I have a 98 Dakota 3.9l auto, i bought this truck about a month ago as it has sat for roughly 4 or 5 yrs because the former owner couldn't get it to run. After spending many weeks chasing down splices in the harness, changing sensors, (map, and crank position, putting dist back in, and making sure rotor was on #1 cyl, bought new pcm programmed to my vin and finally got truck to start..... Barely, after fixing a few vac leaks truck would idle but if you touched the gas peddle it would start popping through intake and occasionally ignite a cannon located somewhere under my truck, (at least that what it sounded like lol) so i figured the fuel sync was out so today i tried the multimeter method but i couldn't find any v6 or v8 Mark on my damper so i used this formula to find the 147° atdc, 147/360*c where c is the circumference of my damper which is 25.5 inches so 147/360*25.5=9 3/16th inches so roughly a tad under 9.25 inches so i marked my damper and set it on the tdc Mark on timing cover then using multimeter back probed the signal wire to right at where it changes from mv to 5v. Put everything back together and went to crank truck and now doesn't start at all, checked for codes and iat sensor high circuit comes up, (but had been even when truck would start), and a code that reads "key on or engine running then test start and pcm detected 4.9 volts at map sensor for * seconds. (2 second i think). Anyways changed map sensor with new one, plus lastly i get a code telling me pcm isn't getting a signal from crk sensor although signal was present at cmp sensor. This one confuses me because if there wasn't any signal from crank sensor i shouldn't have spark but i do indeed have plenty of spark, it lights up my spark tester like a Christmas tree. I also put noid lights on my injectors and my injectors are all pulsing and not at the same time so i have all 3 components to start, (air, fuel, spark) but it doesn't. When it first turns over it sounds like it's going to start for just a split second then just turns and turns over. Also my fuel pressure at the rail is around 60psi. I'm really at my limit here bout ready to go trade this truck in for scrap metal, 1 step forward, 5 steps back constantly on this truck.

 

Oh also i made sure battery was disconnected before doing anything only reconnected it to do the back probe then disconnected before putting everything back together, have also tried putting dist back to where it was( which wasn't very far from where it was after injector sync), still no start, and even tried starting fluid still no start so what gives???? Wtf, Dodge engineers should be condemned to the depths of hell for this wonderful engineering design....

 

does your distributor look like this one at the bottom of the shaft?




If Yes then do this (again if needed)

1) rotate the crank to the TDC mark is aligned with the marker

2) pull the DS valve cover and verify both valves are closed
if not then rotate crank 360*, both valves should be closed
if both valves are never closed with the crank at TDC then the cam timing is not correct (not likely unless the timing chain was removed)

3) pull the cap on the distributor and verify it is pointing at the #1 contact
if not then pull distributor, rotate 180* and re-install so that it is. (It looks like it can only go 1 of 2 ways)

4) verify the plug wiring is correct



5) verify each wire is actually good, measure with ohm meter should be less than 20k on each wire, end to end

6) verify plug gap (if not done already)

7) optional: disconnect the coil and fuel pump and do a compression check on each cylinder

8) optional: if compression check fails do a leakdown test on the failing cylinder

9) optional: pull both valve covers and rotate crank 360* to verify valves on each cylinder are opening/closing as expected



With all that done, now you would know the following:

1) cam timing is good
2) ignition timing is good
3) cylinders hold compression as expected

Next re-assemble and attempt to start, if no start then I would do this:

1) put a timing light on plug #1

2) back probe injector #1 and have a 2nd person crank the motor, verify both #1 plug and injector are firing at the same time

3) repeat #2 for remaining cylinders

If that fails then check the wiring for each injector back to the ECM, you would need a wiring diagram for that one, if it is a JTEC ECU then you may be able to use one of the other 3.9L engine diagrams.

Or

Get a new wiring harness and scrap the one you have <- would be my choice if the current one had splices in it.

Do the steps I outlined again, even if you already did it and report back.

 

Ok so y'all are going to think I'm an idiot but the problem was really really reeeeaaaalllly simple..... Truck won't run without gas in the tank....smdh

 

Don't understand why starting fluid wouldn't crank it though anyways here's the update, after fuel sync truck runs better but still occasionally a pop and hitting gas peddle engine still doesn't seem right so I'm thinking i may have a bad injector or two since truck sat for so long however I'm not getting any misfire codes, i can unplug several injectors individually and only a couple change how the engine runs so i think I'm gonna hit the pick and pull tomorrow for some injectors and see if that does it..... I'm close i can feel it but then again I've thought that several times already lol

 

Exciting news guys so just for ****s and giggles i decided i was gonna test drive the truck, i live in a rural area so going "around the block" is about a two mile drive, as i pulled out my driveway i was really considering turning around cause it was really sluggish and hesitating, had some popping in intake but i kept going, pressing gas peddle to much made it feel as it was fixing to die so i played with the gas till it got up to about 30mph and it seemed to be getting better by the time i circled the block the third time i could press gas peddle to for without any popping and truck actually has some acceleration to it lol. Still have some stuff to work out like a strong gas smell after shutting it off, still a little hesitant and if it idles for like two minutes it dies but that could be the iat sensor maybe still getting that code but all in all I'm excited to get this truck back road worthy soon and start driving it. Oh and btw the truck ride well that was surprising as it rides very well super smooth on the road, i was very pleased

 

Plugged exhaust I wonder?

 

I don't think it has a cat anymore but that is a good point i guess I'll check that out tomorrow

 

I would take a look. Could have also been excess carbon buildup. Did you ever pull the plugs and look in the bore?

 

Plugs were already new when i bought the truck one of the few things the previous owner replaced trying to get it to run, plugs, wires, dist cap but not the rotor, (weird) but i put a new one on,, so I'll have to drive it for a bit to see what they look like as far as looking down the cyl bore i don't have the means to do that and my eyesight isn't what it used to be