turbogrill Posted March 9, 2018 Report Share Posted March 9, 2018 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). Quote Link to comment Share on other sites More sharing options...
mender Posted March 10, 2018 Report Share Posted March 10, 2018 Check the distributor for wear by pulling off the cap and moving the shaft around. Shaft end play and side play should be less than 0.020" and preferably 0.010". 1 Quote Link to comment Share on other sites More sharing options...
Craig Posted March 10, 2018 Report Share Posted March 10, 2018 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. Quote Link to comment Share on other sites More sharing options...
rod rammage Posted March 10, 2018 Report Share Posted March 10, 2018 Does it have spring loaded mechanical advance weights? (sorry, it's been years since I worked on on one of these). Quote Link to comment Share on other sites More sharing options...
Eman911 Posted March 10, 2018 Report Share Posted March 10, 2018 How is the dizzy driven? Check chain/belt/gears. 1 Quote Link to comment Share on other sites More sharing options...
Hassan Posted March 17, 2018 Report Share Posted March 17, 2018 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. Quote Link to comment Share on other sites More sharing options...
Bandit Posted March 17, 2018 Report Share Posted March 17, 2018 I'm surprised the factory shows a spread like that at 2500. However, it should all be in by 4000, so I'd look at tolerances like Mender mentioned. If the shaft wobbles it'll give you off the wall readings. 1 Quote Link to comment Share on other sites More sharing options...
mender Posted March 17, 2018 Report Share Posted March 17, 2018 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. 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. Quote Link to comment Share on other sites More sharing options...
Black Magic Posted March 18, 2018 Report Share Posted March 18, 2018 Make sure the vac advance is pulled off for your test. Quote Link to comment Share on other sites More sharing options...
Team Infiniti Posted March 18, 2018 Report Share Posted March 18, 2018 The centrifugal mechanism is all sloppy and needs rebuilt? Quote Link to comment Share on other sites More sharing options...
mhr650 Posted March 19, 2018 Report Share Posted March 19, 2018 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. Quote Link to comment Share on other sites More sharing options...
Ogren-Engineering Posted March 19, 2018 Report Share Posted March 19, 2018 The Nissan has some fancy coil module and a specific coil. Swap the module and coil and see if it changes. I have had faulty coils bounce the spark around. The actual distributer has two trigger wheels or one? I also have the factory shop manual for 5$ and shipping. maybe 20$ total Quote Link to comment Share on other sites More sharing options...
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