Hoping someone has had a similar issue or can provide some guidance. I have started having an issue with my 98 Dakota SLT 3.9 V6 Magnum where it just stalls on me all of a sudden with no prior warning or any MIL lights. I have had it taken to my mechanic twice for this issue and he (1) can not get the issue to happen when he has it and (2) gets no readings that can clue him into the issue and/or why it may be happening. He recently replaced the radiator and water pump for me. We did discover that I have a compression issue and misfire issue in Cylinder 1. I know that the compression issue could cause the problem I am talking about but hoping someone here may have a fix, work-around, or other advice to help me rule anything else out. My mechanic did a flush and BG Compression treatment but it really didn't make much difference that I have noticed from driving. I can't afford to drop a new engine in right now and as my everyday commuter car, the heavy Northern Va traffic keeps me wondering where she's gonna stall on me next. I'm usually able to get her to start back up after a try or two but have had to let her sit for a few hours at times as well.

I appreciate any help.

 

Low #1 compression won't shut the engine down point blank. Actually, very few things will shut down an engine point blank, without first chugging or misfiring.

Does a rough road or potholes or rumble strips cause this issue to happen? Vibration would help a weak relay break contact.

When you've had to let it sit to re-start, have you been able to hear the fuel pump prime at key-up (indicating the ASD relay has fired)?

1) ASD Relay is failing - this would shut down the ignition and fuel systems instantly, by design. It is how the PCM shuts the engine off properly. The relay comes on for about 1 second at ignition-on to build fuel pressure prior to start sequence.

2) Electrical ignition switch or control rod is failing - this would make the PCM think that the key has been turned off, which would kill ASD relay above ^.

3) Fuel pump is failing - unable to provide fuel pressure. Usually there would be a very brief chugging beforehand

4) Ignition coil is failing - unable to provide spark. Usually this leads to a misfire/intermittent-fire situation - rarely is it "all or nothing".

Put a new relay in the ASD socket and start there. If it continues to happen, I'd look at that electrical ignition switch's output.

 

rough road does not seem to be a factor. Mechanic said he has checked the fuel system and electrical and there was no issue but I'm doubting if he really did (at least any more than what the OBD2 put out when he had it for 2 weeks and no replication of issue and less than a week after i get it back ...Stall). when it does shut down it is only the engine. radio and everything else still works if that makes a difference.

I haven't noticed a sound different than it has always been when starting up. is there something specific i should be listening for?

Earlier today it did do some chugging but it kicked right up and never stopped. got close though.

 

Will it start right back up? Or do you have to let it sit and cool for a while first?

 

It varies. I have had it start right back up and be good to go. But, I have had it also start right back and then stall after a min or two. only twice have i had it not want to start back up and have let it sit for 30min+ and then get it to start again.

 

I have a few things u can check as I own a 3.9L 98 SLT. Some suggestions suggested here so I may be a little redundant.
PCM plugs, wiggle them around a little whilst the truck is idling and see if it shuts down
Replace Crank and camshaft sensor, parts are cheap (My crank sensor was bad and got a second bad one, drove me nuts)
ASD (Auto shut down relay, check or possibly swap with identical relay in the engine fusebox)
If you can check your timing with a scanner while running and see if the timing jumps around while driving, this is how I caught mine.
FYI, I was getting a lot of misfire codes as well every so often when it didn't anything to do with misfires, again it was timing caused by the CKS.
Rotate your crankshft slightly while someone watches the distributor, should be no play before the rotor turns, a good way to check your timing chain slop.
Last if not least,the PCM. I have one for your engine that works but the abs part gives a code and there is nothing wrong with the ABS on my truck however, the PCM works fine.
If you exhaust all other tries PM me, maybe I can send it to you to try, pay the postage and then send it back as they are a pain in the *** to get or find for this year.
I feel I know this truck fairly well after owning it forever and working through all it's problems, which were not many. I'm one of those people with a disease and will not stop till I find the problem. I swore I would sell it after I found the problem but that was several years ago and will not part with something I now understand and can fix.
I also have a couple heads laying around, bought them used, cleaned up the valves. Used only one because of the constant misfires on the drivers side. I was impressed how well the old one looked after 225K.....it didn't need gaskets and didn't need to be replaced but in frustration, I tried it all. Hope this helps you out.

 

 

You should hear the fuel pump buzz for 1 second after turning the key on. You may not be able to hear it from inside the truck over the dashboard chimes. Easier with 2 people.

 

I suggest fuel pump I had a few times my Dakota would just shut off and not start first few start attempts.

With me I just rebuilt my engine so it drove me crazy but when it just didn't want to start back up last time and showed an empty gas tank I strongly suspected fuel pump. Had a shop check it out they were not sure also it seamed random but I said replace it.

No more problems

My engine the 2.5 not a 3.9 but gas tank is a gas tank same all engines.

 

I had a very similar issue with my truck. Check all the ground wires near your PCM. They look like flat green ribbons. They tend to disintegrate. I didn't realize mine were broken until my PCM got fried.