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Old 07-18-2009, 07:05 PM   #1 (permalink)
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I've got a '97 Sable Vulcan with what feels like a misfire or simply slightly rough running, but only at idle. Otherwise, the car seems fine. I tested the coil today, and these are the numbers I got:

primary: 1.8 or 1.9 Ohms from the blue/white pin to each of the other three.
secondary: I get infinity (or zero, I forgot to check continuity) between each of the towers and any other *except* for the one across from it. For each coil tower *pair* (mine looks like the diagram below, and I mean when measuring A-B, or C-D, or E-F) I get a very consistent 14.8 or 14.9 kOhms.

A B
C D
E F

The primary seems out of spec (0.5 to 1.0) but, depending on the sources, the secondary resistances seem normal (12.5 to 16.0 kOhm).

What does a higher-than-expected primary resistance indicate, is it likely the cause of my slightly rough idle, and lastly, should I replace the coil pack?

I should note that I've recently replaced the DPFS (or whatever the egr-related switch is), tested the egr, replaced the TRS (twice), cleaned the MAF (properly), carefully cleaned the throttle body (but did not remove it), and replaced the wires and plugs. And yes I've run fuel injector cleaner through it. The plugs look *great*. Mileage seems to hover around 24, but that is 50/50 mixed highway/city.
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Old 07-18-2009, 10:56 PM   #2 (permalink)
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The coil pack resistance readings seem ok.

If the engine seems to be running ok at rpm or up hill with a load on it I'd not suspect the coil pack.

If it misses on a grade when the engine is lugged, maybe suspect spark plug gap.

Does it idle up ok when you turn the A/C on???? if not maybe suspect the IAC (Idle Air Control) it is a common problem part.

Vacuum leaks come to mind too.

If you still suspect the coil pack, most autoparts stores will bench test it at no charge.
If the problem seems to happen on a warm engine, maybe take a hair dryer along to heat the coil pack up for the bench test.

More trouble shooting thoughts for pondering.
Let us know what you find.
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Old 07-19-2009, 07:23 AM   #3 (permalink)
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QUOTE (pawpaw @ Jul 18 2009, 09:56 PM)
Quote:
The coil pack resistance readings seem ok.

If the engine seems to be running ok at rpm or up hill with a load on it I'd not suspect the coil pack.

If it misses on a grade when the engine is lugged, maybe suspect spark plug gap.

Does it idle up ok when you turn the A/C on???? if not maybe suspect the IAC (Idle Air Control) it is a common problem part.

Vacuum leaks come to mind too.

If you still suspect the coil pack, most autoparts stores will bench test it at no charge.
If the problem seems to happen on a warm engine, maybe take a hair dryer along to heat the coil pack up for the bench test.

More trouble shooting thoughts for pondering.
Let us know what you find.[/b]
I'll try to take these in order.
Whenever I leave my house, half of the directions I might go take me down fairly good sized hills. When I return, then, I am headed uphill, at a good grade, for several minutes at least. The car doesn't seem to miss but id does ping pretty good up these hills. Otherwise I never detect any pinging. Under load the car runs great.

The spark plug gap is very close if not perfect, as I checked them when I put them in, and as it turns out this is actually the second set of plugs I've tried. They are dual platinum autolites.

When the A/C is on, it does idle up and down as the clutch kicks in and out.

Whenever I've pulled plugs they all look great - the car runs well pretty much except at idle, at which point it has a slightly rough idle - not even enough to move the rpm gauge, but you can feel it through the steering wheel, exhaust note, and through your seat. It's almost like a partial misfire.

I guess I'll have to find a way to check for vacuum leaks - I've already gone around and listened very carfully (several times) to eat hose, and wiggled it, and so on.

I forgot to note that I've also replaced the fuel filter and checked the PCV valve and lines - they are nearly perfect.

Regarding the primary coil resistance - what does a higher than expected primary coil resistance even indicate?

When a parts shop "bench tests" the coil, what do they do?
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Old 07-19-2009, 08:03 AM   #4 (permalink)
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I would look the coil over for cracks in the insulation. This may show up as a miss. You can also mist the coil with water to see if that triggers a miss.

The primary resistance should be very low. It is a large wire that is nearly a direct short.
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Old 07-19-2009, 08:15 AM   #5 (permalink)
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Get a can of starting fluid and spray all the vacuum hoses ,but slowly , one at a time. If the idle goes up you found your leak. Old trick from my past. very cheap and effective. Same with plug wires and coil packs ,but use a water spray bottle. If the engine misses or stumbles ,replace it. My humble and usually wrong opinion says that your miss sounds like a partly clogged injector. get some b-g injector cleaner or seafoam and lucas fuel system cleaner. put a good dose of lucas (5 -10 oz) in the tank and add some gas to mix it in. suck the injector cleaner through a direct intake vacuum line by dipping a small hose that you added to the vacuum line , into the injector cleaner while someone high idles the car. do not let it stall ,but try to get the motor to stumble . suck a half can or so , then let the motor flood and stall. re-connect the vacuum line , let the motor sit a half hour and fire it up.watch the plumes of white carbon smoke kill the neighborhood kids and see if the motor runs better.
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Old 07-19-2009, 08:26 AM   #6 (permalink)
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Well the difference in the coil packs expected primary resistance, may be due to the accuracy of your test meter, or the scale you were measuring on, but a bench output voltage test would likely tattle on any output problems.

Not sure what parts stores you have in your area, or what test equipt they have, but in my area, the coil pack gets an output voltage test, along with some others.

The ping that you hear on a pull up a grade shouldn't be there & may be a clue on the random idle miss that you feel.

