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Bad spark


Randall008

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Hi, I’ve got a 1988 Ford bronco ii. It’s running like sh*t. I’m not sure exactly where I’m at with it. As in I’m not sure if any of the new parts I’ve put in are marking the problem worse, or if the bad part is getting worse over time. The spark from the coil to the distributor seems ok. The spark from the distributor to the plug is sh*t. Plugs, cap, and button are new within the past three years. So is the tfi. Any ideas?
 


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RonD

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See if distributor has a wobble, bushings can wear out causing distributor shaft to wobble, not spin true
So "button" moves farther away from cap contact making spark weak just on some contacts matching the wobble
 

Randall008

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Thank you for the response, how do I check that?
 

RonD

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Pull up the cap and crank engine over, watch for a wobble, should spin true
Look at the old cap, if you see darker contacts they were getting longer arcs of spark, all contacts should look the same
 

Randall008

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I checked. It didn’t really look wobbly. The ware pattern on the inside of the cap was pretty even as well. I’m not a mechanic, so I could be missing something, but I feel like it should be getting a solid spark... I checked the spark from the coil again. This also looked a little weak and erratic. I have an 87, as well. swapped out the coil, no change
 

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Blue spark is what you want to see, yellow is weak

You can use a volt meter at battery, should see 13.5-14.5v with engine running

All an ignition coil does is to change low volts with high amps into high volts with low amps

12volts IN becomes 24,000volts OUT
So less voltage at the coil reduces the output voltage alot
so 2v less drops 4,000volts at spark plugs

Old coils are less efficient than newer coils, so if both are old coils, it could be both have issues
 
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Randall008

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I pulled a plug. It appears its blue with a yellow tint... also definitely seems intermittent... especially when I have the spark tester between the plug and the wire
 

RonD

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Blue is OK

Do you have a timing light, good way to test if spark is intermittent
 

Randall008

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I didn’t see the rest of your earlier post. I do have low volts at the battery.. I checked yesterday, but I think it was 10.. I’ll check it again when I get home... if this is the problem, do you know what the issue is? ... in regards to your last post, I was wondering about timing, but I don’t have the light to test.
 

Uncle Gump

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I use one of these tester... most electronic ignition should jump this gap. Most times you don't even have to see it. You can hear it.

61437
 

Randall008

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Update: I just got back. Battery is at 10 volts sitting and 12 volts running. I through a battery pack on it a couple days ago, I didn’t test the volts, but it didn’t change the way the truck runs. It hovers between 500 and 600 rpms before shutting off. ... maybe the alternator isn’t putting out enough power to creat a good spark?

Thanks for the advice on the spark tester
 

Uncle Gump

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You should have over 12 at rest... about 14 running.

My guess is you have a bad battery.
 

Randall008

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I might, it is low on volts. It is also undersized for the car, i’ll swap it out to see if that’s the problem but if it were the battery, wouldn’t the jumper level out the truck when it was connected? Or once it’s started, doesn’t the alternator kind of take over?
 

Uncle Gump

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with it running you should have 14 volts...

So with it running you only have 12 volts?

You may have double trouble.

Change the battery with a known good one... see what you have.
 

Randall008

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I just swapped it out. I forgot to check the volts when it was running, but the performance of the car didn’t change with the good battery.
 


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