Engine misfire why?

i have a 1997 ford f150 with 4.6 v8 , and keep getting a misfire no matter what i do, i have put fuel injector cleaner in , changed the plugs, changed the wires, changed the corresponding coil pack to the misfiring cylinders (2 and 4), I tried the screwdriver to the ear trick to make sure the injectors were clicking which they were, I am stumped at this point and would like my fuel mileage to be at a normal rate

Have you checked for a vacuum leak somewhere around the intake? These intakes are also know for leaking coolant down into the spark plug holes. 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.

Haven't heard any whistling from a vacuum leak, and I have suspicion of the intake manifold gasket leaking but is there a sure fire way to know?

Get a can of throttle body cleaner. Spray around the intake. If the idle changes where you spray then you found your leak.

i changed the intake manifold gaskets both lower and upper along with the throttle body gasket , the outcome was an even worse running motor, I have much less power than before and the valves float much more often , could sealing the leak at the gaskets have allowed another leak to arise? it's way beyond my knowledge, please any advice you have would be much appreciated

Ob2 says cylinder one misfire while l drive. How do you correct problem? how do you do a compression check on cylinders?

Hello,

Here are a couple of guides to help you get going in the right direction:

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

and

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

Please let us know what happens so it will help others.

Cheers, Ken

This ole truck is cursed, new plugs and wires, cleaned MAF, cleaned EGR valve, using higher octane fuel. But the slight miss comes and goes to the point where it’s unreliable. In the morning three miles is fine until it warms up and it will start to miss enough that the dummy light blinks. Please help me good mechanics. I could replace the MAF, and EGR. Which one is it?

A blinking check engine light is a severe misfire to damage the catalytic converter. That will definitely post a misfire code. Have a parts store scan your vehicle for trouble codes and post them on here to get a better idea as to what is going on? If you can get a scan reader here is a link on how to retrieve the codes:

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

Let us know what codes come up please. From there we should be able to guide you to where to check for the fault.

engine warm misses when started give it gas it stops what could it be? I replaced plugs, wires, distr. cap, rotor buttom, idle control, mass air sensor, fuel filter

Engine running rough or misfiring can be cause by a bad fuel injector. 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.

Front engine seal leaking which seems to cause all cylinders to misfire.

It is unlikely that an oil leak would cause all the cylinders to misfire so we need to confirm all cylinders are misfiring using these guides below.

https://youtu.be/QTE8k06MzwQ

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

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

Do you have misfire codes for all the cylinders? If not, do you have any codes?

Let's start with this info because this will determine the best course of action. The only way I can see that an oil leak would cause this is if it were leaking on an ignition component like a coil that is causing it to fail.

Let me know about this info and we can go from there. Thanks

I need help diagnosis of obd1 port. customer has changed plugs, wires, coil, distributor, idle air control valve, fuel pressure regulator, map sensor.

Hi JVM,

I need you to clarify the misfire a little bit. Does it run rough or is it just setting a check engine light for a misfire? Meaning does it appear to be an actual mis or does the computer just think it is? Can you feel it?

Next, we need to check base engine operation. That means compression, spark, and fuel delivery.

Next we need to define when it is misfiring. Does it do it at idle, under load, or in all conditions? Does it every smooth out?

Here are a couple of resources to read through when figuring this out. Once you get this information and if you still can't figure it out, let me know what your findings are and we can go from there.

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

https://www.2carpros.com/articles/engine-vibration-at-idle

I have a 5.0 1990. It started having a bad miss about 6 months ago. I changed the plugs, wires, cap,rotor,coil with no change.

What it does is when starting cold it seems to run OK. I can start off and after about a mile to mile and half it then seems to start have a miss almost like a dead cylinder or something. It does not miss under full pedal and also if I keep the rpm above 2200-2400. It has now started to spark knock a little and lose power when going up hill even with the RPM up.

I thought it may be the trans as it seems to miss or maybe it was the converter bumping or something as it seemed to happen when the trans would go into OD.

