1995 f150 5.0L
Just got done installing a new engine into my truck.
it's running great, but at idle when I turn on the headlights it kills the engine. I can rev the motor way up to turn them on, and then it's fine until I turn on the brights, and then the motor just stops. I tried to bump up the idle to compensate, but it's at 1200rpm and still killing it.

it feels like the alternator is pulling _really_ hard on the engine, almost like a jake brake in a semi or something.. if I unhook the alternator headlights work fine. alternator gauge shows it charging fine.

any ideas?

 

Congrats on the new engine. I am still feeling the pain of a motor swap myself. I'd suggest checking for a short. All that work under the hood can lead to some unintentional wire damage.

Did you go with a stock replacement engine, or are there some mods?

 

Clean & tighten the battery wire terminals (all 4 ends).

 

it's a motor I pulled a couple of years ago for another project.. a 351w fuel injected with a computer from a 93 mustang.. rpm head, etc. etc. 420hp/550tq.. you look at the accelorator now and the 33/10.5 tires spin over... it's a little much. wireing was a major pain, but it's so much better than a carb.

it all works great except for the headlight problem. I'm gonna go clean the terminals and check the body ground.

 

did not work... any other ideas?

 

Take it to a parts store that tests charging systems free in the parking lot. Many have a roll-out machine that measures starters, alternators, & batteries. If it's the alt, buy a US reman. If it's the battery, buy a MotorCraft or Sears DieHard Gold.

If you know what you're doing, you can test them all with a cheap digital multimeter, but it's intricate & requires precise procedures to yield useful results. (Alliteration is kool! )

 

Fixed it - replaced the negative battery cable, the small body ground cable had been abused.. works great.

it is wasn't so cold I could take it to the exhaust shop to finish it off.. just don't want to burn the valves with 32 degree weather and open headers.

Thanks for the help.

 

did you go with full length headers on the new engine ?