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.

 

[bh13coupe]

OK, latest update

plugs swapped out, coil packs look original, Merc blue label style, def not after market.
car fired up no problem, definitely smoother running (the i6 woosh was back) however still not 100% smooth, a very loud ticking noise from front of the engine was the next issue, initial thoughts were timing chain tensioner not doing its job. Then the alternator started smoking so clearing knackered, this also ties in with the warning lights staying on the dash. So, next step will be to replace the alternator and try again. hopefully the ticking was related to that. I didnt have enough time to zero in on exactly where the ticking sound was originating before the smoke started to arrive.

 

[Will]

It won’t be the timing chain tensioner, they ratchet out to self adjust so would keep tension as it always was.

Could be a sticky hydraulic lifter if it’s mechanical sound from the top end, but as you’ve noticed the alternator start with that first and run it up again.

After that, you might as well flush with new oil if you’re recommissioning it after ten years.

 

[Pontoneer]

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

one thing well worth doing is get down to Halfords and buy a complete set of new fuses for the car . These continental fuses are notorious for corroding at each end , and also corroding their contact points in the fusebox - this can give rise to all sorts of electrical issues . Replace every fuse in the fuse box and at the same time clean up around the little holes where the fuses make contact .

A drill bit of a diameter similar to the fuses will be fine to clean up around the small holes where the fuses go - just wrap the drill bit in insulating tape , except for the very end , so as not to short across any of the contacts , then just holding the drill bit in your fingers , use it to clean up the contacts - best to disconnect the car battery whilst doing this . Replace the fuses one by one , taking care to match each old fuse with a new one of the same colour .

Doing this will make a big difference to any older car that has sat around for a while as corrosion happens over time and is not related to use ; most of these fuses are made of a dissimilar metal to the copper fusebox contacts , and this also promotes corrosion in this area .

It will only cost a few pounds to get enough fuses to replace the lot ( just count up how many of each colour you need before buying them ) Halfords sell them in little packs of four or five of each colour ( current rating ) . They are known as Continental , or torpedo , fuses .

Although it was replaced before , given the car has sat for 10 years , it is possible that the engine wiring loom has deteriorated again , especially given it is now 25 years old , but leave that for now .

Either inspect , clean or replace the spark plugs , depending what you find - a small wire brush dipped in petrol will be quite effective for cleaning sooty or oily plugs up , just let them dry out before re-fitting .

The other possibilities include ignition leads shorting somewhere against the block - watch the engine running in total darkness with the plastic cover down the middle removed , and look for blue flashes , which would be from ignition leads leaking spark to ground - don't handle them while the engine is running or you could get a shock , but if you see sparks , stop the engine and rearrange the leads so they don't touch metal anywhere .

Another test you can do if an engine is misfiring , is with an INSULATED tool , pull the lead off each spark plug in turn while the engine is running - if you hear a change in the engine note then that one was working - if there is no change in engine note , then that plug was not firing .

The other possible cause of two cylinders not firing is that one of the three ignition coils might be faulty - each coil supplies spark to two plugs at a time , even though at that time only one of them will ignite the mixture ( the other is known as a 'lost spark' ) .

I would start with replacing the fuses and checking/cleaning/replacing the spark plugs because these things don't cost much to do .

Things like ignition leads , coils and engine wiring loom cost more , and I always try the cheapest things first !

 

[Pontoneer]

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.

Unburnt fuel not good for the catalytic converter either , assuming a 94 model has one ( I suspect it will ) .

 

[Pontoneer]

OK, latest update

plugs swapped out, coil packs look original, Merc blue label style, def not after market.
car fired up no problem, definitely smoother running (the i6 woosh was back) however still not 100% smooth, a very loud ticking noise from front of the engine was the next issue, initial thoughts were timing chain tensioner not doing its job. Then the alternator started smoking so clearing knackered, this also ties in with the warning lights staying on the dash. So, next step will be to replace the alternator and try again. hopefully the ticking was related to that. I didnt have enough time to zero in on exactly where the ticking sound was originating before the smoke started to arrive.

Could be a hydraulic tappit as Will says ; other possibility is noise coming from one of the pulleys at the front of the engine as they can seize up and make odd noises ; there should also be a tensioner for the poly drive belt .

Mentioning the poly belt , do inspect it for signs of the rubber cracking or perishing - it is well worth replacing that belt if the car has sat for 10 years - if that fails when you're driving , you will lose water pump ( hence engine cooling ) , alternator , power steering and , if fitted A/C .

Re the alternator , worth checking if there is a Bosch Service Agent near you - they can rebuild the original alternator good as new , with a warranty , for a lot less than the cost of a new alternator .

 

[Bellow]

Unburnt fuel not good for the catalytic converter either , assuming a 94 model has one ( I suspect it will ) .

If the engine was at full operating temp it would be problematic. Not at this limited running though.

Another test you can do if an engine is misfiring , is with an INSULATED tool , pull the lead off each spark plug in turn while the engine is running - if you hear a change in the engine note then that one was working - if there is no change in engine note , then that plug was not firing .

That's bad practice with modern higher voltage systems. It creates a risk of the voltage bursting a lead or flashing back across the ECU. Where it needs to be done, it is better to devise a method of shorting the voltage to earth - with or without the engine running during that 'switching'. Otherwise, there's the risk of introducing a new problem. Monitoring exhaust branch temps on (non-siamesed) heads fulfills the identifying the duff cylinder(s) brief here more safely.

 

[scillyisles1]

The fuses advice is sound - putting new fuses in and cleaning the contacts can make a huge difference particularly if the car has bene left in a damp location. If the wiring loom has been replaced and the car is still not running smoothly I would suspect one of the coil packs might be faulty. They age and where they are they are subject to a lot of heat. I have replaced quite a few on mine over the years. The leads could also short in this area as mentioned earlier.

 

[abecketts]

Delighted to learn you still have the car, I remember buying 4 alloys off you for my old E320 estate about 18 years ago.