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In theory....no spark = boom?

Mbeas96

Mbeas96

Member
Joined
Aug 7, 2017
Location
Charleston
What happens when you lose spark during boost?

Cylinders that don't have spark get washed in fuel, then when spark comes back it hopefully burns it away? Can't be healthy...

But what dangers does this have? Any difference in losing spark at 1psi rather than 14psi? It can't knock if there is no spark right?
 
Knock is not your only enemy.
A wet cylinder contaminates the oil.
Unburned fuel in the exhaust may lead to a muffler explosion.
 
Generally, a gasoline engine is not going to knock if you suddenly lose spark. Just not enough compression to ignite the fuel without a plug. Now, if the tune is **** then yes, you could get knock without spark but let's assume everything works like it's supposed to.
 
If the spark comes back after some fuel delivery you'll have an epic backfire that may damage all sorts things from the valves all the way to the exhaust.
 
lummert said:
The fuel pump relay may shut off the pumps if there's no spark.
Click to expand...
Only if the engine RPM falls to zero though. If you're coasting down the road in a manual trans car it would keep fueling as it doesn't know it's lost spark. More modern vehicles would shut off individual injectors if the per-cylinder missfire counter indicates incomplete/improper combustion.
 
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A stock EMS would probably just result in some raw fuel getting pushed/sucked out of the exhaust port on the 4th stroke. If the cat is hot enough it may ignite downstream of the header. My 940's old EMS had some sort of weird boost cut that either retarded the timing so much that it was igniting on the 4th stroke or the turbo was hot enough to light that **** up because that car had some truly epic fireballs at boost cut around 6500 rpm. ****ty chinese turbo/wastegate...
 
With Bosch Breakerless, as an example, with a manual car, if you lose spark, the tach drops to zero. Fuel pump relay shuts off. It will continue to run, as long as the transmission is coupled to the crank and the wheels are spinning. Just does full-on engine braking. Dealt with a random no-spark issue on an '82 242Ti. Ground wire for the ignition box was corroded to heck. The constant idle system did open the idle air valve a bit more when the spark dropped out, since that system wasn't receiving its signal.
 
John242Ti said:
With Bosch Breakerless, as an example, with a manual car, if you lose spark, the tach drops to zero. Fuel pump relay shuts off. It will continue to run, as long as the transmission is coupled to the crank and the wheels are spinning. Just does full-on engine braking. Dealt with a random no-spark issue on an '82 242Ti. Ground wire for the ignition box was corroded to heck. The constant idle system did open the idle air valve a bit more when the spark dropped out, since that system wasn't receiving its signal.
Click to expand...

Forgot the tach ran off the coil rather than the crank sensor. Good call
 
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