Modded Mustang Forums banner

1 - 14 of 14 Posts

·
Registered
Joined
·
672 Posts
Discussion Starter #1
So I have a few questions. When I first bought this car this past may, it was throwing a misfire code and never got fixed. I have a bama tune on it now and I don't think it will throw a code because of that but you can clearly hear the misfire at idle and deacceleration. Plus it vibrates the motor.

My question is in terms of changing the spark plugs, what would be the ideal torque settings? Because I heard alot about our motors blowing out plugs and thats the last thing that I want to happen. And the ford dealer wants over $800 dollars to do the plugs and packs, which I refuse to pay.

Is there a way to test my coil packs individually? I don't think they're the motorcraft brand, but they're really expensive and I just don't want to have to replace all 8 of them at once.

In terms of fuel injectors, is there a way that I can take them off the car and clean them by hand? The car has 46k miles on it , so I don't understand how fuel injectors can go bad that quickly. I was thinking that they're just dirty, but was wondering if there's a way to clean them by hand.

The fuel filter was replaced when I bought the car so I don't think that will be an issue, but other then those three things what else could cause a car to misfire like this?

Thanks in advanced!
 

·
Registered
Joined
·
380 Posts
Try pulling plugs individually and crank the motor. Be sure to pull out the fuel relay first though, you wouldn't want the engine firing over without a plug in one of the cylinders. If it's a bad plug or coil, you should be able to find out this way by seeing which one isn't sparking.

As for injectors, there is not really a way to clean them by pulling them out. There's a little solenoid in there that opens and closes when it needs to. With the engine running, put a screw driver up to each injector individually and put your ear up to the other side of the screw driver. You should be able to hear each injector tick. Whichever one isn't ticking, that's the bad one.
 

·
Registered
Joined
·
655 Posts
A misfire can have several causes. Like states above, you can test individual coil packs, and even fuel injections, by running the motor and unplugging one at a time and checking for a change in idle. If you find a COP that 'isn't working,' switch it to a different cylinder and see if the problem follows the swap.

As for spark plugs, they're cheap. Buy a set of OEM motorcraft ones and throw them in there. Torque them to 13 ft/lbs.

If the misfire is only on one cyclinder it's probably either a spark plug, COP or fuel injection. If its a random misfire chances are you have a vacuum leak, or your intake manifold could even be on it's way out.
 

·
Registered
Joined
·
2,936 Posts
You can perform a go/no go test on the COPs by reading the primary and secondary coil resistance with a multimeter.

Place one lead on each of the COP's primary terminals--the terminals at the top. This should read between 0.3Ω and 0.8Ω. Should it read less than 0.8Ω to 1.0 Ω, the primary is likely shorted. If it reads in the Mega Ohm range, the coil has likely burned/broken open completely and will certainly cause a misfire.

(Note: When reading such low resistance values the resistance of the test leads themselves becomes a component of the meter's readout. Before making the primary coil measurement short (connect together) the test leads and note the meter's display--this is the resistance of the test leads, it should be subtracted from the reading you get when testing he primary.)

You can also measure from either of the primary terminals to the spring in the plug boot. This should read between 4kΩ to 10kΩ. Any less would indicate a shorted secondary, more than 12kΩ to 15kΩ, or infinite resistance, indicates the secondary is open.

The best way to test them is to get an adjustable gap spark tester. Set it to a 1/2" gap, connect it to the COP and turn over the engine (pull the fuel pump fuse and run it "out of fuel" first to prevent it from starting). Any COP that will fire across a 1/2" air gap has nothing wrong with it.

Check out the boots as well. If they smell burned, or are hardened or cracked, then replace them. Most FLAPS will have them in stock, or you can get them online for $3 a pop.

And as others have said do not focus entirely on the ignition system; fuel, compression/leaky valves can cause misfires as well. The PCM's misfire detection routines only check the crankshaft rotation for expected rotational acceleration and velocity--they do not watch the spark or fueling.

The spark plug torque recommendation is 11 to 13 lb-ft, or 132 to 156 lb-in. Get a 1/4" drive torque wrench from Harbor Freight. A 3/8" wrench could be used but the 1/4" drive is better as the recommended plug torque falls within the top end of it's 200 lb-in capacity--I.e. the most accurate end of its range. With a typical 3/8" wrench you'll be in the lower 25% of its range, any 1/2" drive torque wrench is unsuitable for torquing the spark plugs.
 

·
Registered
Joined
·
672 Posts
Discussion Starter #7
Thanks for the responses, I'm gonna work on replacing just the plugs tomorrow as well as the serpentine belt (only because it needs it) One question though, I already have this 3/8" torque wrench. Would I be able to use this or is it too big for the job? Meaning too much leverage? And if I do use this wrench is it best to set it at like 12 ft.lbs just too be safe?

 

·
Registered
Joined
·
2,936 Posts
I would set it at 13 to 14 lb-ft, a tad more than the spec but not enough to create a problem. For over a year I have been using a torque limiting spark plug socket that ticks over at 14.5 lb-ft:



Only sort of off-topic, here is a nifty tool for calibrating your torque wrenches, a digital torque adapter from HF.



I do not use it for its intended purpose, but rather as a calibration standard. I checked it with dead-weight loading and found it to be very accurate (more accurate than most "clicker" torque wrenches) and happens to be on sale now. For $30 it is a steal...
 

·
Premium Member
Joined
·
5,519 Posts
Another big tip for installing plugs is put a little anti-seize on the threads. If you don't your torque reading will be incorrect, and you'll be more likely to strip out a thread.
Depends if its a dry torque spec or not.

Sent from my XT907 using AutoGuide.Com Free App
 

·
King Trashmouth
Joined
·
21,891 Posts
Depends if its a dry torque spec or not.

Sent from my XT907 using AutoGuide.Com Free App
Most claim that it's a dry torque spec, but the aluminum in the heads is so damned soft it's easy to strip them out without the anti seize, as well as the fact it helps prevent galvanic corrosion, which can also cause problems during removal.
 

·
Registered
Joined
·
672 Posts
Discussion Starter #13
Alright so I pulled out a plug this morning and it was gapped perfectly and hardly saw any wear on it with the exception of black on the part that was in the motor. Also did the cop unplugging and they all seemed to be working fine. I did unplug the cop's while the motor was cold. Would it make a difference if the motor is cold or if it was driven a little bit in terms of getting a misfire?

My next question is about vac leaks. Where exactly should I be checking for vac leaks at? And is their a sensor that I should replace that can cause a misfire also?

Getting back to the fuel part of this misfire, is their a way that I can test my injectors or have a garage test them for me to eliminate the injectors as being a problem?
 

·
Registered
Joined
·
2,936 Posts
Have you pulled the code(s) to see which cylinder(s) are misfiring, or if it is a random misfire?

The injectors can be tested, however there are not that many places equipped to do so properly--it is usually a "mail order" process unless you are fortunate to live near a shop with that capability. Most don't because they are just parts changers and have no problem charging a customer for new injectors.

Google "mustang vacuum leak testing" for more than you will want to know about it.

Also keep in mind that though 45k miles is not very much, 9 to 13 years is. I do not know whet year your New-Edge GT is, but at best it's 9 years old. When they get that old anything can, and will upon occasion, break...
 
1 - 14 of 14 Posts
Top