Dakota with the 3.9l V-6. Android code reader is worthless, no CEL, and my calibrated nose says it's rich/flooded when it stalls. Doubtful it would run all the way down to the nearest parts joint to get stored codes read. So until I either buy/borrow a different reader tomorrow possibly noon, any clues on these odd behaviors which I couldn't find referred to searching this forum?

1. Suddenly dies when the temp gauge moves up to what looks like 140F. First line above the 130, first line in the arc that has 210 at the top and another unlabeled line at about 2:00 before the red 260 mark.

2. Suddenly dies again when the temp gauge gets one needle-thickness above that first line described above. Could not get it to start again today after that. Battery and power supply started flagging before signs of firing.

3. Turning the steering wheel makes the idle show considerably--enough that I stopped before killing it. Last time taking it on the road turning a corner would make it stall.

All 3 above stalls stop IF we can get the engine up to full operating temp.

I even tried a small bit of Google-fu and go nothing.

Fuel system was supposedly fixed a few years ago after it was dumping so much into the exhaust that the catalytic converter plugged up. I suspect it's doing that again but without any exhaust pressure data it's all a guess. Wondering if (like another system I knew quite well years ago) too-low fuel pressure is making it run rich and puking the control systems. Perhaps among other things.

 

Put a gauge on the fuel rail. Should be 45-55psi (ish).

How long since Oxygen sensors were changed? Primarily upstreams.

JTEC is a dumb FI system. It only listens to the O2 sensors and will force itself open loop or stall if it doesn't like O2 output. At that point, a faulty MAP input can wreak havoc. It doesn't check fuel pressure at all; low pressure would cause a lean condition compensated into fuel trims (usually STFT) based on O2 output until it either hits the fuel trim wall or goes open loop (bad lean).

 

Thanks, Magnethead. Pretty sure I have a fitting that will fit the fuel rail tomorrow. Been a bit lazy in my rush--do the manuals available here have systems "logic loops" or whatever to get me up to speed on the operating theory? I'm going to look around some right now.

Oh, here is what I was describing on the temps when it stalled this afternoon. Tell me if my tecknikal writing skillz were up to snuff. [mutter, mutter.. .]

Second stall

First stall

 

Fun fact with our dakotas.... turn the key on engine off 3 times and look at the odometer. Will give you any P codes you have. Useful little trick if you have a CEL and no scanner handy. Then google the code numbers!

this worked on my 03 3.9L!

happy trails and good luck

 

Thanks, Bock!

Code 12 is the only thing that shows up. The dead battery for a few months is probably behind that one. Confirmed the dash lights work, including check engine. Fuel pressure at the rail stayed at 45.2 for well beyond 5 minutes. Now looking at the other fuel pressure tests. Meh.

 

Need to find out what is missing when it won't start. Test for spark, and injector pulse. (since you know you got good fuel pressure.)

Do you hear the fuel pump prime when you cycle the key when it won't start??

 

Fuel pump delivered 300 ml through the rail (don't have the tool to take the fuel line off) in about 6 seconds of cranking, so that confirms that the fuel pump humming is doing what it's supposed to. Fuel delivery rate at least. And pump does start when keyed on. Engine hasn't started since yesterday, though it did fire and cough once today.

O2 sensors are original. So was thinking it might be a $150 or less plus skinned knuckles fix. Since the reports are that out of range sensor outputs can make the ECU puke.

BUT
NO spark now from a screwdriver in the plug terminal to nice shiny metal on one of the brake lines under the hood. Can't imagine how that could be related to the drop in idle RPM when power steering load was added yesterday, but electrics are funny and full of mystery.

Off to another line of inquiry. Spark plug cables all look good, perhaps the newest stuff under the hood.

 

How long since coil has been replaced?

 

Coil has never been replaced. Looking at supply voltage and signal and that stuff tomorrow. High tension wire spark test was directly to negative on the battery. Failed, no spark. Getting the wiring set up to check for spark at the top of the coil will be first thing looked at.

Many experiences with many electrical failures of all sorts of things makes me suspect that when the spark WAS happening, something temperature-related was then stopping the spark. Coil itself tops the list, less likely would be the PCM, and the CPS last on the list because I don't believe it would be temp sensitive in a failure mode. PCM is full of quite durable electronics, but when electronics do fail, heat related in common enough.

And huge thanks to VETEEN for his thread pointing to the tech manuals. The 2001 FSM got me through the fuel pump tests in terms I could understand.

​​​​​​​This board is awesome. Helping me remember some engine stuff I forgot I had forgotten.

 

Coil has never been replaced. Looking at supply voltage and signal and that stuff tomorrow. High tension wire spark test was directly to negative on the battery. Failed, no spark. Getting the wiring set up to check for spark at the top of the coil will be first thing looked at.

Many experiences with many electrical failures of all sorts of things makes me suspect that when the spark WAS happening, something temperature-related was then stopping the spark. Coil itself tops the list, less likely would be the PCM, and the CPS last on the list because I don't believe it would be temp sensitive in a failure mode. PCM is full of quite durable electronics, but when electronics do fail, heat related in common enough.

And huge thanks to VETEEN for his thread on the manuals. The 2001 FSM got me through the fuel pump/pressure testing easily.

This board is great. Helping me remember things I forgot I had forgotten.