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Problem with misfiring cylinder

A

abyssius

CEG'er
Joined
Jun 27, 2008
Messages
64
Location
Long Island, New York
Sorry for the long post. I didn't want to leave anything out. My car is a 1998 Mystique LS, 2.5. I've owned since new. I recently changed the plugs for the first time by myself at 120,000 miles. The only other ignition work I've done to this car is in response to a no-spark condition, I replaced the coil pack (which turned out not to be necessary) and replaced the crankshaft position sensor (which turned out to be the cause of the problem). This I did last June, and the car ran flawlessly after that.

Recently, I was experiencing a slight bucking/hesitation on light acceleration. I decided to replace the spark-plugs. I removed the coil pack as I have done before, and I also removed the EGR vacuum regulator (which it turns out I didn't have to do). When I removed the EGR vac reg, some of the small plastic hoses were brittle and consequently cracked. I carefully replaced these hoses with new rubber hose, before I reinstalled the EGR vac reg.

Anyway, after replacing the spark plugs (gapped to 1.3mm) I started the car and it ran okay at first. But, after a while it was running very rough at idle. I noticed that the check engine light began flashing. When I turned off the engine, I observed smoke coming from the connect-pipe that ties the exhaust manifold to the Cat convertor. I checked this forum, found out that a flashing CEL means misfiring. I re-checked the plugs and discovered that cylinder #3 was not firing - (wet plug). I checked the resistance of the wire and I checked continuity all the way through to the tip of the plug. I replaced the coil module with my spare. Restarted the car and still no firing of cylinder #3. I then swapped the wires between cyl 2 and cyl 3 to see if the the no-firing followed the wires, but cyl #3 still failed to fire. I swapped the new plug with an old plug and still the problem remains.

There are slight differences. It seems that after I reset the computer (removed and replaced fuses 4 and 11). The car felt fine and I had full power and RPMs. However, after driving for about a mile, the CEL starts to flash, and I notice a slight roughness in its driveability. The smoke condition has not returned however.

I know I should probably try replacing the wires, but I'm not in a position right now to throw money at this car without knowing for certain this is the problem. The car has never burned a drop of oil since I've owned it and I've always used synthetic oil. I don't want to think that I have a bad cylinder all of a sudden, especially since the car was running okay until I decided to change the plugs. Any tips as to how to proceed would be greatly appreciated. I've grown to love this car and it is still in pretty good shape body and interior wise.
 
Bad Wire?

Bad Wire?

If you cannot afford new plug wires at this time try swapping a wire with another cylinder. If the problem moves with the wire you have your answer. If not you eliminated a possible problem. You can run you car in the dark with the hood open (Car must be parked. Do not drive with hood open. Very unsafe. My lawyer made me write this disclaimer.) Inspect the plug wires for arcing to the engine manifold. This can identify bad wires.
120,000 miles on the wires probally exceeds the max life of the wires. If you do need to change wires most members seem to prefer motorcraft oem wires. Some also like Autolite plugs and wires. Both brands seem to work with the tempermental ignitions. I have read that some member recommend changing plugs and wires at the same time to avoid good plugs ruined by bad wires or vice versa.
If you have codes to post it does help members diagnose problems. It is not recommended to drive the car with flashing CEL. This indicates a misfire. Can damage other parts such as cats. Dan
 
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Letting the misfires happen is probably the cause of the persistence of your problem. Plugs and wires should be replaced at the same time. Misfires usually damage the plug AND the wire on the associated cylinder.
 
abyssius said:
... My car is a 1998 Mystique LS, 2.5. I've owned since new. I recently changed the plugs for the first time by myself ....
Click to expand...

Humor me. Recheck your spark plug wiring order.


V6 Duratec Spark Plug Wiringorder

Note the 4-6-5 for the coil pack at the firewall side.

Firewall side
4- 6 -5 <--coil pack
3-2-1

1-2-3 <--engine
4-5-6
Radiator side

Spark Plug gap 0.054 inch
 
@Tony2005 The wiring order was okay. Got the 4-6-5 thing.
@Dan-the-rug-man I swapped wire 2 with wire 3 and the misfire stayed with cyl 3. This got me really nervous.

I think I fixed the misfiring problem. MY ADVICE: Don't buy $1.75 Autolite 764 plugs from Autozone. Apparently, the Autolite copper core plugs and platinum core plugs use the same part number. The cheap ones suck! I threw back in my fairly worn Motorcraft plugs and the car began to run on all cylinders again. The check engine light stopped blinking. However, the CEL came back on after about 30 miles of driving. The idle is slightly shakier than it was before, but I seem to have full power and RPMs. I must have screwed up the vacuum tubes somehow. I haven't had a chance to get the codes because it's been raining like hell up here the last couple of days. I hope I didn't destroy my CAT. I hear what sounds like a 'ticking' exhaust gasket leak that wasn't there before. I guess I need to get the codes before I proceed any further. Thanks for the responses. This forum is great.
 
