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Discussion Starter · #1 · (Edited)
Hello all....Brad here out of Spring, Texas. I'm having some odd issues with spark on my 2005 Ford Taurus SE with the 3.0L SFI. Really hoping that some of the knowledgeable folks here could help me out with.

The car was running fine until about 2 weeks ago. The battery started going bad to the point where I was needing jumps more often than not. Then, about a week ago it started running 'real' ruff to the point it was almost dying at lights. I went and replaced the battery to solve that problem and asked about the rough running. I was told that the probable culprit may be the IAC valve.

So, I took it to Autozone to have the codes read and this is what they can back with.

PO511
PO352

Well, I ran a test on the IAC (unhooked it while engine was running to see if made a diff....it did. Died right away). Even though I thought it was still good I bought a new one anyway. Slapped it on and no change at all.

Checked the ignition coil and found that number 2, 3 and 4 weren't throwing any spark. So I bought a new ignition coil. It brought the spark back to # 2, but # 3 has 'very' weak spark and #4 still has none at all.

My question....is there anything else that would cause the coil not to fire on numbers 3 and 4????

Any help would be greatly appreciated....Brad
 

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P0511 - Idle Air Control (IAC) Circuit Malfunction
P0352 - Ignition Coil B Circuit Malfunction

Unplugging the IAC would cause the P0511 code FYI. If you had this code before you unplugged it, the sensor might have been bad or you have a wiring problem.

The ignition systems on these cars is a waste spark type. There are only three coils, and the spark is always fired in two cylinders at the same time (one cylinder is on the compression stroke and one is on the exhaust stroke). Your code was for coil B in the center of the pack which fires 2 and 6. That seems to be better with the new coil pack, but now you have a problem with the coil C firing 3 and 4. Because this is a waste spark system, you need to have companion plug installed and working well to see good spark. So if you had 3 out while testing 4 you might not see any spark and vice versa. You could also have problems if you had a bad spark plug. I would recommend taking a look at them, but if you want to test the spark with the plugs installed, ground one of the leads (e.g. 3) to the block while holding the other a half inch away from the block in a different location. It's also possible that you got a bad replacement coil. If it tests bad again take it back.

If it sill runs rough at idle you might also have a vacuum leak or dirty MAF. Get the coil and plugs sorted out first.
 

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^+1 & also check the plug wires end to end resistance. They should measure about 1000 ohms per inch of length 30K ohms max, no matter the length.

Let us know what you find.
 

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Discussion Starter · #4 · (Edited)
I'm testing for spark directly at the coil by pulling the boot off the # 3 and 4 and using a multimeter. I'm sticking the ground to the neg battery terminal and getting the poss wire close to each terminal on the coil. 1, 2 5 and 6 are all throwing good spark while the other two are not.

I will try your method a bit later today and see what I find.

As for the IAC, I did pull the plug 'before' having the codes read so that is where that came from as you noted.

I have already checked the wire resistance and they all checked out fine.

The plugs on the other hand could probably use replacing (scheduled tuneup), but with me checking for spark directly at the coil I figured that they couldn't be suspects.


I'm just baffled as to why I see such good spark on 1, 5, 2 and 6 terminals and not 3 and 4 even after replacing the coil.
 

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Several possibilities for weak spark come to mind. The new coilpack is faulty as has been suggested, so did you have it tested Before leaving the store with it???? I make a habit of having the store check all of my expensive electrical purchases Before leaving with them. Just because they're new, doesn't automatically earn them a pass, I've seen plenty of bad new parts right out of the box!!!! Most autoparts stores can & will bench check the coilpack at no cost.

The old coilpack, if bad, could have damaged the computers ground switching driver, not a good thing if thats happened.

You may have high resistance wires, or connector contact problems in the B+ feed to the coilpack, or in it's ground lead or connector contacts back to the computer. SO, check for B+ to the coilpacks electrical connector, to make sure the coilpacks primary windings are getting full B+ feed at KOEO.

Check the coilpacks primary & secondary resistance readings. Ford doesn't have a published ohm spec for the primary, but it's typically less than one ohm. Compare the good spark windings primary numbers to the windings that yield the weak spark.
The secondary winding resistance should be between 13-15K ohms. with the plug wires removed, measure the secondary coils resistance across the secondary terminals.

Let us know what you find.
 

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Discussion Starter · #6 · (Edited)
My wife will be home with the car soon and I'm going to jump into it....First thing I'm going to do is take the coil back up to the parts store and have it tested....I will post my results later this evening. :D
 

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Discussion Starter · #7 ·
Well, I went up to Autozone trying to get the coil tested and was told that they didn't test coils....only ICM's. After that I had some family time to tend to and never got back to the car. I told everyone not to make plans for this evening and will dig into it tonight.
Hopefully I'll be able to shed some light on the problem.
 

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If you can't find an autoparts store that can do a coilpack output test, try performing the primary & secondary winding resistance checks & do the KOEO B+ coilpack feed checks to each primary winding to see how they measure up to the values I posted above. If ok, maybe lift & support the coilpack for a ground probe test underneath & let us know what you find.
 

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Several possibilities for weak spark come to mind. The new coilpack is faulty as has been suggested, so did you have it tested Before leaving the store with it???? I make a habit of having the store check all of my expensive electrical purchases Before leaving with them. Just because they're new, doesn't automatically earn them a pass, I've seen plenty of bad new parts right out of the box!!!! Most autoparts stores can & will bench check the coilpack at no cost.

The old coilpack, if bad, could have damaged the computers ground switching driver, not a good thing if thats happened.

You may have high resistance wires, or connector contact problems in the B+ feed to the coilpack, or in it's ground lead or connector contacts back to the computer. SO, check for B+ to the coilpacks electrical connector, to make sure the coilpacks primary windings are getting full B+ feed at KOEO.

Check the coilpacks primary & secondary resistance readings. Ford doesn't have a published ohm spec for the primary, but it's typically less than one ohm. Compare the good spark windings primary numbers to the windings that yield the weak spark.
The secondary winding resistance should be between 13-15K ohms. with the plug wires removed, measure the secondary coils resistance across the secondary terminals.

Let us know what you find.
Might add:
KOEO is key on engin off.
In the pic, the red wire is supposed to have battery volts with key on.

I measured my poor performing, (randon miss) coil (no name no number) and from the left as seen post to the other primary pins 0.6 ohms with my Fluke. (good meter) measuring ohms in that range is "iffy" due to lead wire resistance.
My secondary resistance was 10K on each. Measured post to partner post on each coil pictured. I got a JY Motorcraft coil and car runs with no random miss. Possible contact issue but I did not bother, just got a used coil and compared performance. I did ohm the Motorcraft but do not remember the numbers.

Good diag call on your part on bat volts to the supply lead to the coil.

Happy sparking.

-chart-
 

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Discussion Starter · #10 ·
Well, between honey do's and the kiddo's I haven't been able to crawl under the hood yet. I've got work and kiddo's tomorrow so hopefully I can snag a little time soon.

Thank you everyone for all the great info, I will definetly keep y'all posted on my progress.
 

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If you have an ohmmeter and a chiltons or haynes service manual for your car, they have the coil primary/secondary resistance tests how-tos and specs. I would at least carefully visually inspect the coil for cracks (esp. on the bottom), corrosion, bulges and general damage.
 
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