Likely MAS/ECU issue?

[Wezzel]

Going back to MAS's, my car had the classic symptoms last week. Wouldn't rev past 3000, rough idling and low power. All would be fine following a restart.

I took the car into TM Motors in West Molesey, Surrey (good indie) yesterday and they replaced the MAS probe. The part was £60.

touch wood, all seems fine now.

Interestingly they told me that after fitting a new MAS the computer has to be rebooted for it to work correctly. This contradicts other members posts who have simply bought the bits from ebay, fitted them and driven off.

Edit:

I forgot to mention that the car has done 157k and as far as I know this is the first replacement it has had (perhaps this is a record!)

 

[Shude]

So, another service done and the geniuses at Whitefield have put on the service report: "engine missfires, possible MAS problem". The car works perfectly at idle and only missfires if more than about half-throttle is used, so that pretty much eliminates the MAS, not that changing it wouldn't improve things anyway.

Now it's suggested it could be the throttlebody sensor, if such a thing exists. Anyone ever removed or cleaned it? How difficult is the job? The servicing guy seemed to think it was pretty easy.

 

[Dieselman]

The car works perfectly at idle and only missfires if more than about half-throttle is used, so that pretty much eliminates the MAS, not that changing it wouldn't improve things anyway.

How does that eliminate the MAF? The more you press the pedal the more air is injested. If the MAF fails to read the additional volume then the ECU will underfuel the engine causing low power and possibly a missfire.

 

[Shude]

How does that eliminate the MAF? The more you press the pedal the more air is injested. If the MAF fails to read the additional volume then the ECU will underfuel the engine causing low power and possibly a missfire.

It isn't the Mass Airflow Sensor, it has been replaced with no improvement.

I think it may have something to do with fuelling.

 

[BenzComander]

Sorry to resurrect this post, but my misfire is back with a vengeance.

Exact same symptoms as Shudes, while idling no misfire, when accelerating hard no misfire, but when driving with just partial throttle, it misfires, to the point that it shakes the whole car sometimes. Seems to be throttle pedal position related.

So far, have changed all the plugs, leads and the MAS. Funnily enough, after my last B service it disappeared for a while as well.

Any ideas please, do I have a throttle position sensor?? Car is 1997 W210 320 petrol.

 

[Shude]

Latest update: Coil packs replaced, still misfires!

We've done sparkplugs, coil packs, MAS so far...

What's next please?

 

[GazCaff]

I haven't read all of the thread but I'm aware you were having problems. Seeing as you have changed the coil packs, have you checked the crank angle sensor?

 

[Shude]

I haven't read all of the thread but I'm aware you were having problems. Seeing as you have changed the coil packs, have you checked the crank angle sensor?

I believe the crank sensor would cause misfiring at all times including idle if it was faulty and would not require anything to make it misbehave.

It is a fairly cheap sensor though so it's still an option.

 

[GazCaff]

I believe the crank sensor would cause misfiring at all times including idle if it was faulty and would not require anything to make it misbehave.

It is a fairly cheap sensor though so it's still an option.

Sometimes you cannot apply logic to white-mans magic!

I used to have an Omega with a faulty crank angle sensor. It was a bitch to start, but ran beautifully once it fired up, Electonical wiggly amps and suchalike are funny things.

 

[GazCaff]

Just had a thought, it would be worth checking two things. Firstly the condition of the bonding strap from the engine/gearbox to the chassis and also measure the alternator output accross the battery at varying engine speeds. I'm wondering whether you have been curing symptoms rather than the faults all this time.

 

[BlackC55]

I have just remembered a repair that I used to do on your type of engine wiring loom.

Where the throttle flap and air intake is situated; underneath that there is some plastic ducting for the engine wiring loom. Inside the ducting there is a large section of loom that is soldered together. These soldered wires can become a poor connection and need to be re-soldered. I have done a few for missfire faults on 230k's but most of the time it brings on the engione warning light.

Have you considered an injector(s) may be at fault too?

Also I would be looking toward the Engine Control Unit as a likely suspect by now also.

 

[Shude]

I have just remembered a repair that I used to do on your type of engine wiring loom.

Where the throttle flap and air intake is situated; underneath that there is some plastic ducting for the engine wiring loom. Inside the ducting there is a large section of loom that is soldered together. These soldered wires can become a poor connection and need to be re-soldered. I have done a few for missfire faults on 230k's but most of the time it brings on the engione warning light.

Have you considered an injector(s) may be at fault too?

Also I would be looking toward the Engine Control Unit as a likely suspect by now also.

All interesting things!

I have thought for a long time that the problem is fuel starvation, others have disagreed. I thought this because the car was FIXED and would not misfire just after the fuel filter was changed during regular servicing, this lasted about 1-2 months and then the problem came back.

If I replace the ECU (at huge expense) and it doesn't fix it then I'll be annoyed. So far this problem has set me back about £500 with no obvious improvement and has been p*ssing me off for over 2 years!

 

[BlackC55]

It maybe worth getting the ECU overhauled anyway, rather than replacing. (www,bba-reman.com)

Have you done a compression test? The miss maybe also a mechanical fault too.

 

[BlackC55]

I would love to get my hands on it.......

 

[Shude]

It maybe worth getting the ECU overhauled anyway, rather than replacing. (www,bba-reman.com)

Have you done a compression test? The miss maybe also a mechanical fault too.

What are the symptoms of a faulty ECU?

As for a compression test, this will have to be an Ian Walker thing.

 

[BlackC55]

A faulty ECU can cause a whole manner of faults. Missfires mostly though. I think Ian is going to call me about your car today. I hope I can offfer some advice.

 

[Shude]

A faulty ECU can cause a whole manner of faults. Missfires mostly though. I think Ian is going to call me about your car today. I hope I can offfer some advice.

After a casual chat with a bloke at MB Manchester Central it seems the "ignition control unit" could also be causing this problem after I told him the MAS, sparks and coils had been replaced.

Ian: stick that on the list would you please?

This thread gives me some hope regarding the ECU costs: http://www.mbclub.co.uk/forums/showthread.php?t=3356

 

[BlackC55]

No such device Shude.

 

[Shude]

No such device Shude.

Ian: we now know it's not the "ignition control unit", cross it off the list

I did think it sounded a bit suspect when he mentioned it, I'm sure they make these things up on the spot in order to sound knowledgable!

I think the next thing on my list is fuel filter swap, check the fuel pump and fuel pressure.

 

[GazCaff]

No such device Shude.

lol! Stealers technician gets owned again!