Quote:
Originally Posted by NoBozo
Here's the Falacy about inadvertantly flooding the cylinders with fuel: ALL the other cylinders are OPEN to atmosphere via wide OPEN spark plug holes. The piston going down will be sucking air IN through the ALL the open holes...therefore there will be no..or very little "Suction" at the carburetter throat capable of introducing fuel into the engine via the carburetter jets.  NB |
This is true on a naturally aspirated (carbed) engine, as a rule it's a good idea to pull all the plugs when conducting a compression test however it's not necessary per say. If the other plugs are not pulled and the throttle is held open the influx of gas is more of a problem. However there is no benefit to holding the throttle open so therefore no need to do it in the first place.
Quote:
Originally Posted by NoBozo
PS: Fuel Injection "may" be another story..depending on the Type of fuel injection system AND it's computer..??..controls..
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Fuel injection is a different story, soon as the ignition is on the fuel pump kicks on providing gas pressure to the injection system. As a former factory trained tech for Toyota I can only comment on how Toyota does things.
Now when throttle is opened - the throttle positioning sensor relays this to the computer which in turn adjusts several systems as a result - including the delivery, open/close timing, and amount of fuel the injectors fire. Since Toyota primarily uses multi port injection each individual cylinder has a dedicated injector that delivers fuel directly into the combustion chamber. Yes it is possible to flood excessive fuel into the cylinders in this kind of setup therefore care must be taken not to over crank the engine.
Throttle body injection systems are much different in that it's a bastardized carburetor, where the naturally aspirated pressure to deliver gas through the jets from the float bowl is replaced with fuel injectors that deliver product directly into the throttle body. This system still is highly dependent on negative air pressure from the cylinders (suction action) to mix and expel the mixture through the intake to the cylinders. Since it is fundamentally less efficient the use of throttle body injection at least in regards to Toyota was abandoned in early 90s not that it was widely used in the first place. With the plugs out of the engine this kind of injection system is less likely to flood the engine.
One way around the flooding problem on a EFI equipped vehicle is to pull the EFI fuse so the injectors won't fire and the fuel pump will not kick on. Of course when you're all done you'll have to clear the CEL (check engine light) or MIL (Maintenance Req'd light) which will illuminate due to error codes from disconnecting stuff.