My 2003 f-150 keeps acting like it is missing. original code was for cyl3 miss fire and bank1 & bank 2 running lean. Replaced the 8 plugs & 8 "wires" and the coil pack on cyl3. Cyl3 missing code is gone but still have bank 1 and bank2 running lean code. Engine still is acting like it is skipping. Replaced the injector on cyl3 also. Still same problem. There are no vacuum leaks, EGR seems to be working right, and I have cleaned MAF sensor. Problem still exist.

I locked the keys in my truck Friday with it running and the hood up. So I would not run the gas out of it, I decided to disconnect the battery and sufficate the engine to cut it off. As soon as I disconnected the battery the engine quit like I threw a light switch.

This has me wondering. If the alternator is not putting out like it should would it make the engine act like it is missing?

I have been a GM and Dodge man that crossed over to Ford. Please help me not regret doing it.

 

OK new update. I have now changed all of the injectors with new ones. The truck seems to be running better but it still seems to be running rough or skipping. as stated before I have replaced the plugs the boots and coils. The ignition coil on Cylinder three has been replaced. I have cleaned the MAF sensor. I have attached a vacuum pump to the EGR valve and it sounds like it is actuating. I have sprayed starting fluid along vacuum lines and around the egr valve so I know there is no leaks. What should I do next? Replace MAF? Replace EGR? Replace oxygen sensors? Please HELP!!!

 

Good day,

I would say you need to replace your alt as the truck should stay running (AFAIK for a 2003) when you disconnect the battery. I would also invest in some O2 sensors as this is/was the code you are/were getting. If the computer is saying the O2 sensor are seeing a lean condition, you could be dumping way too much fuel into the cylinders as the computer tries to compensate for the bad O2 sensor, causing the misfires. You could disconnect the MAFS to see if there is any change, but I doubt you will see one. Sometimes the engine will stumble if you tap on the top of a defective MAFS with the engine running, however this is not always the case. I had a defective O2 sensor in my T-bird and it made the car run terrible. I disconnected it and the car instantly ran normal. You could try this, but it isn't always a positive outcome. Best bet would be to replace them as they did throw a code and are cheaper than the other two items on the list.

Good luck!!

Cheers!!

 

thanks I will give that a try next. I did not think of just disconnecting the o2 sensor. As far as the altenator goes though I already had it tested and it was good. According to the people at AZ, if you run the truck without battery it can fry the computer. They said the engine cutting off is a built in failsafe.
I will try the o2 sensors today.

 

if you have lean bank codes of p0171,p0174 replacing the o2 sensor aint going to fix it.This is metering issue causing both banks lean. too much FUEL not enough AIR thats your key word (AIR)
you most likely have a vacuum leak you need to check your vacuum line that comes off the pvc valve and goes to the intake if it is sucked in or soft and spongie replace it also if the pcv valve is a aftermarket replace it with a motorcraft one this is a metered sensor not a universal fit.. also you need to take a look at the maf sensor look into the maf you will see to wires one is a hot wire make sure there are no spider webs or debri ie. leaves

also how does the truck run in the morning if it runs crappy and misfires when it is a cold start... your concern will be that it needs a set of lower intake gaskets as the engine warms they will seal, you can spray carb clean around the intake and never find it...

if you know someone with a good scanner that can look at live data have them look at (short fuel trim) pid (sft1 sft2) (lft1/lft2) (long fuel trim) if they are running over 10% on on all four readings to tell if you have a vaccum leak watch you pids while you leave it in park and snap the throttle if the fuel trims change go to (0) you have just confirmed you have a vaccum leak


hope this helps

 

97 F150 4.6 (no ignition coils on each plug)

I had a bad miss-fire. I added a can of sea foam to 1/4 tank of gas and drove around in 1st gear at 4000 RPM. This morning I took it out for a drive and it ran smooth as silk. I shut it off went into a store, came back and the miss/stumble is back.

It's not throwing a code at this point so I cant diagnose using the OBD11 scanner I bought.

The more I think of it the more I am suspecting I have an antifreeze leak which is getting into a plug. There is no white smoke at start up a tell-tale sign of head gasket problems. Although, I can smell antifreeze and see signs its been dripping. I'm going to attempt to locate the source of the leak.

In the mean time I bought some dialectic grease to put in plug boot and on plug to help isolate the moisture. (it can't hurt) and will search for a possible wet plug 1 by one. While I'm at it I will change out the plugs.

I hope you have better luck than I've had at solving your miss-fire.