As I recall, the double Plats are part # APP764. Check the inside of the spark plug boot, look for a white/grey line running parallel to the boot (Carbon tracking). I chased a similar problem for quite a while replacing plugs and wires repeatedly (unfortunately, not at the same time :troutslap:), and the bad plugs kept killing the wires, then the bad wires ruined the new plugs, etc. Changed both at once, and it was good as new. The carbon tracking looks like this:

carbon2ec9.jpg


Also, IIRC, the green vac. tube goes to EGR, and red goes to the fuel press. regulator after sliding under the UIM.
 
Well I though it was fixed!!!! Apparently, the car fires up okay and runs okay while the engine's cold. As soon as the engine begins to warm up it starts to idle rough - and if I drive it for a few miles after that, the bilinking CEL returns. The problem still seems isolated to cyl 3. When I pulled the #3 plug, it was blackened and wet. All the other plugs look fine. So far, I've swapped plugs, swapped coil modules, swapped wires on cyl 3. Still the same result.

Maybe, I shoud preface this with why I decided to change the plugs in the first place. Altough, the car was running okay, occasionally on light acceleration, I would get a very brief buck, almost like a momentary ignition cut-out. Also the CEL would come on. If I reset it , the CEL would stay off for a week or so then come on again. I stupidly, never got the code checked.

After putting up with this for a while, I assumed it I needed new plugs. The car has 120,000 on it now. I last had it serviced at my Dealer under warranty at 75,000 miles. They said they did a major tune-up which included changing the plugs and cleaning the injectors, but when I pulled a plug, they looked a little too worn, so I figured they might have not done what they charged me for.

Anyway, my new question is - could this be a faulty fuel injector? Could a faulty injector cause misfiring and a gas-soaked plug when the engine is warmed up, but work okay while the engine is cold? I think I'm panicking at this point.
 
i was fighting the sane problem for the same cylinder!!! Took to one injector to be cleaned..... said the injector was fine. I have not had a miss fire since! I think that there is a bad connection in the harness for your injectors(connectors are located above the belts) if still no luck then pull everything off and have the one injector serviced. It not that hard of a job, just remeber to oil the injector gaskets before you put the fuel rail on. Good luck
 
Check Codes

Check Codes

The auto manufactures came up with fault codes to help diagnose today complex engines. Using this tool will lessen the amount of time and resources required to fix a fault. A lot of auto parts stores will read the codes for you at no charge. Take the codes, list them on the site and then get really good advice. Dan
 
Alquistador said:
i was fighting the sane problem for the same cylinder!!! Took to one injector to be cleaned..... said the injector was fine. I have not had a miss fire since! I think that there is a bad connection in the harness for your injectors(connectors are located above the belts) if still no luck then pull everything off and have the one injector serviced. It not that hard of a job, just remeber to oil the injector gaskets before you put the fuel rail on. Good luck
Click to expand...

Thanks Alquistador
At least someone else seems to have had the same problem. I'll check the wiring harness for sure. I used a "stethoscope" a.k.a screwdriver to listen to the injector and the rhythm seemed fine. I'm a little wary about taking the manifold off - but I gotta do what I gotta do. Lost my job recently, so there's no mechanic repair in my immediate future!

I wish I had payed more attention to the mechanical aspects of this car.
I had a warranty, so I just always brought it back to Mercury Dealer (I've never found an honest private mechanic around here). And, unlike what other people I know said about my "mystaque" when I first bought it, it has given me great service and excellent gas mileage thus far.
 
Dan the rug man said:
The auto manufactures came up with fault codes to help diagnose today complex engines. Using this tool will lessen the amount of time and resources required to fix a fault. A lot of auto parts stores will read the codes for you at no charge. Take the codes, list them on the site and then get really good advice. Dan
Click to expand...
You're right of course, Dan. I'm trying to figure out where the OBDII connector is then I'm off to Autozone.
 
