DIY_EFI Digest V5 #65

[Vladimir Vooss]

As I realize, after lurking here for a long time, that you are mostly 
engineers and designers, I do need a little education, however 
concerning a fuel related drivability problem I have with an '85 BMW 
528e which I haven't been able to resolve  at the local shop level. I 
would like to beg the group's indulgence to help me figure my way out 
of this by either private email or on this forum, if it's not so 
off-topic.

This is a  car I inherited from my sister, which I drove when it was 
hers when I visited my mother in San Francisco, and they would leave 
me the car in the apartment garage to use. It drove fine for an ETA 
engined car.

When I got it it had huge drivability problems: stuttering and 
hesitating while trying to accelerate, bursting ahead kind of 
surging. A bad throttle position sensor was replaced as well as the 
AFM and the idle control unit and its brain. The problem was not 
resolved. I changed out the fuel pressure regulator, all the interior 
fuel hoses (to and from and around the fuel rail) and then lastly the 
transfer and main pumps and the fuel filter. The balls in the 
acceleration returned, and even though the car is not a 
break-your-neck kind of car,it drives well now. However, it sometimes 
sags under hard acceleration, or if the gas pedal is suddenly jammed 
to the floor, the car goes through a stuttering act which is only 
relieved by letting go of the gas pedal and accelerating smoothly and 
progressively. Sometimes, under a sudden, but not warp speed stabbing 
of the pedal, as in an escape maneuver having to be performed to go 
around someone having a big problem and slowing to a crawl in the 
middle of the rest of the freeway, the acceleration vector wil 
suddenly pull back, and then snap forward, as if suddenly gas is 
being rammed down the pipes in bucket-fulls. Acceleration proceeds 
smoothly. I suspect that perhaps the injectors are misbehaving, and I 
though I'd direct my question towards injector behavior. I wouldn't 
mind replacing the injectors if they were indeed the culprits - one 
shop tested them and pronounced that they cycled correctly. I 
understand this concept, but wonder if there are any other 
performance issues that can crop up while "in cycle"? What are the 
noticable systemic behaviors of aging injectors: do they impart 
anything to the fuel flow that would NOT implicate the fuel pressure 
regulator or the opening or closing of the throttle flap? I also 
remember hearing or reading, though I can't remember where or when 
or, most importantly, if this is actually true - that fuel injection 
systems go lean with age and that they have to be richened, so to 
speak to not only improve drivability, but to be able to pass smog at 
the same time.

I'm sorry to have to take the group around this problem, but I've 
exhausted the bmw related forums. I do have a shop here who, I think, 
would be able to work with me to try to trouble shoot this problem 
with all the correct equipment, but I feel I should be armed with 
some real information with which to negotiate this research.

Thanks again very much for your time, and I hope there can be some 
resolution here for me.

Vladimir Vooss
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