Likely MAS/ECU issue?

[nickmann]

Were you getting blow-by past one of the loose plugs? Is the missfire related to revs or load? (difficult to separate the two on an auto I know)

I'd be inclined to move the injector and see if the noise follows it, to differentiate between injector noise and lifter noise.

Incidentally, how much ATF do you use for "clean-up" duties, and why use ATF instead of an engine flush oil?

 

[Ian B Walker]

we used about a 1/3 of a ltr of ATF. ATF is an agressive oily cleaner. Magic in gearbox's and pretty good in engines too

 

[nickmann]

Cheers, I'll give that a try. Presumably just drop it in a few days before a scheduled oilchange?

 

[Shude]

Cheers, I'll give that a try. Presumably just drop it in a few days before a scheduled oilchange?

Ian reckoned about 300 miles before the oil change. Don't expect the oil to come out looking pretty though

 

[Shude]

Injector cleaner gone, valve cleaner now in the tank. I guess we'll see if it makes any difference in a few days!

 

[Shude]

Ok, just had an A-service and I asked the stealership to have another look at it.

Cylinder 4 is misfiring "intermittently" according to the invoice. They tested the injectors and the electrics, nothing wrong with them.

I asked them if they had any other ideas and someone piped up "mass airflow sensor?".

"needs further investigation" is what the invoice says. I paid £18.70 +VAT for this excellent piece of detective work, still we know what else it's NOT now don't we?

 

[Shude]

Just took the car for a blast.

When the engine is cold no matter how much I floor it the misfire doesn't happen. Once up to temp (about 30 seconds then...) it misfires pretty easily.

Surely someone must have an idea where to look next?

 

[jgevers]

Should be relatively easy to find the fault. If you are in West Manchester give this bloke a ring. He is in our group of technicians that keep each other up to date and are actually interested in vehicle technology.

Tune Up Diagnostic Services
Contact Name: Michael Whitworth

Tel: 01942 204679 Mob: 07967 591079

Specialist diagnostics to the motor trade and motoring public

He is mobile.

regards,

Job

 

[Shude]

Should be relatively easy to find the fault. If you are in West Manchester give this bloke a ring. He is in our group of technicians that keep each other up to date and are actually interested in vehicle technology.

Tune Up Diagnostic Services
Contact Name: Michael Whitworth

Tel: 01942 204679 Mob: 07967 591079

Specialist diagnostics to the motor trade and motoring public

He is mobile.

Cheers, I'm in North Manchester but if it means my car might get fixed I'm more than happy to travel a bit

 

[Shude]

latest update:

R2D2's mechanic buddy has suggested

- crankshaft sensor
- fuel pressure problem (check with gauge)
- fuel pump problem
- mass airflow sensor (hurrah!)

None of those things are megabucks to sort out, there is apparently a very good mercedes independent next door to the place that sorted my aircon out so I might ask them to check out the things listed.

Let's face it, they won't be charging me £100 per hour for a "no fault found" will they?

 

[Wully]

Shude
Any update on the problems, i have the exact same problems on my C180 right now except it's getting worse!

Funny thing is you mention valves, about 12 months ago i a valve replaced and the MAS and it went like a dream up until the last couple of weeks.

 

[Shude]

After almost one year of putting up with this problem I have pretty much worked out that the RPM has absolutely nothing to do with this fault. It is everything to do with the throttle position.

If I push the gas pedal further than about halfway it starts to miss-fire, if I'm really careful I can lift off quick enough for it to recover, if I hold it there then it miss-fires and carries on until I stop the engine completely.

This is a massive problem if I want to climb a hill in traffic at about 50mph, the engine labours and I'm forced to put my foot down a bit, at this point the engine stutters, miss-fires and then I lose about 25% of the engine's power so I'm forced to bury the pedal just to maintain 50mph.

If however I knock the lever into 4th gear, or 3rd it picks up and behaves beautifully, as long as I don't bust the halfway mark on the gas pedal. It will happily accelerate all the way up to the redline without a single cough, the engine sounds great.

