Misfire-Excessive Heat- Melting plastic smell- RPMs stay high after letting off pedal

meshow99

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Apr 19, 2004
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NH
HELP – 1 week old car (to me!)

Well, there are the symptoms. I bought this car a week ago. It’s a 2000 Mustang GT convertible with 53k. Yes, only 53k, so I though I was all set, no problems. WRONG! I had been driving it for the past week without issue, then all of a sudden while on the interstate, I get the service engine light blinking. I drive it slowly home (35 minutes away) and the light alternates from solid to blinking.

Autozone scanned it for me and pulled P0301. After some research I decided to change the coil. This seemed to work and the idle and driveability returned to normal. Once the car got real warm, (don’t know if it was when it reached closed loop) the misfire started again, and this time I could smell a rubber or plastic burning smell. (it is possible this is the new coil reacting to the heat?). I will say that I cant touch my radiator hose cause its too dang hot.

Finally, here is another tidbit, not sure if its related, but since I got the car, there is a lengthy delay until the RPMs drop when I remove my foot from the accelerator. They stay high for about 3-5 seconds after I remove my foot. Is this related? Thanks in advance…
 
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wmburns

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How to troubleshoot IAC Idle problems

Congrats on the new addition.

Regarding the hanging idle problem. These cars are designed with a two step idle process. It will not go to "slow" idle until the car is STOPPED. This is for smog reasons and they all do it.

The the idle is excessively high (over 1100 RPM when moving, 800 when stopped), please review the following post #3

http://www.stangnet.com/mustang-forums/810729-starts-but-dies-idle-help.html

Next problem. The DTC P0301 indicates a mis-fire in cylinder #1 (engine front right). Is this the coil you changed? What about the spark plug? Any moisture in the spark plug wells?

Is the burning smell coming from the Coil on plug (COP)? Is the COP itself hot to the touch (or warmer than the others)? Or is the burning smell coming from the cats under the car?

When the misfire is VERY bad, the unburnt fuel in the exhaust will "flare off" once it hits the cats. This makes the cats run very hot. This will quickly ruin your cats resulting in an expensive repair.

Not a bad idea to do the Normal maintence items for a "new to you" car. Change the fuel filter. Clean the MAF (use only a product designed for the job).

Fuel injectors can also cause a chronic misfire. IMO, we should rule out an ignition problem first.

>>>From Ford Service CD
P0301 through P0310 - Misfire Detection Monitor

The misfire detection monitor is designed to monitor engine misfire and identify the specific cylinder in which the misfire has occurred. Misfire is defined as lack of combustion in a cylinder due to absence of spark, poor fuel metering, poor compression, or any other cause.

Ignition system
Fuel injectors
Running out of fuel
EVAP canister purge valve
Fuel pressure
Evaporative emission system
Base engine

The MIL will blink once per second when a misfire is detected severe enough to cause catalyst damage. If the MIL is on steady state, due to a misfire, this will indicate the threshold for emissions was exceeded and cause the vehicle to fail an inspection and maintenance tailpipe test.
 

joshjwc9

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Jun 12, 2006
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Make sure there isn't any debris in that particular plug which is the first cylinder from the front of the car on the passenger side of the vehicle. Is the connection from the COP to its connection complete (as in seated all the way?). WMBurns covered many of the other issues that might be presented.

The burning smell also could be grease that you may have gotten on the boot of the COP burning off, same thing happens on exhaust when you install a new piece as well, but I would too, make sure it isn't grease by seeing visually if anything is burning.

Good Luck.
 

trinity_gt

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Jan 31, 2003
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You might have a problem with the coil driver in the PCM for #1. Replacing the coil the first time fixed a symptom for a while. What you're smelling is probably the new coil overheating and self-destructing due to excessive heat caused by too much primary current duty cycle.

Start tracing the wiring, where visible, back to the PCM in the passenger-side footwell. The PCM itself may also be suspect.
 

meshow99

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Apr 19, 2004
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OK - New info. It appears to be electrical. I pulled the new COP out and it is fried. Cracked and leaked (see attached pic). Now I put the factory one in cyl 2, and cyl 2 COP in cyl 1 and the one in cyl 1 fried instantly. Melted it.

Now looking at the harness I pulled connectors off coils 1 and 2, an dtested each with the car running, and they both have 12v coming to them. The interesting thing is that the green wire(i think..going on memory) on the cyl 1 connector is very limp as if it may be broken. All other wires have some resistance to them when you bend them slightly, this one does not.

If this wire is broken, would that fry my COPs? I am kind of thinking that the wire was almost broken and finally engine vibration caused it to fully break. Thats why what started out as a cyl 1 misfire (and allowed me to drive home 45 minutes), finally climaxed in instantly melting coils. :shrug:
 

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wmburns

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The COP circuits are ground start devices. This means that the device is activated by completing a connection to GROUND. As a result, there is ALWAYS +12 volts at the COP (RD wire) all the time the ignition is on.

