Twin/ Dual Points on Auto' 240Z with emission control. Switch to EI ?

[jed]

Hi,

Does anyone have thoughts on or knowledge of fitting electronic ignition on a (72) 240Z Automatic with Cali' emission control.

I found this thread (shown below) from 3 years ago which tells me that switching from dual points to EI using a unit from the 280ZX is possible but will having emission control cause an issue?

http://www.classiczcars.com/forums/electrical-s30/38049-duel-points.html

I'm trying to cure a mis-fire. When the car came from the US, it had some US fuel in it and ran smoothly. I put in some UK 95 Octane fuel which I think converts to 91 RON and soon after it began to mis-fire. I've put in some premium unleaded, 99 Octane, but no improvement. It has been for a tune-up, the valves had to be adjusted, the front carb was sooted so this was cleaned up. I'm told that the timing is correct and that nothing was found to explain the problem. The guy who did it has been tuning for 50 years though it seems that the car with dual points and emission control confused him a bit. As well as a mis-fire it will back-fire from the exhaust when revved so I suspect un-burnt fuel is escaping into the exhaust. It doesn't back-fire from the carb. It drives OK, the problem comes at idle and when revving stationary.

I'm thinking that EI will correct this and give a stronger spark.

Any thoughts?

Thanks.

[djwarner]

The dual point distributor work in conjunction with a relay and a temperature switch mounted near the thermostat. The two sets of points have one set advance and one set retarded. When the engine coolant is at low temperature, the switch controls the relay and only the advance set of points receives current.

As coolant temperature increases, the relay also passes current through the retarded points. When the advanced points open, no spark is created because current is still flowing through the retarded points. When the retarded points open, the advanced points are still open so a spark is created. The references I have vary. Both Chilton's and Haynes give the dwell angle for both points at 35 to 41 degrees (a gap of .4 to .5 mm).

Chilton's says the retarded timing will be TDC for temperatures above 30 degrees F and the advanced timing 10 BDC @ 600 RPM for temperatures below 30 degrees F. I suspect this to be in error as there is supposed to be a 6 degree timing difference for the two sets of points.

Haynes says to set the timing with the vacuum line disconnected and the retarded timing set to 10 BTDC and the advance timing set to 16 BTDC. For you mechanic, Haynes says Centrifugal advance starts at 550 RPM and max's out at 9 degrees at 1200 RPM. Vacuum advance starts at 3.94" Hg and max's out at 7.5 degrees at 13.0" Hg.

From what I've learned, you should normally see timing at 10 BTDC at 650 RPM warm. If you have a miss at timing I'd look elsewhere.

I have an electronic ignition distributor from a 1979 280ZX mounted in my 1970 A/T and it works fine though I don't have emissions testing in Florida. The distributor part number is D6K80-031103 and the Nissan part number is 22100-P7901.

[Stanley]

Wow good explanation, always wondered how that worked. Had the stock dual point on my 73 AT. Took forever to start. Put a 72 single point - works good.

[jed]

Thanks for taking the time to reply, the explanation makes me suspect that the emissions don't have any part in the timing/ ignition.

Earlier, I put a strobe light on the crank and had about 17 degrees BTDC whilst the engine was cold (Advance points). I didn't disconnect the vacuum line and plug it to check the retard. I have problems getting the engine warm to temperature as the fan is seized on so checking the retard is difficult plus the tacho isn't working.

I'll have to read up and try to understand the dwell angle adjustment between advance and retard. I don't think I can be satisfied with the timing until I'm certain I've got the distributor adjusted correctly.

I checked the part numbers supplied, Nissan over here want $1K for the distributor new and the other number didn't come back with any listing though D6K8-003 comes back as a 79-81 280ZX distributor with vacuum advance.

I'll consider installing a standard 240Z distributor with a modern EI such as the Petronix, I've read that this combination is more reliable than the 280ZX unit.

Thanks again.

[Stanley]

There's this:http://www.zcarsource.com/distributor-240z-70-73-manual-transmission-rebuilt-de_8_77854_54132.html

[Captain Obvious]

Probably not directly applicable, but here's some info on how the temperature switch works and it's affect on timing, etc. Might be some stuff in here that helps.

http://www.classiczcars.com/forums/electrical-s30/46647-water-temp-switch-what-does.html

[Stanley]

Checked my 72 engine manual - it says dual points were for emissions spec AT's only. AT's elsewhere used single point same as manual. Non-emissions AT's set timing at 17 deg at 700rpm in neutral, manual trans 17 deg at 650 rpm. Setting dual points clear as mud, for me anyway.

So Nissan made the advance set of points come on when it's below 30F for easier starting. Guess if you want to start your emission-spec AT car when it's cold but more than 30F you're just out of luck.

Speeding (and starting?) is bad, um'kay? So don't get rid of that dual point.

Edited October 29, 2013 by Stanley

[jed]

Thank you for your comments.

Sorry I didn't reply sooner, working long hours.

I managed to get a Haynes manual but the way that the ignition set up is written doesn't make a lot of sense to me.

I'll have a read of the threads supplied then see if I can understand how to check the settings to establish if I have an ignition or fuel problem.

Many thanks again.