Howdy folks. My 2000 Dodge 2500, base model 360 gas engine, automatic, had a minor issue. Occasionally, the "check gauges" light would come on, the headlights flicker, and the voltmeter on the dash would peg out to the right. If I shut the truck off and restarted it, it would usually fix the issue. Having seen this issue before on a Jeep, and reading online, I believed that my voltage regulator inside the PCM had failed.

So, I did the external regulator install. I used a regulator from the parts store for an 80s Dodge pickup, and wired it appropriately (blue wire to center post and battery, green wire to side post). Grounded it well, both sanding paint off the fender and running a ground wire to the firewall ground (the one the PCM ground is on). I went to start the truck last night, and the battery was dead, so I got out a jump pack, and it started up, albeit a little sluggish. During this initial test, the voltage was perfectly at 14.7 v. It ran okay, though it felt like the IAC was a little off, holding RPMs after releasing the throttle. But I didn't use a fuse and got paranoid, so I shut it off and installed an inline fuse and put it back together. After that, it wouldn't start anymore. I could get it to try, if I pumped the gas while cranking a long time, but it would at best get to 1000 RPM and then die again.

So this morning, I went out with a freshly charged jump pack and tried again. This time it started okay, but the check gauges light came on, and the voltmeter sat at zero. It idled fine, but died when I gave it throttle. Since that time, I have not been able to get it to run on its own. If I crank a long time and hold the gas pedal down, it'll try sometimes, but it either dies after getting to 1000 rpm as before, or sometimes it'll stay running as long as I hold down the throttle, but runs extremely poorly, sounds like misfiring or running out of time or something, and will die if I let off more than halfway. I have tried a different battery, no difference, jump starting with another truck, no difference, rewiring it back to stock so the PCM voltage regulator takes over (and pulling the fuse on the external regulator so it can't draw power), and that one is at least regulating voltage correctly when it runs, but still won't keep it running. It is still wired in the stock configuration now. I also tried running the jumper cable ground from the battery to the PCM case in case somehow my meddling with its ground was the issue, and no change.

It also smells very very lean when it starts. Like that "burning brake cleaner" smell. I can hear the fuel pump running (and it's new in the past few months) so that's not it. At times, it smells like something is on fire, though there's no smoke anywhere and of course no flames. It sounds awful, very loud and staccato banging and popping, like a misfire. If I keep it running with the throttle, the sound eventually changes, getting kind of muffled from the loud banging of before, and maybe starting to smooth out at higher RPM. The exhaust is extremely hot despite not running very long. I almost think the catalytic converter is plugged, but that would be a very strange coincidence.

The check engine light has always stayed on before, something about a bad speed sensor somewhere, never made a difference to driving. Now, there is no CEL at all.

Does anyone have a clue where to even start here? I'm just at a loss beyond throwing money at it to replace battery, alternator, PCM, etc.

 

Verify all your sensors are properly plugged in. Especially the coolant temp sensor. Sounds like you may have knocked it loose working on the charging system.

 

My temp gauge has never worked on this truck (truck is a $600 rusty pile that likely isn't long for this world, but I still need it for a little while). I don't know if that means the coolant temp sensor is bad or not, but it ran fine before and didn't overheat, so I just ignored it. Could a coolant temp sensor really make such a huge difference? I'll try that when I'm home and let you know. I didn't touch anything else, so I can't imagine I popped anything else off, but I'll try.

Since posting this I did try turning the key back and forth a few times to see if I'd get the dreaded "no bus," but instead I got "P done", so I'm guessing that just means no trouble codes.

 

If the gauge doesn't work... then you won't have any indication of if the sensor is working or not. Gauge uses the same sensor as the PCM. If the sensor fails, the PCM thinks it is absolutely frigid outside, and positively DUMPS fuel trying to get a combustible mixture.

 

You can run the dash test to if there is any issue with the dash. Need to see what the pcm thinks the motor temp is. And these trucks don't like weak batteries, Put a fully charged battery in and don't use a jump box.

 

I'm intrigued as a friend was recently experiencing something kind of like this. In her case it seems to have resolved itself but I'd love to hear updates/resolutions.

 

I don't have a fresh battery or a working charger, so I'll have to experiment with the battery another day, but I got out my code scanner and the PCM thinks the coolant is -20 F. So I think there's at least one answer here. The connection is tight, but I might have broken it while working next to it. I'll replace that and see what I get.

 

Usually -40C is the default if no reading at all. That doesn't quite correlate to -20F but yeah, you've got a problem on that circuit.

That very well could cause hard starting.

I wonder if you could measure resistance and hack in a considerably different resistor just to see if anything changes ‐‐ even just with coolant temp as recognized by scanner

 

I guess for now I'll just replace the sensor and let you guys know what's up in a few days. That is weird, though, that the sensor is very off, but not off in the normal way. The intake air temp, by the way, said between 65 and 75 on the scanner. The ambient temperature is about 30 F.

Also weird, the first try of the day, jump starting it because again I don't know if this battery is any good, it started right up, idled perfectly for half an hour, then died as soon as I tapped the throttle. Hasn't run since then aside from when I got it to run with heavy throttle. I feel bad for my poor neighbors, with how loud it's been while I diagnose it.

 

Update: the truck runs! The problem was the coolant temp sensor, as you guys thought. Upon removing the old sensor, the plug portion was basically melted off the contacts, and the contacts were bent. The new sensor didn't want to start in the hole, but I was finally able to get it (not 100% sure it isn't cross threaded, but this truck won't likely outlive a new Mopar sensor anyway). I have developed a newfound hatred for the Magnum accessory bracketry, as getting the alternator out of the way without removing the AC lines was about impossible. But it's done, and the truck runs better than ever. And the temp gauge works now, which is very confusing, as it previously ran fine but with a broken gauge, so... the sensor was clearly bad before, so why was it running? I don't get it, but it's fixed now.
Thank you guys so much, I don't think I'd have ever thought of that one otherwise.