WTF is wrong with the stupid thing? Is there a throttle position sensor or a throttle body sensor or something that can be faulty or dirty or blocked or something? It certainly sounds like a simple sensor or other electronic failure because otherwise the engine behaves perfectly.

 

[Parrot of Doom]

Can you see the accelerator cable in the engine bay? What happens when you move the throttle body yourself, does the car rev freely?

 

[Shude]

Can you see the accelerator cable in the engine bay? What happens when you move the throttle body yourself, does the car rev freely?

I don't think I have ever managed to get it to miss-fire when stationary or when in N, but the rev-limiter is pretty low when in N. Funnily enough I've not tried pulling the throttle cable when in motion so I'm not sure how I'll test this, maybe with a contraption made from meccano and duct-tape?

Nice idea though, I'm pretty scientific and I like Sherlock-Holmesing my way through problems so I will see if I can try this at the weekend

 

[GrahamC230K]

From a quick skim read, am I correct in that you have not yet replaced the MAS?

Come on, this is such a common failure and you can get a replacement insert at a good price via R2D2 I believe, so get one!! You need one anyway I am sure if you are on the original.

 

[Shude]

From a quick skim read, am I correct in that you have not yet replaced the MAS?

Come on, this is such a common failure and you can get a replacement insert at a good price via R2D2 I believe, so get one!! You need one anyway I am sure if you are on the original.

I am tempted to book the car in at the stealership for a pre-service/MOT inspection, during which they will identify the corroded pipe (gearbox coolant I think) for replacement at the service due in a couple of months and a few other bits and pieces plus change the MAS, check the fuel pump, check the fuel pressure and replace the crankshaft sensor if required.

 

[Parrot of Doom]

I don't think I have ever managed to get it to miss-fire when stationary or when in N, but the rev-limiter is pretty low when in N. Funnily enough I've not tried pulling the throttle cable when in motion so I'm not sure how I'll test this, maybe with a contraption made from meccano and duct-tape?

Nice idea though, I'm pretty scientific and I like Sherlock-Holmesing my way through problems so I will see if I can try this at the weekend

Well if it won't mis-fire while stationary, I don't see how it can be the throttle position sensor

I wouldn't recommend pulling wires while driving, thats a recipe for disaster.

I'd just take it to Greenvale, they've been pretty good to me so far. Forget the stealer.

 

[Dieselman]

Shude

I can't help thinking you are going too deep with this problem.

As Graham said your car almost certainly needs a MAF so just do it before committing further.

You could try running with the MAF disconnected to see if it does it in limp home mode.

If the missfire is definately on a particular cylinder then I would suspect the coil pack. The fault will only show up under load so won't be detected on the diagnostic equipment.

 

[Shude]

Shude

I can't help thinking you are going too deep with this problem.

As Graham said your car almost certainly needs a MAF so just do it before committing further.

You could try running with the MAF disconnected to see if it does it in limp home mode.

If the missfire is definately on a particular cylinder then I would suspect the coil pack. The fault will only show up under load so won't be detected on the diagnostic equipment.

The stealership said that the coil packs and leads were fine, also I had no problems for a short while after the car was B-serviced, this makes no sense to me except that they probably reset some computer settings while it was there.

"under load" is difficult to simulate, but the problem only manifests itself when I push the gas pedal hard, if I shift down a couple of cogs and keep the pedal where it is I can take it up to the red-line in every gear and it doesn't miss a beat - is this not "under load"?

There is a mercedes service/tuning place about 5 minutes from my house I was considering taking it there, from what I have heard they know their onions.

 

[mobeyone]

Shude,

My car is going back mid next week to have a number of sensors changed - one was a fuel sensor and the other was an emmisons sensor coupled with my buggered purge control valve.

John at repsonse (wigan) said this woudl give the car a rough ride and i think you have the same problem as me. Mine is perfect when cold but becomes troublesome when warm on occasion.

I will let you know what the fault codes were etc tomorrow when he phones to tell me what it will cost but still nowhere as to why my car does not start sometimes....

He also told me the rear sam maybe playing up on my car which is why i am getting an esp not available aswell as abs and brakeline wear messages (even though all work)... so i will be speaking to s&r motors very soon.