Have a 2017 F250 6.7L that has been having some starting issues recently. At first it was having issues starting but would start after being on a jump for a bit. Went and got both batteries tested with the tester they bring outside and it said both were good, along with the starter and alternator. Next morning it had the same issue, so I jumped it and drove around to charge back up and then went home and disconnected the batteries to see if there was maybe a drain from the truck. Next morning one tested low and when hooked to the truck it wouldnt even try to crank so took both out of the truck and took them to the store. Had them retest them on their bigger standalone machine and one tested good while the other tested good but said it was in the last 1/4 of its life. Went ahead and replaced that one, and only that one since its all I could afford at them moment. (Have been out of work but am starting back in 2 weeks so figured I would replace second one with my first paycheck). Went home and put the new battery in the passenger side and went to start and get nothing but cranking.

That leads to where im at now. Both batteries test good with voltage when tested separately while disconnected. Tested voltage while trying to start the truck and got between 9.6-10 on the passenger side but the driver side stays the same. Voltage on drivers side doesnt move while trying to start. Is that normal? I would've thought with them being in parallel that it would draw off it as well but not sure if there is a computer that regulates and only pulls when needed? My other thought was fuel but I changed both filters around a week ago and also pulled the supply line to the engine filter to verify that its getting plenty of fuel at least to that point. It really seems like its an electrical issue since it was starting off jump before but not now, I just cant figure it out.

 

It turns over, cranks, but doesn't fire?

Well, when they replaced my batteries yesterday, they hooked a scan tool up, I believe the pcm needs to be reset for new battery install.

 

See if I have this right, it would start when jump started before the 1 battery replacement, but won't start at all, even with a jump, after replacement? Dies it slow crank, no crank, fast crank but no start?

 

Both of you are correct. Before it would start off a jump. Now after replacement of one battery it turns over but just constantly cranks but doesnt start, even with a jump. The crank is a fast crank. Makes no sense to me.