'99 3.9L Auto, 2WD.

My nephew's truck died while in a fast food drive through. He was able to restart it, pull into a parking stall, shut it off, then it wouldn't start again when he came back out.

It was cranking pretty slow with a month old battery, so I thought maybe alternator & low voltage. I took the battery out, charged it, put it back in and no change. Still cranking slow.

Stopped by Autozone with it on the trailer but no codes...guessing because I had the battery out for several hours?

When I turn the key to ON, I hear the fuel pump and have ~50 psi at the rail.

Getting enough spark to light the tester and the timing light.

Ignition coil checked out. Cam position sensor / dist. pickup checks out.

Crank position sensor checks out. When I rotate the engine I count 6 signals per revolution, with every other one having a brief "second" signal shortly after the first.

When the volt meter registers the CPS is closing the circuit I hear a relay actuating and also a fuel injector ticking. The fuel injector makes sense. The relay not so much as it seems like if a relay closed every time a cylinder fired it'd be pretty short lived? The other slightly screwy thing was that rather than 5 volts like measured on the cam sensor, I was only showing 4 volts on the crank sensor circuit.

I've shot a fair amount of starting fluid down the intake and even though I've got spark (new plugs, wires, cap & rotor too) it's not trying to start.

Sounds to me like the timing's off, bad. I also reason if it was internal it would have happened, died, and that would have been that. Given that it died, started back, and just wouldn't restart leads me to think it's not internal.

I'm down to the ECM, but not much into excessive parts changing to find a problem...especially for a $400 part.

Any thoughts/advice/experience to lend?

Thanks,

Mike

 

Pull a valve cover off turn it over see if the valves are moving.

Just a guess but Im thinking your timing chain died if your valves dont move thats it.

cost nothing to check

 

"Still cranking slow..."

What's the voltage on the battery with no load? What's the voltage while cranking? Dakota's hate low voltage, less than about 11.

You could still have a bad battery.

As you said you should have 5 volts on the CPS.

Is the distributor turning?

 

Forgot about checking the distributor easier to check than a valve cover.

 

a flat lobe won't show up in the distributor

 

Battery voltage ~12.6V no load, ~ 10.5V cranking. However, I have a 95 full size w/ 5.9L sitting right beside it with a larger but 4 year old battery. It only drops to about 11V cranking the 360 (I unhooked the coil signal wires to keep it from starting). The same battery in the Dakota drops to about 9.5V cranking.

Good thought on the valve covers & lobes. I know the distributor is spinning b/c I could see the circuit closing from the cam sensor/distributor pickup.

I guess my next steps are to pull the covers and make sure all the rockers are rocking, and make sure #1 intake closes just before TDC.

I pulled the plugs (had a new set anyway) to turn the motor over by hand when checking to make sure the crank sensor was working. As hard as it seems to crank with the plugs in it seems probable the cylinders aren't "breathing".

I had a Chevy 305 that rounded several cam lobes that still fired and ran though, albeit fed from a single wire HEI and Edelbrock 600. This 3.9 is showing no desire to hit.

Starting to think there's some witch craft going on here!

 

Of course the 16 year old kid could have nearly cooked the starter trying to get it to restart...may be why it's cranking so slow???

 

a flat lobe would still run, just run like crap. For it to not try to start, even with starting fluid, sounds like you're missing an ingredient, and I'm pretty sure it's not air. If you're able to fire the timing light on all 8 wires, then you've got spark. If you're dumping starting fluid in it, you've got fuel. Fuel + air + spark = should run. Even if it was 180 out, it would still at least cough and backfire.

 

What kind of tester are you using to check spark? Pull a wire and see what's going on.

You didn't lose all the cam lobes in the drive thru lane.

 

Ive checked spark2 ways: in line light bulb type tester and timing light. So I guess I haven't seen the spark, just seen evidence of electrical current through 2 random plug wires. The coil resistance checked out on both primary & secondary sides.

I suppose I could check using a plug for actual spark one wire at a time. Maybe pull the coil off the 5.9 and try it?

The boys description doesn't fit an internal engine failure since it started back and ran until he shut it off after it initially quit.

This brings me back to the ECM. Something is causing some power through the plug wires. Could the ECM be sending a low and or random voltage to the coil resulting in weak and random spark?

I've got to get the Dakota fixed before I give in and send him down the road in the 360 Ram!