Weak spark

Tiny
SERCANET
  • MEMBER
  • 2006 FORD TAURUS
  • 3.0L
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 160,000 MILES
Got a P0351 code. Examined coil pack and found numerous cracks. Replaced coil pack. Still runs rough. Weak spark at #2 cylinder coil tower; possibly also at #6 (same internal coil.) Test light shows voltage at input for coil and pulsing signal at all wires from PCM both positive and negative. Oddly (to me) the signal pulse for the #2/#6 coil seems much brighter than the signal pulse for the others even though the secondary spark seems weak. Resistance for all three coil secondaries is around 11kΩ each.

Any ideas?
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Friday, April 28th, 2017 AT 4:12 PM

13 Replies

Tiny
STEVE W.
  • EXPERT
Is this a new OEM coil pack or? Brighter light generally means it's drawing more current which could be a partially shorted coil. That would also give you a weaker spark.
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Sunday, April 30th, 2017 AT 3:22 PM
Tiny
SERCANET
  • MEMBER
Haven't checked current, but all three coil signals show 14V. The coil is an aftermarket (Driveworks from Advance Auto). I may take it back and see if they'll replace it. Plug wires are 5 year-old Autolites, so I'll replace them. Plugs are only a year old ( 8K mi) and look good.

Thanks for your response.
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Sunday, April 30th, 2017 AT 3:38 PM
Tiny
KEN
  • ADMIN
Please let us know what you find so it will help others.

Cheers, Ken
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Wednesday, May 3rd, 2017 AT 10:11 AM
Tiny
SERCANET
  • MEMBER
Haven't found much yet. I put the old coil back on and returned the one I bought to Advance. It idles a bit better, but still misfires at load. So far no return of the P0135 code. Still get a bright pulse on the #2/#6 primary terminal, but voltage is still 14V at all primary terminals and spark is weak at the secondaries. When I get time to work on it some more, I'll replace the plug wires and coil again. I'm beginning to suspect PCM problems. I don't think this car has a CCRM, but there is a cluster of three relays (with a fourth empty slot) in a case next to the battery, which could perform the same functions, so I may try moving those around.

Any more ideas?
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Wednesday, May 3rd, 2017 AT 10:24 AM
Tiny
KEN
  • ADMIN
I don't think it is a ECM problem, more like old plug wires will cause that, have you changed them yet?
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Wednesday, May 3rd, 2017 AT 12:28 PM
Tiny
STEVE W.
  • EXPERT
I'd hunt up an OEM pack and see what you get. Very possible the original coil has an issue and the after market was a POS.

Power wise the system is simple. 12 volts gets applied to pin 4, pins 1, 2 and 3 are pulled to ground by the PCM as it fires the coils.

Easy way to test the pack is to apply 12 volts to that same pin, then tap each of the other pins with a ground and watch the spark output. All 3 shouls throw the same spark if the coils are OK.
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Wednesday, May 3rd, 2017 AT 1:45 PM
Tiny
SERCANET
  • MEMBER
Ken,

Won't have time to get the plug wires on for a few days (death in family). Not clear why old plug wires would cause a brighter test lamp or a weaker spark to a grounded test lead, but they're due for replacement anyhow. Will let you know what happens.

Steve W,

I'll test the original coil as you suggested and then get a new one to see what kind of spark it produces Like I said, it will be a few days.
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Wednesday, May 3rd, 2017 AT 5:58 PM
Tiny
STEVE W.
  • EXPERT
Sorry to hear the news. No rush.
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Wednesday, May 3rd, 2017 AT 11:45 PM
Tiny
KEN
  • ADMIN
Yep, sorry to hear let us know when you get back to it. God bless
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Thursday, May 4th, 2017 AT 9:21 AM
Tiny
SERCANET
  • MEMBER
Okay. Got back to it yesterday with a new set of plug wires. Immediately idled better, even with the original, cracked coil pack. Still got a misfire under load, but no codes. Replaced the coil pack with a higher-grade aftermarket. Seems to run well, though haven't had the chance to drive it a lot.

It has occurred to me that a weak plug wire might cause the computer to compensate with a stronger primary signal; hence the brighter test light, which had me ready to blame the PCM. Thanks for talking me out of it. It just never entered my mind that there could be two related and simultaneous problems.

Maybe I'll next figure out what's up with that occasional complete power loss on this car during hot weather. Everything dies (usually idling at a red light) and the outside temp on the panel reverts to compass direction, meaning, I guess, that the PCM has lost power. Always starts right up again and goes on. Probably AC and cooling fans triggering a systemic power loss of some sort.

Thank you both for your help and words of sympathy. Is a contribution in order?
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Tuesday, May 9th, 2017 AT 5:35 PM
Tiny
STEVE W.
  • EXPERT
Good news on the coils/wires. Here's hoping you got it fixed.

What kind of heat triggers the engine shut down? That sort of issue could have been related to the cracked coil pack as well. Another common heat failure are crank sensors, but those don't usually start back up until they cool a bit, but yours could be at the starting point of failure. These types can be "fun" to track down. Do you have a scan tool that can read live data? If so go through and write down all the data info it can give you with the engine cold and then warmed up to full operating temperature. Now wait for a day when you think it is hot enough to shut down. Keep the tool connected as you drive, when it shuts down, pull over don't touch the key at all, and write down that data (or if your tool can record data even better) Now compare the data and see what is different. If you think the ECM is losing power it should show as a data loss.
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Tuesday, May 9th, 2017 AT 7:45 PM
Tiny
SERCANET
  • MEMBER
I don't think it's so much the heat as the fact that both the AC and cooling fans fire up at the same time. You may be right about the old cracked coil being the culprit. We'll see when the summer heat hits. Not a priority right now. It's an annoying problem, but not one that I'm going to waste a lot of time on.

Thanks to you guys for your help. Anything I can do for you?
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Wednesday, May 10th, 2017 AT 6:23 AM
Tiny
STEVE W.
  • EXPERT
Sure, return any time you have automotive questions and tell others about the site. When you want to try figuring out the issue we will be here.
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Wednesday, May 10th, 2017 AT 10:34 AM

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