Trying to help get my dads 2003 Ram back on the road. It has the 5.9L magnum around 175k miles.

So currently it will crank fine but has has a rough idle bouncing from around 700 to 1000 rpms at first and if u let it run for 10 or 20 secs it steadies out a bit but still is rough. Then if u rev it up it'll go up to maybe 1200 rpms then cut out and bounce back and forth for a sec before it just shuts off. The only code that its giving is a P0601, so looking that up and its a PCM fault or bad PCM. So would a bad PCM cause the truck to run like this? Also the truck was running fine and giving the same code before this. Not sure how long it has been showing the code but I know it had been at least a week before the truck finally wouldn't go and just started cutting off when u hit the gas.

I was thinking it may be the fuel filter/pump/regulator. From what I've read its an all in one unit on top of or in the tank? I'm new to most this stuff btw, but trying to learn. I connected a gauge to test the fuel pressure. The pressure holds pretty steady at idle but when I reved it up some, the gauge went crazy. Would that mean the fuel filter or regulator is bad or something? Or could a bad PCM cause that? (also, think I checked the pressure the day before it started running horrible, at that point it would idle pretty smooth but when u reveal it up it would go from 1500rpms and drop to 500 and bounce around like that while i had the pedal steady. But if I hit it and went up to 3000rpms it would hold steady. Doesn't do that now though, now if I try to rev it up it just dies out)

So just messing with it trying to narrow it down I checked the vacuum hoses best I could. Don't see anything wrong there especially for as bad as its running. Changed the plugs and wires, but haven't checked the distributor cap or rotor (should I? Haven't messed with it because thought I would get a misfire code or something if that was bad or messed up) I cleaned the throttle body and tps. I decided to change the pcv valve since its just 2 dollars (but since the truck is old and all the rubber gaskets and grommets are hardened and the plastics are old and brittle i couldn't get the old one out and ended up breaking it off into the valve cover lol, so now has new pcv valve and new valve cover gasket after I removed the cover to get the broken bits of plastic out) I changed the O2 sensor out before the cat. Haven't messed with the one after the cat. Could a clogged cat cause this problem? Had a few people tell me that may be it but since I got the crazy reading on the fuel pressure I would think its fuel related or the PCM causing my problems. And just a FYI, it has had a steady coolant leak. I think my dad told me it was coming from the water pump or something. I mention that because I had read something about the ect sensor causing strange issues so is that something to look into? And along those same lines what about the crankshaft position sensor or any of the other sensors that could cause this issue?

So now im thinking about changing out the fuel pump/filter/regulator but I hate to put more money into it that I really don't have unless I know thats it. Amd if its the PCM wouldn't I just have to get a shop to come pick it up so they could flash it? And im a better part swapper than troubleshooter but im trying to learn so if it sounds like im doing something wrong please let me know lol. I'd appreciate any help at all putting me in the right direction to get this truck back on the road. Thanks yall.

 

I'll tell you the troubleshooting steps I would do in your situation. Just my input and I welcome corrections from other members.
My limited experience with 0601/bad PCM is the problem is caused by a fault outside of the PCM. Usual culprits are battery, battery connections, or ignition coil. So I recommend you first check battery voltage while static, and, when you are experiencing the surging. Check that the battery connections are clean and tight, and check static battery voltage using the engine block as ground point. Also check resistance of each ignition coil.
Remove the dist cap and check that the contacts and rotor are clean with no excessive wear.
You mention fuel pressure fluctuations. It looks like your truck has a fuel pressure regulator so you want to check pressure after the regulator. See part # SKPR323 to know what the regulator looks like.
How old is the fuel in the tank? What work and mods have been done to the truck?

 

The P0601 is a memory checksum error in the PCM. I.E. The pcm has a serious issue, and you need to fix that first, before anything else is going to make a difference.

 

ok thanks, the truck doesn't have any mods at all and its a daily driver so the fuel isn't old. Already had checked the battery, the ignition coil resistance is good. gonna pull the dist cap off in a little while just to check. And i did check the fuel pressure after the regulator, the port is on the fuel rail going into the injectors. I'm waiting on a call from a shop now that i used the other week, got them to flash an ECM in a cadillac for me. The Cadillac ECM was dead so i pulled a used one from a pull-a-part. Can't find one near me that would work for this motor, do you think i would need a new PCM or that the shop could fix this one? Or probably wouldn't know until they check it out im guessing right?

 

They *might* be able to re-flash it..... but, it could also be a hardware problem within the PCM...... I suppose having them reflash it wouldn't hurt, see if that solves the issue.

 

replace the MAP sensor... they degrade over time and will affect performance to a point. Cheap and quick...

 

I'm not so sure on these new ones, at first I thought timing issue, or maybe bad time chain jump a tooth from being worn.

 

Hey all, was just gonna give an update so this thread might help someone else with the same issue. It ended up being the PCM, good call HeyYou. I cant find a trustworthy site online to buy one for under $500 so i've been keeping an eye on the local Pull-a-Parts. Ended up getting 3 different ones before i found one that worked, but they exchange parts with store credit so no big deal except for the time it took. The truck fired right up with the first one i got but none of the gauges or anything on the cluster worked. The next one wouldn't even let the truck crank, i think i got it from a 5.2L which i had read somewhere that it would work fine on a 5.9, well it didn't. And the final one i have now came out of another 5.9 that was in a Durango. Motor cranks and runs great, only issue is the oil gauge isn't working. When the key is turned and all the gauges move at first the oil gauge moves then but after that goes dead and isn't getting a reading. I initially thought this might be a problem that could be fixed if i got the PCM flashed but after talking to some other people it doesn't seem like it. So I'm using this one for now and i have connected a manual oil pressure gauge. But im still searching for a new PCM. If anyone knows a good reputable site to buy them at a decent price please let me know. I found several on ebay and then i looked up the site they come from and they have mixed reviews that mostly trend negative. Wouldn't mind spending 200 or so but not wanting to drop 500+ on this truck right now. So for now the manual gauge works fine with me. Thanks again for the help

 

I had PCM problems a few years ago. Here is the link, someone recommended a company in that thread. Good luck !
https://dodgeforum.com/forum/3rd-gen...placement.html