Bill51sdr

Here's one for you gang! When I encounter relatively minor bumps accelerating at WOT, the engine will hesitate, almost feels like the timing is being retarded for a time. My initial reaction to this is the knock sensors are at the root of this problem and are reacting to the sharp jolts going through the driveline. Perhaps the knock sensors are in need of replacement, but just wanted to see if anyone has BTDT, or has any other suggestions/theories. Thanks!

Fogey1

Loose ground wire somewhere? Anything else flicker?

Will

Bill51sdr

Nope, engine doesn't cut out. just feels like it's lacking power when the rear axle hits the bumps. Recovers seamlessly after the bumps are traversed. No flickering or any other untoward behavior.

T_MaX

With tires on the wheels and a good set of motor mounts, I can hardly imagine road vibrations being able to effect the knock sensors.

I guess maybe if the were just laying on top of the motor loss.

Another good thread to keep my eye on, Bill I hope you get some good replies!

Steve J.

Same thing happened to me. Had me stumped for quite a while. Turned out to be the fuel pump relay. Reseated in the socket and all was well.

Bill51sdr

Thanks Steve, I'll add that to my list of suggestions, at the very least I'll swap it with another one.

drnick

...mine was either the lh or ezk relay and took ages to track down after repeatedly changing the fuel pump relay!

Bill51sdr

Ha! Nick!

I had a problem that turned out to be the EZK relay on another 928S I owned previously. The relay was cleverly disguised as the 'Fuse Tester' and silly me, just never occurred to me that it was in fact a (mal)functioning relay Some lessons we learn the hard way. May have to go through and replace a few relays just to be safe.

TroppoShark

Thanks to this thread, I've just eliminated this problem in my shark today.

She just wasn't developing full power, and every time I drove over bumps or corrugations she felt like there was an ogre behind, tugging on a rope (in 'Twilight Zone' manner, I looked, but couldn't see him). A few times she even stalled. Seemed to be gradually getting worse.

I started thinking about going through the tests in chapter 28 of the WSM Ignition System, but found this thread first.

Turns out that Red plug X (power supply for electronic ignition and LH fuel injection; very bottom right hand corner) was not fully pushed in, but sort of leaning out by 15 or 20 degrees.

I've recently had an immobiliser fitted, so I think that's how it came ajar.

Pushed it in firmly, and went for a long test drive.

Sweet again...

Cheers,

Phill.