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Hello, e46 325 cab  auto se 2004 92k.

Not long after I bought the car she started to run poor so after loads of coil packs, new plugs and a few air leaks sorted we went on to buy top range petrol but she still runs irractically but only when hot.Going to work this morning (20 min trip) she was perfect, on the way home after 15 mins she started to what seems like miss fireing but when pushed she was like the devil, awesome.

We had a light on saying no2 sensor was faulty but they were cleared last week and nothing has come back. I am doing 26 mpg around town and 37 on a mixed run which I thought was OK.

A little bit stuck here so any help please ?

 

Mart.

Edited by martauto

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Have you had the codes read?

By no means a petrol expert but sounds like a dodgy coil pack?

If it was fuel related i'd expect it to do it all the time. As it's only sometimes it makes sense (to me) that it's something on the ignition side that's failing. I'd replace the spark plugs anyway.

Not sure how you'd find which coil needs changing? Would it show up in diagnostics?

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spark plugs and all coils have been replaced and no lights on the dash but there was an old fault of oxygen sensor no2 which is not there.

 

Mart.

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That's the extent of my petrol knowledge then! 😂

Fingers crossed you get it sorted mate! Hope someone more knowledgeable can offer insight..

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3 hours ago, momo said:

That's the extent of my petrol knowledge then! 😂

Fingers crossed you get it sorted mate! Hope someone more knowledgeable can offer insight..

Thanks mate,

 

Mart.

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Considering how dead this forum is these days - have you asked on one of the Facebook groups?

They're massively active these days so hopefully someone should be able to offer a solution. Starting to feel like there's only 5-6 of us on this entire forum these days.

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Thanks mate but hell would freeze over before I joined facebook etc but cheers anyway.

 

Mart.

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I'm a bit late to this party as I got locked out with password issues but try disconnecting the plug on the MAF sensor (on the intake boot after the air filter box) and see if it runs better with it disconnected. 

If so it will be your problem. It will throw up a light with a code you'll have to clear though.

Otherwise I suspect that you still have an air leak, intake or vacuum to find. Not something that will necessarily throw up a code.

The rubber boot that the MAF sensor is in often splits lower down out of easy sight. Have you checked or changed that one yet?

I'm on Facebook and there are a million keyboard mechanics on there who are full of crap, so wading through posts trying to find out who knows what they are talking about is a bind.

Kirkynut 

 

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Thanks for that mate !!

I have just been let back on here too.

Coming home tonight from work (10.00pm) she ran superb so I have to say it is temperature related BUT I will check out your advise and report back.

Many thanks  Mart.

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7 hours ago, martauto said:

Thanks for that mate !!

I have just been let back on here too.

Coming home tonight from work (10.00pm) she ran superb so I have to say it is temperature related BUT I will check out your advise and report back.

Many thanks  Mart.

Good luck!

Kirkynut 

 

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Well it rained all morning and it still is now so I had no time to look at what you said but I will, I dont ignore good advise mate.

She ran like a dream to and from work today,,,,,,,,,,,,,,,,,,,,strange.

 

Mart.

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OK so I took off the connector after the air cleaner and it seemed to run very slightly better but that could have been in my head. I have checked all the other stuff and they are just fine.

Educate me please ??  What does what I have unplugged actually do ?

 

Cheers Mart.

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18 hours ago, martauto said:

OK so I took off the connector after the air cleaner and it seemed to run very slightly better but that could have been in my head. I have checked all the other stuff and they are just fine.

Educate me please ??  What does what I have unplugged actually do ?

 

Cheers Mart.

It measures the amount of air entering the engine which, along with the emissions that the lambda sensors give the ECU, the throttle position, oil temperature, coolant temperature and other bits of information tell the engine what ignition timing to run and how much fuel the injectors should squirt in at that moment for the engine to run it's best. The ECU works this out thousands of times per second. 

We've even got variable valve timing on both the inlet and exhaust on these with the Vanos system. 

The ECU effectively takes all of these values given by all of these sensors and refers to a table (MAP) that tells it what to do to make the engine run as it was programmed (Mapped) to do so. So you can see how with all those parameters an engine tuner is a talented person. 

When you un-plug the Mass Air Flow (MAF) sensor as I suggest, the engine uses a set of parameters it knows are safe to provide a stoiciometric air/fuel ration of 14.7:1. This air/fuel ratio gives the cleanest and most efficient burn for petrol. You'll likely see no difference in how the car drives but it will not be as fuel efficient. 

Here's this copied off the interwebs:

"The ideal (theoretical) air-fuel ratio, for a complete combustion, is called stoichiometric air-fuel ratio. For a gasoline (petrol) engine, thestoichiometric air-fuel ratio is around14.7:1. This means that, in order to burn completely 1 kg of fuel, we need14.7 kg of air."

If your symptoms occur with the MAF sensor unplugged, the problem isn't that.

So leave it un-plugged for a week or so when you'd expect the problem to arise during and if it doesn't arise, replace the MAF sensor. 

I hope that wasn't too long winded! I struggle with concise!

Kirkynut 

 

 

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WOW......Thanks for that, I now know I am not harming things with it unplugged.

I took her out this morning and it seemed to run a touch better but with no symptoms so you may be on to something here, I hope lol

 

Is there any way I can tell if it is no good ??

 

Many thanks and I will keep you posted.

 

Mart.

Edited by martauto

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Time will tell because it was a sporadic fault. Faults that are not constant are a pain to identify and with no codes to assist it really is a case of educated guess work. The trouble with that is some people are happy to throw parts at a fault until they hit the jackpot and fix it by luck. Garages do that with other people's money!

Some keyboard mechanics, particularly on Facebook are like it too as they think they know everything. 

That's why I suggest un-plugging the MAF sensor plug first as it's free.

If it's not that we'll have to have a re-think but there's air leaks and things to consider that are likely and can be found for little or no cost too.

Kirkynut 

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I think air leaks are off the menu so far as my guy has gone through all of this and found a small couple but I will stick with what you have said so far as it looks good and so far she drives good.

Work in the morning at 5.20 ish so lets hope mate !!

 

Mart.

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Well she ran to and from work really well today only to idle a bit high on stopping but soon settled down.

I`ve never had two good work runs in succession for a long time so I bought a cheap maf for £25 so lets really hope this is it.

I saw a vid on u-tube about this and we were more or less in the same ball park with symptoms , lets hope it continues.

 

Mart.

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I've got my fingers crossed for you!

Have you fitted the new MAF sensor and deleted the code from it being disconnected?

Kirkynut 

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The maf is on its way and today was day four too and from work and its like a different car.

Do you think there will be a code for this as no one else has picked up on the maf, this has been going on for weeks now ?

Mart.

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I'd have expected the Engine Management Light to have come on and there to be a code. 

Is this bit the case? It was in my Mrs 325i when I forgot to plug it back in once.

Kirkynut 

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The light is on but I have nothing to read it by so will have to wait until it arrives and see if it makes a difference.

Another good day, I have pushed her more today and she was not left asking !!

 

Mart.

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