Hesitation - Possible Causes

[e34.535i.sport]

When the capatin was revving it up last night I was looking under the bonnet for anything unusual - eveything looked fine but after a few revs there was a serious smell of fuel...

Could the popping/hesitation and smell be injector related?

[anonymous1]

Hi,

I have noticed over the last few weeks that I have a hesitation on accel between the lower end of revs. Generally happens at about 1-2.5rpm. When this happens I seem to be getting what sounds like a misfire (popping type) noise from the engine. The noise only happens once and then the engine seems to pick up fine. (Although by this point I have already been beaten from the line by the clapped out Rover Metro with 26 grinning passengers next to me!) :D

I have replaced the rocker cover gaskets and this hasn't made any change. Replaced all spark plugs as thought they may have been damaged by previous oil leak from the gaskets.

Wondering if this could be a vacuum leak or what the other possible causes could be? I don't know if the previous owner ever had the fuel pump changed, although I haven't heard any whining noises coming from the rear.

If there's any extra info you need me to provide let me know.

Thanks in advance.

[finalanarchy]

My mums car used to have a bit of hesitation of the line, turned out to be something like sparkpulg master lead, can't remember exactly what he called it.
Hope that helps.

[filip00]

try sparkplugs first if they're old, then if it still continues go test injectors

[whiskychaser]

Hi,

I have noticed over the last few weeks that I have a hesitation on accel between the lower end of revs. Generally happens at about 1-2.5rpm. When this happens I seem to be getting what sounds like a misfire (popping type) noise from the engine. The noise only happens once and then the engine seems to pick up fine. (Although by this point I have already been beaten from the line by the clapped out Rover Metro with 26 grinning passengers next to me!) :D

I have replaced the rocker cover gaskets and this hasn't made any change. Replaced all spark plugs as thought they may have been damaged by previous oil leak from the gaskets.

Wondering if this could be a vacuum leak or what the other possible causes could be? I don't know if the previous owner ever had the fuel pump changed, although I haven't heard any whining noises coming from the rear.

If there's any extra info you need me to provide let me know.

Thanks in advance.
You can mask all sorts of ills by revving it a bit more. What's the idle like? If its lumpy you might be looking at an intake leak. Check it by removing the oil filler cap-the idle speed should change a bit. But dont get too excited. It might not if your filler cap isnt sealing in the first place.

[anonymous1]

Cheers for the input.

At the moment I have already changed the spark plugs a couple of weeks back and while this seems to have made the car run smoother, it hasn't got rid of the hesitation as I hoped it would.

The idle is smooth and does not rumble at all, so thinking this may mean it's not a vacuum leak. Or can one be caused by a bad intake manifold gasket as accel is applied?

Had a look at the engine yesterday and seems the petrol smell is coming from the injector area. (If I haven't been running the engine for long, I can sometimes smell it faintly when I walk around the front of the vehicle - which might explain the smack heads queuing up to sniff my engine whenever I pull up at lights! :D ) A couple of the injectors look pretty old, but they weren't noisy. Is it possible if I had a leaky one, that it would only have an affect when the engine was at low revs.

Whisky - Your right on the masking with higher revs, if I keep the revs around 1.5-2K as I start off and take each gear fairly high, then I don't get the issue. Just concerned in case it's something that may get worse with time.

Cheers again.

[anonymous1]

Hi,

I was considering changing the leads to the sparks in case it is bad wiring that has been causing my issue. I have spoken to the Stealer and they have advised I can't buy individual HT leads, but rather I need a whole new harness and that will be £700 approx + VAT.

Just wondering if anyone knows if this is right or if I can replace/buy individual leads?

Also wondering if I can smell petrol from the area of the injectors if they can be repaired or would I need to replace the suspect one on confirming if it's leaky?

Cheers in advance.

[e34.535i.sport]

Just wondering if anyone knows if this is right or if I can replace/buy individual leads?


Found this bro...

http://www.bimmernut.com/forum/showthread.php?t=33749&highlight=m50+coils

[e34.535i.sport]

Even better...

http://www.bimmernut.com/forum/showthread.php?t=12329&highlight=m50+coils

[anonymous1]

Hi,

I have been looking in to replacing the ignition coils and this seems to be a pretty expensive if I can't work out exactly which one is causing the issue. (If it is this)

I took one of the ignition coils off before and noted that the top of the spark seemed to have a glazed look. Checked the rubber spark plug socket on the bottom of the coil and this appears to have oil in it as well. (I presume this has got there from when the rocker cover was leaking into the wells) Now I'm wondering if the oil could have gotten on the contact point in the spark plug socket? If this was the case, would it potentially cause my low rev hesitation/misfire?

I have checked with BM and they sell this part separately for £8 inc VAT, so not too bad if I do have to replace them. Or would it be OK if I just cleaned them instead (although this could be tricky - cotton buds may be the order of the day) with brake cleaner for example or anything else you can suggest?

I am referring to #3 in this:
http://www.realoem.com/bmw/showparts.do?model=CB12&mospid=47441&btnr=12_0425&hg=12&fg=05

Another thing I am not sure if could be the cause is this hose:
http://img28.picoodle.com/img/img28/4/4/30/f_DSC000921m_88839d2.jpg (http://www.picoodle.com/view.php?img=/4/4/30/f_DSC000921m_88839d2.jpg&srv=img28)

It seems to be loose, but not sure what the hose does and if it matters how tightly fixed in place it is?

