Engine misfire why?

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.

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.

And it reads the code cylinder three misfire so I replaced the injector that fixed it thank you.

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

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.

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.

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.

the PCM was bad I got a rebuilt unit runs perfect

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.

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

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.

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

it was a bad connection at the fuel injector all set now thank you for your time.

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!!!!

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)

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.

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

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.

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

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

Stan:
With that low of mileage, it isn't common. However, the modules do have some history of problems. Have you ever replaced the spark plugs? It may help. Also, make sure there is nothing arching as a result of a bad wire. Check it at night when it's dark and easier to see sparking.

Let me know what you find.

Joe

I will change the spark plugs and check the wires in the dark, great help, thanks, runs great now.

I have a skip if I put engine under a load. Doesn't happen all the time. also skips worse when A/C is on. no engine light on, idles fine and drives fine. But if I step on gas pedal a little harder than normal driving it will skip. this also happens sometimes with normal driving.. but definitely when I put a load on engine.

Good morning,

The most common issue for this is the spark plugs. The gap gets too wide from wear and ends up with a weak spark.

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

https://www.2carpros.com/articles/how-to-change-spark-plugs

Also, it could be dirty injectors as well.

https://www.2carpros.com/articles/how-to-test-a-fuel-injector

What recent work has been done?

Roy

I got a new set of coils that did it , runs great once again.

Truck skipping and popping after plugs and wires changed.

Hi:

Either the wires were put on in the wrong order, or the plug gap was closed when installed.

check out these guides

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.

I attached a picture below. It shows the firing order and where each plug wire starts at the coil pack and which cylinder it goes to. Confirm they are correct.

Next, if that doesn't help, pull diagnostic trouble codes to see which cylinders are misfiring. If the wires are correct, then pull the plugs on the affected cylinders and check them.

One other thought, make sure the plug wires are properly routed. They can melt if against the exhaust manifold and that will cause a misfire as well.

Let me know if this helps and what you find.

Take care,
Joe

vehicle was and has ran perfect.alternator went out,i was selling vehicle and buyer said he wanted it with faulty alternator,put alternator back on and when we first turned the engine over it backfired and smoke came from the engine compartment.was no fire but when we started engine back up it revs to 2500 rpm(without missing)then when it goes to idle it backfires and misses horribly.(makes sounds like it is firing in the crankcase)i bought a code reader and replaced the alternator but it still does same thing.it came up with code p0102.i replaced mass air flow sensor with new one and it still does same.when you start it it starts perfectly but as soon as the rpm comes down from 2500 it goes to about 500 and misses,backfires and most of the time stalls.i can give it fuel and it revs back up to 2500 then goes back to 500.It only misses and backfires when it it at idle.The vehicle cant be driven because it wont hold any rpms.I have also cleared codes a couple of times.I lastly unhooked battery and left off for 6 days then went and hooked it back up and vehicle done the same again,so here we are.

I have the same truck and have had the same problem. If you look at the left side of the engine you will find the PCV valve feeds some black vacuum lines and tubing. The line snakes around to the back of the passenger side of the intake manifold into a black 90 degree rubber fitting. It plugs into a 5/8" vacuum nipple on the back of the manifold. You will have to feel for it as you cannot see it from the front. This black elbow will crack and will cause a very large vacuum leak.

In my truck I removed this rear line and capped of the rear vacuum plug. I left the PCV valve feeding to the front line. If you have the original setup you can just get that rear elbow from Ford. I am sure it is a commonly replaced part.

Ed

As noted above, I have a misfire on 4 and 8. When it first happened I replaced all the plugs (60,000km since last plug/wire replacement). Misfire still occurred. I took it to a mechanic (he told me it was 4 and 8 that were misfiring), and suddenly it started running fine and he was unable to diagnose the problem. 1000km later it misfires again, so I replaced the wires, and now it is still misfiring. (a note about those 1000km, they all happened in one day, the day following the testing)

So 3 questions-

1. Where should I look next?
2. Is there an inexpensive method of testing I can use that will allow me to eliminate electronics and look at the fuel injector?
3. How much damage am I doing by running it on misfire (I need it to work)

Thanks in advance for any suggestions or advice you can give.

Misfires are tough to find and but not impossible if you put some time into it. A misfire can be caused by a ignition problem, fuel problem or a compression problem. You have already narrow it down to cylinder #4 and #8 . You also have elimated the plugs and wires so far. I would also at least inspect the cap and rotor. If the car is equipped with coil packs test the coils resistance for #4 and # 8 . Other causes can be fuel related, a vacuum leak or a compression problem. Next check the car for a vacuum leak with a valcuum gauge. It should be between 17-22 steady. Dirty or clogged injectors can cause a lean mixture and cause a misfire. A weak or fautly injector can also cause the same thing. You can add fuel injector cleaner and see if the problem goes away. You can test the suspected cylinders by checking the resistance of the injectors with a ohm meter and see if they are with in specs. And the last thing is compression. Check the engine with a compression gauge and make sure the readings are with in specs. :) Good luck

If 4 and 8 share a coil pack replace it. Ive seen many coils and injectors go bad in those trucks.But if they share a coil it should take care of the problem

Great, thank you guys. :)


Does it make sense that occasionally it would run ok if the problem were a coil pack, or an electrical problem in general? The other day it ran great for a few km and then out again.

Editing the post to say I just checked for spark, and I have spark on all 8 cylinders (method I used - insert old spark plug into wire, ground to the engine and turn over). Does this mean I should look into the fuel system as the problem, or should I start to check the resitance at the coil pack (Learning all this by reading the Haynes manual), or replace the coil pack altogether?

Lots of questions, I know. Sorry.


Thanks for your time.

Yescoils can intermittently short out.I have seen both coils and injectors create misses in Fords. The odds of two injectors on opposing sides going out is slim.If 4 nad 8 share a coil try that first. Alot of what we do is trial and error, seen this many times.

Thank you. I will try that this weekend, then. :)

So, in the end, reluctant to spend any more $$ on an unsure bet, I bought a Ohmmeter and consulted my Haynes manual.

I tested both my coils - they were fine.

I tested all my injectors, and one was bad, so I replaced it, and now the truck runs fine.

I'm somewhat impressed that I was able to fix this problem, and also somewhat surprised that, after educating myself, it took less than 30 minutes for me to diagnose the problem.

I'm more than a little dissappointed in the garage that charged me 3 hours of labour in an attempt to diagnose the problem. If it took me 30 minutes to figure it out once I knew how to look for a problem, at the least it should have taken them the same amount of time?

I can't be certain of the original diagnosis - they said I had a misfire on 4 and 8, and they checked it after I changed the plugs. I replaced the injector on #8, so that part of the diagnosis was correct, and I can only assume that when I changed the wires after they looked at it, that doing so fixed #4.

Well anyway, I fixed it, and I did it myself. Not bad for a carpenter. Thanks again for your help - I'll be sure to recommend this site to my friends.

Glad to see you fiix it yourself. :D

I have a 98 f150 2 wheel drive standard with a 4.6 the engine has a miss and when I put it on the scanner it comes up with a miss on cyl#4 I have replaced the fuel injector the plug the wires and the coils on the engine but it still has a miss. I have checked for vacuum leaks and found none. I am at a lose as to what else it could be. Can you help me please?

Check its compression to see if it varies with other cylinders. check out these guides

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.

I did a coil change out that took care of the problem.