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i have a2003 expedition with a 4.6L with 315K miles it has a misfire, i can feel. last couple of times it has been a coil But I have always got a check engine light. no light or code. I get misfire rate of about 12% on forscan mode 6 test, but no cylinder misfire.
I changed the plugs to no avail, and tested the coils with a meter, all read about 1 ohm.i also sprayed some starting fluid lightly around the engine bay to see if it would pick up any kind of leak with no luck.
I am at a loss here if anyone can help it would be great.
all the plugs looked ok, except #3 which had some black soot on it. all the plugs were well worn to a gap of about .065.
Thanks
How old is the fuel pump and filter ? Loss of fuel pressure will cause a misfire and usually no code. If you have a fuel pressure test kit get a fuel pressure reading at the fuel rail schrader valve with the system primed and key ON. Should see 50-55 PSI of fuel pressure. If you don't know the last time the fuel filter was changed do that too. Depress the blue buttons on the quick connects to release the fuel lines from the filter. It's very easy.
i am guessing about 200K miles ago for a fuel filter. never for a pump. I think the local auto parts place rents tools. i will see if they have a pressure tester. and the reading you gave is when running correct?
If your scan tool or Forscan is set to read live data, you should be able to see the number of misfires per cylinder...if any. The misfire counts reset when the ignition is turned off, so take it for a quick drive, and when you come back, leave the engine running when you go and view the live data.
If your scan tool or Forscan is set to read live data, you should be able to see the number of misfires per cylinder...if any. The misfire counts reset when the ignition is turned off, so take it for a quick drive, and when you come back, leave the engine running when you go and view the live data.
^This is what I actually just did. I used ForScan Lite and search all PIDs for the word "Misfire". I added all Misfire PIDs to my live data view and could see a bunch of misfires happening. It was only happening under load on the highway, like light acceleration without the transmission downshifting. But I was feeling bucking/surging when it was misfiring. No DTCs came up for it no matter how severe the misfiring was. I had replaced the spark plugs with Motorcraft plugs 72k miles ago, but didn't know the condition of the coils back then. I bought new plugs and a coil boot/spring kit and replaced those items. The current coil boots didn't have any cracks nor rot.... they looked fine. The spark plug electrodes had some wear but looked to have some life in them. All plugs were nice and clean and evenly worn. I didn't have high hopes once I got all 8 plugs out and examined the boots, but after putting it back together with the new spark plugs and boots/springs, I have had absolutely no more misfiring / surging / bucking. Runs really strong again. No connectors were loose or anything so hard to say exactly what the culprit was, but if the resistance on the coils is reading fine then maybe you just need to replace the boost/springs like I did. If the spark plugs have some mileage on them, might as well just replace them with new Motorcraft plugs while you're in there if money allows. Just my $.02.
my next day to work on it is on Monday
To answer some questions,
Yes I used forscan light, it picks up misfires, but not for any cylinders. just a total miscount. and it counts quickly like 700+ per minute
I have driven this for a couple of months and cant get a code to come up. but my wife drives it like a granny, dont tell her i said that...
the miss is at idle, and at light acceleration. No miss on deceleration. now it misses so bad that it feels like the car wants to die when in gear and stopped.
so i will do the fuel pressure test,
Also if this were a compression issue, it should not come and go?
anything else i should be looking for right off? I have read a lot about vac leaks at the intake?
Thanks again for the help.
Replace the fuel filter regardless. They're usually replaced every 50k miles. A restricted filter makes the pump work harder, and a hard working pump accelerates the burning of the fusebox relay, which requires fusebox replacement.
i ordered 8 new motorcraft coils from ebay. i have a mismash on there now. also ordered a wix fuel filter to the local parts place and i will start there on Monday.
so i replaced the fuel filter. and no change i am getting 48 psi at the fuel rail. i cleaned out the sparkplug holes with brake clean, and air, installed 8 new motocraft coils and my issue has improved. still no specific cylinder. total misfires is about 2% as opposed to 12-13% before that was done.
it is drivable again. but is that an acceptable misfire rate? if it has been misfiring for a long time, which it has waiting for a code, will it improve with time?
Wat steps if any should i take next. ]
Thank you
^This is what I actually just did. I used ForScan Lite and search all PIDs for the word "Misfire". I added all Misfire PIDs to my live data view and could see a bunch of misfires happening.
Use live data in Forscan to find the PIDs for misfire on each cylinder. There will be eight. There's also a PID for total number of misfires. This data is the actual number of misfires, not a percentage. The Torque Pro app also can display these PIDs.
You will be able to see which cylinder is misfiring. My '97 V10 only has 5 or 10 total misfires every trip, even long ones. Sometimes it has less than.
You may have some damaged wiring to a COP or you vehicle may just have moderate misfires...??
so this is what I am seeing in forscan. no misfires per cyl. and just engine rate misfire
new to this, it has always set a code after a while, but not this time.
it is much better, but doont know were to go from here, i just have the free version. do i need the paid?
Click on the "graph" or "oscilloscope"icon in Forscan. This will open the real time PID function. You have to select the module you want to scan for data then add PIDs to the list. Too difficult to explain in this post. Finally press the play button to start reading data. Start the vehicle and you will see live data.
PIDs are the key to troubleshooting along with reading codes.
****EDIT'**** the link does not appear to work.
This post in the Forscan forum helps explain what you need to do.
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