Like a bucking bronco

E28 technical advice asked and given! Troubleshooting, modifications and more.
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krazydog27262
Posts: 16
Joined: Nov 12, 2021 6:50 PM
Location: North Carolina

Like a bucking bronco

Post by krazydog27262 »

I have a problem with my 1985 535i. It drives fine for a while and then it starts bucking as if you floor the pedal and immediately let off several times in succession. I've replaced crank position sensors, fuel filters, fuel pressure regulator and idle control valve. And suggestions would be appreciated. Thanks!
gwb72tii
Posts: 113
Joined: Sep 21, 2021 4:58 PM
Location: Washington state

Re: Like a bucking bronco

Post by gwb72tii »

The car I just purchased exhibits the same behavior if I gave it too much throttle too suddenly.
I think it’s a fuel pump not supplying enough gas under acceleration. I’m putting in an in-tank fuel pump this weekend so I’ll see if the problem goes away and report back.
With my car if I accelerated gingerly there was no problem, only when I tried to give it more gas than the pump will pump, I think.
My car would also just buck and just die when tooling along at 70mph
Mike W.
Posts: 25488
Joined: Feb 12, 2006 12:00 PM
Location: California Whine Country

Re: Like a bucking bronco

Post by Mike W. »

Not likely to be the fuel pump, weakness there is generally like you're running out of gas, because in a way you are. I'd go for a new cap and rotor and maybe spark plug cables. Or at least a very close inspection thereof.
krazydog27262
Posts: 16
Joined: Nov 12, 2021 6:50 PM
Location: North Carolina

Re: Like a bucking bronco

Post by krazydog27262 »

gwb72tii wrote: Dec 04, 2021 2:21 PM The car I just purchased exhibits the same behavior if I gave it too much throttle too suddenly.
I think it’s a fuel pump not supplying enough gas under acceleration. I’m putting in an in-tank fuel pump this weekend so I’ll see if the problem goes away and report back.
With my car if I accelerated gingerly there was no problem, only when I tried to give it more gas than the pump will pump, I think.
My car would also just buck and just die when tooling along at 70mph
Yeah, let me know if this cures the problem. Thanks!
krazydog27262
Posts: 16
Joined: Nov 12, 2021 6:50 PM
Location: North Carolina

Re: Like a bucking bronco

Post by krazydog27262 »

Mike W. wrote: Dec 04, 2021 2:45 PM Not likely to be the fuel pump, weakness there is generally like you're running out of gas, because in a way you are. I'd go for a new cap and rotor and maybe spark plug cables. Or at least a very close inspection thereof.
Will do. Thanks!
gwb72tii
Posts: 113
Joined: Sep 21, 2021 4:58 PM
Location: Washington state

Re: Like a bucking bronco

Post by gwb72tii »

sorry krazy but i won't get to the pump until this weekend
krazydog27262
Posts: 16
Joined: Nov 12, 2021 6:50 PM
Location: North Carolina

Re: Like a bucking bronco

Post by krazydog27262 »

That's cool.
gwb72tii
Posts: 113
Joined: Sep 21, 2021 4:58 PM
Location: Washington state

Re: Like a bucking bronco

Post by gwb72tii »

krazydog27262
Posts: 16
Joined: Nov 12, 2021 6:50 PM
Location: North Carolina

Re: Like a bucking bronco

Post by krazydog27262 »

gwb72tii
Posts: 113
Joined: Sep 21, 2021 4:58 PM
Location: Washington state

Re: Like a bucking bronco

Post by gwb72tii »

sorry to report that the bucking issue I have has not been resolved by replacing the factory fuel pumps with an in-tank fuel pump. funny that it only occurs under load going up hills but not when on a level road, even when accelerating quickly.

I'm shelving this for a while as I can limp to various body shops for estimates on body work before I disassemble the car.

good luck krazy and please report back if you solve the issue
krazydog27262
Posts: 16
Joined: Nov 12, 2021 6:50 PM
Location: North Carolina

Re: Like a bucking bronco

Post by krazydog27262 »

I will. It is exactly the same problem as yours.
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