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Engine misfire why?

Tiny
MICHELLE JONES4
  • MEMBER
  • 2001 FORD F-150
  • 5.4L
  • V8
  • 4WD
  • AUTOMATIC
  • 140,000 MILES
Cylinder three misfire. Changed spark plug and coil pack several times. It runs really rough and bad. Runs good for a week then has a code cylinder three misfire, help.
Tuesday, October 30th, 2018 AT 4:10 AM

67 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good afternoon.

The first thing I would do is a compression test to see if the cylinder has any internal damage. Low compression will cause this.

Also, when you changed the plug, was there any oil, coolant or fuel on the end?

https://www.2carpros.com/articles/how-to-test-engine-compression

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

You will have to scan it for codes to see if anything like a sensor has gone out.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

I would do a full tune up with coils this guide should help and check out the video below it.

https://youtu.be/e68QXyBAiZo

Please run down these guides and report back.
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Tuesday, October 30th, 2018 AT 9:52 AM
Tiny
MICHELLE JONES4
  • MEMBER
  • 10 POSTS
No there was not. We just changed spark plug and coil pack a week ago and it ran fine for a week. Then it started hesitating and sputtering.
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Tuesday, October 30th, 2018 AT 9:57 AM
Tiny
MICHELLE JONES4
  • MEMBER
  • 10 POSTS
And it reads the code cylinder three misfire so I replaced the injector that fixed it thank you.
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Tuesday, October 30th, 2018 AT 9:58 AM
Tiny
KJDANIELS1987
  • MEMBER
  • 5 POSTS
  • 2001 FORD F-150
  • 5.4L
  • V8
  • 2WD
  • AUTOMATIC
  • 200,000 MILES
I have a misfire in cylinder two. I have changed the spark plug and coil that goes to that cylinder. Still misfires. I switched the coil from cylinder two with the coil from cylinder one and still misfire in cylinder two. I ran Seafoam through the vacuum system (brake booster vacuum hose) and poured it into my fuel system (tank). Still running like it has a miss. I have check the harness that plugs into the individual coil while it is plugged in and I have 12 volts on one side and the other side is supposed to pulsate, but it seems more like its a solid 12 volts. It is hard to distinguish. I am using a test light for this test. I ran the test on the cylinder one coil and you could tell it was pulsating but I just could not tell if cylinder two was. I would say that it was not if I had to choose. My AC compressor will also engage for about thirty seconds and shut off and not come on again. I do not know if these two are linked in any way. I am stuck and could use your assistance. Thanks
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Monday, May 10th, 2021 AT 11:01 AM (Merged)
Tiny
PATENTED_REPAIR_PRO
  • MECHANIC
  • 1,853 POSTS
To check for a pulse you need a noid light tester or what I think it is a led (light emitting diode).
Also, check the camshaft lift on the intake and exhaust valve.
If no tool just compare the lift to another cylinder. If you have a flattened down cam lobe that will misfire all the time, both at idle and floored.
If the pulse is good, the cam lifts are okay, then move onto a compression test and then a leak down test if the 32 failed the compression test.
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Monday, May 10th, 2021 AT 11:01 AM (Merged)
Tiny
KJDANIELS1987
  • MEMBER
  • 5 POSTS
Okay, so I took a known working coil and spark plug and plugged it into my second cylinder harness and nothing happened. No spark. I took the same setup and plugged it into the first coil plug and it shocked the heck out of me.
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Monday, May 10th, 2021 AT 11:01 AM (Merged)
Tiny
PATENTED_REPAIR_PRO
  • MECHANIC
  • 1,853 POSTS
Okay, I assume the wire colors and pink/white and red/light green. Make sure the red/light green has battery voltage with the key on run/engine off. If okay, then make the the pink/white wire has continuity to the 104 pin of the PCM so disconnect both ends and use an ohmmeter. Rule of thumb is 5 ohms.
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Monday, May 10th, 2021 AT 11:01 AM (Merged)
Tiny
KJDANIELS1987
  • MEMBER
  • 5 POSTS
The PCM was bad I got a rebuilt unit runs perfect
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Monday, May 10th, 2021 AT 11:01 AM (Merged)
Tiny
FORDMISFIRE
  • MEMBER
  • 3 POSTS
  • 2000 FORD F-150
  • 5.4L
  • V8
  • 4WD
  • AUTOMATIC
  • 11,400,000 MILES
Developed misfire in number 1 cylinder. After much head scratching, found out the intake manifold had cracked at number 1 port. Changed out intake, EGR valve, PCV, idle solenoid, injector and coil.
Engine misses at cold idle and smooths out when it warms up. If I reset PCM the misfire doesn't comeback until about 500 miles of driving.
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Monday, May 10th, 2021 AT 11:03 AM (Merged)
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good evening,

Did you check the compression on number 1? I would verify that.

https://www.2carpros.com/articles/how-to-test-engine-compression

Resetting does nothing but make the ECM forget the code until the misfire counts get to a certain number.

Does it still miss when it is cold? It could be a carbon build up as well.

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

You will have to scan it for codes to see if anything like a sensor has gone out.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

I would do a full tune up with coils this guide should help and check out the video below it.

https://youtu.be/e68QXyBAiZo

Please run down these guides and report back.

