1998 Dodge Dakota 3.9L

Got a very intermittent problem as of recently (last two weeks). First sign of trouble was leaving work, start truck, then 5-10 seconds it shuts off, but fired right back up and was fine. Few days later while driving into work, ~30 minutes driving, it seems like it has a random misfire only does it maybe, 2-3 times with a few minutes in between. Last friday, I get in the truck after work, pull around the building, and it shuts off as I'm coming to a stop, again, fires right back up no problem. Only actually killed the truck twice, both times started instantly. Ambient temp was around 90F. This morning, however, I find out those "misfires" actually seem to have been short shut-offs. This morning the truck shutdown while I was cruising to work, again, the same 25-30 minute area. Only for about 1-1.5 seconds, then started firing again on its own, no need to stop and restart, wasn't even long enough to drop speed.

My first thought (when I thought it was a "misfire") was maybe the aftermarket CPS, I put a Standard brand. So I plopped my old OEM back on last night, and got a result this morning, so can rule that out. Then I thought maybe the crank sensor, but I rule that out on the basis that the RPMs DID NOT drop or fluctuate when it shut off this morning, the RPMs stayed consistant, so the sensor was still reading. This leaves me with only a few ideas.

Coil: New, put it on last year, may swap the old one back on as a test later.
Fuel Pump: Previous owner said they put a new one in before selling the truck, and when it shuts down, there's no stutter or such like pressure dropoff.
Relays: This is what I'm thinking is the issue, I want some feedback on your thoughts.

I opened the relay box under the hood, noticed some dried dirt inside, so apparently it's had splash-up and got moisture in at some point. Pulled the ASD and fuel pump relays and noticed some light corrosion that looks like it leaked out of the relay, not on the pins. I swapped the ASD and fuel pump relay for the lulz to see what it will do later, likely end up changing them anyway cause they're around $5 on Rock Auto.

ASD Relay:
kx5yhFg.jpg

Fuel Pump Relay:
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Thoughts? Think this is the most likely cause?


EDIT: Definately leaning towards bad relay now. Did a little relay shuffle, started the truck, then it died and wouldn't start back up. Swapped it with the horn relay, fired right up. Also noticed the previous owner must have done some relay shuffling as well, as the 'damage' on the center pin of the ASD relay matches up with some corrosion in the socket of the AC clutch relay socket. Maybe instead of replacing relays, they decided to replace the fuel pump instead. I'd rather replace a relay, thank you very much.

AC Clutch Relay Socket: Relay that was here has no corrosion.
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Bonus image of my relay box lid:
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Sadly, I'm not sure which relay is really bad, or intermittently bad... Hopefully I dropped the bad one in say, the horn socket until my pair of new ones come in. I'd hate for it to be in the trans socket.. Sadly they only had two in stock, so I'll have to shuffle around when they come in and order more at a later date until I simply replace them all.

 

Fuel pump relay wouldn't instantly kill the motor, nor would it allow an instant restart. (would have to rebuild pressure in the system.) I would more suspect the ASD relay. It supplies power to the coil, and injectors. (most certainly a possible cause for instant shutdown.)

 

Could also be bad plugs, bad IAC or bad TPS.

 

All of those are new, bought them when I was chasing the phantom misfire codes last year with a full tune up. Plugs are about 2 months old. I wouldn't think the IAC would cause a shutdown, especially holding the throttle open cruising. It would also cause more of a stall as the engine suffocates wouldn't it?

 

Hm, edit button isn't showing... double-post go.

https://imgur.com/a/IfmuKjq

Little album of adventure time! Yesterday it was perfectly fine all the way home, heading to work was fine until the last road, died at a red light, then a stop sign. With some extra time before work and break, decided to pull the throttle body. I also happened to have a spare new TPS and IAC, so let's try to rule those out for sure. Despite cleaning it about this time last year, went ahead and gave the TB another cleaning, replaced the TPS and IAC, and noticed some idiocracies of the previous owner (surprise... not). Still finding little stupid things, last time I noticed the purge solenoid was upside down, this time? Grounding issues. Passenger side was a 3-way ground, one end was grounded to the frame, on the stud the cruise control mounts, the middle was grounded to the frame above the wheel well, and the other end was grounded to the frame by the headlight. Grounding the grounds to ground, hmm.. Decided to take the end near the headlight and plop it behind the alternator. On the driver side, when unplugging the sensors, I noticed a ground just hanging under the brake booster, attached above the booster, routed behind it likely just out of the way, and free hanging. Routed it around and attached it to the back of the fuel rail.

