#1 and #3 injector misfiring

[JimmyR]

I have a 01 f350 with 7.3 It has 140,000 miles on it. It start missing and finally would not start. I have replaced the electric fuel pump and filter and cleaned out the tank and lines. Truck will start now but is still missing. I took it to a buddy of mine and ran a buzz test. It says #1 and #3 cylinder misfire. I put in 2 new injectors and still missing. Sometimes the buzz test says test pass and sometimes #1 and #3 and sometimes 1,3,5,7 misfire. I have changed out both computers and tried a new wiring harness for the injectors. I'm trying to check the wiring to the computer now. Should I just buy a new harness or could it be something else. Please Help I need the old girl @ 100%

[arisley]

I would definitely look at the wiring harness, check the connector in the valve cover gasket also. When you say you replaced the injector harness, are you talking about the Under Valve Cover Harness? The harness between the valve cover and the PCM has been known to chaff and short out before. Could also be something in the fuel line for that head. The so called "check Valves" have been known to get dirty.

[JimmyR]

Installing new wiring harness today. Hopefully this will fix the problem. #1 and #3 for some reason are firing at the same time and grounding each other out. I think? I would like to buy a new truck but dont want more problems than I have or the terrible fuel mileage.

[Banshee34]

Hopefully the harness will fix the problem. Also, can't help but think that a vehicle that isn't running correctly will inevitably get poor mpg.

[JimmyR]

My f350 when running correctly will get 15-16 around town. Not complaining about that. The new 6.4 is reportedly getting 9-10 mpg. The new truck is sharp but I cannot afford 9 - 10 mpg @ 3.85 a gallon diesel.

[Banshee34]

Originally Posted by JimmyR

My f350 when running correctly will get 15-16 around town. Not complaining about that. The new 6.4 is reportedly getting 9-10 mpg. The new truck is sharp but I cannot afford 9 - 10 mpg @ 3.85 a gallon diesel.

Me neither! Heck when regular rose to $1.29 back in the day, I had to get rid of my F250/460. <- only got 4 gallons to the mile.

[SCUFFY828]

if its failing buzz test , it is an electrical problem, probably not fuel related , check all wiring good