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2004 Mustang GT random misfire issue

15K views 31 replies 7 participants last post by  Thedunzelmon 
#1 ·
Hey guys/gals. I am new on here and have a question for some fellow mechanics.

My 2004 Mustang GT has been a victim of a very strange misfire problem since late July. It began when the car was 80 percent of the way during my travels to Mustang week from New Jersey. It only happened once on the way down (670 miles) and once on the way home. Weeks after I got home it started to happen every time I drove the car. Which then and now is once a week the most. I changed out spark plugs and Coils on plugs and thought I had the issue under control.. for about 2 and a half months and it began to happen again. Not as frequent but the problem was still there. To this point everytime it has happened it isn't at idle, or under load. I find it popping up while cruising at highway speeds or just cruising in general. No specific speed either just anywhere from 50-90 mph. The service light will begin to flash, there is a noticeable change in the tone of the motor and anywhere from 10-30 seconds later it stops and it'll running fine. I recently scanned the codes and I had a random misfire code, as well as misfire codes for cylinders 1, 3, 4, 5, and 6. The car is pretty much full bolt ons with comp 262 camshafts full exhaust cold air intake bigger throttle body and throttle plenum. Car has had an MPT tune on it for the last half year. Just changed back to my brenspeed tune (never had an issue with misfires with the car tuned by brenspeed) just to see if it's a tune related issue but I don't think this is the case. If anyone has any pointers or have had a similar problem please help a brother out. I think I'm going to start by testing o2 sensors and fuel injectors. Thanks in advance!

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#3 ·
That's what I was starting to think after reading some articles. It seems to be too random to be a fuel/spark issue. I read one forum on another site. Guy said it was his tune and since he changed it it was running fine with no problems. I'm going to invest in both those sensors to see if my problem is solved if the car acts up on the brenspeed tune. Never had this issue with them

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#4 ·
My 03 is doing the same thing under load, no codes found, and with the hood open I can hear a rattling sound when you rev engine on top of motor around no. 3 cylinder, coil area, I am going to pull plugs this weekend, any idea what the rattle sound is?
 
#5 ·
Yeah my car isn't doing it under load it's only doing it while cruising in 5th gear. Rattling noise huh? My best guess is that it's something loose in that area. Did you change your throttle body out because that is right in that area. Make sure that's nice and tight.

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#26 ·
Eight Motorcraft COP, plugs and fuel filter. Runs like a champ now
 
#6 ·
What's up Dunzy! You could confirm you have good fuel pressure as well as get a noid light to check that the injectors are getting power and pulse from the PCM. If all that's good, then you can test the injectors. I think our local Ford dealership has an injector cleaning service, but I'm not sure exactly what all they do, but it's more than just dumping an additive in the tank.
 
#8 ·
What's up my man! Yeah that's where I'm going to start. The misfire is so random and so inconsistent that it makes me wonder if it's a fuel issue to begin with. I'm not getting codes for lean or rich conditions. I'm just getting misfire codes. I've driven 120 miles with my old tune on the car and so far no problems. Still a bit too early to tell if it's a tune issue or not.

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#7 ·
Ever get a P0320 code? If so, its prolly a crankshft position sensor. Try disconecting the electrical, spray with electronic parts cleaner and while your at it, spray an wipe the magnetic pick up.
 
#9 ·
I won't go crazy into detail but multiple guys on here can vouch for me.

I would start with cam and crank sensors. They are cheap and very very easy to replace.

Maybe even a fuel filter if it's been awhile since it's been changed. Usually coils don't go out frequently. Random misfire codes tell you that it's not specific to a cylinder, so that rules out plugs and coils. The cam sensor tells its position and has a lot to do with firing.

Crank sensor usually is most noticeable bad when you have a starting issue, but it's still a possible culprit.


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#10 ·
The COPs i put in were oem motorcraft coils. I cant imagine 6 out of 8 went bad that fast. I have never changed the fuel filter before, now that I'm thinking about it. So I'll definitely be changing that as well as the cam and crank sensors. I haven't gotten codes for either of those sensors yet, but I read online that it won't always throw a code. After running for some time with the issue like I stated above it had misfires on cylinders 1, 3, 4, 5, and 6. I'm not getting codes for lean or rich conditions either. So I believe my o2 sensors are in good order. I'm going to test for fuel pressure too as Lee suggested before. Is it possible for the EGR valve to be causing this issue as well? Maybe it's getting stuck randomly? I would imagine that's less then likely.

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#11 ·
Do the cam sensors before the crank.

Fuel filters are dirt cheap and easy to change, literally takes 2 minutes.

I was agreeing that I doubt cop's had anything to do with it usually they don't go out especially not multiples at once. But good choice going oem. Oem or msd on those.

If it's not throwing a code specific to the o2's or lean or rich they are fine. Emissions related dtc's are very particular and if it's them causing the issue you'll get the code.

If you suspect the egr at all and don't have emissions testing in your area delete it. Really cleans the engine bay up, doesn't recirculate **** back in, less **** to go wrong if it's gone.

Engine Auto part Vehicle Fuel line Car


Cheap and easy mod, mines gone.




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#12 ·
Yeah that engine bay looks mint ? I had the MSD coils on before I swapped back to oem. Unfortunately NJ is an emissions state.. but my car has been overdue for a year ? are there two cam sensors? I was under the impression there was only one? But considering there's a cam on top of each head 2 would make sense. I've been looking online and can't seem to find cam sensors anywhere but found a crank sensor. Just going to change both to see if this helps my problem.

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#15 ·
So after some trouble shooting, thorough investigation, and talking to several ford techs, it seems like we narrowed the problem down the camshaft sensor. Fuel pressure and compression is nominal as well as spark and AFR. Going to be changing that soon as well as the crank sensor just to get that out of the way. Thanks for everyone's helpful tips and tricks! More helpful then the other forum I posted this too.

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#18 ·
I'll let you know how I make out. If it's not this my guess is that it's an electrical short.. worst case senario is my motor is shot ? but compression is good on all cylinders so I don't believe that is the case

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#20 ·
Quick update fellas I just finished swapping both cam and crank sensors. What a breeze! Took me less then an hour to swap both. The crankshaft sensor was a bit tricky cause you have to take the ac compressor off to make room but once it's off its cake. Hopefully this issue is fixed now. Discovered a kinked vacuum line today as well and took care of that. Along with that notorious throttle cable slack ?

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#22 ·
I took it for a ride about 25 miles.. feels alot better then it did. Accelerates smoother and cruises smother and idles smoother. As far as the throttle slack goes, used some nylon hose and cut it down the center. Pulled the slack from the cable and put the hose in place and secured it with a hose clamps and 2 zip ties

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---------- Post added at 01:24 PM ---------- Previous post was at 01:23 PM ----------

Pretty much got rid of all the slack from the cable

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