Okay, I reset the CEL then drove down to Autozone. The CEL started blinking by the time I got there (approx. 2.5 miles). They retrieved 4 codes as shown below:

Codes Detected:

  • P0300 - misfire detected random cylinders
  • P0301 - cylinder 1 misfire condition
  • P0303 - cylinder 3 misfire condition
  • P0305 - cylinder 5 misfire condition
Possible causes:

  1. Ignition-system fault-spark-plugs, ignition wires, coil
  2. Vacuum leak
  3. Injector fault
  4. high or low fuel pressure
(1) I know the answer is replace the wires, but right now due to a recent job loss I don't have $50.00 to waste if this is not the problem. The reason why I'm hesitant is that the wires all test okay with an ohmmeter even when I wiggle them. I tested continuity all the way from the coil connector to the plug tip for each wire. I've swapped between two coil packs I have. Both past all the continuity/resistance checks. I've swapped between two sets of plugs, one set brand new.

(2) It could be a vacuum leak, as I cracked some brittle vacuum hoses connected between the EGR valve and the vacuum regulator, but I replaced them all very carefully. The engine does have a shaky idle which it never had before, but is this due to misfiring or a vacuum leak? I never knew that a vacuum leak (unless catastrophic) could cause cylinders to misfire.

(3) I was going to try swapping injectors, but now according to the error codes it seems I'm getting misfires in more than one cylinder (originally, I thought it was just cyl. #3).

(4) I'm fairly sure the fuel pump. etc. is fine. I can hear it prime up and the car always starts immediately.

Does these codes help my in anyway? I suppose I should be grateful I didn't get any other codes. I'm just not sure what these codes are telling me, or what to do next.
 
Random misfires that jump around from one cylinder to another (read: P030x codes) also will set a P0300 code. The underlying cause is often a lean fuel condition, which may be due to a leak in the intake manifold or unmetered air getting past the airflow sensor, or an EGR valve that is stuck open.
Click to expand...
I found this on another forum. How do I test to see if the EGR valve is stuck open? I did originally start the engine with the vacuum tubes between the EGR valve and the regulator broken.
 
Random Misfire

Random Misfire

With the codes posted the problem appears to be confined to one side of the engine. I would look for broken / damaged vacuum line on the radiator side of the engine. Also I would look at possible leaks at the intakes allowing in unmetered air. It seems unlikely that the plugs, wires or coil are the problem. (although due to the assumed age of the wires I would look at replacement when cash flow allows.) On one site I visited it listed the following items to check:
Plugs, wires, coil

o2 sensors You could swap the sensors front to back to see if the problem follows.

fuel injectors plugged or leaking. Due to one side of the engine with the condition check out possible damaged wires on the front bank.

Burned exhaust valves Can be checked by a vacuum gauge attatched to manifold. Depending on how vacuum fluxuates will help with answer.

bad cat rotten egg smell at the tail pipe

EGR inoperative or blocked passages. Due to one side issues this would be lower on my list

Cam position sensor This could be giving the engine incorrect firing info. This would rate a serious look in my book.

Finally a faulty PCM. I think this is fairly unlikely but not out of the question.

I know that some of the potential problems should throw their own code. Given the fact that all the codes were cleared prior to auto zone, the other codes could re-appear with continued use. I would suggest checking items that will not cost you much to investigate first. Personally I advacate preventive / routine maintainence. That would clear up the ignition system being part of the problem. Dan
 
you most lik;y have to buy the gaskets for the plenom to valves. everything else is remove and put back
 
Tony2005 said:
Test the Ignition Coil Pack.

autozonelink
http://www.autozone.com/autozone/re...le=Ignition+Coil+Pack&partId=0900c152800a88c1
Click to expand...

Tony - Apparently it was the coil pack! When I first tested the two coil packs I had, one had high primary resistances (approx. 2.7ohms) I rejected that one. The other one I had was bought from Autozone about a year ago. The primary resistances averaged about 1.2 Ohm. This might be high according to the Autozone test, but it didn't seem to me how this could make much of a difference, and I did buy this coilpack new. The secondary resistances all measured correct. But, after I installed it and the car warmed up the same problems occured. I decided to re-check the primary resistances on the car, and I was surprised that they appeared to fluctuate and increase about 6 Ohm when the coilpack was hot! This seemed amazing to me. But, my meter is working okay. I even changed the battery on the meter to make sure.

Anyway, I was able to find another coil pack out of a Taurus for $25.00 - stuck it in, plus the cheapo plugs I bought at Autozone and voila, the car runs great! In fact, it hasn't felt this good in many months. I'm not sure technically what the problem was, but I now have full RPMS, no 'bucking' - the CEL is off! I'm still suspicious - but I have this feeling that it's fixed, even though I'm using a taurus coil pack! I'll run it for a few days and if it seems okay, I'll spring for the correct coilpack.

BTW, Autozone rocks! Those instructions were better than my repair manual. Apologies for 'dogging' the autolite plugs - $1.75 ea. and they do the job.
 
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