I am starting a new thread related to one I started earlier at the following link https://www.ford-trucks.com/forums/1...-confused.html because the title may be a little misleading on my original. I titled it a TPS issue when the real issue is a misfire. You can click on the link and read up on what has been said already but I will go ahead and give you a quick rundown of things so far.

I got a code the other day for cylinders 2 & 8 misfiring. These are companion cylinders so they use the same coil pack. I replaced the plug wires the yesterday since it was already in the works and to no avail, I am still having issues. I was planning on it changing them anyway before this happened because I didn't do it when I changed the plugs this past fall. I also put replace the #2 & 8 plugs and it ran fine for a bit and started missing again. So here is a list of what I have checked so far.


IAC cant remember voltage but it was good.
TPS 4 volts @ CPS/ .3volts @ WOT Huh you say? Thats what I said too!
Coil Packs Primary 0.6 ohms / Secondary 11.3k - 12.9k ohms
#2 & #8 coil was the 11.3

So now the reason I labeled my origianl thread a TPS issue is because the voltage is reversed on the TPS. It is reading 4 volts at closed throttle when it should be 0.5 - 1 and vice versa at WOT. The question was already asked if I mistakenly checked the Vref pin thinking it was the SIG pin but I assure you I did not because I checked that too and I used the reference right out of my service manual. I test drove it with the TPS connected and with it disconnected and there was no difference in the way it was running so I am thinking it may not be the TPS or it is a combination of things.

I found coolant on the #2 cyl spark plug wire boot so I checked the tightness of the intake manifold and it was good. Thinking maybe it is time to replace the intake manifold gasket though. The funny thing is that the thermostat housing is on the left side of the engine and the #2 cylinder is on the right and there isn't anyway the coolant could run across the top of the block to the other side. Could an intake leak cause the plugs to foul out?

 

Accel is crap. I had 3 or 4 COPs go bad out of a set of 8. Buy something that works.

 

The 4.6L doesn't have COP's, it is the EI system with standard wires and coil packs. Had them on for 3 years until now without issue. Thanks.

 

It is the same brand though. I had trouble tuning their fuel injectors to.

 

doesnt it sound odd that the missfire is on TWO cylinders and they happen to share the same coil ? I might be leaning that way. Can you switch the two packs and see if the codes change ?

 

It does indeed. That was my next endeavor, I kept the stock coil packs just in case so now I just have to dig them out if I can find them.

 

So I have to eat my words, I realized that the picture of the pins in my manual showed the connector removed and facing me which inverted the pins, basically they were upside down. TPS is fine.

 

Time for a slice of humble pie. So it was the coil pack. Something didn't seem right when I checked them the first time when the coil for 2 & 8 checked out at 11.3k ohms and all the others were at 12.8k ohms. I checked again and found that it was dead which would explain why it suddenly started running even worse when I was checking the MAF sensor. Found the old ones and swapped them out and she runs as smooth as butter. Thanks for pushing me in the right direction and forcing me to take the path of least resistance. I love this place, it forces me to start simple which is sometimes hard for me because I tend to overthink a lot of things. Thanks again.

 

whats the best way to find out which coil pack needs replaced? im having this problem with my 2000 f150. i found out by lookin on here its more then likely a coil pack..next step-figuring out which one it is...any ideas?? thanks!

 

Not sure what engine you have but I have the 4.6L, the 5.4's have a Coil Over Plug setup. You will need a multi-meter to check for the primary and secondary resistance on each coil pack. I can't tell you what the specs are for your specific vehicle so it would help if you had a service manual, either a Haynes or Chiltons would be fine for this. It would be worth the money to invest in one. Just going off memory here, but I think on mine the Primary Resistance was 0.5 - 1 ohms and secondary should be about 5k - 11.3k ohms. The manual will explain in detail how to properly check your coil packs. If you are having 2 cylinders misfiring you need to determine which ones by getting the codes pulled at your local parts store. Most places have code scanners you can use right in the parking lot. If they are on the same coil pack there is a good chance that they are companions meaning they share one of the coils on the coil pack. You need to know the firing order to determine this and you can find that in the manual as well. If they are companions, then you should check the resistance for that coil and compare it to the resistance of the other 3 coils. If there is a noticable variation in resistance, i.e. the coil in question has considerably lower or infinate resistane compared to the others, that coil is bad and the coil pack needs to be replaced. Hope this helps. You should definately get a manual though, they are cheap and are a great resource when trying to troubleshoot. Let me know what you find out.

 

When I had a misfire I went to my local garage to see if they could find it. They informed me that the machine to find out is only made for Foed unless a garage wants to buy it for $3000. I then looked in mt tuning program and found I could datalog a misfire on each cylinder. I had 3 Accel COPs go bad out of 8. Other than that you can buy one new COP and replace them one at a time till u find the bad one. Another thing I did was measure the resistance of each coil comparing them to see if it was bad when I removed it.

 

That is always an option if you are not comfortable with working on your own rig. But in all actuality, all you need to know in order to be able to find out if you have a bad coil pack is to find out which cylinders are misfiring, determine if they are companions and from there you can use your multimeter to determine if the coil is faulty. Or you can just test your coil packs with a multimeter measuring the resistance on each coil, if you have a bad coil, you will know it. Unless you want to pay your local dealership a couple hundred bucks to hook up a diagnostic machine to it and tell you what you can find out on your own for little or nothing.