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Electrical Gurus Needed - Wierd Ignition Issue!!
#1326009
10/25/12 06:13 PM
10/25/12 06:13 PM
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Joined: Jul 2007
Posts: 1,526
North Carolina
cjskotni
OP
pro stock
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OP
pro stock
Joined: Jul 2007
Posts: 1,526
North Carolina
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Guys, I have been grappeling with a strange, elusive issue now for the past 6 weeks and it's got me about to torch my Charger to the ground!  Car is a 1973 Charger. Everything on the electrical system is stock except for a 100 amp alternator (3 wire) and dual electric fans. Ignition is factory electronic ignition and MP distributor. Engine bay wire harnesses are all NEW repro. I had this car dyno'ed back in August and tuned and it had run fine for about 25-50 miles worth of driving. Started great, good power, never died... Problem "began" when I was driving the car and it simply cutoff while I was crusing. Just lost power and died. This was the first time I had run with hadlights so I figured this must be a low voltage situation. I went ahead and upgraded the alt to a 100 amp unit. Problem still existed. I then replaced or swapped the following to see what the issue was: - ECU box (tried two new ones) - VR - coil - ballast resistor - cap/rotor - dist pickup Replacing all these parts has done NOTHING to fix this issue. Double checked and all grounds are great. I can crank the car (bit of a harder start now) but it runs fine for about 10-15 minutes and then just idles down and dies. Doesn't misfire or pop...just dies. It cannot be restarted until it is cooled off. I have monitored battery voltage and even disconnected the cooling fans and the charging circuit is not the cuplrit here. After the car dies, it still has plenty o' juice to crank (or try). Heck it will even die when the battery is charging at 13+ V. After getting the engine to die, I pulled the #7 plug wire and hooked to spark plug tester. Seems to be erratic/no spark when this problem arises which would make sense. We have a running motor that just dies....no spark, right? So afer replacing/swapping all these parts, problem is still there! What gives?  What else could cause this? Just about the entire ignition system has been replaced. Is there a underdash wire that could be shorting or something? I am assuming this must be heat-related as we run OK until it dies.... The funny thing is, this problem just came out of the blue. I had not changed ANYTHING ANYWHERE to begin this cycle... I am running out of ideas here and wasting a lot of time in the garage. Much more time on working this issue in the garage and my wife is going to serve me divorce papers!  Any help or ideas here are appreciated. What else could stop a running motor and kill its spark? Please  !
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Re: Electrical Gurus Needed - Wierd Ignition Issue!!
[Re: cjskotni]
#1326011
10/25/12 06:46 PM
10/25/12 06:46 PM
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Joined: Jan 2003
Posts: 26,000
Rio Linda, CA
John_Kunkel
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 26,000
Rio Linda, CA
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Check/clean the firewall bulkhead disconnect terminals.
The INTERNET, the MISinformation superhighway
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Re: Electrical Gurus Needed - Wierd Ignition Issue!!
[Re: Andrewh]
#1326012
10/25/12 07:04 PM
10/25/12 07:04 PM
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Joined: Jul 2007
Posts: 1,526
North Carolina
cjskotni
OP
pro stock
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OP
pro stock
Joined: Jul 2007
Posts: 1,526
North Carolina
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Quote:
well eliminate some of the wiring.
run a hot directly to the VR sensing line.
it should back feed the ecu, balast resister/coil.
see if it will continue to run.
the next step would be if it still dies, to start swapping old parts back in during the won't start period until it does.
Is this the blue wire? Just jumper from + on battery to this?
Quote:
Check/clean the firewall bulkhead disconnect terminals.
These pare pretty darn clean as the engine bay harness is new. The underdash harness is old though so that's why I was wondering if that could be an issue. I have a new dash harness I have yet to put in but I'd like to clear this up before I install that.
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Re: Electrical Gurus Needed - Wierd Ignition Issue!!
[Re: cjskotni]
#1326014
10/25/12 10:37 PM
10/25/12 10:37 PM
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Joined: Nov 2003
Posts: 36,041
Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
Joined: Nov 2003
Posts: 36,041
Lincoln Nebraska
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I'd hook a timing light to the coil wire & double check that it ain't firing then I would make up some jumper wires and jump 12V to the upstream side of the ballast then from the downstream side of the ballast to the coil positive primary terminal and jump 12V to the hot input wire at the ECU pentastar connector and seperate the pickup connector and jump from it (2 wires) to the ECU pentastar connector. Then jump directly from the coil negative primary terminal to the black/yellow wire pigtail on the ECU pentastar connector. I would strip the (4) wires at the ECU pentastar connnector several inches out from the connector base on the pigtails to make SURE there's a Direct Connnection to confirm/deny that it's a wiring problem. EDIT If you dont want to do any unsightly T ing into the pentastar harness you could unplug it & use some female butt connectors to connect your jumpers to the ECU pins if you choose to do this
Last edited by RapidRobert; 10/25/12 10:48 PM.
