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Well was playing around a little 4800 rpms was round 8psi 3/4 throttle and let off. The rpms dropped to 400 or so barely running. Sounded like I had a cylinder down. Wideband pegged lean like a cylinder was just pumping air. Limped home thankfully right around the corner. Hopped on the laptop and fired the injectors found 3rd cylinder wasn't firing. Ohmed it out. Toast. What are the chances it fires back up and it didn't lean that cyliner out and shmoked it. Will one cylinder running dry effect the o2 of the other 3 under load? I like to tell myself it happened after i let off. Ha what are the odds of that.
 

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Hopped on the laptop and fired the injectors found 3rd cylinder wasn't firing. Ohmed it out. Toast. What are the chances it fires back up
Smaller than the chances it fails again.


and it didn't lean that cyliner out and shmoked it. Will one cylinder running dry effect the o2 of the other 3 under load? I like to tell myself it happened after i let off. Ha what are the odds of that.
Considering o2 sensors and widebands sit after manifold collectors and turbos the answer is yes. The O2sensor read the combined and mixed exhaust from all cylinders, the exhaust pulsed from the cylinders 1,3,4,2 but as it bottlenecks into the turbine housing the exhaust pules catch up to each other and get blended by the turbo. Each cylinder fires once during a cam rotation, the came rotates once for every crank rotations, so at 800 rpm (idle) the cam rotates 400 times in a minute and each cylinder gets fired 400times per minute to make a total of 1600 piston combustion per minute or one exhaust pulse every 0.0375 seconds ( that's at idle), At 4800rpm there is an exhaust pulse every 0.00625 seconds.

Look at each cylinder as a value 0-21 and combine them, so say your running 10.8a/f or 43.2 of 84(air) / 4. Do the math again cyl 1 10.8, cyl 2 10.8, cyl 3 21, cyl 4 10.8 = 53.4 of 84 / 4 = 13.35 A/F's.
So ya one cylinder pumping air would give a lean reading on a wideband even if the other 3 cylinders where still rich.

The good news is that air doesn't detonate so without fuel in cylinder 3 the most pressure the cylinder saw was it's compression stroke of forced air, then it released it out the exhaust valve.

The symptoms of something bad happening would be feeling a bit more acceleration in a pulsing manner similar to running with a miss firing cylinder only instead of a no power stroke every 2 rpm it's a more powerful stroke every 2rpm until detonation. As the cylinder leans out it starts to generate a bit more power but does so in a dangerous manner, without extra fuel or retarded timing to keep the cylinder cool, heat builds up and detonation occures, so after the pulsing power every 2rpm comes a pulsing low power stroke every 2 rpms.
Now when an engine is leaned out to the point it doesn't make power, say a low gas tank, full throttle in a corner and the pump draws air and the engine just chokes, or you hit the rev limited and the ECU shuts the injectors down. This kind of lean has very little chance of causing engine damage because there isn't enough fuel in the combustion chamber for the spark plug to ignite making it impossible for heat and pressure alone to ignite.
 

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That makes a lot of sense i appreciate the input! I'm going to buy a new set of injectors with more capacity. I've had these injectors for round 5 years or so. Haven't had an event like this happen before so I didn't know if the engine just grenades that cylinder or not. It definitely makes sense that it should just be compressed air. While I'm waiting on injectors ill do a compression test. What kind of compression would you say is acceptable? Should I be testing the engine hot or cold? Should I use the compression tester gauge indicator as if all engines test compression the same? It sounds like they would. Does valve overlap have anything to do with compression test? I can post the specs to my cam if It does have any effect.

Side note. I'm playing around with my cam regrind, dual valve spring, head again. Tore into the valve train and re primed all the lifters. Theyre all solid now. No ticking noise!!! Need to get it on the dyno to see if the power output is consistent but right now the valve train seems to do fine with it.
 
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