Hello!
How can I check the coil pack on a 1999 F150 5.4 to see if it is bad or not, all I know is that I have to ohm it out but Im not sure how. tnx in advance

 

Welcome to the site!!
According to Haynes manual:
The resistance for the primary circuit (between the two terminals) should be 0.55ohms and for the secondary circuit (between one of the termainals and the spring that contacts the spark plug) should be 5,500ohms.
I don't think the secondary is an exact no. and they didn't specify a range but when I tested mine, I got the 0.55 on all the primarys but the secondary readings ranged from 5,410 to 5,570.

 

thanx.
I will check to see if this is the case, so I can get my truck back to 100%

 

Flametip,

01screw gave you the correct resistance figures from the Haynes manual, but you should be aware that they don't neccesarily tell the whole story. I just finished going through the ordeal with a no. 7 cylinder misfire, and the coil resistance measured exactly what it was supposed to. The new coil I purchased from Autozone was way off spec on the secondary resistance. Instead of the called for 5,500 it had 4,250, so I replaced it with one from Advance Auto, which I tested in the store before I purchased it. I tested all eight coils and they all read within 5,500-5,300. The moral of the story is of course the coil that tested good was actually bad. I could not find any absolute evidence of external damage, but there did appear to be one harline crack in the coil body.
I am curious as to why you would suspect the coil? Have you pulled a misfire code?

 

Karkfump,

Yeah, I got a code that read P0304 and I replaced the spark plug and it kept doing the same thing, so I was told that the problem would be the coil. Any other ideas would be welcome.

 

You really should not have to look any further than the coil here. The scanner indicates a no. 4 cylinder misfire, and if you have proper voltage coming through the wire that snaps into the coil (12 volts-key switch on, engine not running), and your plug is not defective, then the odds are that is simply a defective coil. I should clarify that my resistance measurements on my 5.4 did not match what the book called for. The primary calls for .55 ohms, but all of my coils tested .8, .9 or 1. I don't know a lot about testing with a voltmeter, but this is what I came up with on every coil testing the two terminal that the electrical connector plugs into. The coil cost me around $52 at Advance Auto.

 

I did a lot of research and foubd the grantelli coil packs to be the best i could find. I put in the ones guaranteed for life. Better quality and since have had to have one replaced. They did not cost me any more than the oem. I highly recommend. I have 125k miles on my f159. 5.4 triton.2006. I may have to replace another. All i have to do is send it in. I did keep. Theold ones so i would have a spare.