Good Evening,

New to join but been scouring these forums for the past 3-4 days...

I bought a 1998 Ram 2500 V10 with not much rust and about 125k miles and it came with two plows for an incredibly good deal. He had receipts for a recent transmission rebuild and having the heads re-worked. But the kicker was that "some days it starts and others it doesn't" I'd done a little research before contacting him and it seemed like it would possibly be an easy fix - and at the price I was willing to take a risk.

It fired up at his place and ran ROUGH - you could tell it was running really rich. He claimed that he thought he'd done something wrong when installing the new dash because that's when the problems started. He said the dash was out of an '01 and his buddy had said something about how the wiring was different...? Not sure if anyone knows anything about this but I checked and things all seem to be working they way they should that would be dash-related(?) other than the heating/cooling controls don't seem to work and the headlights wont turn on. I had my own theories on the headlights and will be removing/redoing the plow wiring because what he'd done was.... Interesting to say the least.

Got it started and into the shop yesterday and scanned codes and these came up:
P1296 - No 5Vs to MAP Sensor
P1391 - Interm Loss of CMP or CKP

Now, I've already ordered Crank and a Cam position sensors the day I went to pick it up as a precaution and figured I'd have them if one or both were a problem (as I'd read the crank sensor was a common issue and sometimes hard to get) and if they weren't I'd have them for later in the truck's life if they failed. They're due to come in this coming week. I'd also ordered a manual for the truck - as I do with anything I buy - but it'll also be here next week.

I checked the plug at the MAP sensor (because of P1296) and found that I had 5v on both the Violet/white and on the Green/red. From what I could find I'm only supposed to have 5v on the Voilet/white wire and it appears that the Green/red is supposed to be a signal back to the PCM?
Thinking there could be a short I pulled all of the wire loom and separated all of the wires to find that none of them had any sign of damage - let alone none melted to cause a short with a 5v source... I clipped the green/red wire close to the PCM and found that I still had 5v on the wire. This leads me to believe something is going on inside the PCM to make it send a 5v signal when it should be waiting for one? I also looked at the Crank and Cam sensors they look like they're been replaced fairly recently - in addition to new plug ends on the harness side.

For some unknown reason I decided to fire the truck up with the wire clipped and it fired up instantly and ran GREAT. Let it sit for a few minutes waiting for things to go back to how they'd been but no. Idled normal - could rev the engine and it was responsive and there was no stumble or miss and also didn't seem to be running rich anymore. Kind of odd... Not that it'd matter at that point but the MAP wasn't plugged i either.

My neighbor called me and needed help so I shut the truck down and about an hour later I came back and figured I'd at least get all the wiring buttoned up. Got it all taped as close to OEM as I could and got the split loom back on and taped and went to fire it up to pull it out of the shop and it would crank all day long but wouldn't start.

Checked codes again and P0320 showed up in addition to the two codes that had been there before. Based on a quick search that meant that the PCM didn't know the cam or crank positions so most likely why it wouldn't start now - maybe this code was coming on the days it wouldn't stat for the previous owner? I don't think he'd ever checked the codes... I also read that this can pop up due to a PCM failure...?

At this point I'd decided it was time to stop searching the forums all the time to try and apply what I'd read and go inside and join and make a post...I'll probably need more help in the future sorting more of the PO's work out...

Any ideas on more that I can be checking? Should I order a PCM - looks like that about a $400 venture for a rebuilt/reprogrammed one... Any thoughts on what he was talking about when he thought it was when he installed the dash being the problem? I did take the bezel off and found that he'd butchered the wiring for the lighting controls pretty good - somehow they "work" but there's melted and exposed wire all over and a few of them just twisted together with a tiny hint of solder being applied but then left exposed - so will be fixing that as well...

 

If you are are getting 5 volts OUT of the PCM on the MAP return signal wire.... That is certainly not a good sign. Unfortunately, diagrams for what it looks like inside don't exist in the public domain.... So, if it ain't behavin' right, replace it. It will have to be flashed to your vin at some point, but, it should run without doing that.

