1991 E36 318i with M40b18 engine misfiring anywhere past 5k revs help!


Thread: 1991 E36 318i with M40b18 engine misfiring anywhere past 5k revs help!

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  1. 1991 E36 318i with M40b18 engine misfiring anywhere past 5k revs help! 
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    kizerfluid's Car Details
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    Hi everyone once again i am back with another BMW issue i can't work out.

    First i will start you off with a little history of the car so you can see it from my point of view:
    it has been very well looked after and it on 133k miles body work is dent and rust free and only has very minor scratches. For a 25yr old car its driving like a 4 year old car brakes are really good and work as soon as you touch the pedal clutch engages nicely and bites just under half way on the pedal, steering is nice and tight and its just sailed though its MOT with no advisory's.

    I have service history dating back to first purchase and its been serviced ever 5k to 8k miles up to 128k Engine was replaced by BMW under warranty at 40k miles so engine only has about 93k on it Cam belt has been changed ever 25k - 30k miles last changed at 104k

    It only has one annoying issue and i assure you i have spent the past 4 days googling trying to find the answer to this issue but it seems like no one else has had this exact problem.

    Up to 5k revs the car drives fine but as soon as i hit 5k revs the engine loses all power and starts misfiring to the point of where it will not accelerate any further even if in neutral also i have noticed at the point of where it starts misfiring it puffs smoke out the exhaust like its running lean.

    here is the tests iv run:
    driving in gear it will hit 5k revs and lose all power and won't accelerate any further and when i come off the accelerator it will continue to misfire for a short time then go back to running fine.
    in neutral if i slowly rev the car it will hit 5k and start misfiring and won't rev any higher when i let off it will misfire for a short time then return to normal.
    in neutral if i floor it from idle i can get the revs to 6k and have managed to hit its limiter once doing this method but the engine really is not happy upon letting off using this method the engine will not return to idle and will stall upon trying to restart the engine will crank over and extra 1/2 times before firing up and idling normally.
    if in gear and going down hill the revs will pass 5k but the engine will be supplying none of the power and as long as kept in gear when slowing down after a lot of juddering and misfiring the engine will return to normal if taken out of gear it will not return to normal it will stall.

    from the research i have done i have ruled out the diff speed sensor as from what i understand it will limit the revs to 5k in gear but in neutral it will allow the car to rev normally

    from the symptoms i am more inclined to think this is a fueling issue rather than electrical and i am suspecting a failing fuel pump / fuel filter / fuel regulator that when the engine reaches 5k rpm something is stopping the fuel rail being pressurized to 3 bar / 2.5 bar

    the only other things i can say i have noticed which are out of the ordinary are when at idle the car fluctuates in rpm very slightly to the point of where the rpm dip dose not effect the rev counter and you can only notice it if stood by the exhaust and are listening for it. Also on 2 occasions now after throwing the tail about a bit the engine will idle at 2k rpm and will not come back down unless i turn off the engine and restart it and even then (its done this both times its happened) the 1st time i restart it. it will idle at 1.5k so i will turn it off and restart it again and it will idle normally (just below 1k)

    Anyone think of something other than a fueling issue here? i am stumped and don't have a fuel pressure tester to test if it is a fuel pressure problem.

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    tonyfox's Car Details
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    e34 525tds
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    Sep 2010
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    Had this several times in my BMW indi garage .

    had it down to a quick diagnosis except once, get to that later.

    Drop the 4 bolts on the exhaust downpipe leaving a gap to eliminate exhaust back pressure, go on a quick test drive and see if problem solved. If it is the problem is obvious, blocked exhaust luckily usually rear box especially if after market.

    That will represent the 20% of the cured cars.
    Now for the usual problem,(you must eliminate the exhaust first) ,
    Worn camshaft lobes!
    Remove the rocker cover (5minutes) and look at the lobes, flat , excessively shiney = worn out due to mileage and the oiling tube being blocked.
    Retired now or would give you the measurements of a "good camshaft lobe", you could ask to see a new one at gsf or ecp's and quickly measure the height. Dont be fooled by looks alone as I have seen many that looked and sounded ok, measure and replace camshaft (1 hour) and Vroom Vroom again! 80% of the cars.
    Not saying a fuel problem couldnt cause this, assuming the filter has been replaced within normal service regime , just never saw one in 20 years.

    Saying that I did have a "faulty" replacement camshaft that was being replaced due to a blocked oil tube and noise, but car had full performance.
    Many tests including reinstalling the old camshaft proved that the new camshaft was the correct lobe height, but the "timing" was wrong, obviously a cheap aftermarket one.
    Replaced with another new one and vroom vroom again.

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