Weird problem......
New User
Joined: Oct 2002
Posts: 8
Likes: 0
From: Baton Rouge USA
Weird problem......
I have a 1999 Ford Expedition 5.4L (coil on plug) in the shop right now and heres the problem:
Came in with a misfire after the owner nearly ran out of gas. The Check Engine light was and the code was P0305f which is a cylinder 5 misfire. Easy enough right?? Wrong. Just to see if the computer was still picking this up, i cleared the DTCS and road tested it. Too no surprise the engine was missing like crazy but oddly enough no code was set in pending DTC memory or Stored Memory. I drove it for roughly 25 minutes like this and the misfire was there the whole time. Only problem was it was an intermittent miss and not a dead miss. thinking that maybe some trash from the tank got in the injectors, i ran a fuel injector cleaning on it and no luck. keep in mind this truck has 50,000 miles on it. Next i ran an injector bleed down test by pulsing the injectors for a set period of time and all the injectors bled the same amount of fuel pressure for the given time. No clogged injectors. The miss felt exactly like a bad spark plug wire or boot that is arching to ground. I tried switching the number 5 and number 1 coils to see if the misfire would change and/or set a different code. Still no codes and still a misfire. next i inspected all the coils and boots looking for a carbon trail or something awkward. of course the number 4 coil didn't want to come and the boot tore and it took an hour just to get the boot out but thats besides the point. No problem visually on any of the coils. I ohmed all the coils and they all ohmed the same. I pulled and replaced all eight spark plugs and then put the system back togther wih a new coil in number 4. Road tested and found the miss to be gone but i was still skeptical. Sure enough after about an hour or so the miss returned. this time i pulled each coil while the engine was running to see how powerful the spark output was. All equal. Just to see if the computer was really dumb, i unplugged the number 5 coil and low and behold a code popped up. So now i know the computer isn't that stupid. the engine misses the most at low rpm loads. (ex. accelerating to 45mph and letting the torque converter lock and then applying a little gas at roughly 1500rpms). Saddest part is that we have two other Expeditions/Navigators in the shop with the same problem. One had a dead miss on number 2 so naturally a new coil fixed that. haven't messed with the other yet!
what the hell do i do next? i am not a ford dealer so i don't have all the cool gismos that they have but we have enough to diagnose most problems. ANY SUGGESTIONS?
I will be checking this in the morning so please reply soon!!
Thank you all!!!
Darren
STEEDA (powered by Ford)
93 Mustang GT STEEDA
Came in with a misfire after the owner nearly ran out of gas. The Check Engine light was and the code was P0305f which is a cylinder 5 misfire. Easy enough right?? Wrong. Just to see if the computer was still picking this up, i cleared the DTCS and road tested it. Too no surprise the engine was missing like crazy but oddly enough no code was set in pending DTC memory or Stored Memory. I drove it for roughly 25 minutes like this and the misfire was there the whole time. Only problem was it was an intermittent miss and not a dead miss. thinking that maybe some trash from the tank got in the injectors, i ran a fuel injector cleaning on it and no luck. keep in mind this truck has 50,000 miles on it. Next i ran an injector bleed down test by pulsing the injectors for a set period of time and all the injectors bled the same amount of fuel pressure for the given time. No clogged injectors. The miss felt exactly like a bad spark plug wire or boot that is arching to ground. I tried switching the number 5 and number 1 coils to see if the misfire would change and/or set a different code. Still no codes and still a misfire. next i inspected all the coils and boots looking for a carbon trail or something awkward. of course the number 4 coil didn't want to come and the boot tore and it took an hour just to get the boot out but thats besides the point. No problem visually on any of the coils. I ohmed all the coils and they all ohmed the same. I pulled and replaced all eight spark plugs and then put the system back togther wih a new coil in number 4. Road tested and found the miss to be gone but i was still skeptical. Sure enough after about an hour or so the miss returned. this time i pulled each coil while the engine was running to see how powerful the spark output was. All equal. Just to see if the computer was really dumb, i unplugged the number 5 coil and low and behold a code popped up. So now i know the computer isn't that stupid. the engine misses the most at low rpm loads. (ex. accelerating to 45mph and letting the torque converter lock and then applying a little gas at roughly 1500rpms). Saddest part is that we have two other Expeditions/Navigators in the shop with the same problem. One had a dead miss on number 2 so naturally a new coil fixed that. haven't messed with the other yet!
what the hell do i do next? i am not a ford dealer so i don't have all the cool gismos that they have but we have enough to diagnose most problems. ANY SUGGESTIONS?
I will be checking this in the morning so please reply soon!!
Thank you all!!!
Darren
STEEDA (powered by Ford)
93 Mustang GT STEEDA
Posting Guru
Joined: Sep 2002
Posts: 2,297
Likes: 0
Weird problem......
You're right, a weird problem. And it didn't crop up before nearly running out of gas? When you performed all the injector tests, were you using pressure generated by the truck's fuel system, or did you have another fuel source tapped in to the system?
What kind of problems can crop up after running low on fuel? A few possibilities:
1. The fuel system picked up a load of crap from the bottom of the tank. Could the inline fuel filter (or the section of the line just before the filter)be clogged? When is the last time the filter was replaced?
2. The fuel pump could be damaged from crap or, if it is the in-tank type, by overheating. Is the owner in the habit of letting the vehicle run low on fuel? The latest event may have been the last straw.
3. How much fuel is in the tank now? I remember someone who was having a fit with his Volvo. The lower part of the in-tank fuel screen was clogged and didn't allow adequate fuel flow unless the tank was over 3/4 full.
If the problem is within the ignition system, I wonder if you just have a heck of a coincidence (i.e., not related to low fuel) How could fuel starvation affect the ignition system?
What kind of problems can crop up after running low on fuel? A few possibilities:
1. The fuel system picked up a load of crap from the bottom of the tank. Could the inline fuel filter (or the section of the line just before the filter)be clogged? When is the last time the filter was replaced?
2. The fuel pump could be damaged from crap or, if it is the in-tank type, by overheating. Is the owner in the habit of letting the vehicle run low on fuel? The latest event may have been the last straw.
3. How much fuel is in the tank now? I remember someone who was having a fit with his Volvo. The lower part of the in-tank fuel screen was clogged and didn't allow adequate fuel flow unless the tank was over 3/4 full.
If the problem is within the ignition system, I wonder if you just have a heck of a coincidence (i.e., not related to low fuel) How could fuel starvation affect the ignition system?