After reassembly, started right up with a tap of the key and idled fine, albeit high, around 1k. However, it always seems to idle high for a little bit after I reset the ECU, usually after about 3-5 starts it idles at about 600-700. I let it come up to temp, all seems fine so far, but it hasn't gotten real 'under hood' temps yet. We'll see how it goes, my relays should be in Saturday.

EDIT: Issue persists. After work, pulled truck around building, put in park, after about a minute it shut off. Fired immediately back up, didn't even wait 2 seconds before trying. Didn't have any further issues on the way home at any lights, signs, etc. Truck is running great otherwise, even had an OBDII tool up and did a 0-60 in 13.3 seconds! (from a stop, turning left across 2 lanes, and then up a steep on-ramp) So I figured 13 seconds isn't horrible, along with the A/C on. Checking voltages, 13.8V while running no matter the load. Battery voltage after sitting is 12.8V so I don't think it's the battery. I guess it rules out the IAC and TPS... Need to grab a fuel pressure tester, but I have never used one.

 

fuel pressure gauge just screws onto the check port on the side of the driver side rail under the TPS. Have a rag handy, it'll spray a bit of fuel going on and off (schrader valve like a tire)

 

If the truck just quits, I don't think this is going to be a fuel pressure issue. If pressure was the problem, the engine would run rough, and stumble before it actually quit. Might wanna check the connections at the PCM, Make sure everything is clean, and tight.

 

Edit button is being funky, click edit, it made a new post, and then it allowed me to edit this one... wtf.

 

Yeah, that's what I was thinking and leaning more toward relays or such. I got a spare crank sensor I'm going to toss in today during lunch after the engine cools... I'm good at changing it, and I hate that I am... :/ In a way, I hope it's the crank sensor and not any wiring issues, it IS a junkyard sensor in it.

EDIT: Put the new crank sensor in, old one had kind of a rusty oil on it, started with a tap of the key, RPMs go up, and come back down to zero, dying. Immediately starts back up and it takes a couple seconds before dying. Immediately restart, it begins to idle. pull the throttle valve a couple times to rev it, and it dies. I don't think it's the CKP. Starts immediately back up a 4th time. This time, I wiggled every harness I could find, TPS, IAC, Map, CPS, CKP, ECM, Fuse box, even wiggled the relays and it kept running. Wiggled the wires at the alternator and other bundles, hit the throttle valve again to fast-rev and it came back down to idle. When trying to get it to die, it wouldn't... :/

Also note: This is going to turn into a review as well, didn't have another mopar CKP so it's a 3rd party, if I solve this issue I'll keep tabs on it and see how it fares. I'll update with info on it if it works out or not.

EDIT2: Starting to look like an ECM... For a test, dropped one from a 1998 Dodge Ram 1500 3.9L in, started up and ran fine, everything works, couldn't get it to stall. Sadly, I can't use this one except for testing... The one thing that doesn't work: shifting. The brake and ABS lights come on and doesn't shift out of 1st. Reverse and first is fine, but that's it. Anyone got a spare ECM laying around? Checked four localish junkyards, NONE of them have a 98. All years except, and they've been on the lot long enough to already have the ECM taken most likely (all have been on site for over 2 months). Also since I was under the hood, I know how picky these trucks are when it comes to electricals (obviously...) went ahead and cleaned the battery terminals/posts and also since my fuse box has obvious splash evidence, took the main terminals off it and cleaned them with some fine grit diamond paper. I've been foiled by dirty terminals before, although usually that simply cuts all power, not stalls, but cleaning can't hurt.

 

If you hold your foot on the gas a bit, will it continue to run?