1999 4x4 SLT

Did a voltage test on the battery and it passed with about 12.6v the built in hydrometer was green indicating 75-100% charge. Fuel pump relay and ASD relay make constant clicking noise when battery is disconnected and reconnected. When key is turned I hear the fuel pump prime and all the dash lights come on, all the electronics work. When I try to crank the engine we hear a clicking from the starter relay then nothing.

We attached jumper cables to the battery and it started cranking very slowly and sputtering. I gave it alot of gas and it came to life but as soon as I let off the gas it quietly died out.


Need help please.

If you need more details feel free to ask.

 

check battery cables for corrosion. remove and clean.
battery voltage can be deceiving. a load test is a better test than a noload test.
you can do this by checking voltage while trying to crank it.

if you don't have a voltage tester, turn on the headlights and try to start it. if the headlights dim significantly, then the battery is no good.

 

Strangely before I read your post I did the headlight test and they were very dim and went out when I went to start. But then there is the question why does the engine run at high RPM but die when I let off the gas?

 

the low voltage f***s up the reference signal to the IAC or TPS, not sure which, which causes it to not idle right. its sort of a common problem with the ram trucks and low battery condition. i'd guess the durangos would share the same problem.

 

Ok that helps man thanks a bunch.

I have also determined that my mother, god bless her heart. Had a DEEP-CYCLE battery installed in the D instead of a regular automotive battery which explains why it could run everything else but not the high current draw the starter needed.

So we are getting a new battery regardless.

 

yup definetly needs a new battery, and it runs at high rpms bc at those engine speeds the alternator spins fast enough to make adequate voltage to keep everything running, but at idle it doesnt, that is why these trucks behave badly when the battery gets weak the pcm doesnt recive a proper signal from the sensors bc the input voltage drops and therefore the signal voltage is not what the pcm expects and when it cant make the proper adjustments to get readings within the expected parameters the truck wont keep running if the sensors are reading outside of expected tolerances for a few reasons, one being the air/fuel mixture will be off, and it will think something serious is wrong and shuts down to save your engine from any major unrepairable damage

 

Close but no cigar.

When the battery is low (usually under 12 volts) or a bad connection/dirty connection, the system has to come up to 12 volts at least to run correctly. While the system is in low voltage, the 12 volts or better goes to the PCM for the final regulation to 12 volts for the system. The overage goes to the battery to charge it usually running at 13.2 volts to 14.2 volts. You need to have at least 12.8 volts to charge the battery to 100% but at this voltage it would take a very long time!

Problem is the battery is low so it sucks up the voltage creating a void where the power can go. Now off the battery is where 12 volt power going back to the diodes in the rectifier bridge for the alternator. An alternator is actually a A/C generator but the output gets converted to D/C power hence the name "Alternator". Now without the proper power to convert the A/C generator to D/C current, the output of the alternator isn't up to the volts needed to run the system. If you bring up the RPM it creates more power faster thus creating more current and thats why the motor stumbles at idle.

Also this is the reason that if you take the battey out the motor stumbles some. In the old days this was a way to see if the alternator is working. But the old days had external voltage regulators and no PCM to deal with. Now if you pull the battery connection off during running the excessive voltage HAS to go somewhere. It will burn out the PCM regulators and if this happens it will fry the electrical system........SO DON"T DO IT!


Now, for the regular newbies here I don't go into the whole thing and usually spill out only whats needed. But now you know.


Here is some great info on voltage and current that I wrote up in the Durango 1st generation threads.
Alternators
Alternators and Alternating Current.
https://dodgeforum.com/forum/1st-gen-...questions.html

 

You dont think i damaged the PCM do you?

 

No.


You have a bad battery, bad starter or bad connection.

Test the voltage with the key in the on position across the batery posts (not terminals) and have someone turn the key to start (engaging the starter) and read the voltage drop across the battery posts (not terminals). If you see it drop down about 1.4 volts or so the solenoid is gone and grounding or bad contacts so you will need a starter. If nothing then it's a bad connection. Check the terminals and connecting points on both ends.