live every 24 hour block of time like it's your last day on earth
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Re: Electrical Gurus Needed - UPDATE
[Re: dvw]
#1326018
11/11/12 05:22 PM
11/11/12 05:22 PM
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Joined: Jul 2007
Posts: 1,526
North Carolina
cjskotni
OP
pro stock
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OP
pro stock
Joined: Jul 2007
Posts: 1,526
North Carolina
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Guys, I appreciate the suggestions. I have checked grounds, run dedicated ground jumpers to the VR and ECU box housing. I have tried jumping from the starter relay to the blue ignition circuit after the motor dies. I cannot figure this out!  Since my last post I have done the following: - went ahead and put in the brand new dash harness and fuse block. All connections cleaned and packed with dielectric grease - gauge cluster is out of car and the two ammeter leads are just tied together and taped over - rebuilt steering column and put in new ignition switch After doing all this - no change! The motor starts just fine from cold and will run 15 minutes or so and then you see it start idling lower and lower for about a minute and then it dies! No surging/missing/popping...just dies. After this, can't restart until cooled off again. When dead, checked voltage on coil in "run" it gets ~3V and "start" gets ~7.5V. I hooked up a spark plug tester and I am getting spark at the plugs so coil is firing. I am at my wit's end here! I have replaced just about everything on the ignition circuit and can't shake this problem. I have jumpered grounds, swapped parts, and bypassed the hanress numerous times/ways! EVERY single wire on this car is new! We aren't even dealing with cruddy 40 yr old wires! Where do I look now? Could this be a mechanical issue?? I can't see what could be wrong with the motor itself that would go from purring to dead in 15 mintutes everytime! Carb issue?? I am about 99% sure I'm getting fuel though.... I wouldn't mind taking this to a mechanic but I don't know of any that would know this old stuff and be any better at this than I am! Any other ideas?
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Re: Electrical Gurus Needed - UPDATE
[Re: cjskotni]
#1326022
11/11/12 10:02 PM
11/11/12 10:02 PM
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Joined: Feb 2003
Posts: 518
COLLINGWOOD, ONT
71_deputy
mopar
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mopar
Joined: Feb 2003
Posts: 518
COLLINGWOOD, ONT
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I see that you have changed the coil- but was it a new one or old/borrowed one??? almost sounds like as it warms up it shorts out!! my 
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Re: Electrical Gurus Needed - UPDATE
[Re: 71_deputy]
#1326024
11/11/12 11:34 PM
11/11/12 11:34 PM
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Joined: Jul 2007
Posts: 1,526
North Carolina
cjskotni
OP
pro stock
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OP
pro stock
Joined: Jul 2007
Posts: 1,526
North Carolina
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Quote:
I see that you have changed the coil- but was it a new one or old/borrowed one???
almost sounds like as it warms up it shorts out!!
my
Coil I swapped in was the stock replacement from Advance Auto, brand new.
Ok here is what I get when I go from run to start with the starter motor disabled (all volatges across + to - coil terminals):
With coil leads off the coil: ~10.6V run and ~11.5V start
With leads connected to coil: ~3V run and ~7.4V start (spikes @ 10.6V momentarily)
This leads (no pun intended) me to believe the coil is almost a large short (lower resistance than ballast) so it "takes" less of the voltage than the ballast...hence the voltage difference between the connected/unconnected leads.
Remembering back from how a generic coil should work, this makes sense, low current draw at first moments then goes to almost a short as time goes on...
Also the coil shows primary resistance of around 1.2 ohms and secondary of ~6.2 Kohms. It is an MSD Blaster II.
Is this normal? Can anybody tell me here what a "healthy" coil voltage should show in "run" position with leads connected? I pulled the harness apart and I am pretty sure the wires are fine from ballast to the coil. Wires look fine from coil back to ECU as well...
Pulling out what little hair I have left here! 
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Re: Electrical Gurus Needed - UPDATE
[Re: cjskotni]
#1326025
11/12/12 05:46 AM
11/12/12 05:46 AM
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Joined: Dec 2010
Posts: 208
Norrland, Sweden
Swedcharger67
enthusiast
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enthusiast
Joined: Dec 2010
Posts: 208
Norrland, Sweden
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I can't comment on blue and brown sides of things, but generally speaking: - the 11.7V at the "high side" of the ballast resistor seems low. You should have full battery voltage here (i.e. about 13-14 volts engine running). The low voltage may indicate you have a bad connection in the feed to the ballast resistor (i.e. from the ignition switch/bulkhead connectors). - Your measured resistance is 1.2 Ohms (coil, normal for a Blaster 2 if I remember correctly) and 2 Ohm (probably normal for a ballast resistor). This means you have a current which is U/(1.2+2). With 11.7V the current is 3.66 Amps. This means that the voltage drop across the ballast resistor is 3.66A * 2 Ohms = 7.3 volts (if you measure to ground you have 11.7-7.3= 4.4 Volts on the positive terminal of the coil) Now we come to the problem with measuring: - On the "low side" of the ballast resistor you have a square wave type voltage, and the same on the low side of the coil (towards the ECU). With a normal universal multimeter you cannot get an accurate measurement, because these meters can only measure a DC voltage/current, and an AC sine wave voltage/current. But you have a square wave (not pure DC, not a sine wave AC), and all readings will be incorrect. They can however be used for indications, but not for any accurate calculations. Hope this gives you some ideas how to compare with your measurements. Basically your values seem correct, the low voltage to the ballast resistor would interest me. You can always put a direct 12V feed to ballast resistor, and see if the engine keeps running. The ignition coil will be a bit slow to start drawing current (because of the inductance, like to start spinning a wheel), but it increases rapidly and remains constant at Ucoil/Rcoil i.e. 4.4V/1.2Ohms = 3.6 Amps. The time usually allowed by electronics to charge an ignition coil is approx. 5/1000 seconds (5 milliseconds). An old points system is different with a variable time (longer for low rpms, shorter for high rpms...). Sorry for the long text, early morning here and new energy...good luck in finding the bad connection. 