Something as simple as an old worn out PCV valve, that's clean inside & rattles when shaken, but not sealing well when it should, because it's worn inside, could cause an unprogrammed for vacuum leak, that'll cause mischief, so if it's due, or past due for replacement, why not change that low cost puppy out????

Are you using the specified heat range plugs in your engine????

Is the cooling system in good condition & is the thermostat keeping coolant temp in check????

Is your 3.0L Vulcan a flex fuel engine????

More thoughts for pondering.
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Old 07-19-2009, 05:34 PM   #7 (permalink)
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I'll try to take these in order again. I also forgot to mention that the cam synchro was also replaced at the same time that other stuff was (although the DPFS and the TRS were slightly later).

Today I replaced the PCV valve (it was cheap). No change.

I have been running fuel injector cleaner for 1/2 of a tank now, Chevron Techron. Periodically I've also run other stuff like the O'Reilly Auto stuff, etc.. when the mood hits. No change.

The multimeter I used (digital) is auto ranging and fairly accurate - I have used it for much more sensitive projects (electronics and motorcycle stuff) in the past. I note the primary coil resistance is clearly out of range, but what I don't know is what that *really* means.

I put one of those "show me the spark" sparkplug things on the front three today (in turn) and they all seem fine, but since I wasn't *in* the vehicle it was also hard to tell if it was misbehaving, too.

Since somebody made note of it, I've been paying much closer attention and, unfortunately, the car *does* ping even on mild acceleration, uphill or level. It /really/ pings good (no check engine lights) on uphills which is why I noticed it.

So, lots of pinging (or at least some kind of preiginition - it's certainly not knocking). It sounds like my old Buick 350 when I used 87 octane. I'm using good quality 87 octane, now, too.

Yes on the plugs - I don't recall the exact number but they are the recommended autolite dual platinums.

Cooling system just got flushed not 3 weeks ago - it was good then and should be perfect now. Never overheats, temp gauge comes up just so, laser themometer thing shows 180 to 195 on the stuff I can get at, and for the brief period I could borrow a scan guage it showed 195 to 205 but never more.

Lastly, it's not a flex fuel engine but all the gas around here has 10% ethanol.

Odd that it's pinging. The engine was very well taken care of by the previous owner - at or before scheduled maint. and always with high quality everything.

I've also done the "water in a spray bottle test" without luck. No change, no misbehavior, nothing.



QUOTE (pawpaw @ Jul 19 2009, 07:26 AM)
Quote:
Well the difference in the coil packs expected primary resistance, may be due to the accuracy of your test meter, or the scale you were measuring on, but a bench output voltage test would likely tattle on any output problems.

Not sure what parts stores you have in your area, or what test equipt they have, but in my area, the coil pack gets an output voltage test, along with some others.

The ping that you hear on a pull up a grade shouldn't be there & may be a clue on the random idle miss that you feel.

Something as simple as an old worn out PCV valve, that's clean inside & rattles when shaken, but not sealing well when it should, because it's worn inside, could cause an unprogrammed for vacuum leak, that'll cause mischief, so if it's due, or past due for replacement, why not change that low cost puppy out????

Are you using the specified heat range plugs in your engine????

Is the cooling system in good condition & is the thermostat keeping coolant temp in check????

Is your 3.0L Vulcan a flex fuel engine????

More thoughts for pondering.[/b]
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Old 07-19-2009, 07:46 PM   #8 (permalink)
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OK, more good feedback.

Not likely any need to fixate on the coilpack primary resistance, as I understand it Ford doesn't specify a primary resistance & yours is within a normal expected range.

The secondary is specified & yours is within spec, you haven't posted any misfire codes, you've done a coilpack wetdown test & other than ping, you say the vehicle runs normally. So I'd set this aside for now, unless you come by some clues that would call for another look.
If you just can't set it aside, pull the coilpack & have it bench tested.

I would be more concerned about the ping problem, as it could cause more than aggrivation, like engine damage!!!!

Also finding & fixing the ping problem, may also fix the random idle miss.

Did the idle miss & or ping problem come about suddenly after some event, or slowly over time?????

Is there any change in the miss or ping between the vehicle being cold & fully warmed up????

Is there any difference in the idle miss when the vehicle is in gear, or in "N" or "P"?????

When you checked vacuum lines, did you also check the evap system vacuum line between the intake manafold & the vapor recovery canister???? It's a common vacuum leak source when it dryrots & cracks, that'll also cause engine ping, as I found out on my 94 3.8L.
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Old 07-19-2009, 11:46 PM   #9 (permalink)
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I assume your car has a SPOUT plug ... are you sure the plug is in place and making a good clean connection. The pinging sounds like a timing problem.
It wouldn't hurt to check the timing advancement with a timing light.
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Old 07-20-2009, 08:00 AM   #10 (permalink)
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QUOTE (Gary123 @ Jul 19 2009, 10:46 PM)
Quote:
I assume your car has a SPOUT plug ... are you sure the plug is in place and making a good clean connection. The pinging sounds like a timing problem.
It wouldn't hurt to check the timing advancement with a timing light.[/b]
What is a SPOUT plug?

EDIT: I don't think I have a SPOUT plug, mine is a '97.

I did clean the MAF, but is there an easy test for the MAF (like a voltage test?)

My understanding is that the EGR comes in to play mostly when steady state cruising - I have pinging even under light acceleration, so it shouldn't be the EGR.


Also, the idle miss seems to be slightly worse in N or P, and it only misses when fully warmed up.
I've had the car less than 3 months, but I don't recall it pinging nearly this bad. The car did sit for almost a year between owners, but the previous owner (a good friend of mine) says it did not ping for him.
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