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Question for DatzenMike


Rickie B

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On a Z24 duel coil, if you switch the coil wires at the coils ,another-words unplug the coil wire from one coil and plug it into the other coil and visa-versa, what effect will it have if any ? on how the motor runs

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All that will do is switch the spark from the intake to the exhaust side and visa versa. No effect what ever if the ignition is working properly to begin with.

 

In operation, the distributor module signals both coils to fire together at the same time. The power to the coils comes from two sources though. One side (intake) comes directly from the ignition switch. The exhaust side comes from a fuse in the fuse box that is powered by the ignition switch. If this fuss should blow the exhaust side coil has no power and stops working. This fuse is the first one on the left side of the box closest to the door.

 

If one coil is not firing, the engine will run, but poorly, and will act like the ignition timing is severely retarded.

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Mike,the reason i asked,a couple weeks ago i gave my 720 a complete tune up,NEW everything , valve adj. ,timing, i thought maby  i crossed the coil wires,i set the timing per specs 3 deg, BTC.Just came back in from working on truck,evidently it does not like 3 deg. so i kept advancing it till it smoothed out ,final setting is 13 deg.Now idles very nice,took it for a test drive runs great and no more bog off idle .Mike thank you very much for the quick response ,you answered my question .Have a great weekend

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Remember.... I said that if one side stops working it will act retarded??? The cure would be to add more timing like you just did. The ideal thing is to get all the plugs firing.

 

 

I would say from the description that one side is not firing. Pull each coil wire off, put an old plug in the end, lay on a well grounded surface and have someone turn the engine over with the starter. Either there will be spark or there won't.

 

If one side is not firing replace the first fuse on the left hand side of the fuse box. 10A I think. This is the power source for the exhaust coil.

If still not working (I see you have an '85) look at the distributor harness wires. There will be 3 wires together and a single 4th White wire with it's own plug. Disconnect it and re-test for spark.

 

 

Now this assumes that you are timing the engine properly in the first place. (no offense intended) Sometimes we assume or just make a mistake. It happens.

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I will give this a try,i have a new digital timing lite with RPM reading,i disconnect the vacume advance hose and pluged it,there is a sticker under the hood showing me the correct timing mark 3 deg. BTC @ 800 RPM,i set the timing at this mark and 800 RPM, idles very rough ,if i hold the RPM at 2000 it misses,So thats when i messed with the timing,i kept advancing it and it started to smooth out,at 13 deg. idles smooth and at 2000 RPM no more missing.I will defiantly check the coils using your method,sounds simple enough .Will let you know what i find.Thanks Mike

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Mike,before i tackel the spark check i want to make sure i understand you correctly ,do i put the plug directly in the coil wire,or am i missing something? back in the old days we would just pull off a plug wire put in a plug, ground it, start it,check for spark

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Pull each coil wire out of the distributor cap and check for spark. If there is spark on both, then try one of the plugs on that side (maybe the rotor is bad) but I expect one coil is nor firing.

 

This does not mean the coil is bad. It just may mean there is no power to it.

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Had minor set back,looks like i left the lights on :blush:  ,had to charge dead battery .OK all is good,had spark from both coil wires to distributor cap,both coils seem to be fireing,went one step further,pulled the plug wire off #1 intake,insert a spark plug,ground it to valve cover,start it up,plug fires very nice,did the same thing to #1 exhaust,again plug fireing very nice.Final timeing 13deg.BTDC @850RPM.Truck idles very smooth and no more bog from the little Weber .Took it for a drive up in the hills ,ran great,could not get it to ping even when luging it  .Mike thank you very much for your time and input ,i really do appreciate it  :thumbup:

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