or electromagnetic AIR pump clutch (Y33)) - I have NO air pump and NO air pump clutch on my car so this is also not the issue (I believe :pray: ).

I suspected plugs / high voltage wires or coils but was unsure.

Now I will start from step 1 - buy new plugs (the last change was 7 years (45K) ago). You've noticed that there should be basic ones.
Are these good ones: Bosch Super Spark Plug F8DC4??

They are the OK plugs. The NGK equivalent is BCP5ES - it might be hard to find those Bosch plugs now.
45K's and 7 years is getting up there for plain old $3.00 plugs. This "maybe" your issue.

Wring harness done :occasion5:

[Igorniko]

Thanks again! Will change them and then report on the result!!