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Old 05-09-2005, 04:47 PM   #1 (permalink)
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2002 Taurus SEL 3.0L Duratec engine, ( 93,000 KMS)
Have annoying engine miss at idle, most noticeable when in drive, stopped
at traffic lights. Service Engine Light did not illuminate.
Miss is that noticeable that it is felt throught car by all occupants.
Ford delaer ran diagnostics and road test, no faults recorded. They recommended
replacing plugs / fuel and air filters, done by Ford dealer, problem still exists.
Ford dealer suggested wait till Servicre engine light comes on, and then return
to garage. Several thousand KMS since, and still no light illuminating.

Acceleration to highway speeds do not feel smooth.

In recent days I have noticed that when heater/AC is turned off, miss is
gone, turn on heater or AC and engine begins to miss.

When the heater is turned on, you can hear a heater or ac vent door closing
or opening, is the heater and ac system, and within a minute engine begins to
frequently miss.

Seems very strange that turning the heater or ac system on, could cause this miss.

I have already spent $600.00 for tune up / diagnostics and no closer to finding
problem, do not want to continue troubleshooting at these costs.

Any suggestions or ideas.

Thanks
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Old 05-09-2005, 07:35 PM   #2 (permalink)
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The following info is about gen3, but might be similar on gen4. When the HVAC system is on in any setting except Vent, and it is warmer than 50 degrees, the A/C compressor clutch will engage as the cycling control deems necessary to provide good cooling. Perhaps there is too much drag from the A/C compressor, or there could be some other problem that adding the extra drag from the A/C makes worse.

In any case, the way that the HVAC system effects the engine is by engaging the clutch that couples the compressor to the the engine. Otherwise, the pulley spins, bit the compressor does not turn.
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Old 05-09-2005, 08:05 PM   #3 (permalink)
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Maybe there's looseness in the AC pulley/clutch assembly that's causing it to feel like a miss, but it's actually the vibration of the pulley assembly. Try cycling the AC and having someone watch the pulley, carefully of course.

Another idea: The HVAC vent doors are operated by engine vacuum. Perhaps there's a broken line somewhere, causing a slight vacuum leak.

If it were actually misfiring that badly, it should set a CEL.
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Old 05-10-2005, 01:34 PM   #4 (permalink)
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I have a 2000 Taurus w/ the Duratec (30000mi). I think I have a similar situation.
No check engine light has ever illuminated for me either.
I'm not sure what a misfire feels like but my engine will 'pulse', that is felt throughout the vehicle, and I can even hear it.

However, it only occurs after the vehicle is warmed up and has been driven for a while. Turning off HVAC did stop it, but for only a short time, pulse came right back.

Acceleration also is not smooth when this begins to occur.

I'm going to my local library to pull all of the TSB's (Alldata account at the library).

Do any of you think getting a OBDII scanner to capture the event as its happening will work (remember no check engine light ever comes on)?
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Old 05-10-2005, 03:03 PM   #5 (permalink)
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Pardon the hijack....

One of the reasons I had the issue of the A/C at idle on my mind is because my 96 Duratec also does this. When it gets hot, it will start pulsing at idle. If I turn off the A/C or put it in neutral, it will stop pulsing momentarily as the engine load changes, but then starts again. The acceleration will degrade. At the first stoplight after a long freeway drive it will stall out. If I keep driving it will eventually get so bad that it stalls at every stop.

Never a code.

It's has literally done this for years. The frequency of the problem never gets worse other than seasonally (worst in the dead of summer, never in winter) so I never get hacked off enough to actually fix it

Plugs changed, wires changed, fuel filter changed, transmission changed (it had other problems) intake removed cleaned and replaced. I need to get off my lazy butt and measure the fuel pressure when it gets into the failing state. The fuel pump may be acting up when it gets hot.
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Old 05-10-2005, 09:33 PM   #6 (permalink)
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I guess I'd say check the EGR system (valve, DPFE, EVR). If there's too much EGR, you will have a misfire. That should set a code, but certain combinations of failed components can elude detection.

Also, check your ignition coils. Faulty ignition coils will often seem fine when cool, but fail when hot.

You might expect that a misfire would cause the MIL to illuminate, but it isn't necessarily so. The OBD-II misfire monitor has two types of misfire: Type A and Type B. A Type A misfire occurs when a misfire is detected in more than 15 percent of a cylinder's firing opportunities during 200 crankshaft revolutions. This will immediately flash the MIL and set a code.

A "less serious" Type B misfire occurs when a misfire is detected in two percent of a cylinder's firing opportunities during 1000 crankshaft revolutions. This will set a code, and light the MIL if it occurs during two consecutive trips.
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Old 05-11-2005, 12:02 PM   #7 (permalink)
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May be a coil pack starting to go bad or just not working to spec. The coil pack may not be bad enough to throw on the light, but bad enough to feel a slight misfire. I had an F150 with a bad coil pack with similar symptoms, and I drove it that way for a long time before the coil pack finally went altogether and threw a code pointing to that cylendar.
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Old 05-11-2005, 12:15 PM   #8 (permalink)
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Coil pack was was I was going to check next, if the fuel pressure looked good. It's easier to get to the fuel pressure than the coil pack (mounted behind the snarking intake manifold.)

onamission
I guess that's the upside/downside of having a coil pack. It can keep running a long time with only one of the coils marginal, but is harder to diagnose

holedigger
Is that general OBD-II information, or specific to the Ford PCM? This is exactly the sort of thing that would be crucial to diagnose these non-code failures!

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Bob's points about the A/C are almost certainly better than mine.
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Old 05-11-2005, 12:55 PM   #9 (permalink)
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Is this a coil on plug engine or does it have spark plug wires?
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Old 05-11-2005, 01:12 PM   #10 (permalink)
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Mine (96 Duratec) has plug wires and a pack of 6 coils under the UIM on the firewall side of the engine. I'm pretty sure the 02 (of the thread starter) has then same setup.
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