M104 Intermittent problem

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w124nut

Active Member
Joined
May 9, 2004
Messages
568
Location
Somerset
Car
Mercedes W124 E320 cabriolet
Can anyone offer advice on the problem I have with my W124 M104 6 cylinder engine?

From cold, the engine starts first time without problems but just for 2 or 3 seconds or so before the engine shakes as if it is not running on all cylinders.

If I keep my foot on the accelerator (1,000 to 1,500 revs) the shaking continues for about 2 minutes then stops and she runs smoothly.

After this happens (on two separate days), I drive the car for about 30 miles with town and motorway driving and she responds perfectly.

The car is kept in a dry garage but as she is run only on dry days, sometimes the interval between runs may be several weeks.

The battery is fine as it is linked to a battery conditioner. The engine has covered 87,000 miles and has been serviced regularly throughout its life.

The vehicle is going in for an "A" service on 2nd December.
 
A lifter draining down oil overnight and not opening the valves properly on one cylinder?
I would do a compression test at cold start and also check the fuel pressure at cold start
 
Has the main engine loom been done...?
 
Yes the engine wiring harness was completely replaced 8 years ago (10,000 miles) as was the head gasket.
 
If you release the fuel tank vacuum before starting does it make any difference at all?
 
If you release the fuel tank vacuum before starting does it make any difference at all?

I haven't done that but......when it first happened, I went to the petrol station and filled up with Shell Vmax as is the norm juice I use.
 
Same for MAF, if this is disconnected does it make any difference at all.

Maybe also think about replacing the charcoal evap canister...
 
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My M104 has a HFM-SFI engine management system that feeds the spark plugs through the coil pack and therefore does without the need for a distributor.

All electrical leads are dry and clean.

I will disconnect the MAF soon when I get out into the garage.

As I said in my first post, the engine starts perfectly and runs for about 2-3 seconds before the very lumpy tick-over begins. I keep the engine running with the use of the throttle (1,500 revs) for about 2 minutes during which the lumpyness disappears and she runs as sweet as a nut.
 
OOPS failed to notice it was a later M104 -- I was thinking early M104/M103.:eek:

People do have problems with moisture/cracks on the plug extenders under the coils sometimes. If its CHG related its due to water seeping back into the cylinder head when the engine cools down. This can cause a misfire on start up from cold till the water is blown out. Normally if this is the case there will be evidence on one or more the spark plugs that this is happening.
 
I have just returned from my garage where I have been tinkering along the line of suggestions that I have received. Started the engine and the same problem manifested itself.

I am going to contact my local MB garage and put the problem to them and will post on here the outcome. Thanks all for your interest and help.
 
I had a problem of slightly rough running when cold a few months ago which was remedied with a new fuel filter followed by a can of bg44k.
 
I had a problem of slightly rough running when cold a few months ago which was remedied with a new fuel filter followed by a can of bg44k.

An interesting and non technical suggestion that I can relate to. I will keep this in mind, thanks.
 
do you have one of those codes readers to see if any fault codes have recently appeared ? That would be my first move.

No I do not have a fault code reader, a good suggestion to get one though. Where do you buy them?
 
Today I picked up the car from the garage after it having spent time there being tested since Friday.

The garage arranged for me to drive the car there on the Thursday evening so it will be cold and ready for them to start work the following day. After starting it from cold, I
couldn't believe it as the car engine ran smoothly without problems on my 4 miles journey.

During the 2-1/2 working days that the car was worked on, the lumpy engine fault did not occur once. However the garage carried out various tests, some listed as follows:

engine cylinder compression test
checked out the coil packs
fuel pressure at cold start
checked the sparking plugs
engine leads were checked over for cracks and cleanliness
cooling and heating system were pressure tested for leaks

Nothing was found that caused concern but I did ask the garage to renew the sparking plugs as they were 5 years/4,000 miles old.

This afternoon I did a drive on A roads and M5 for around 40 miles without any problems arising. It is frustrating that no definite cause was identified but I hope that the change of plugs will cure it, only time will tell.

Thank you to those who have given suggestions to the possible cause, they were noted.
 
Today I picked up the car from the garage after it having spent time there being tested since Friday.

The garage arranged for me to drive the car there on the Thursday evening so it will be cold and ready for them to start work the following day. After starting it from cold, I
couldn't believe it as the car engine ran smoothly without problems on my 4 miles journey.

During the 2-1/2 working days that the car was worked on, the lumpy engine fault did not occur once. However the garage carried out various tests, some listed as follows:

engine cylinder compression test
checked out the coil packs
fuel pressure at cold start
checked the sparking plugs
engine leads were checked over for cracks and cleanliness
cooling and heating system were pressure tested for leaks

Nothing was found that caused concern but I did ask the garage to renew the sparking plugs as they were 5 years/4,000 miles old.

This afternoon I did a drive on A roads and M5 for around 40 miles without any problems arising. It is frustrating that no definite cause was identified but I hope that the change of plugs will cure it, only time will tell.

Thank you to those who have given suggestions to the possible cause, they were noted.

You have not given us any info on fault codes.

Were they not checked ?

Was it a Merc Indie you used ?
 
The garage was an MB dealership.

I didn't cover fault codes in particular in my conversation with the service engineer as it was said that tests were carried out without any faults indicated.
 

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