so i just dropped a new cam in my 5.0 a few days ago and i just have been getting the timing dialed in on it. and heres the issue. i had set it at 14btc and from there on i was driving it accelerating past 60 and out of no where the truck dies. and when im on the side of the road i sat for about 5 minutes or so, and went to start it. the engine itself turned over but my rpms were at zero. then i turned the key off and the needed started bouncing and going crazy for a few seconds. so i just was looking in the engine bay for another ten minutes or so. couldnt really find anything loose or unplugged so i get back in and after a few cranks it fires up. but runs rough and the battery gauge moves lower and the rpms at idle dipped down under 500. i got home and replaced my negative battery terminal as it wasnt in the best of shape, and put the timing at 12btc. and it fired up after a few turns. what could caused the no start and the dying at full speed...? thanks

 

Perhaps the ground to the motor or chassis is in bad shape. Others thoughts could be failing alternator. I don't know what else could cause the problem other than electrical failure or weakness. I had a similar problem few years back and my alt was at fault, but wouldn't completely kill the engine unless I had the headlights on and blower. It killed it once and the next time I had to flutter the gas pedal to keep it running. I yanked it off the next and got a reman. It solved the problem even though I didn't suspect till I had numerous accessories on.

 

I just found a broke ground wire on the passenger side frame rail to the cab, ill fix that. Because ive had my alternator replaced recently

 

Make sure the tach signal wire isnt shorting against something. I worked on a chevy that would intermittently die and thats what fixed that. Since your tach is getting funny readings it would be a good thing to check.

 

Do u know where that wire is located at??

 

Sounds like you have a ground or power connection issue most likely, possibly a bad computer.

You may have already fixed it when you replaced the negative battery terminal. There are a couple of grounds that run into the harness and are for the computer. Mine are 2 black wires about 10 guage that are right next to the battery, coming out of the harness at the core support and running to the negative terminal. Yours are probably in the same place or close.
I also have an extra ground running to the alternator bracket. Sometimes the alternator can lose its ground and do strange things as it will ground itself wherever it can. Probably not the problem in your case since you just replaced the alternator and the cam so you should have regrounded everything when you removed and reinstalled the bracket and alt, but wouldn't hurt to put an extra one there. The ground wire to the starter could also be bad, or the connection which might make the system try to ground through the computer.

While we are on the subject of alternators and wiring, do you have the second generation alternator or did you upgrade to the third generation? The bottom connector on the second gen (2g) is known to cause problems and will even cause fires in some cases. Ford has a TSB out that tell you to replace the connector whenever you replace the alt or bat, but upgrading to the 3g is a better idea, it has way better output and eliminates the fire hazard. So, if you have the 2g, the bottom connector could be losing contact.

Those are a couple of places to look at in particular along with checking the rest of the grounds and ground wires.

On the power side, you might want to check the fuseable links at the solenoid. The one for the computer is a large yellow wire with a blue(?) fuseable link attached to the solenoid. They usually just burn through, but might just be failing intermittently.

Intermittent problems are a pain to find. If cleaning and checking connections and wires don't solve the problem I would keep a multimeter in the truck and when it acts up you can check for grounds and power right then.

Another really handy tool is the led type test light. The kind that hooks up to both the + and - terminals at the same time. The led turns green for a ground and red for hot. Its much faster and more convienent for finding intermittent issues than a regular test light.

Oh, I don't believe you have a seperate tach wire like a chevy. The tach signal comes from a pin on the computer if I recall correctly.

 

I thought the tach wire came off the coil. Green colored wire. I'm not positive it means much to the SD trucks, rather than a reference point for DDs and mechanics'....Someone correct me if I'm wrong. And didn't mean to step on your toes..just want to be sure I wasn't informed incorrectly.

 

Thanks for the input bdelmar2, I had the better alternator put im pretty positive its good, but I know ive had issues with my selenoid in the past so now ill go out and check it out along with the grounds

 

Dark Green/Yellow on the coil. That feeds to the IDM pack, which sends the Tach signal to the cluster via Red/Light Blue and the IDM signal to the PCM via Dark Green/Yellow.

courtesy of OldFuelInjection.com

 

Cool, thanks for the info rla2005. Learn something everyday.

 

yea that forsure is some good info.

 

Appears I was incorrect on there not being a dedicated tach wire.

Not sure how I got the idea the tach was fed off a pin on the computer, I wonder if newer trucks use a pin on the computer, I had to check the pinouts on a 2004 a couple of weeks ago so I may have seen it there and gotten them confused. I should have checked before saying anything, sorry.

Thank you for straightening me out.

Oddly enough, I've never had an issue with the tach in my truck so I haven't had to actually chase those wires down, or not yet anyway.

 

We all learn something here almost everyday!