2007 Ignition Coil Pack Resistance Range - Ford Mustang Forum
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post #1 of 8 (permalink) Old 10-10-2010 Thread Starter
Laoryn35's Avatar
Joined: Oct 2010
Location: Portland
Posts: 8
2007 Ignition Coil Pack Resistance Range

Hi Everyone,

I am troubleshooting some detonation issues in my car (2007 Mustang GT, stock, with SCT 9600 Livewire tuner/Bama Tunes).

The detonation occurs in the stock tune as well, but it was more pronounced in the Bama/Preloaded SCT tunes, which is why I noticed it.

I am running a can of Seafoam through the gas as I have read a lot about carbon buildup with these engines, but in reading tons of posts from this forum and others, I have come across the fact that there seem to be a lot of Coil Pack failures on the s197, and somehow these misfires can lead to / sound like detonation. I tested my coils, and I am not sure it they are in an acceptable range as all resistances are above the stock specs.

Does anyone out there that understands electrical resistances enough to advise if the following values are acceptable, or I should replace the Coil Packs, or maybe someone with a Service Manual that lists the acceptable ranges instead of the specific values I have found?

Here are my results:

Spec Primary: 0.55

Cyl 1 Primary: 0.90
Cyl 2 Primary: 1.00
Cyl 3 Primary: 0.65
Cyl 4 Primary: 0.80
Cyl 5 Primary: 0.75
Cyl 6 Primary: 0.75
Cyl 7 Primary: 0.75
Cyl 8 Primary: 0.75

Spec Secondary: 5.50 k

Cyl 1 Secondary: 5.78 k
Cyl 2 Secondary: 5.68 k
Cyl 3 Secondary: 5.62 k
Cyl 4 Secondary: 5.66 k
Cyl 5 Secondary: 5.54 k
Cyl 6 Secondary: 5.53 k
Cyl 7 Secondary: 5.55 k
Cyl 8 Secondary: 5.51 k

Thank you,

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post #2 of 8 (permalink) Old 10-10-2010
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Detonation is actually a second combustion of the unburnt fuel and air after the initial timed combustion. Knocking, pinging, etc. are all pre-ignition. This could be caused by carbon build up creating a hot spot, wrong heat range on your spark plug, wrong a/f ratio, low octane/bad gas amongst other things. A misfire should feel like a studder or loss of power. If anything it should sound more like a back fire since unburnt fuel is now being dumped through your exhaust and onto your hot cats.

What octane fuel are you running? Have you read your plugs? Have you thrown any codes to make you think you have a misfire? Do you have any modifications?

I hate to say this but some owners have experienced this same problem on stock motors and after several trips to the dealer the only resolution was to run higher octane.

post #3 of 8 (permalink) Old 10-10-2010 Thread Starter
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Joined: Oct 2010
Location: Portland
Posts: 8
Ya, I have read a lot of those posts too, and I am grasping at straws as I feel there must be a better solution than covering up the symptom of whatever the issue is with higher octane gas.

I am running the 87 Octane, and you are 100% right, when I run the 89% the issue fades. The same with the custom tunes, If I use the 89 custom tune with 91 octane, it works fine, but the 91 octane tunes with 91 make the nice Rattling/Tinny noise noise under heavy load. There is no stuterring at all, under load or at idle sounds smooth, just makes the rattling noise under heavy throttle, and the engine coolant temp jumps with heavy throttle.

I have 0 mods on the car currently. I just paid it off so hopefully that will change when I get this licked.

Car is running stock plugs (Originals actullay, and 30,000 miles on them, was thinking of swapping those too even though they are supposedly good to 45,000).

Wrong A/F - Don't have a wideband, so not sure.

Bad gas... This one bugs me.... I can find no info on how to tell good vs bad gas brands. I generally use Mobil which is supposed to be Top Tier, but I can still find no specific ratings on Ron vs Mon values accross brands to see how it compares.
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post #4 of 8 (permalink) Old 10-10-2010
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Mobil is a quality gas chain so if this has been a continuous problem then I would probably rule out bad gas; however, if you always fuel up at the same station you may want to try another just to see.

I see you tried SeaFoam in your fuel but have you also tried pulling it through a vacuum line? There are several things you can try but they all either cost more at the pump or reduce performance ie pulling timing, increasing fuel.

I tried looking around for the thread started by another forum member (just can't remember if it was this forum) regarding preignition issues and dealing with Ford. I couldn't find the one I wanted but I did find this one:

post #5 of 8 (permalink) Old 10-10-2010 Thread Starter
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Joined: Oct 2010
Location: Portland
Posts: 8
Thanks for the read. I did not find that post. I have only run a 1/4 tank with the seafoam. So, maybe I just gotta wait until I run this tank and fill up again, and see what happens.

If the issue is just carboin build up, then I have no problem seafoaming every six months to fix it, because I have an answer, and that is the important piece to me: knowing what it is and feeling confident that I am not hurting my engine.
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post #6 of 8 (permalink) Old 10-11-2010 Thread Starter
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Location: Portland
Posts: 8
I ran a can of Seafoam through the vacuum line like you said in your post (never done it that way before). I left a cloud behind my car like a smoke bomb. Then I drove it for a few minutes, and the detonation is gone on my stock tune, and was 99.9% gone on my Bama Custom tune (One little tick at 4k, but that disappeared as I drove it).

You've made a believer out of me
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post #7 of 8 (permalink) Old 10-11-2010
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Nice work! I was a little worried this was going to turn into a horrid story of taking the car to the dealer and never getting any answers. You may also want to install an in-line air/oil separator. This will help reduce the build up and since oil has an octane rating of almost nothing, it should reduce some of the preignition.
post #8 of 8 (permalink) Old 10-11-2010
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Sounds like you might have just hit a bad gas station or some build up, etc.

Change fuel filter/plugs regularly. Even the best of gas stations occasionally have a "bad batch". I noticed some marbles rolling around in my engine this morning.

There's a half-assed Sunoco around here I filled up at last night. I know better, but it was convenient. That's what I get.

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