If the return wire were broken, the results would be "no spark".

The COP is burning up because of excessive dwell. In other words, the ground return is on too much (or all of the time). The challenge is to figure out why.

This could be a ground short in the return wire. This could also be a bad PCM coil driver. If the PCM is bad, the only repair is a new PCM.

First, with the key on, measure the resistance between COP #1 LG/WH and battery negative. Repeat the test with the key off. Post the results.

Remove the battery negative cable. Disconnect the main PCM harness and the COP connector. Test the wire path LG/WH wire to PCM pin #26. If the wire path tests OK(good continutity and no ground faults), then the PCM is bad.

Do not continue to drive with this problem. I recall another poster that did. The post was updated with the results of the engine fire damage and repairs.

Edit: here is a link regarding an engine fire.
http://www.modularfords.com/forums/showthread.php/152912-2v-gt-2000-.-1-coil-keeps-blowin-help!
 

meshow99

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Apr 19, 2004
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OK, so key on about 92 ohms, and key off, about 12 ohms. Any idea what that means? Also, i am not sure how to perform the test at the PCM #26 and COP harness. Can you give me step by step?
thanks!
 

wmburns

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The numbers posted do not seam quite right. Confirm that the test was done with the COP electrical connection disconnected from the COP itself. As Ohm's law is I=V/R. This means at 12 Ohms, there is an amp flowing through the coil at all times. But it does not make sense that the resistance is lower with the key off.

Please repeat the Ohm measurement on the other cylinder's COP. Be sure to test the return wire (not the RD or WH/BL supply wire). Post the results.

Also works to use a "noid" style test light across the COP connector. The light should flash with each firing pulse. If the flash is too long (or on constantly), this indicates excessive dwell.

Regarding a step by step return wire test. Disconnect the battery negative. Disconnect the COP connector and the PCM connector. The PCM is located in the driver's kick panel area. Locate the COP return wire and the correct return at the PCM connector. Measure the resistance through the wire (and only the wire). The number should be very low indicating a good return wire path.

Next measure the resistance between the return wire and a known good ground. This should be very high (several meg Ohms). This will test for a ground fault in the harness.

Once excessive dwell has been confirmed and the wire path has been confirmed good, the only thing left is the coil driver in the PCM itself.

Note, the odds do not favor a wiring problem unless something has happened to comprimise the wiring harness (recent work, water damage, rodent activity). However, replacing the PCM is a big expense and PIA that most ppl would not want to undertake for diagnostic reasons.

Please review diagram 21-5 for the Mustang GT ignition system.
 

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meshow99

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Ok so the wire common to all the COP harnesses is white w/blue stripe. That has 0ohms with key off and 100 w/key on. Other wire measures 32ohms with key on and 8 ohms with key off at cylinder 1. Cyl 2 measures same at white/bl wire and other wire measures nothing either way.
 

wmburns

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The wire common to all COPs is the +12 volt supply wire. The supply wire is either RD or WH/BL depending upon the MY.

The other wire is the return wire. Please look at the attached wiring diagram for the specific colors for each cylinder.

Regarding the measured Ohm value. Zero Ohms is a dead short (very low). Where as infinity is an "open" circuit (very high Ohm).

We need to confirm if the return wire for #2 is reading very low (short) or very high/infinity (open).

FWIIW, I expected the working COP's return wire to read open or a very high value. The fact that #1 has a measureable number indicates there is some current flow all the time. This likely confirms the diagnosis of excessive dwell. It does not pinpoint the source (wiring or PCM).

In any case, unless you are willing to buy a PCM for diagnostic purposes, a full return wire path test is needed to confirm the problem source.

Good luck.

PS, as a reminder should you decide to purchase a replacement PCM. Often ppl will forget about the anti-theft system (PATS). The cluster and PCM are programmed for each other. A salvage yard PCM will not work without disabling PATS or re-programming.

If purchased from an autoparts re-manufacturer, the PCM normally arrives with PATS disabled. PATS can also be disabled with a hand held tuner such as SCT.

If going the salvage yard route, try car-part.com. Also get a PCM from the same engine, transmission, calibration code, and MY if possible.
 

meshow99

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Apr 19, 2004
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Lemme try again. I am doing this from outside....wh/bl measures 83ohms with key off at both cyl. Cyl 1 grn wire has 2 ohms and cyl2 red wire has 0ohms.
With key on all wires have 0 ohms except. Grn wire at cyl 1.
 

meshow99

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Apr 19, 2004
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To further clarify, I say 0 ohms it means no reading on digital ohm meter. It displays a 1 which is open circuit
 

meshow99

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Apr 19, 2004
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Heres the scoop. I performed all test WMBURNS. wire path measured about 1 ohm resistance, as did the the COP harness to a known ground. I beleive this means the return wire is contacting ground somewhere.