I think before replacing ANY other parts, or doing any other troubleshooting, solve the PCM issue. The rest of it might just be a result of a bad pcm as well.

Welcome to DF. I drive a 98 V-10 as well. Don't expect stellar gas mileage. If you get into double digits, yer doin good.

 

Alrighty - if you're saying grab a new PCM then that's definitely what I should be doing. I'll get a new one ordered now. I've got a page open already waiting on the confirmation that's what I need. This company supposedly flashes the PCM to your VIN before sending it out and offers a lifetime warranty. Hopefully don;t need it but I like the idea. Haha

I hope it solves it all! That'd be really cool. In the mean time I can still get the lamp switch and plow wiring straightened out.

No thoughts/comments on what he said about the '01 dash being different than the '98? I've been trying to look up information and not sure I understand what he could've meant by that...

And thank you! Yeah - I was reading that single digits could probably be expected. Luckily I don't plan on commuting with it! Mainly keep it around for on the farm work and plowing the farm/neighbors in the winter - be nice not to have to move the tractor between properties in the winter time.

 

I think the PRNDL is different on the 2000 and up, but, that's about the only change I am aware of...... There may be other changes as well.... (location of the fog lamp switch??) I just don't know.

 

I was looking through the local marketplace and found someone parting out a 1995 and someone else with a 1997 v10, automatic with 4wd - both like mine except for the year being different and I guess color haha

If he has the PCM still available I was debating about grabbing it as well - if it's cheap enough..
I've already ordered the remanufactured one that will be programmed to my VIN.

The reason I bring this up - HeyYou had mentioned that if I were to get a hold of another PCM that I would need to have it reprogrammed but it the engine could at leasr start/run off of it.
Whats the reason for getting it reprogrammed to a specific VIN?
Even though it's a 1995 or 1997- everything else would appear to be the same so would this one need re-programmed after all?

Mainly just curious...

 

The 95 won't work at all, It's OBDI, totally different system. The 97 won't work either, as too much changed in 98. EVERYTHING in the cluster 98 and newer is driven by the PCM, including the frigging gas gauge. The 97 PCM might run the engine, but nothing else will work.....

 

Well, dang...

I guess I should have known better on the 95 but that sucks about the 97. Oh well. Thank you for the reply! I guess Ill just have to wait for the new computer - was hoping I could pick up a working one for a lot cheaper and end up returning the new one if it all worked out. haha

OR wait - so would anything 98+ v10 PCM theoretically work then?

 

98 or 99 I think. Things changed on either side of that range.

 

Thanks for the info! I'll make sure to only look at 98-99 if I continue to look for another used one.... Though it's looking more and more like I'll just have to be patient and wait for the PCM I ordered on Saturday.... I know you said to wait to do anything until after I get my new PCM but my brain can't help but wander/think about other things that could be issues with the truck...

While I wait - I suppose a malfunctioning PCM could cause all sorts of problems - but is it unheard of for it to cause the truck to dump so much fuel that it's flooding itself?

I was doing some reading before I discovered the PCM was an issue and in another thread I'd read that a bad temp sensor or connector could cause the truck to try and start like it was -40 out and run really rough/rich... I believe HeyYou had even said that it's in a bad location and it's common to have problems with the connection (something like that). I was poking around yesterday and it seemed like that connector was pretty crappy - it wasn't holding onto the sensor very tightly at least - there was a lot of play/wiggle to it.

On my break I was looking it up and the temp sensor is like $20-something and a new connector end was something in the teens. I'm half tempted to grab/replace them... Maybe consider it some "preventative maintenance"...? haha!

I'm not sure how long it'll take to actually receive my new PCM...

 

Wouldn't hurt to replace that sensor if the connection is questionable.

My main concern is, the PCM is having issues with its 5 volt bus, which is EVERY sensor on the truck.