P0320 - Ignition/Distributor Engine Speed Input Circuit Malfunction

Disclaimer: not a mechanic, but my dad was and is trying to help me solve this before taking it to a shop (limited income). I figured I'd make post here since y'all are always super helpful and could possibly give us some starting points for troubleshooting.

My '99 B2500 has been having some real issues for a few weeks now. I've had the vehicle since '08. The problem first showed up when I was on the highway. I would be trundling along at 65 mph and my RPM would shoot to zero and the truck would buck and power would drop sharply. Then it would go back to normal. I ended up getting stranded at a light where it died and I had to push it to a nearby gas station. Further starts would see the issue worse and I had no power. I've had problems with the MAF before (with the exact same symptoms that disappeared when we cleaned it), so my dad and I figured that was the issue, so he and I just replaced the sensor and disconnected/reconnected the battery to clear the system. After that I drove it for two weeks (light driving, less than a few miles each way though I always tried to get it to operating temperature) with zero issues, even feeling like it was running better than ever, until yesterday when it cropped back up with no warning.

I'm extremely confused honestly. Both times the only code that's being thrown is P0320, and it's only visible through a handheld reader. The Check Engine light doesn't even pop up even though it clearly works when you turn the key and the dashboard lights up. Plus it seems to run well enough comparatively speaking when the MAF is completely disconnected. It doesn't run well, but I can get down the street unlike when the MAF is connected. About the only thing that might make things funky that my dad and I noticed was that one of my terminal clamps has a huge crack in it that might be causing some sort of voltage issue, but that wouldn't affect the car when it's already started would it?

EDIT: Just tried to get it home and unfortunately it died about 3/4 of the way there and about a half mile from the mechanic I wanted to take it to. It won't even start now. I'm completely stymied. Tow truck it is then.

 

I have an update on this. I towed it to a mechanic and had to have an astonishing amount of work done. Some of it was likely due to my negligence in preventative maintenance. First they diagnosed the code and discovered that it was indeed a faulty Crankshaft Position sensor. Then going further it turns out that my plug wires were arcing, something I'd known about since 2015 and put off until now. Due to this, I think my ignition coil pack gave out and caused the intermittent issues with starting and dying. Ultimately I had to get about $1500 worth of work done, some of it involved things that had nothing to do with the issue but I thought I might as well have done so I don't have to do it later.

In addition to all this, I've had it back for about a week now and today after I passed my inspection, I'm getting P0171 thrown in the computer. It's a lean code for bank 1, and I'm assuming it could be a number of things. I think the most likely culprit is my old O2 sensors, all of which are way beyond the 12 year expiry date since they've never been replaced to my knowledge. Fuel pump/filter is probably the next likely culprit, and I already did the IAC test so I think I can rule a vacuum leak out.

 

Yes, change the O2 sensor

 

Gonna order them and see where it gets me. Thank you for the affirmation!

 

Update! I haven't gotten those O2 sensors installed yet, but I tried to go for a drive on Sunday and had the damn thing die on me again. Got it started back up and parked and threw my code reader on and was getting the same code P0320 (Ignition/distributor Engine Speed Input Circuit). So now I'm putting it back in the shop since they didn't resolve the issue, but now I'm really at a loss for what is going wrong. I think while it's there I'll have them change out those sensors, and hopefully the thing will be fixed this time. It's run properly since I got it back, so I'm not sure why it's died again.

 

Another update. Not much really going on until today. The guys at the shop told me to come get the truck because they couldn't figure out what was going on. The truck was behaving itself, and of course I cleared the codes by accident (before I took it to the shop a couple weeks ago) since I didn't trust the car enough to drive it to get the battery tested so they didn't have anything to go off of. Well I walk up there to get it and the tech started to bring it around front and it decided it didn't want to actually go anywhere. Yay? I guess it felt good to be validated and that I wasn't going crazy, but I did waste a walk up there. Tech seemed a little embarrassed about it, but I wasn't really shocked, just relieved it didn't do it to me on my way home.

Anyway, sorry for the triple post, but I feel like this should be documented for anyone that has similar issues in the future.

 

Final update on this particular issue. Ended up costing me over $2400 bucks, and about $500 that my parents chipped in, so $3100 in total.

Ended up towing the thing to someone else. The shop I took it to was one I did out of convenience/necessity (walking distance), and after getting the run around for so long and almost bleeding me dry, I was urged by my parents to take it to someone who frequented their church. Finally at the end of my rope and my savings, I agreed and within an hour of towing it to him, the man had a diagnosis. Turns out the issue was found within the wiring harness between the sensor and ECU (diagnosed with a good ole multi-meter and some patience). I imagine it was intermittent because the wiring was just starting to degrade enough to feed faulty info. It could have been just that too, no need to replace any sensors, or order a new ECU. None of that stuff. I won't know either way, but it cost me the rest of my savings and involved rebuilding at least part of the harness (maybe some other stuff too). It probably should have cost me much more, but he cut me a break.

It took about two weeks to get it back, but whatever wizardry he performed did the trick. Been running like clockwork since then until about a week ago where some new issues cropped up and I'm probably back to throwing some parts at it with my dad. No codes being thrown again, but it's probably something that's been needing replacement for years now. Wish me luck.

And as for the shop I used, I'm beyond disappointed. It definitely feels like they gave up on me and tried to get me to go away. The fact that the truck died in the parking lot felt like an act of providence, but I feel like the guys didn't even try to do more diagnosing and instead opted to throw parts at it. I'm trying to be charitable about it too. I don't want to feel like I got cheated, but given it didn't take more than an hour for this other guy to get me a promising diagnosis it certainly feels like I was taken for a ride. It's been a month now and I still feel angry, but I really don't want to jump to conclusions and leave a bad review without at least hearing their explanation. Anyway, thanks for sticking with me, guys.