My son has an '02 quad with the 3.9 automatic. He put in the smaller charging alternator when given the choice, and also has a lower CCA battery than suggested.

That said.... the RPM drops when he puts it in reverse and even dies some times. Putting into drive is not really an issue, rarely.

Any advice is appreciated!

 

I don't think that makes any difference does his headlights dim on him at any given time? If not then I don't think the alternator is the problem unless he received a bad alternator

No codes?

The Battery is for startup only once started the alternator does all the work

I think the problem is in the automatic trans

 

I won't go into technical detail why, but call it a SNAFU. It has to do with hydraulics and how the trans is designed. There's nothing really wrong.

 

He's asleep right now, but I think he said it mainly happens when it's cold(er). Perhaps the solution is to allow the engine to heat up a little more... to prepare it for the load...

 

Try reverse with the steering wheel at full lock. That's almost a guaranteed stall.

The way the transmission is designed, the hydraulic pressure about triples in reverse compared to drive (I've been told 250PSI reverse and 75psi idling in drive). That puts alot of load on the engine, and the V6's don't make a whole hell of a lot of power. Add the strain of the power steering system, and it will pretty much try to kill the engine (there is actually an 'idle-up' pressure sensor on the steering system to combat this load).

The crank position sensor (Behind passenger side cylinder head) can cause stalling in reverse, it's impossible to explain, but it fixed my issue and one that Wes Garret on here had. But we both banged our sensors putting the transmission back in the truck. If it was going bad on it's own accord, I think there would be more symptoms than just stalling in reverse.

 

Great input. Thanks!

 

I'd clean the throttle body and IAC. It can't hurt for one thing and it's often neglected in maintenance.

If the voltage gets low, due to the battery or alternator (which doesn't put out much at idle to begin with) it can also stall.

 

Why he put a battery in that is lower than needed in Cold Cranking Amps is my question as most people always put in a higher Amp battery than is called for to guarantee a good strong startup? A basic Amp alternator is fine unless he has extra lights or other power hungry devices like a winch or other such device.

I would also look at the things 00DakDan suggests as they regulated idle checking the sparkplugs is also a good idea or a good all-around tune-up.

How's his air cleaner/filter look is it clogged up?

 

Mine does the exact same thing Rob. Only ever in reverse, drive is fine. I've replaced my crank sensor due to another issue and also cleaned my TB but the way magnet just described makes sense.

 

I've also experienced this stalling problem. Only happened to me once when I was parallel parking. The wheel was at full lock like magnethead had mentioned and it stalled as soon it went into reverse. Panicked for a moment thinking something went horribly wrong and that something was going to **** the bed soon. Good to know it only happens under certain circumstances. Appreciate the explanation magnet. +1 to you sir