I hooked up the ohmmeter to a ground and to the return wire after looking at the harness and it seems i have removed the contaced point of the wire (albeit accidentally). There is an open, however I was able to get a reading at one point while playing with the harness, so there is definitely something there. It seems to be in the back of the intake area. Should I remove the harness altogether? I can see some places the sheath has split, though i did not have the vantage point to see if there was exposed wire. What should I do?
 

wmburns

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This sounds like a classic good news/bad news story. At one level it is a relief to find the problem. At the other level, repairing an engine harness can be a PIA.

The really good news is you didn't buy a replacement PCM only to have the problem re-occur.

How to fix. That depends upon your skill level and how you view your time and $$.

Some ppl would simply get a new/used harness and be done with it. It's a fair amount of work to replace a harness, but it is a job that the average DIYer can do. Remember to TAKE PICTURES before starting.

Other ppl would attempt to repair the harness themselves. NOTE, if there is an open/short in the harness, these things almost never happen in a vacuum. There is an external factor affecting the harness. Examples include rodent activity, wire chaffing from vibration, water damage, or heat damage.

One method to fix this is to run a replacement wire external to the harness. This involves cutting the return wire at the COP and again at the main engine harness. It will be necessary to perform a professional splice. That includes SOLDER and shrink wrap on each end.

However, this method does not address the cause of the original failure. If the original failure was due to vibration, it is reasonable to expect that sooner or later, more wires will be affected (if they haven't already).

Of course, you could remove the harness and perform a bench repair. This will give great access and allow for a more professional result. IE, it would be possible to cut open the harness, do the repair, and then re-tape so it is a good as new.

I suggest that a through inspection of the harness be performed to see if you can locate the source. Only then can a good decision be made.
 

meshow99

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Apr 19, 2004
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WMBURNS - Thanks so much for your help. Couldnt have done it without you. I pretty much disconnected the whold passenger side harness so I could basicall give myself enough slack to see the part that rests near the rear of the engine. There is a pic of the culprit. Clearly this area had a friction problem. It had worn through. Luckily all other wires were intact. I managed to unwrap enough to get some slack on the wires and repaired the exposed area, then I did a thorough re-wrap of the bundle, then I got new sheathing, and wrapped that all in high temp tape. Finally I secured the harness intermittently along the length which should eliminate this from happening again.

Thanks so much again. Its nice of you to share your time and expertise. I am a recent fox body convert, and quite knowledgeable about them,so I will be sure to pay it forward. God Bless.:nice:
 

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wmburns

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Glad I could help. Obviously, you deserve some credit for yourself. You stuck with it long enough so that when the "harnes wiggle" test was done, you could see/understand the results. I am sure that helped with the understanding it truely was a wiring problem.

I got the sense that maybe at first, you didn't understand what the Ohm tests were for and what the results meant.

Did you have an "Eureka" moment when it was found? Sometimes in my case it feels like a great weight has been lifted when the solution for a difficult problem is finally found.

How long did it take you to actually find the problem and then do the repair?

I suspect you may have found one of the reasons the prior owner sold the car.

PS, are you still having the "hanging idle" problem?
 

meshow99

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Apr 19, 2004
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I maybe didnt understand the ohm tests, but as I learned the function of this return wire it makes sense how the exposed wire grounding out would cause excessive dwell. i had actually connected a wire into the COP connector, and wrapped it around one of the ohmmeter leads, then I secured the other lead to ground. I had it on the audible tone setting. As I wigled the harness i did get a beep last night. I wasnt able to duplicate it today, so i chose to focus on the suspect area of the harness. As soon as i was able to get slack i looked at it and saw what I thought was an exposed area. This was easily confirmed by simply taking the probe off ground and touching that area. I heard a tone. Problem solved. Total work to find, repair and fix (with travel time) was a couple hours today, along with a couple yesterday.. better than paying money out...

Hanging idle is apparently not so much of an issue, as I have read that the RPMs do nt fully return to idle until the car is stopped. It seems that my condition is not really a condition. Hopefully!

thanks again.
 

trombonedemon

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Jun 25, 2009
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U.S.A, U.S.A., U.S.A.!
Glad to see this got resolved, I love reading a good tech thread!
Ya darn tooten, this thread was sweet, I don't want to say we need more threads like this cause I don't like to see people w/car problems, but when problems do occur they should read just like this thread went.
Burns, one my teachers, whom of which used to be a G.M. master tech, once stated he knew a gentleman whose daily job was just going around to mechanics and diagnosing there vehicles for the mechanics. Thats all he did, and he made a really good living out of that. You ever considered doing that for a living if you havn't done that already?
 
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