Alterantor Or Trailing Coil? - NoPistons -Mazda Rx7 & Rx8 Rotary Forum
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2nd Generation Specific 1986-1992 Discussion

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Old 03-26-2004, 04:13 PM   #1  
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ok....i start my car, sometimes the tach works somtimes it doesnt....as long as the rpms are up while driving it seems ok but a little jerky.....when i go back down to idle it dies....



when the tach does work at around 3k rpm (cruising) the volts are between 12-13 volts,,,,, but at idle if it doesnt die it will sit a around 11-12 volts.....if my headlights are on when i rev my car they will brighten with higher rpm and then dim when rpms are below 1k.....



my car once warmed up is a real bitch to start too....it will just crank over for at least a minute and sputter...you can hear the battery loosing power.....eventually starting but dies if i dont keep my foot on the gas....



my knowlege tells me that the alternator is going bad...also maybe the trailing coil is bad too thus the reason for no signal to the tach....



but i have read somewhere that if the charging system and battery are going bad that the car will disable the trailing coils to save power...



help me guys.....i need to get my car up and running again



trevor
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Old 03-26-2004, 05:18 PM   #2  
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Well, the tach not working is a definate sign the trailing coil isn't firing. Could be an issue with the alternator as well. To be honest I really don't know what would cause that. Try grounding it in a bunch of spots and see if that helps.
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Old 03-26-2004, 05:23 PM   #3  
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i have whole motor re-grounded
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Old 03-27-2004, 09:29 AM   #4  
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anyone else?
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Old 03-27-2004, 05:38 PM   #5  
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^^
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Old 03-28-2004, 07:06 PM   #6  
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well i had my alternator checked....its good.....



i fixed my idle by adjusting the throttle cable....



my tach still isnt working....i need a trailing coil ithink



and my battery is dead.......not sure why that is if my alternator is good
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Old 03-29-2004, 12:21 AM   #7  
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Don't drive around with a dead battery.. Your alternator assumes all the load to keep the voltage up and you will burn it out as well.



I don't know where you read about the trailing coils being disabled on low voltage.. ? If the voltage was low your battery light would come on.. The stock gauge isn't 100% accurate either.. Mine reads a tad low when idling.



If you still have a bad tach signal then your trailing coil is probably in need of replacement. Try cleaning the coil mount (which is it's ground) and see if it makes a difference. If not, time for a new coil then.



I suggest getting a beefier battery. But don't drive around with the dead battery and good alternator or else you will burn the alternator out.
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Old 03-29-2004, 02:55 AM   #8  
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Well the good ( and I guess kinda bad ) news is that coils almost NEVER go bad. Under regular operating conditions, Ive never seen, or heard, one fail.



Also, if youre only getting 11-12 volts at idle, you need a new alternator. It has to be above 12.5 ( I think...Maybe 12.6 or so... ) to even charge the battery. I dont know who tested your alternator but I think they didnt know what theyre doing or their machine was bad.



Never heard about the energy saving thing with cutting the trailing spark, but you never know. I do know that if youre tach isnt working, 99.9% of the time it means your trailing plugs arent firing.





Hope this helps some.
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Old 03-29-2004, 09:45 AM   #9  
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Miscellaneous ramblings from the FNG . . . . . .



- If youíve drained a several year old battery while cranking the starter, the battery is probably toast.

- In looking at almost any automotive wiring schematic, without a good battery, all bets on electrically dependant systems are off.

- Any voltage measurement is dependant on a working battery, and dead batteries donít work.

- Costco sells brand new batteries for $35 where I live.

- You can burn up a perfectly good alternator with a defective battery.

- For 100 points: Does the ECU operate properly on substandard voltage? For 50 bonus points, does the ECU control the trailing coils? (Aside from not operating properly, itís possible to fry an ECU using low voltage, but thatís not your problem . . . . . . yet . . . . . . . we hope . . . . . .)



I would start by replacing the battery.
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Old 03-29-2004, 09:56 AM   #10  
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Quote:
Originally Posted by adamlewis' date='Mar 29 2004, 12:55 AM
Also, if youre only getting 11-12 volts at idle, you need a new alternator. It has to be above 12.5 ( I think...Maybe 12.6 or so... ) to even charge the battery. I dont know who tested your alternator but I think they didnt know what theyre doing or their machine was bad.
This was the reason for my comment on the stock volt gauge.



I was testing my battery and alternator output with a DMM back when I had the stock FC alternator. It was charging about 12.7, 12.8 at low idle, and a hare above 13 when I blipped the throttle.



However in the same manner, but reading from the stock gauge, I was looking at similar output to what he described.



The alternator probably is fine, but the battery isn't holding a change anymore or something. But who knows how long the alternator will be good for when you drive the car with a dead battery like that..



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