Hey guys,

I have a 1990 F150, 4.9L 5Spd. Basically, the truck won't start sometimes. It just cranks very slowly. I thought it was the starter or the alternator but we took them to autozone and they said they're fine. Thought it was the battery but they said it was fine too. The guy tested the alternator while it was in the truck and it failed once. Tested it off the truck and it passed. Put it back in the truck, tested it and it passed again. They said it was because my power steering pump throws fluid out (which it does)and it got in the magnetic field. But I think it may be something more. What could cause the truck not wanting to start like that? It'll start with a jump starter, it just seems like the alternator isn't working while the truck is running. (which is another thing the autozone guy said.) Could it be a faulty alternator? Any help is appreciated. Also, as a note, it's been 20-30 degrees out lately

 

Could be, but your Battery light would normally come on while running.
See link: https://www.f150forum.com/f33/how-big-3-upgrade-46822/

For an otherwise stock electrical system 4 awg will fly. I think I settled on 2 awg.

 

did they check the battery under a load ? also is the battery connections clean and tight . corrosion will seep inside the wire insulation and break the wires .
if the vehicle starts easily when jump started the problem to me seems to be w/ the battery and its wires . how old is the battery it may not be holding the charge . adding water over time will dilute the acid . good luck .

 

Good points & why I suggested the wire upgrade. Also as far as strong starting w/o the assistance of a chargeing system of another vehicle (alternator assisted), the proper ground paths need to be in good shape & well connected to complete the circuit to your battery.

He mentioned a new installed battery did not help. Not sure what "new" means.

 

Right on guys. I'm gonna give the tutorial a try. Thanks for the help, everyone

 

I'm not sure if this will help you resolve the problem with my grandmothers 89 f150 it had a hard time starting and we did all the test the you have done then we checked the silonid <spelled wrong so that might be something to check

 

Solenoid. Ya, that ones a b!tch sometimes w/o spellcheck.

Solenoids are not considered a "life of the vehicle" component. Higher amperage draw from poor connections shorten their life considerably. Jumpering across the large posts momentarily, will tell you if it's the solenoid.

It will actuate the starter, but not for the faint of heart, as it will usually melt a spot off the posts where you make contact w/ your jumper & whatever you jump w/. Be it heavy gauge wire or pliers. Just like if you were making contact for a wield. So don't use your favorite pliers!