Question about 2002 Mercury Mountaineer

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Intermittent miss at idle and steady speeds

There is an intermittent miss at idle in a drive gear, when running at steady speeds below 60, and under light to moderate acceleration. The check engine light is on, it flashes sometime under moderate acceleration but has no miss at all under hard acceleration or speeds above 60-65. It has had a heal-a-coil installed on 1 cylinder and the problem was apparent after that. My daughter had the vehicle when the plug blew out and it was driven for a short time after until she brought it home with the "Dad, it's broke" thing. The wires and coils were installed new, new PCV valve, and the Mass Airflow sensor was cleaned with a cleaner designed for that application. I believe it to be some sort of electrical problem or possibly the speed sensor on the drivetrain? The stereo system/clock shorted out but I do not remember if it did before or after this problem. AND, I forgot to mention, if I remove the ground cable for a few minutes the check engine light stays off long enough to drive 15 miles or so with a VERY slight miss the, when it comes back on, it's back to the same.

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  • rick hardin Nov 10, 2014

    I already ran a code on this do not remember the code but it was a miss on cylinder 8 which was the cylinder that blew the plug out. The vehicle does not loose power on hard acceleration nor is the miss rhythmic according to firing order or for that matter, even constant in that sometimes there is no miss at all. It is only there when idling in drive, driving at a steady speed, and at mild to moderate acceleration. It is not present when idling in Park 90 % of the time, nor is it present when driving at speeds above 60 after it has shifted into

  • rick hardin Nov 10, 2014

    …Guess I hit enter by mistake… after it shifts into OD it does not miss. However in second and 3rd gear when driving about 1600-1800 rpm it is there very bad sometimes. It is not there when driving fast enough to be in OD. If it were a plug misfiring wouldn't it misfire at any rpm and loose power the harder you accelerate. It only throws the 1 code according to O'Reilly Auto Parts scanner. There is not an explanation that I can come up with from anyone why it only throws this code but performs the way it does. A miss is a miss when it is plug but tis is sporadic not following a regular firing order. I'm confused and so is everyone I have ask AFTER they drive it. It's like they think I'm crazy until they do and it performs this way. It has been scanned 3-4 times by different people. Hope this helps, thanks.



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If the ck engine light comes on it should give you code which cyl in causing the problem could be a plug wire or coil

Posted on Nov 10, 2014

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You need to hook up a computer scanner to the engine to find out what the fault code is [indication of what is causing the miss]. The CHECK ENGINE lamp lights up when a fault code is detected and set in the computer's memory. ALWAYS replace all the spark plugs on a Ford when there is a miss. Those "alleged" 100,000 mile spark plugs are really only good for about 60,000 to 65,000 miles. Using them longer than 60,000 miles causes the ignition coils to overheat [from trying to fire the huge gaps on those worn out spark plugs] & fail. Hopefully, you will get a fault code to tell you which cylinder is the problem. When you disconnect the battery, you give the PCM [engine computer] a case of amnesia, and it forgets the fault codes it has stored in it's memory. That's a foolish move, as it only removes the info a "real" mechanic needs to solve the problem. Use only Motorcraft, NGK or Denso spark plugs. Other brands won't last in a Ford product.

Posted on Nov 09, 2014

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  • Charlie Nov 10, 2014

    OK, most likely it was P0308. That indicates a miss on cylinder #8. Late model Ford products with COPS [coil over plug system aka individual ignition coils] have failure symptoms which are almost the opposite of what a coil with distributor has. Often they miss at or just above idle and also under light accelleration or cruise. Yet the miss will go away when you stomp on the throttle. Other possible issues are a dirty fuel injector. You can try switching the #8 & #7 fuel injectors. If you then get a miss code for #7 [P0307] you have found the problem. It's also possible that the shop damaged the new spark plug or the new plug is defective. However, from the symptoms you describe, the most likely cause is a bad #8 ignition coil. FYI ALWAYS write down and remember ALL fault codes, so you can give us that info. Also include the mileage and engine size [when more than one engine is available]Otherwise, you are simply asking us to guess.

  • rick hardin Nov 11, 2014

    I'll give these things a shot. Thanks!

  • Charlie Nov 11, 2014

    Rick, the best strategy is to install a new spark plug in #8, swap #8's ignition coil with #7, swap #8's fuel injector with #6. Road test then check for fault code with a scanner. No more problem means it was the spark plug in #8. P0307 code [#7] means that the ignition coil is bad. P0306 code [#6] means the fuel injector is the problem. If codes stays on #8 [P0308] that means you have a mechanical problem with the #8 cylinder & the cylinder head will need to come off to repair it. I should have mentioned this in my last post.



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SOURCE: 2002 Mercury Sable-shakes with acceleration

You describe this as an acceleration problem however, if the car does throw a check engine light it should be recorded in system memory so it can be pulled by scanning with and OBDII scanner. It sounds as if the car is being starved for fuel on acceleration. Check the fuel lines for kinks as well as check the fuel pressure. The problem could be a faulty fuel pump that has yet to completely die.

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check for dirt or rust in those injector screens

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SOURCE: I have a 2000 Mercury Sable. runs at speed and

There are many possibilities on this. Anything from bad Gas, Bad Ignition Wires, Bad Distributor/IgnitionCoil, Intake Air Leaks, Bad Sensors etc.
It sounds like a malfunctioning Idle Air Control Valve. You can take this off and clean it with Carb Cleaner. Reinstall and check operation. If it helps but does not solve completely the problem: Replace this.
Check your Ignition Wires and Distributor/Ignition Coil.
The Idle Control Valve is available at
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SOURCE: engine light on, idles rough. had engine light diagnosis.replaced

See if you can get the codes. If it is still number 4 only (probably a P0304) it could be the fuel flow through injector 4. Try some Techron cleaner and make sure number 4 plug isn't fouled. Also get the compression checked on number 4.

If not, it could be the ignition control module assuming all other changes have been made. If you get a code it will help. A P0300 would point toward the ICM. If it is number 4 only it could still be the ICM. Expect around $150 for the module if you do it yourself. The ICM may be under the coil pack. If you are getting a P1361 and/or P1362 it could be the Cam position sensor. They are around $40 and are usually near the number one cylinder. Mine is hiding under the water pump pulley. It is a Buick with the 3.8 engine but the principal is the same.

Posted on Mar 14, 2010

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