Martin, 67 Charger, 512 cui, E85, MegaSquirt MS3X sequential ignition & injection
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Re: Electrical Gurus Needed - UPDATE
[Re: Swedcharger67]
#1326026
11/12/12 08:56 AM
11/12/12 08:56 AM
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Joined: Jul 2007
Posts: 1,526
North Carolina
cjskotni
OP
pro stock
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OP
pro stock
Joined: Jul 2007
Posts: 1,526
North Carolina
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Quote:
I can't comment on blue and brown sides of things, but generally speaking:
- the 11.7V at the "high side" of the ballast resistor seems low. You should have full battery voltage here (i.e. about 13-14 volts engine running). The low voltage may indicate you have a bad connection in the feed to the ballast resistor (i.e. from the ignition switch/bulkhead connectors).
- Your measured resistance is 1.2 Ohms (coil, normal for a Blaster 2 if I remember correctly) and 2 Ohm (probably normal for a ballast resistor). This means you have a current which is U/(1.2+2). With 11.7V the current is 3.66 Amps.
This means that the voltage drop across the ballast resistor is 3.66A * 2 Ohms = 7.3 volts (if you measure to ground you have 11.7-7.3= 4.4 Volts on the positive terminal of the coil)
Now we come to the problem with measuring:
- On the "low side" of the ballast resistor you have a square wave type voltage, and the same on the low side of the coil (towards the ECU). With a normal universal multimeter you cannot get an accurate measurement, because these meters can only measure a DC voltage/current, and an AC sine wave voltage/current. But you have a square wave (not pure DC, not a sine wave AC), and all readings will be incorrect. They can however be used for indications, but not for any accurate calculations.
Hope this gives you some ideas how to compare with your measurements.
Basically your values seem correct, the low voltage to the ballast resistor would interest me.
You can always put a direct 12V feed to ballast resistor, and see if the engine keeps running.
The ignition coil will be a bit slow to start drawing current (because of the inductance, like to start spinning a wheel), but it increases rapidly and remains constant at Ucoil/Rcoil i.e. 4.4V/1.2Ohms = 3.6 Amps. The time usually allowed by electronics to charge an ignition coil is approx. 5/1000 seconds (5 milliseconds). An old points system is different with a variable time (longer for low rpms, shorter for high rpms...).
Sorry for the long text, early morning here and new energy...good luck in finding the bad connection.
Thanks for the analysis so I don't feel quite so stupid now.
I should have noted that all these measurements are with the engine off. So the voltage loss through the bulkhead connectors/ignition switch is about 1 V compared to the battery + terminal.
Robert, what do you think could be wrong with the carb? I had this car tuned before this stuff happened and everything was fine (no dying issue). The guy went through the carb as well. I don't have another carb unfortunately but is there anything I should look for?
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Re: Electrical Gurus Needed - UPDATE
[Re: moparmarks]
#1326028
11/12/12 11:10 AM
11/12/12 11:10 AM
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Joined: Nov 2003
Posts: 36,041
Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
Joined: Nov 2003
Posts: 36,041
Lincoln Nebraska
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I'd let it idle in your driveway till it acts up then see if the AP still has a squirt & have the timing light ready to go & hooked up to the coil wire & immediately see if you have spark. Is the pickup gap good? I'd maybe take the top off of the carb & the idle mix screws out & blast it with a can of starting fluid but as said it sure sounds like a classic ign part acting up when hot. It's possible & does happen pretty regularly that one of the new ign parts you subbed in is bad tho it'd be out of the question to replace some or all of em again without knowing which one was bad. I'd start by using the timing light & if it confirms an ign prob then bypassing all of the harnesses with jumper wires to confirm/deny it's a wiring issue which I dont think it is then assuming it ain't the carb/vac leak/fuel starvation that only leaves the ign hard parts. Seperate the pickup pull apart connector & drag/tap the male end of the eng half of the conector across a ground & if the large coil wire (dist end) held 1/4" from ground now sparks (key on) then that points to the pickup being bad. With a jumper wire make/break to ground the neg primary terminal on the coil & see if the coil wire now sparks & if so that points to the ECU (& or it's supporting wiring) as the culprit. Have to work fast & get em while they are hot & may need to warm it up between tests. Keep us updated!
live every 24 hour block of time like it's your last day on earth
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