I took to trans shop and they said the trans seemed fine but it had a miss.

Someone said maybe a ignition module or something.

In a nut shell if you are going down road after warmed up when it goes into OD with any kind of pull at all it starts a bad missing/jumping like motion. Only does this under load. Even when warm it runs smooth (mostly as it does have alot of miles). Is has a slight miss when reving up up but the bad miss is when driving under load, makes the truck actually bouch like with real bad vibration like in motor/trans area.

It has to be something that changes after warming up.

Any ideas?

Is the check engine light on? or has it been on? 02 sensors, egr come online after warm up, PCM is in closed loop, and runs rich during warm up, 02 sensor info is not used, and egr is closed in closed loop, check thos 2 out. also look for vacuum leaks, get a can of spray throttle body cleaner, and spray around vacuum hoses and the intake manifold, if idle changes, you found a leak.

Merlin2021,

The check engine light has not been on. Is there an easy check for the 02 sensors-egr-PCM. I know what you mean looking for vacume leaks. This has got to be something simple but finding it my not be.

Thank you.

Try unplugging the 02 sensor, this will make the ECM use a mid value, and may smooth out engine, if it does, you just replace the 02. if not let me know and we will test the ecm.

merlin2021,

I unplugged the 02 sensor with no change. I did find a vacuum leak yesterday that I fixed but it had no effect.

The motor starts good, idles smooth, takes gas well no bogging or missing. The only time there is a problem is when the truck is going at speed for the trans to go into OD and the converter locks up, it then has a vibration almost like a drive-shaft, when it comes back out of od or at high rpm in od it does not seems to did it nearly as bad.

The trans guys told me twice the trans is fine, but with it only doing this when it goes into OD at a low RPM and when you start giving more gas it then either misses or something is virbating, I had a van that would sometimes kill a plug and with the dead cylinder it also feels the same.

I know this is long winded but this is driving me crazy. I don't have the money for a complete shop check out so I have to try to do it myself.

I appreciate your help very much.

You are starting to loose me...Is it a misfire, or a vibration?

Takes off fine seems like goes shift in second gear has trouble starts jerking then idle rough. Replace plugs and wires new fuel pumps and filter. Still does not run right.

Sorry, it has a mis-fire that seems like a vibration as in a cylinder not firing maybe. I have a van that would sometimes kill a plug and it made a bad shaking/vibration in the motor.

I am at my wits end not knowing what else to do. Could a bad injector cause this? If so how does one check for that?

Again thank you as I know you are putting in way more time that my little $10 is worth!

Good morning.

The first thing I would do is a compression test to be sure the engine can produce power. If you have low compression it would explain the rough running.

Did you replace the cap and rotor as well?

Roy

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

https://www.2carpros.com/articles/engine-vibration-at-idle

Usually if an injector isnt firing, it will run poorly even cold, but tou can try starting the engine, unplug each injector 1 at a time, the rmp should drop about 100 rpm momentarily, if this happens at each injector, they are working OK, plug the unplugged one back in and then go to the next one. You might also clean out the throttle body with throttle body spray cleaner, follow the directions on the can.

I just drove it about 25 miles. When it started (started just fine) it worked great for about a mile. Going through all the gears. While it is working ok seems to me like the converter after shifting into od is running at a little higher RMP but as soon as it goes bad, (the converter seems to go into another shift or something and then it starts making the jerking motion. On the drive over it was on a scale of 1-10 say a 8 but on the way back it was noticeably worse. It makes spark knock more on the way back and has a over all miss that you can feel continuously. On any pull it spark knocks and loses speed (just a little). When I get off the interstate I have to turn off the OD or you can't hardly drive it, keeping the RPM's up helps it.

It sounds like a bad MAP, that's the sensor, located by the air filter. This one controls air/fuel mix combined with barometric pressure. Unplug it and go for a ride, if it improves, replace it. Can be out of range without setting a code.