out of ideas on hesitation problem

[fatalvipe]

I've got a 1989 manual transmission, bmw 525i. Upon heavy acceleration, at approxametly 3500 rpm in 2, 3 and 4th gear the vehicle jerks and hesitates until it passes approx 4000 rpm. The throttle being depressed further does not alter the rpm at all. However if I accelerate at aprox. 1/2 throttle moderately, it feels fine and has no acceleration problems. Any ideas?

[ShadeTreeBill]

I have an 89 525 auto, but have not had the problem you describe. However, what I think I am hearing is that normal driving is OK, but when you try to accelerate (to pass someone, for ex.) the car jerks, hesitates, until it hits 4000 rpm? Then it runs smooth?

I have fixed a lot of different problems on my car. Most recently a fuel pump that died. The car would not start at all, and there was no fuel delivered to the injectors, even though the fuel pump motor was running. My car exhibited hard starting for months before the pump died, and when I put the new one in, not only was the hard starting fixed, but I noticed that the car had much better acceleration response. The pump had been marginal for years literally.

I have heard that poor fuel pressure can contribute to this kind of problem. When the demand for fuel spikes (acceleration) the pressure drops dramatically until the pump catches up. Then runs OK again.... Fuel pressure regulator comes to mind, certainly easier (and cheaper) to change than the fuel pump. A fuel pressure test could be done to make sure you don't waste the $250 on a pump if you don't need it.

I suppose the fuel filter also could cause this. Even cheaper than the regulator, but a little harder to change. You have to raise the back of the car.

Have you replaced any parts trying to fix this?

[fatalvipe]

just figured out the problem. Thanks for the input. It turned out to be a bad ignition coil. No visual signs of it being bad however upon doing some forum searches it was a good idea to try.