Ok this is my wifes truck. We have replaced a coil that was bad fixed a coolant leak. Has had a tune up in the past 6 months. She states she is getting 1 mile per gallon. Any idea's as to y this would be?

 

I would look for a fuel tank leak . or buy a locking gas cap.

 

That's about 30 miles to a tankful of fuel, have you confirmed this yourself? Any married man full well knows the exaggerational skills a wife uses to try and get her husband to to get done what she thinks is important.

 

That's just it. When something is wrong with her truck she knows she has to pay for it. And she is really good with tracking it. She is going with the digital display and also checking manualy with miles traveled compared to golons of fuel purchased.

 

I think a locking gas cap is needed here also. You don't have a teen age son with a car do you?

 

Lol I have a teen child but she lives in nj and I live in pa. She and I are the onlt ones with a key?

 

Well that eliminates at least one possibility, and I have yet to meet a female that would siphon gas. They would rather walk 5 miles through a blizzard first.
You might look for a leak at the fuel lines with the truck running and the system under pressure.
You might also set up a night vision camera that is not easy to see and let it watch the truck for a few days. Something like a "Nanny Cam". If you don't find a leak anywhere.

 

If the engine was running so bad as to only get 1 MPG, then there would be a ton of black smoke billowing out of the tailpipe. That aside, the engine would not run at all if it was plagued with such a major issue.

 

I'm wondering if the coil the parts shop was for a 5.4 and not a 4.6 and may be giving it problems. But has no check engine light. Grrrrr.

 

The coil does not care what engine it is used on, all it wants is electricity, some dwell time to build the current and a signal to release that current to the sparkplugs.
There has to be another issue causing this mileage drop.

 

Dont know. Which is one of the reasons ive come here