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92 3.9 no crank, no CEL

4K views 23 replies 4 participants last post by  Tim Keith 
#1 ·
1992 Dakota 3.9 auto stalled while driving, towed it home. Won't crank, no CEL. I replaced the ignition switch with no resolution. Lights on dash instruments work when key is on. Battery is strong.

Before this occurred I had been jumpering the starter relay to start the truck, which is why I thought the ignition switch was the defective.
 
#2 ·
If you jump the starter relay, does it now crank? Or not?

If it doesn't, then you've got the wiring to the starter, and the starter itself. Or possibly battery wiring (battery connectors or the connections at the other end of both wires), but a quick test is to turn the headlights on and see how much, if any, they dim when you jump the starter relay.

Check the wiring on the factory service manual, page 8W-44 .

RwP
 
#6 ·
And of course that means it could never have burned out since the last time you tried it.

You can try a meter on the proper pins on the OBD1 connector under the hood, see if it bounces when the CEL should be blinking.

Also, it'd be worth it to triple check the fuses both in the PDU and under the dash.

Last but not least, working off the FSM's wiring diagrams, check and make sure you didn't have an ignition switch fail.

RwP
 
#7 ·
I can hear the fuel pump when I turn the key to the 'on' position.

The truck had died while driving on the highway, hasn't cranked since. The day before I had left the lights on and fully discharged the battery, a tow truck driver gave it a jump start. The only active light on the dash is the oil pressure warning light, and the warning buzzer. I'll diagnose using the FSM.
 
#8 ·
Ah.

Step 0 - Charge the battery.

You may be pleasantly surprised - Dodge ECUs are more than slightly twitchy; you may be high enough to run the fuel pump, but not high enough for the ECU to wake up fully.

That would also match the "Won't Crank".

Also, check battery cables, BOTH ENDS, to make sure some oxidation hasn't crept in.

RwP
 
#12 ·
When I turn the ignition switch to start I can hear the starter relay click.
I replaced the relay with another because sometimes they click, but the
contacts are too worn. Anyway, that would only affect the starter, not
the ignition circuit to the PCM.

Again, the truck stalled driving down the highway. There is no CEL when
the ignition is switched to 'on'. The CEL is supposed to briefly flash once.

Tim
 
#14 ·
I needed a flasher relay for my Honda, went to Autozone,
decided to get relays for the truck too. I replaced them and
the truck started like it had been parked yesterday. Looks
like there is a dummy slot for a spare relay - I'll get another
relay for that.
 
#19 ·
Fuse is #D 30 amp (yellow) SBEC(1992)

Truck was running, but lost power, stalled. The motor wouldn't crank. No headlights told me that a cable was loose. Tightened a battery cable and the motor cranked. Then, I noticed the blown fuse. Replaced fuse but fuse immediately blows when key is switched to 'on'. Fuse was $4.00 at Autozone, so I can't be too liberal with replacing those.

I read that I can use a high amp headlight as a test fuse replacement and that the lamp will draw enough current to not harm the wiring. Then, begin to disconnect wires on this circuit until the lamp goes out - that will identify the connection with the short. Has anyone else used this method? I know that if I jumper across the fuse terminals the wiring will be damaged, it seems reasonable that a high amp lamp would prevent damage from doing so. I don't want to cause further damage.

Tim
 
#21 · (Edited)
Can a loose battery cable cause this type of failure ? That's why the motor died.


I've read that a loose battery cable causes feedback from the alternator
and that spikes from the alternator won't be filtered which can blow the
SBEC. I've got a spare computer, I could swap that to see if its fixed.

Tim
 
#22 ·
Keep battery cables clean. I may add a TVS diode in the
circuit to the ECU and maybe another to protect the
alternator. The day this original scenario occurred was
when I failed to turn off the headlights and discharged the
battery and called a tow truck for a jump start. That should
have been my first clue.


"In modern automotive designs, all on-board electronics are
connected to the battery and the alternator. As indicated in
Figure 2, the output of the alternator is unstable and requires
further conditioning before it can be used to power the vehicle’s
other systems. Currently, most of the alternators have zener
diodes to protect against load dump surges; however, these
are still not sufficient. During the powering or switching of
inductive loads, the battery is disconnected, so that unwanted
spikes or transients are generated. If left uncorrected,
these transients would be transmitted along the power line,
causing individual electronics and sensors to malfunction
or permanently damaging the vehicle’s electronic system, "

https://www.littelfuse.com/~/media/...utomotive_tvs_diodes_application_note.pdf.pdf
 
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