Thanks in advance.

[genphreak]

Fix that front hose connector. It has an o-ring that will be undersized now and leaking. You can buy the whole thing from BMA. But do the other one too- the one under the manifold, behind the throttle body. Hint, be prepared to use monkey arms (getting your own arms under there is an art, so trade them with a Chimp for a day). Since this is a BMW, you must also take teh right path and remove the Throttle body to get at it- and that is almost an art too. It's that hard getting under there to re-seat the connector and chk the pipes.

The later M50 connectors might be a better design thatn the early ones. (This has a fat pipe that goes to the ICV). Be sure to check the t-connector under there also, and the small pipes are sealing at the ends and are not cracked.

Don't clean the ICV on an M50 either, best to get a new one. The seals die in them and can't handle cleaning agents.

[anonymous1]

Fix that front hose connector. It has an o-ring that will be undersized now and leaking. You can buy the whole thing from BMA. But do the other one too- the one under the manifold, behind the throttle body. Hint, be prepared to use monkey arms (getting your own arms under there is an art, so trade them with a Chimp for a day). Since this is a BMW, you must also take teh right path and remove the Throttle body to get at it- and that is almost an art too. It's that hard getting under there to re-seat the connector and chk the pipes.

The later M50 connectors might be a better design thatn the early ones. (This has a fat pipe that goes to the ICV). Be sure to check the t-connector under there also, and the small pipes are sealing at the ends and are not cracked.

Don't clean the ICV on an M50 either, best to get a new one. The seals die in them and can't handle cleaning agents.


Thanks for the advice.

Do you know what the pipe is called, so I can locate the part? When you say I can get the whole thing, do you mean including a new hose or just the connector? I have traced the pipe and it seems to connect onto the MAF big hose, there are two hose coming off the big hose at the back of the MAF.

If it's tricky to get the pipe under, then I pretty much have no chance. I couldn't even fit my arms in far enough to sort one of the fuel lines when that was leaking a bit due to the hose clip being a bit lose! I can definately see my breaking something else while I'm there. ;)

I'm cleaning the spark plug connectors that fit onto the coils today, so will let you know if this resolves the misfire/hesitation. (Fingers crossed)

Cheers

[anonymous1]

Hi,

I have taken the coils off and cleaned them, quite alot of dirt on the contacts from what I can make out, so hoping it's this.

However, I have found 4 of the coils have what I think are cracks in them, all seem to be in the same place on each one. Does anyone know if these will need replacing (pics below) and if they do if this could be causing a misfire at the low rev end?

http://img29.picoodle.com/img/img29/4/5/3/f_DSC000931m_22831aa.jpg (http://www.picoodle.com/view.php?img=/4/5/3/f_DSC000931m_22831aa.jpg&srv=img29)

http://img30.picoodle.com/img/img30/4/5/3/f_DSC000941m_83f9368.jpg (http://www.picoodle.com/view.php?img=/4/5/3/f_DSC000941m_83f9368.jpg&srv=img30)

I have found some on ebay for £10 each, as they are from a car that was a breaker so will replace if needed. Although BM charge £65 each, which is just ridiculous.

Thanks in advance.

[anonymous1]

I have now cleaned the coils and also replaced a small fuel hose that I noticed had been leaking (Probably the cause of the fuel smell) and at present haven't noticed the misfire since. Hoping this was the problem and it doesn't return with a bigger and badder cousin to ruin my ride. ;) Although I will still be replacing the connector mentioned by Genphreak in case this is causing any issues.

Thanks for the input on this.

[genphreak]

I have now cleaned the coils and also replaced a small fuel hose that I noticed had been leaking (Probably the cause of the fuel smell) and at present haven't noticed the misfire since. Hoping this was the problem and it doesn't return with a bigger and badder cousin to ruin my ride. ;) Although I will still be replacing the connector mentioned by Genphreak in case this is causing any issues.

Thanks for the input on this.There are three connectors on an my early M50. One goig into the valve cover (front case), two going into the manifold up under where you have trouble getting to them. One is behind the Throttle Body. Remove that and you can get to both alright- but if you aren't really cool with it, just do waht you can get to.

[anonymous1]

Hi,

I have now changed a few more things in pursuit of getting rid of this bang noise, that brings a hesitation with it. These being:

Fuel Pump
Fuel Reg
Charcoal Canister and breather hose
Exhaust manifold gaskets
Exhaust down pipe gaskets
Intake gasket
Crankcase vent fitting
Hose to the ICV, which was cracked
Spark Plugs
Throttle body gasket
Checked coils and showing right voltage in leads and ohms at coils themselves.

Going to be checking the resistance on the CPS, but otherwise I'm stuck for what could cause the bang. Now seems to be coming from the drivers (right) side of the vehicle... Is it possible the Cat could have a block and is blowing back into the manifold? Still seems to be happening at lower revs when I attempt to accel. :(

Any ideas are welcome, TIA. :D

[whiskychaser]

If you are getting the meter out, you might as well have a look at the camshaft sensor too. We know it wasnt chucking any codes but its worth spending a few mins to do both