help -i cant get my '92 520 m50 to run right.

[johnboyairey]

hi, i'm very new to this forum stuff, so treat me gently. i bought a slightly underpowered 1992 vanos 520 touring, and as i'm used to old style carburettered cars, all this super hi tech ecu stuff is driving me nuts. -i'm very handy with cars, but this one i'm sure is simple, -(to you chaps. ) the car starts, revs, but has a massive lowdown flatspot, it will rev freely at around 3k to the redline, sounding lovely, but the flatspot, is a bit like a 'cold engine' pull the choke out a bit more, type of revving, (in neutral) . i had access to some substitute parts from a 525 m50 car, (mine is a 520 m50) and i have changed the following. (and back again) -the main ecu in the row of four behind the steering wheel, in fact all four have been changed. the MAF, the throttle position sensor, the camshaft posn. and the crank sensor too. the vanos has been bled, the 6 inch by 1 inch 'black box widget' under the rear seat, it doesn't appear to be an bulk engine fault, more a mapping fault. the timing chain setup has been gone through meticulously, inc vanos chain, and all spot on, . ie flywheel locked, cams dead-flat at the back, pre-tensioner out, vanos removed, and all back as per Bentley book. all cylinders are equal compression. -it is auto, and if i stall test it, i can only get 1500 rpm. (cold and hot) doesn't use water, overheat, smoke, missfire, could it be the actual gearbox? its not stuck in third, (limp) the flat spot is present during revving and driving. fault is from cold start so dont assume the lambda. hasn't got a cat i dont think. what about something like the widget that tells the car its cold and should richen, or the reverse. -though it does it cold and hot. it doesn't have a OBC so cant get any hints, also, i'm miles from a mechanic with a code reader, and it's undrivable, (no mot) if it cant be sorted in the next couple of weeks it's in the small ads. tidy red metallic touring, 124k, grey cloth. damm thing! i'm now getting a cold beer! any directions lads, -please!

[DaveVoorhis]

Not sure I'm following here... You mean it bogs out and doesn't develop power before 3k? Have you checked for intake and valve cover gasket leaks?

[johnboyairey]

Not sure I'm following here... You mean it bogs out and doesn't develop power before 3k? Have you checked for intake and valve cover gasket leaks? yes, gutless, to around 3k, nippy after that. checked for leaks, intake mani. off, and on, MAF hose checked.

[DaveVoorhis]

Have you compared its performance to any other 520i Tourings? My 525i is pretty sluggish below 3k; I imagine a heavier 520i would be worse. Or is it bucking, chugging, rough, takes all afternoon to reach 3k and then surges ahead, etc.?

[johnboyairey]

Have you compared its performance to any other 520i Tourings? My 525i is pretty sluggish below 3k; I imagine a heavier 520i would be worse. Or is it bucking, chugging, rough, takes all afternoon to reach 3k and then surges ahead, etc.? i have bought another touring since, a manual 525i -superb. very free revving, not a rocket, but nice. this 520 t in question is very poor, i just want to fix it,, and let someone else enjoy it now. takes the morning and afternoon to get going. same when revving, Is there a symptom of a poor torque converter? i have been told it's a perfect or nothing sort of part, but just keeping all ideas in the equation. could the cold engine think its warm and map a warm mixture? trouble is, it's the same when hot! -not really chugging or bucking, or banging, when high revving, exhaust rasps like a good engine, not a mufffled boom. have tried vanos disconnected, -no real difference but assume thats not the problem, as redundant at low revs. - am i thinking right, willing to try anything, has become a small crusade of understanding the modern car.

[DaveVoorhis]

A manual 525i is a completely different beast from an automatic. I used to have an auto M20 525i -- very sluggish until the revs built. My non-VANOS manual M50 525i is kinda weak below 3k, but just fine above it. All the small six BMW engines are vaguely reminiscent of two-stroke motorcycles -- the power is only found in sufficient revs. Also had a manual E28 M20 520i -- it was equally inclined to do snail impersonations until the engine built up a head of steam. An auto 520i touring would, I expect, be ponderously slothful until that heavy flywheel gets a good bit of spin in it.

Is it reluctant to rev even in neutral? Checked the fuel pressure and fuel pressure regulator? Changed the spark plugs?

One other thing: Are you sure pressing the throttle all the way opens the throttle body fully?

[johnboyairey]

thanks for replying, but we are not trying here to get more boy racer power, just trying to drive it is nearly impossible. -i was aware of the fault, when i bought it, and figured it would be an afternoons work. . yes, the throttle opens wide, and there is no slack etc. i will substitute the fuel pump and regulator components tomorrow, if its not raining. you're right, the manual is a drivers car, -the engine is so giving, and free-revving. with just a tiny amount of pedal for lots of noise, compared to this faulty auto car, which needs a much firmer press to get high revs. i'll also change the induction componats over too. perhaps a hairline crack? however it would seem to me to be an obvious hose off, or wrongly connected one way valve or something. - have oyu any thoughts on a small plug in componant on the nearside innerwing, with a small 10mm hose going to the engine? sits behind the airfilter box. that is clicking, i seem to remember. I may have overlooked that, -i'll have a look in the bentley manual. -however, mine is only an amarican 525i-530i pdf version. is there still a 520i 1992 one online. ????

incidentally,, can the manual stick in the 525i be adjusted to the right, as it seems way too over to the left, with a bit of a loose feel. 1st is where you would try for reverse. 190k miles though, and FBMWSH, perhaps set up for left hand drive? mine is right hand drive, uk car. anyway, i digress, i'm more interested in sorting this 520i m50 have another read from the start. -john

[DaveVoorhis]

Have you tried the coils from your parts car? Checked intake vacuum? Checked for exhaust system restrictions? Made sure a leaky valve cover gasket hasn't flooded the plug wells with oil?

Not sure about the component on the inner wing without seeing a picture, but it might be the purge valve for the charcoal canister.

I'm not aware of any alternate versions of the Bentley manual. A 520i is essentially the same as a 525i, anyway.

Sounds like the stick in the 525i has worn bushings.