Slight Misfire and Loss of Power When Hot

[seech]

Guys, anyone experienced a slight misfire and loss of power when the engine is hot? When my E34 M50B20 gets hot (hot day, jam, etc.) it develops a very slight misfire when idling and the power just disappears. Floor the throttle and it just accelerates very slowly.When cold no such issues. Power good (for a M50B20 anyway....).Anyone got any ideas what the issue could be? Thanks.

 

[teejay]

check your ignition coil rubber boot/sleeves, when hot, possible crack in boot could lead to current leak

 

[anakin]

check your ignition coil rubber boot/sleeves, when hot, possible crack in boot could lead to current leak

I always luv this guru...I always gain something by reading your post...hidup bro Teejay!!!:rock:

 

[seech]

thanks teejay, misfire doesn't occur all the time but will check it out.

 

[teejay]

thanks teejay, misfire doesn't occur all the time but will check it out.

which is exactly morre likely it would be the faulty boot/sleeve, heat conducts electricity better at higher temp due to energy that agitates the surrounding air causing better conductivity of dielectric materials, this case the boot is torn so heat would also expand the part rubber part plastic causing leak in electricity flow- which means the spark plugs dont fire or has a weak spark.this is very common in the older m50 engines. only setback is it could be caused by 1,2,3 cylinders at any one time, thus you hae to change all 6 just to cover for 1 or 2 torn boots, and sometimes you wouldnt be able to see the tear.

 

[ess530i]

can anyone tell me the signs of a misfire? i think i'm experiencing misfires but cant be sure. during acceleration the car seems to jerk slightly off and on. i suspect its my new spark plugs

seech, check your plugs...

 

[fssiaw]

Hi,
I think I have misfire as well, sometime ago, It happens quite frequently. Ihave changed the ignition coils but not all 6. mechanic checked the car but concluded gear box problem. is it or is it not?
sifus, any suggestion on how to determine the coils are malfunctioning?

worry about gear box.

thanks

 

[teejay]

Hi,
I think I have misfire as well, sometime ago, It happens quite frequently. Ihave changed the ignition coils but not all 6. mechanic checked the car but concluded gear box problem. is it or is it not?
sifus, any suggestion on how to determine the coils are malfunctioning?

worry about gear box.

thanks

the coils have a resistor value, i can't remember off hand the values, but it can be measured by a digital ammeter

measure the values and the ones that are off, is probably spoilt
did you check the rubber boot when changing the coils?

 

[johnathan540]

Got a picture to show of the rubber boot? My m20b25 has been tuned quite a few times but I'm experiencing loss of power, unstable idling (up and down like having high-cams) and a slight dip when accelerating lightly. Even the tappets sounds louder and I've just overhauled the engine. Again, when its cold everything is fine, but once I use the car for like 20 mins, it starts acting out. Very frustrating. Pls help and sorry for disturbing your thread bro.

 

[teejay]

Got a picture to show of the rubber boot? My m20b25 has been tuned quite a few times but I'm experiencing loss of power, unstable idling (up and down like having high-cams) and a slight dip when accelerating lightly. Even the tappets sounds louder and I've just overhauled the engine. Again, when its cold everything is fine, but once I use the car for like 20 mins, it starts acting out. Very frustrating. Pls help and sorry for disturbing your thread bro.

jonathan,
please go search the forum on the m20 problems, this particular problem has been discussed before. M20 and M50 have different approach when solving certain problems, and i won't be answering your problem here in this thread

 

[fssiaw]

Thanks Teejay,

I will ask my mech to check the rubber boot.

cheers

 

[pyccce]

I've a similar case with my car E46 325! After changing my plug,oil and valve cover gasket.Still happen again.And I've even check the coil no crack what so ever.Can anyone help me on this?Thank u

 

[ALBundy]

IN my case, it was the ignition coils. Replaced two of them after swapping in and out over a period of one week to determine which one was faulty. The tricky part was, the misfiring was sporadic, so I had the tools and spare coils in the car and once it misfired I would do the elimination process to determine the bad coil.

Cheers

 

[3er]

This happens in my M54 when it was only a couple of years old also. Usually when i'm sitting idle in traffic jam for a long while then accelerate. It usually clears after i give it a good kick. A good >4000 rpm kick! Not that it eliminates the problem, it still happens every now and again when i idle for too long.

 

[seech]

teejay, my misfire was ok for some time after my first posts but started to get quite bad last week. Usually its just some slight hesitation then its ok but last week there was actually a jerk so decided to bite the bullet and get it done. Changed all 6 boots. Changing the boots was inexpensive and easy to do but the results have been amazing. Idling is smooth and no more hesitation. Power still not good when engine is hot but at least no more hesitation.

Many thanks for the advice. TQ TQ TQ. :top:

BTW, if the coil itself fails would the symptoms be the same or would the cylinder not fire at all?

which is exactly morre likely it would be the faulty boot/sleeve, heat conducts electricity better at higher temp due to energy that agitates the surrounding air causing better conductivity of dielectric materials, this case the boot is torn so heat would also expand the part rubber part plastic causing leak in electricity flow- which means the spark plugs dont fire or has a weak spark.this is very common in the older m50 engines. only setback is it could be caused by 1,2,3 cylinders at any one time, thus you hae to change all 6 just to cover for 1 or 2 torn boots, and sometimes you wouldnt be able to see the tear.

 

[teejay]

you'll get more hesitation and rough jerks, almost to the pint of cannot drive, but if its just 1 cylinder, then it wont be noticeble at high revs.
Suggest you get your spark plugs check, if power is not so good when hot, 1st thing to check are the plugs as you may have stretched the life alittle too long becuase of the earlier misfirings

 

[seech]

will do.... master teejay....

any recommendations on the plugs?

must listen to see foo more closely.

 

[teejay]

will do.... master teejay....

any recommendations on the plugs?

must listen to see foo more closely.

use original ratings or similair heat range ratings
do a search on performance s.plugs , but keep it within the heat range unless your engine has a modified performance heat range, i.e. bigger injectors, F.I., adjustable FPR, etc

if you dont use the proper plugs, it will affect your engine in along run.....