I have a 99' f250 I purchased a few months ago. Here's what happened. Today I was driving down the road and it started to surge. I pulled over and shut the truck off. When I went to start it, the motor turned over slow for a sec and then clicked. When I put a jump pack to it, it fired up. I took it home with the jumper still hooked to it and checked voltage. The alternator was throwing 33.4 volts!! I went to the auto parts store and bought a new battery and alternator. Now the battery shows 11.7 volts steady. The alternator still reads 33.4. Also, if I unplug the positive lead while it's running, the truck shuts off. And one more thing. If the key is off and I reconnect the positive lead, I can hear the fuel rail pressurize. What is going on? I hate electrical gremlins.

 

First, testing is better than guessing. Why did you replace the battery? You had a classic symptom of a failed alternator. Was the alternator AND battery tested BEFORE replacing anything? If not, why not?

Your voltage checking procedure needs some clarification. The NEW battery should test 12.6 V or a little higher. 11.7 V is discharged. 34 V from the new alternator does not make a lot of since either. Where are you putting the plus and minus leads of the meter while testing.

Two things that you did WRONG. 1. Do NOT continue to run the engine with the jumper pack attached. Remove it IMMEDIATELY after the engine is running. 2. NEVER disconnect the battery with the engine running!!!. You could get away with that on the older (NON Computer ) cars, but it can cause MAJOR problems on newer vehicles.

Most electrical "gremlins" are the inexperience or lack of knowledge of the tester.

Be patient, be careful, and be sure that you are testing properly.

 

I replaced the battery because it was 5 years old and since I was at the parts store already, I figured it was as good a time as any.

I have the neg lead on the neg post of the battery. The possitive lead is on the post coming off the back of the alt. Meter reads 33.4 v. With the leads going just to the battery, it reads 11.7v.

I was not aware of the jump box issue. I won't be doing that again, Thanks. It was just to get me 2mi down the road, but thanks for telling me.

I was also not aware of the battery disconnect while running thing either. Learn something new every day. BUT, isn't that still strange that it shut off? Or is that normal for "newer" technology?

 

It would be normal for the engine to shut off when you pulled the battery cable if the alternator was not working. Pulling the battery terminal off while running can cause serious electrical spikes that can destroy solid state (anything using transistors or microprocessor)components. It sounds like your new alternator is either not working or there is a problem in your electrical harness. It also sounds like your new battery has discharged, either by running the engine without the alternator charging or because of a harness problem draining the battery. You might want to take it to the parts store where you purchased the alternator and see if they will test it on the truck. In a normal situation, you should be reading 12.6, or a little more, volts directly across the battery with the truck not running and a fully charged battery. With the engine running, you should see about 14.1 to 14.7 volts across the battery terminals. Next step is to verify that the alternator is good. Then verify that the alternator and battery cables/harnesses are good.
If it is not something fairly obvious, you may need a wiring diagram to check for the location of fusible links.

Good luck with it and be sure to post back what you find.

 

100% correct

 

Well I found the voltage issue. The starter solenoid on the passenger fender has the wire from the alternator going to it. The end was broken. After putting a new end on, the voltage is at 14.2 at the battery. And 14.2 at the alternator. So it looks like that's all good. Now the bad. For some reason after the key is off, there is still power to the injectors. If I unplug the battery, you can hear a click somewhere in under or behind the firewall. When I hook the battery back up. You can hear the fuel rail pressurize. So now if I shut the truck odd for more than 20min or so, it won't fire back up unless I disconnect the battery for a second and hook it back up. Has anyone ever had this problem or heard of anyone who's had one?

 

Well, you could try pulling the codes to get some direction as to where to look for the problem. You could also try to find the problem by looking for a key off battery drain. Here is a video on how to do that.