Misfire on M40 318i, Please Help..FIXED!!!!

[Jem]

I'm still trying to get to the bottom of the misfire on my 318i

I've so far changed:

Sparkplugs
Plug Leads
Fuel Filter
Distributor Cap (their not cheap )
Rotor Arm

The airfilter is nice and clean.

I have cleaned with carb cleaner:
AFM
Throttle body (didn't take it of, just sprayed into the body with the throttle closed and open)
Idle Control Valve

I've also used some fancy Redex stuff to clean the fuel system/injectors. It's run through the whole tank with the Redex (been to Swindon and back today), and I've refilled it with BP Ultimate).

It's slightly better, but still a LONG way from running smooth

I've pulled the plug leads off one by one with the engine running, and they all cause the engine to run rougher.

I've had the cam cover off, and the cam looks in good condition.

I've done a compression test:

1 = 161 psi
2 = 165 psi
3 = 165 psi
4 = 165 psi

I'm running out of ideas. What would you check/change next?

I've just checked the new plugs 'they have done 300 miles since fitted) and they are a nice light brown colour.

Please help

[Brianmoooore]

Misfire when? At idle? Under load? High revs?

[Jem]

Misfire when? At idle? Under load? High revs?

Sorry, it's at idle. Seems fine under load, and has plenty of power, but the mpg is in the high 20's on a long run.

I've also checked the hose from the AFM to the throttle body, and there's no splits in it.

[Brianmoooore]

Air leak on the induction side is first thing to thoroughly check. This includes the crankcase breathing system.

[Jem]

Air leak on the induction side is first thing to thoroughly check. This includes the crankcase breathing system.

Would that account for the poor fuel consumption?

[gazza]

i had the same trouble i tried everything on my m40 ...then i cahanged the cam/rockers and it all went away ...as did my noisy top end ....i thought that if the cam was badly worn it would affect the valves opening and closing properly ....anyway no more missfires,i did the same as you it cost me for leads dizzy rotorarm still did not go away ...good luck

[Jem]

The camshaft looks to be in good condition. Cant clearly see about the rocker arms or the hydraulic followers, but to change them gets pricy.

[Jem]

I'm starting to think it is the cam/valve gear, as it is quite tappy from the head. Would I need to change the hydraulic followers as well, or would changing the cam and rockers surfice?

[Simon]

Try changing the blue temp sensor too, this can cause lots of fuelling problems.

[Jem]

Try changing the blue temp sensor too, this can cause lots of fuelling problems.

It's interesting you say that, as I have noticed it's nice and smooth when started from stone cold for about 3 mins, then starts to get rough.

[Simon]

Try changing the blue temp sensor too, this can cause lots of fuelling problems.

It's interesting you say that, as I have noticed it's nice and smooth when started from stone cold for about 3 mins, then starts to get rough.

Give it a go, it doesn't cost much either, I can't quite remember much bout the M40, but I'm pretty sure it's under the inlet manifold somewhere.
The blue sensor is for the ECU, and any probs can cause all sorts of running probs.

[Jem]

I've just ordered one from my local BMW dealer, as they didnt have one in stock. Should be here on Saturday.

[Jem]

Another little update:

I've just taken the top half of the inlet manifold off, and checked all the pipes etc for cracks or anything that could cause a leak, can see anything amiss. I have taken the throttle body off the manifold, and given is a good clean with carb cleaner. Now looks all shiny I did find one thing wrong though, the TPS wasnt clicking when the throttle was opened. I've adjusted it so it now clicks as son as the throttle is opened. I'm going to leave the manifold off till I've changed the temp sender, but I'm going to change two gaskets for the manifold and the one for the throttle body too.

[jonbuoy]

Try changing the blue temp sensor too, this can cause lots of fuelling problems.

I thought this sensor was just for the gauge on the clusters? As the M40 has'nt got an Air Temperature sensor.
And the blue plug sensor goes into the block on the M40, not directly under the Inlet Manifold.

[Simon]

Another little update:

I've just taken the top half of the inlet manifold off, and checked all the pipes etc for cracks or anything that could cause a leak, can see anything amiss. I have taken the throttle body off the manifold, and given is a good clean with carb cleaner. Now looks all shiny I did find one thing wrong though, the TPS wasnt clicking when the throttle was opened. I've adjusted it so it now clicks as son as the throttle is opened. I'm going to leave the manifold off till I've changed the temp sender, but I'm going to change two gaskets for the manifold and the one for the throttle body too.

All the above should help in eliminating any possible air leaks, also check the intake pipe that goes to the throttle body, iirc too there's a small pipe with a block on the end somewhere on the throttle body on an M40, these tend to split and cause air leaks.

Good thing you've adjusted the TPS, it should click just as you open the throttle to come off idle.

[Simon]

Try changing the blue temp sensor too, this can cause lots of fuelling problems.

I thought this sensor was just for the gauge on the clusters? As the M40 has'nt got an Air Temperature sensor.

It's not an air temp sensor, it senses engine temp, and adjusts fuelling accordingly. M40 has both blue for ECU and brown for temp guage.

[jonbuoy]

Try changing the blue temp sensor too, this can cause lots of fuelling problems.

I thought this sensor was just for the gauge on the clusters? As the M40 has'nt got an Air Temperature sensor.

It's not an air temp sensor, it senses engine temp, and adjusts fuelling accordingly. M40 has both blue for ECU and brown for temp guage.

