84 US no start?? resistor ?? SOLVED
03-24-2010, 12:35 AM
#1
Race Director
Thread Starter
84 US no start?? resistor ?? SOLVED
Okay the lemons racer has developed an issue.... I haven't gone up there yet to check it out...but it will not start and one of the two resistors between the coil and pin 15 of the ignition brain gets extremely hot and the other is ambient?
My initial thoughts are one of the resistors is blown causing the failure? The common "green wire" has been replaced....
My initial thoughts are one of the resistors is blown causing the failure? The common "green wire" has been replaced....
Last edited by IcemanG17; 03-27-2010 at 05:34 PM.
03-24-2010, 02:53 AM
#3
When the key is left in the on position for a long time (such as when you are attempting to start an early 928) those coil resistors seem to get hot. I am saying this because I am not sure that its related. I have started a 928 no problem and the resistors were so hot I could kind of hear them sizzling.
03-24-2010, 03:35 AM
#4
Team Owner
the resistor should be getting hot thats what they do if one is not then i would check the resistor for continuity it might damage the coil if one has failed
03-24-2010, 04:23 PM
#6
Race Director
Thread Starter
03-24-2010, 04:29 PM
#7
You don't actually need the resistor wire, supposedly, to start the car. The directions for some of the mini-starters say you don't need it.
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03-24-2010, 04:56 PM
#8
Rennlist Member
What happens is that when you operate the starter, one of the two resistors in series with the coil primary are shorted out to give more volts to the coil, and hence more volts to the plugs.
But except under very adverse conditions, this shouldn't be necessary.
BTW I can now offer a repair service for these early spark boxes. Thanks to Colin (Lizard) for supplying me with a box to work out the circuit and components used.
But except under very adverse conditions, this shouldn't be necessary.
BTW I can now offer a repair service for these early spark boxes. Thanks to Colin (Lizard) for supplying me with a box to work out the circuit and components used.
03-24-2010, 07:21 PM
#9
Rennlist Member
Look on Sharksin's website. He has a 16V ignition section. Hot resistor sounds like excessive current; either a shorted coil or other wire. Check some voltages from his website instructions.
Good luck,
Dave
Good luck,
Dave
03-24-2010, 07:24 PM
#10
Race Director
Thread Starter
I'll have to check Daves site.....I did talk to 928intl and the resistors are well known to fail and cause no start issues
I do have a spare spark box from the 79...... so at this point I would say its probably
1: Blown resistor (the cool one)
2: Dead coil
3: something else (maybe brain)
I do have a spare spark box from the 79...... so at this point I would say its probably
1: Blown resistor (the cool one)
2: Dead coil
3: something else (maybe brain)
03-24-2010, 08:55 PM
#12
Administrator - "Tyson"
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I drove my 81 around for a few days last year with them bypassed.
Awesome news!!!
03-24-2010, 09:05 PM
#13
Chronic Tool Dropper
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Brian-
Simple voltmeter check to see if the resistors are doing the job. Meter plus to coil terminal 15, measure to ground with the key in the RUN position. Make Sure you are on the 15 terminal on the coil before you turn the key on. Should see somewhere around 10 volts IIRC. If you see anything in that neighborhood, both resistors are fine. If you see voltage there only while cranking, one has failed. No voltage at all could be faulty ignition circuit to 15 bus, or one of the resistors has failed. You can check them end-to-end with key off and meter on ohms, coil wire 15 (solid black) lifted.
Simple voltmeter check to see if the resistors are doing the job. Meter plus to coil terminal 15, measure to ground with the key in the RUN position. Make Sure you are on the 15 terminal on the coil before you turn the key on. Should see somewhere around 10 volts IIRC. If you see anything in that neighborhood, both resistors are fine. If you see voltage there only while cranking, one has failed. No voltage at all could be faulty ignition circuit to 15 bus, or one of the resistors has failed. You can check them end-to-end with key off and meter on ohms, coil wire 15 (solid black) lifted.
03-24-2010, 10:44 PM
#14
Race Director
Thread Starter
Brian-
Simple voltmeter check to see if the resistors are doing the job. Meter plus to coil terminal 15, measure to ground with the key in the RUN position. Make Sure you are on the 15 terminal on the coil before you turn the key on. Should see somewhere around 10 volts IIRC. If you see anything in that neighborhood, both resistors are fine. If you see voltage there only while cranking, one has failed. No voltage at all could be faulty ignition circuit to 15 bus, or one of the resistors has failed. You can check them end-to-end with key off and meter on ohms, coil wire 15 (solid black) lifted.
Simple voltmeter check to see if the resistors are doing the job. Meter plus to coil terminal 15, measure to ground with the key in the RUN position. Make Sure you are on the 15 terminal on the coil before you turn the key on. Should see somewhere around 10 volts IIRC. If you see anything in that neighborhood, both resistors are fine. If you see voltage there only while cranking, one has failed. No voltage at all could be faulty ignition circuit to 15 bus, or one of the resistors has failed. You can check them end-to-end with key off and meter on ohms, coil wire 15 (solid black) lifted.
Whats odd is it ran fine....then we remove the starter to drop the pan....put everything together and it won't start..... It seems odd that the resistor would die causing the failure at precisely the same time when it ran fine literally minutes before we pulled it apart....
Its test #6 on Dave's ignition troubleshooting guide...& its specs "at least 3V".....so anything ABOVE that is good
03-27-2010, 05:36 PM
#15
Race Director
Thread Starter
Sure enough it was a resistor that fried....the lower one, not the one going to the starter......resistance on the .4 ohm resistor was WAY out of spec...far too high at over 3 ohms.....so new ones are on order
Whats kinda odd is I was getting really odd readings from the coil too?
Whats kinda odd is I was getting really odd readings from the coil too?