help understand timing of fuel deliver

[jeff huffman]

I am trying to understand how the Timing works. On a sbc the timing gears line up dot to dot on compression. Which is at the start of the intake cycle. So when putting in the distributor you turn the crank 360 which opens and closes the #1 intake and that puts fuel charge in the cylinder and then it fires on compression strock. Which puts the dots on the timing chain both at 12 oclock. Now on the gn national the dots in line at crank up and the cam dot down should be the start of the intake cycle. Is this when the injectors start the fuel charge and after the the intake cycle after the 360 on the crank it fires through the ecm with the timing marks at 12 oclock on both gears? Just thinking the timing set on the crk sensor at the start of the intake cycle is when the injectors should start . Is that why you set the cam sensor with gears at 12 oclock crank and 6 oclock cam?

 

[No disintegrations]

Use a book to find correct cam installation marks. Many if not all American pushrod engines are done in a very similar way. The marks can be in diff spots but it's still tdc compression stroke.

Turning the engine is done to double check you work. The intake should open then close then you should feel compression. Then the exhaust should open then close immediately followed by the intake opening again.

 

[jckcolarusso]

Buick vortex that will help u

 

[Nick Micale]

I...... . Is that why you set the cam sensor with gears at 12 oclock crank and 6 oclock cam?

We do NOT set the cam sensor with the gears at 12 and 6 which is TDC on the compression stroke, it is set at 25 degrees After Top Dead Center on the compression stroke.

Like was said, check it out on Buick Vortex.

 

[earlbrown]

Lining up the dots is for setting the cam timing. (and the correct way is with a degree wheel.

The cam sensor is set to deliver a fuel shot right as the intake valve opens. It's called a cam sensor but it actually sets the fuel timing based on crankshaft degrees.

That's why big long duration cams respond better when you give the sensor an extra 1/16th of a turn or so. It keep the intake valve from cracking open and sucking a dry shot of air before the injector gets on the clock.

 

[jeff huffman]

I understand the the Timing of the gears and timing of the injectors. I guess the real question is sbc you are setting firing of plug after intake closes but the buick you are timing injectors to spray at the beginning of the intake valve opening. Is this correct?

 

[jeff huffman]

Next question is. Has anyone ever her timing gear threads pull from the cam or is it usually the the bolts stretching. Mine was the bolts?

 

[gunzandgearz]

I understand the the Timing of the gears and timing of the injectors. I guess the real question is sbc you are setting firing of plug after intake closes but the buick you are timing injectors to spray at the beginning of the intake valve opening. Is this correct?

I think you are talking about two different things, and when you talk small block chevy are you talking old school carb or modern efi, also what generation efi as these don't work the same either.In any modern day fuel injection engine, or at least all of the ones I have worked on the crank sensor is responsible for telling the computer when to fire the plugs and the cam sensor is used for firing the injectors, and this will be done at different times for obvious reasons.

 

[bison]

Since we're talking about fuel injection timing the reference point that was used for service is 25* ATDC compression. As most know the fuel injection timing has little to do with anything. It can be off and it won't effect how the car runs much at all. Maybe noticeable to some at idle but most wouldn't know otherwise. If the fuel is injected on the exhaust stroke it will just sit on the valve waiting for it to open. If the cam sensor is too far off the spark timing will be at the wrong time. This will be very noticeable.


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[jeff huffman]

Got it thanks everyone!