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Spark timing all over the place at high RPMs (Distributor)


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Hi,

 

At idle the timing is very steady at about 15 degrees advance, however when I rev up to >4000 RPM the timing jumps between 30 and 40 like crazy. 

 

Is this expected for a distributor based system?

Car is a 1980 280zx. The distributor uses a IC to create the pulses for the coil (not mechanical points).

 

I have a new engine that is prone to detonate due to high compression and bad head design. I am worried that it will start detonate when the timing is all over the place like this. 

(I do have megasquirt and potentially parts for a spark control install, just no time to install it).

 

 

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2 hours ago, turbogrill said:

Hi,

 

At idle the timing is very steady at about 15 degrees advance, however when I rev up to >4000 RPM the timing jumps between 30 and 40 like crazy. 

 

Is this expected for a distributor based system?

Car is a 1980 280zx. The distributor uses a IC to create the pulses for the coil (not mechanical points).

 

Not expected, and I vaguely recall we had an issue where a bad ignition module on the Mustang had similar symptoms: base timing was fine but it fell apart when it tried to advance.

 

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Does it have vacuum advance? If so is the vacuum stable at while you are seeing the erratic ignition timing?

Maybe remove the vacuum advanced hose and see if the timings stable?

I am looking at a spec for a 1981 280zx manual I have and it looks like the total ignition timing can vary almost 10 degrees on a nominal system.......... FYI.

5aad7a40be821_280zxIgnitionTiming.PNG.7b42a64e4293385c43f4c284272f1c66.PNG

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2 hours ago, Hassan said:

Does it have vacuum advance? If so is the vacuum stable at while you are seeing the erratic ignition timing?

Maybe remove the vacuum advanced hose and see if the timings stable?

I am looking at a spec for a 1981 280zx manual I have and it looks like the total ignition timing can vary almost 10 degrees on a nominal system.......... FYI.

5aad7a40be821_280zxIgnitionTiming.PNG.7b42a64e4293385c43f4c284272f1c66.PNG

Jumping around by ten degrees isn't the same as have a range to set the timing in.

 

2-3 degrees movement is about all you should consider normal.

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Back when I ran I distributor I just welded it. In the engine speed ranges we use on the track centrifugal or vacuum advance doesn’t really do much for you. Even now that I have ECU controlled timing with a pretty 16X16 table to set the timing, if I run a histogram of timing after an on track session it hardly ever varies from maximum wot timing.

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