I'm sure this has been posted here a million times, but I hate distributors and I don't work on domestic vehicles so I need someone to idiot-proof some of this advice for me.

Picked up a 1997 3.9L Dakota Sport at auction, minor collision damage, the works. Battery is dead, but we threw a jump box on it and we get power at the dash and all that jazz. Unfortunately, that's about all I'm getting.

We threw it at our shop, because usually they enjoy this kind of work, and they're saying I need to replace the ECU - a fine solution, if that's what it takes, but I'd like to poke around a bit and verify that before I spend the money.

I personally replaced the Crank Sensor, roadside, at the auction. Took a lot of work, and the wiring seemed a smidge too short to reach the connector, but we got her on there. Still nothing. The shop has replaced the rotor & pickup coil in the distro, because there wasn't any power there (although I've learned that's normal under these circumstances), and I believe they may have replaced the Cam Sensor as well, but hell if I know. They don't like a 20-something girl reviewing their work, so they've been less than forthcoming.

I haven't done much diagnostic work on it, largely because I don't know what specs I'm looking for, but here's what I can tell you:

1. Code scanner does communicate with the vehicle. No codes, but since she won't start and the battery has died, that's to be expected.
2. When you turn the truck on, there is the loudest, angriest clicking I have ever heard from a vehicle. It sounds like it's coming from near the radio, but I can't even confirm that. It's jarring, obnoxious, and lasts about as long as the seat belt dinging noise - maybe a bit shorter.
3. The scanner is reading no pulse from the CKP or the CMP when on/cranking/any other variation of situations that I'd expect to see pulse during. When I replaced the CKP roadside, the CMP did show a pulse. I don't know what caused the change.
4. She'll crank for days, and sounds fine when doing so - but when she fails to turn over, the dash kindly asks me to "CHECK GAGES". I'm not sure what that light means, or what it wants from me.
5. (Editing to add) - there is absolutely zero spark, and I can't make any testament to the fuel pump because of how loud the clicking is when you turn her on.
6. The fuel gauge does work, she should have about 3/4 of a tank per the gauge.

I know I should replace the ASD Relay (I think?) and check for power at the Crank Sensor (at the connector? backprobe the purple wire?). I know the #115 splice would be a reasonable explanation for my issues if the truck was older. And I know I should verify we have fuel pressure (my scanner does have a data stream labeled "Fuel Allowed?" and it does say "Yes", but who knows how useful that is). Am I overlooking some glaring solution to my problems? Should I replace the ECU just so I don't have to worry about it? Any insight yall can offer is much appreciated. Thanks in advance.

 

Love your description.

The angry click-fest is generally from low system voltage..... Not really surprising if you are running it off a jump box.

Check and see if you are getting voltage TO the cam, or crank sensor. Should be in the neighborhood of 5-8 volts, key on, engine off. That power should be there whenever the ignition is on. Coil and injectors will only see power for about three seconds at initial key on, until the PCM sees the engine turning. If you aren't getting voltage to the sensors, it will never see the engine turning, so, no power to coil/injectors/fuel pump.

 

Testing power for the CKP is the purple/white wire at the engine bay connection, correct?

 

Could be. I don't have wiring diagrams for those. Having them is going to be EXTREMELY useful for you though.

 

Okay, I got back out to her and we have some exciting developments... sort of.

Fixed the "no signal on CMP" - guys at the shop hadn't tightened the distributor cap, lmao. That's fixed now.

But uh. I tried to backprobe the CKP, got frustrated, unplugged it and tested the vehicle side of the harness. I'm getting 5v on two wires - signal and power. I'm pretty sure that's not how it's supposed to work, right?

 

I "think" The sensors are open collector transistors, so yes there may be voltage on the signal line.

 

Actually, no, you aren't supposed to see voltage on the harness side, with the sensor unplugged. There is a short somewhere.

 

THANK GOD. Would that short explain why that 5v on the signal side of the unplugged harness becomes exactly 4.32 V at the PCM connector? (Backprobed, very cautiously, verified multiple times).

 

Yeah, voltage drop across the wire. That seems a bit excessive.... but hey, its electrical. Roughly related to Black Magic.

 

Okay so, new question... where does that wire go? Are there known shorts/failure spots? Or is this just my own personal hell?
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