Waking up the M104 after 10 years (e320 Coupe 1994) advice needed.

[bh13coupe]

Good Morning

I am no means a qualified mechanic and would like guidance if possible.
I have my 1994 e320 coupe which i am bring back to life. The engine was turning over but not starting, checked the Fuel pump relay and that was pushing voltage to the fuel pumps (result). Changed out the dual fuel pumps and filter, emptied the old fuel (that looked like diet pepsi) replaced with the good stuff and managed to get her fired up after 20 secs of turning over. However the car is running like a 4 pot diesel and not like a smooth straight six. No smoke at all out the exhaust which was a surprise. No leaks in the coolant piping. Oil is golden and in good shape. Also all the warning lights are lit on the instrument cluster. so I would like to see if I can have answers on the following for my next steps please.

Shall i leave the car running to get it up to temperature? I didnt run it for longer than a minute. I dont want to cause any damage excessive wear if not necessary.
Would the next step be a spark plug swap? the lumpy running I am guessing is that the car isnt running on all 6 cylinders.
The warning lights, would this be a potential Alternator issue? or do i have a wider problem with ECU/wiring?
Any other jobs/checks that I should consider or look into?

Any wisdom/experience feedback would be appreciated.
thanks

PAW

 

[neilrr]

EZL proving spark on all 6 leads?

 

[Will]

Also all the warning lights are lit on the instrument cluster.

I’d be starting from there before you take spark plugs etc out. Plugs are probably fine, could be something like a blown fuse or stuck relay (OVP?) etc.

 

[bh13coupe]

EZL proving spark on all 6 leads?

will check

 

[ray_hennig]

will check

No EZL on a 320, only on the 300-24 M104.98x engine and earlier engines.

Has the eco wiring been replaced? If not, it must be. The wiring looms can be rebuilt by people like HOME | Mysite

But certainly ensure clean plugs first.

RayH

 

[E55BOF]

1994? Mercedes of that era were fitted with biodegradable (as it turned out) wiring looms.

You won't do any harm running it up to temperature once to see what happens, but I wouldn't be at all surprised if a couple of the ignition leads were faulty; check those first.

 

[bh13coupe]

No EZL on a 320, only on the 300-24 M104.98x engine and earlier engines.

Has the eco wiring been replaced? If not, it must be. The wiring looms can be rebuilt by people like HOME | Mysite

But certainly ensure clean plugs first.

RayH

eco loom was replaced 25 years ago approx

 

[Bellow]

Run for long enough for the exhaust manifold to take heat and monitor each branch for cold ones. They are the cylinders that are misfiring - if confined to specific cylinders.
Do not run for longer than necessary misfiring. If it's missing due to electrics there'll be a shit load of unburned fuel heading for the crankcase and/or exhaust (explosion risk in the latter).
If the cylinders that are missing can be identified, remove their plugs and assess condition. If the misfires are not cylinder specific, remove all plugs for assessment.

 

[carat 3.6]

If all of the dash lights are lit up the alternator isn't charging, this can be down to a sticky OVP relay or the alternator itself.

The OVP would also cause the engine to run a little rough, but if you think it's only running on 4 cylinders it's more likely to be one of the coil packs or HT leads.

The HFM M104's like yours have a feature built into the ecu of cylinder deactivation, if the ecu detects a bad enough misfire it will shut off the affected cylinder and it's twin. You'll need to change the spark plugs first anyway as the car has been sitting for 10 years, but if the misfires are still there we can guide you through the process to find the cause. One other thing to mention is the older bosch ignition coils with a blue label are known for causing trouble, and should be replaced at the earliest opportunity if you still have them fitted.