Roy
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Monday, May 10th, 2021 AT 11:03 AM (Merged)
Tiny
FORDMISFIRE
  • MEMBER
  • 3 POSTS
Did a leak down test via Ford scan app, which passed, will do actual compression test this week. 2 weeks ago it started rough, I changed the oil used Castrol edge high mileage.
Ran smooth, Did a 350 mile road trip ran great, 3 days later missing on cold star again smooths out when it comes off cold idle. Actual miles on vehicle 11,045. I'm thinking weak valve spring.
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Monday, May 10th, 2021 AT 11:03 AM (Merged)
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Valve spring would do it all the time. If you want to double check, do a running compression test. That will tell you if you have a bad valve spring.

A vacuum gauge will also tell you.

I still think it is a carbon issue.

Roy
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Monday, May 10th, 2021 AT 11:03 AM (Merged)
Tiny
FORDMISFIRE
  • MEMBER
  • 3 POSTS
It was a bad connection at the fuel injector all set now thank you for your time.
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Monday, May 10th, 2021 AT 11:03 AM (Merged)
Tiny
ROMOSBUDDY
  • MEMBER
  • 1 POST
  • 2000 FORD F-150
  • V8
  • 2WD
  • AUTOMATIC
  • 16,500 MILES
Ok so my 2000 f150 starts misfiring, then doesn't start, had it towed and come to find out a 30 amp fuse blew to the PCM. PCM has a bad cyl.6 driver. I get a new ford PCM, Motorcraft cop, plugs, injector, cleaned the egr, cleaned the maf sensor, did a compression test and still a misfire in cylinder 6. The truck doesn't have any engine noise and when you push the pedal to the floor it takes off, but as soon as she goes into OD it gets rough. I've spent a whole lot of money and man hours into this. PLEASE HELP!
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Monday, May 10th, 2021 AT 11:03 AM (Merged)
Tiny
MATHIASO
  • MECHANIC
  • 1,209 POSTS
Hello romosbuddy

According to the diagram, the PCM and the COPs share the 30 amps blown fuse
(Coil on plugs).
There is a capacitor on each side of the COPS. Check them.
Replace the coil on #6.
Pay close attention to the tube that wraps around the spark plug. Cracks can allow voltage to jump to ground causing a misfire.
Clean the COP connector and wiring harness terminals. Corrosion at either place can cause intermittent operation and loss of continuity, which may contribute to component failure. Applying to these connections can help prevent corrosion and assure a good electrical connection.

(sending this diagram to your email)


https://www.2carpros.com/forum/automotive_pictures/46384_0900c152801e5700_2.jpg

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Monday, May 10th, 2021 AT 11:03 AM (Merged)
Tiny
JACKNUT
  • MEMBER
  • 65 POSTS
  • 2000 FORD F-150
  • 4.2L
  • V6
  • 164,000 MILES
Every now and then not all the time. Sometimes not for days, but I'll get a little skip I don't drive it hard. Kind of drive like a old lady most times, lolol. But every know and then I'll get I little skip. Not a bad one but I feel it.
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Monday, May 10th, 2021 AT 11:04 AM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Hi,

There are many things that can cause a misfire. Has the check engine light ever come on while the engine is running identifying that there is a trouble code stored?

Things such as a tune up, engine vacuum leak, fuel pressure and so on can cause this type of issue.

Here is a link that explains how to fix a misfire, but it does it based on diagnostic trouble codes related to the misfire. If the check engine light isn't on, this may not help.

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

Do me a favor. Because this is intermittent and doesn't happen often, it is difficult for me to identify a specific issue. However, can you tell me if there is anything that seems to cause it? Does it happen at any time or does the engine need to be cold or hot?

Anything you can think of may help.

Let me know.

Joe
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Monday, May 10th, 2021 AT 11:04 AM (Merged)
Tiny
JACKNUT
  • MEMBER
  • 65 POSTS
Always when warmed up and when driving with steady pedal. It will happen when I give it a little more throttle. Should have good fuel pressure since it has a different fuel pump and it did same with old fuel pump also.
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Monday, May 10th, 2021 AT 11:04 AM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
If it did the same with the old pump, I agree it most likely isn't the problem. When was the last tune up? Also, has the check engine light ever come on when the engine was on?

By any chance, do you have access to a live data scanner? If you do, it may help if you provide me with both the short and long term fuel trims.

One other thought is a possible vacuum leak. Here is a link which explains how to check for one:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Let me know.

Joe
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Monday, May 10th, 2021 AT 11:04 AM (Merged)
Tiny
JTBMUGABI
  • MEMBER
  • 2 POSTS
  • 2000 FORD F-150
  • V8
  • 4WD
  • MANUAL
  • 50,000 MILES
Hi. I drive a 2000 Ford 150 Supercab 5 speed 4.8 with only 50,000 miles. This truck has started to act up once again. When I need the power to climb inclines it seems to bog down and buck like a bronco until I downshift and find the power. Once I level off it runs smoothly. I have had a similar problem last year where I had to replace two modules on the spark plugs, very expensive! Is it common for these modules to go all of a sudden and with just 50,000 miles? How much should one cost to replace? Could it be bad gas or fuel filter? Thanks for your time. Stan
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Monday, May 10th, 2021 AT 11:04 AM (Merged)

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