New (to me) throttle bodies. What are these?

Lots of engines have a "dead spark" at the bottom of the cycle, so actually fire the plugs twice per full engine cycle. It's easier to engineer this, than have another sensor on the cam to decide if the engine is actually on the compression/ignition stroke.

[Sid Squid]

Originally Posted by wideguy

I can't figure out what could actually go wrong with the throttle body itself?

Short of the bodies being physically broken or wearing either the spindles or the bodies where they fit - and you'd have to have a stratospheric mileage for that to occur - neither can I. The throttle body is a tubular bracket that holds the injector, the spindles/butterflies and connects the airbox to the inlet rubber - there's nothing to go wrong.

650 doesn't have a cam position sensor, 1000 does.

[yorkie_chris]

Originally Posted by wideguy

I think the plugs fire on both intake and exhaust strokes. The firing order is determined by the cams and valves.

Yes of course it is.

How does the ECU when initialised know which stroke is firing and which is intake?

It senses the suck as it needs to inject fuel on intake, not on power stroke. No point making a super environmental high-pressure super atomising uber lean burn system... and then gobbing fuel onto the back of a closed valve is there!

[yorkie_chris]

Originally Posted by atassiedevil

Lots of engines have a "dead spark" at the bottom of the cycle, so actually fire the plugs twice per full engine cycle. It's easier to engineer this, than have another sensor on the cam to decide if the engine is actually on the compression/ignition stroke.

Not at bottom of cycle... some degrees BTDC on the exhaust stroke. Curvy works this way. Term is wasted spark.


And throttle bodies themselves are pretty bombproof... it's all the other crap attached that can be problem. Throttle position sensor is massively important, so is STV servo and STV position sensor, injectors etc.

Originally Posted by yorkie_chris

Yes of course it is.

How does the ECU when initialised know which stroke is firing and which is intake?

It senses the suck as it needs to inject fuel on intake, not on power stroke. No point making a super environmental high-pressure super atomising uber lean burn system... and then gobbing fuel onto the back of a closed valve is there!

Chris, I was thinking (as is normal for me) about engines with carbs, which don't need to time the fueling- when they suck, they automatically suck fuel.

If the injected 650 doesn't have a cam position sensor, how does it know when the intake valves are opening? When you say it "senses the suck", that implies that the MAP sensor provides the information for injector opening timing. That seems pretty imprecise.

[Sid Squid]

MAP sensor would give which-stroke-are-we-on info, exact engine position is given by the crank pickup.

[Bibio]

this might help

Thanks Sid, crank position sensor works for me for the basic when precisely to start delivering fuel question.

[yorkie_chris]

Originally Posted by wideguy

Chris, I was thinking (as is normal for me) about engines with carbs, which don't need to time the fueling- when they suck, they automatically suck fuel.

"Carbs good, complicated shi'ite bad."

Works for me too!

[Sid Squid]

Originally Posted by Bibio

this might help

How?