Nice one mate

Just gonna pop down the road

[Jem]

Just popped a multimeter on the TPS, and it's working nicely dectecting both idle and WOT

[jd05]

I have just sorted out out a similar problem with my 318i M40.
It had a misfire at idle, and an intermittent (quite violent) misfire under load.

Like you I changed plugs, leads, distributor cap, rotor arm, checked all the hoses for air leaks etc but it was still the same.

I booked it in for a crypton tune and they said it was the mixture on the AFM, which they adjusted and said it was OK. It was for a day, then it returned.

The car then went to a BMW specialist who then checked the fuel pressure, fuel pump and checked that there was no water in the fuel. He also said that the wrong plugs were fitted and that these engines run better on Bosch plugs. After this the car was still the same. As the main fault was intermittent, it was hard to track down.
I was advised to check the injectors and ECU.
I had the injectors ultrasonically cleaned and refurbed but the fault was still there.

By now I had gone past being frustrated and was nearly suicidal, so as a last resort I bought a 318i for spares which did not have the problem and started swapping bits!

Until I did this, I did not realise that there was actually two faults with the car.
The first fault - a hesitation under quick acceleration (even just blipping the throttle quickly) was a combination of the AFM and ICV. At its worst, the car would actually backfire!
The second fault which is similar to yours only happened when the car had been running for a few minutes. I changed the ECU, coil etc but it would not go. It only went when I changed the engine wiring loom.

This is not a major job and took about 1.5 hours.

Sorry for the long post but I wanted you to know the background of how I got to the bottom of this fault.

I hope this is of some use to you

Justin

[Jem]

Thanks Justin, it's worth bearing in mind. I'm going to see what difference the temp sender makes before doing anything else, but it wont be too hard to change the engine loom.

[gcorky]

got a m40 cam,bought new-fitted to 1992 1.8 head -done 0 miles
reasonable offers invited.

bilstein febi from motormec.

[Jem]

Well I fitted the new blue temp sensor this morning, and it's running alot smoother Still not perfect, but I'm pretty sure thats being caused by the cam/rockers.

BIG THANKS for all the help guys!!!

[Jem]

Umm, seems I was a little premature with my last post. Just been to pick my wife up from work and it's just as lumpy as before Does seem more intermittent now, it will be fairly smooth sitting at one set of lights, and lumpy as hell at the next. Once on the move it seems pretty smooth though.

[E30Mark]

Have you run it low on fuel recently? if so the fuel pump could be on the way out....

[Jem]

I'm not sure it's the fuel pump, as it's got plenty of power if you boot it.

[E30Mark]

Have you tried having the fault codes read?

[Jem]

Have you tried having the fault codes read?

No, is that something that can be done yourself or is it a dealer/specialist only job?

[E30Mark]

Have you tried having the fault codes read?

No, is that something that can be done yourself or is it a dealer/specialist only job?

Specialist job, you need a fault code reader, i have a basic one. if your near Dorset pop in!

[Jem]

Have you tried having the fault codes read?

No, is that something that can be done yourself or is it a dealer/specialist only job?

Specialist job, you need a fault code reader, i have a basic one. if your near Dorset pop in!

Thanks for the offer, unfortunatly I'm in Cambridgeshire.

[Jem]

I dont know if anyone is still reading this, but if you are

I took the car down to a local mot/test/service place today, and had the fault codes read.................nothing there.

He did also but the car on an exhaust gas analyzer and found the mixture was very weak. He tried to adjust it with the screw on the AFM but couldnt. He did say he thought he could hear an air leak though. I've just got home and sprayed carb cleaner on all the joints for vacuum pipes and the inlet manifold, and there is deffinatly a leak there somewhere, so the whole inlet manifold is coming off this afternoon to have new gaskets fitted, and all the pipes checked for splits etc

[jonbuoy]

I done the samething with the inlet and it's been fine, just got to change the Temperature sensor and all should be well

[Jem]

I'm hoping new inlet manifold gaskets and a good check of ALL the vacuum pipes will sort it. There is clearly a leak some where. I think it's where the manifold meets the head for cylinders 1 and 2, as the idle picks up and smoothes out when that area as swiming in carb cleaner.

Would it be worth running a bead of slicone based 'instant gasket' on both sides of each gasket, or is it better to use the gaskets dry?

[Brianmoooore]

Air leak on the induction side is first thing to thoroughly check. This includes the crankcase breathing system.

If you go back to the start of this thread, you'll find this.

Instant gasket shouldn't be needed with new gaskets on clean surfaces and properly torqued.
The inlet gasket failure on one of my cars I posted about a couple of months ago was caused by the engine having been rebuilt a year before, and a nut left completely off. (I have names!)

[Jem]

Yeah, I know you posted that, and it was the first thing I did check. Clearly I didnt check it enough. I'll have the gaskets on Thursday. If it is a vacuum leak, I'm not worried about the cost of the bits I have replaced, as they were in need of changing anyway.

[Jem]

It's Fixed!!!!

Once I took the bottom half of the inlet mainfold off, it was very clear what had been causing the problem. The inlet manifold gasket looks like it had sliped when it had been fitted buy a previous owner/garage . It was very missaligned round the port for cylinder 1 Also looks like the injector had been firing directly at the missaligned gasket. I cleaned up the head and manifold surfaces, bolted it all together with new gaskets, and now it's smooth as silk

Big thanks for all the advice guys