1998 Ram 2500 v10 Bad PCM?
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From: Iowa
Quite a resume! Haha! You've definitely got a lot of experience under your belt! Through all of my reading on all the threads over the past weeks I've been wondering: "how's this guy know so much?!" 
I've just got a lifetime of taking stuff apart and putting it back together. Oddly at my age, I seem to do a lot better with old carb/early TBI era stuff than anything. As long as it's mechanical it's an easy one. Though I'd like to consider that I'd be able to brain my way through electrical... it's what's gotten me where I am with machinery at the shop I work in. Haha! But this one makes me question all my confidence....
Too bad we're not in a clear proximity! Haha!
I'm in the same boat with the brain exploding part...
I'd love for this third PCM to have proven me right from the beginning but two PCMs down I feel significantly less confident.. haha!
I've just got a lifetime of taking stuff apart and putting it back together. Oddly at my age, I seem to do a lot better with old carb/early TBI era stuff than anything. As long as it's mechanical it's an easy one. Though I'd like to consider that I'd be able to brain my way through electrical... it's what's gotten me where I am with machinery at the shop I work in. Haha! But this one makes me question all my confidence....
Too bad we're not in a clear proximity! Haha!
I'm in the same boat with the brain exploding part...
I'd love for this third PCM to have proven me right from the beginning but two PCMs down I feel significantly less confident.. haha!
Last edited by Keymo; Mar 31, 2024 at 10:06 PM.
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From: Clayton MI
That's because I am old.
What I find absolutely hilarious though, is I can generally fix anything on a computer controlled car, but, give me a single-cylinder, carbed lawnmower engine, and I am stumped. I can generally fumble my way thru it, and have a running engine at the end, but, the process is what I would describe as "painful".
What I find absolutely hilarious though, is I can generally fix anything on a computer controlled car, but, give me a single-cylinder, carbed lawnmower engine, and I am stumped.
I can generally fumble my way thru it, and have a running engine at the end, but, the process is what I would describe as "painful".
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From: Iowa
Haha! Not enough for you to think about when it comes to those small engines
Well, the parts store never called so I called them and they said that the won't be able to get a hold of a PCM for me...
Found another refurbishing site that has a PCM available - they're a little more expensive than the first one I ordered from, which is why I didn't' order for them in the first place.
Put in an order for a PCM and gave them my VIN and put in a request for a refund with the other site.
We'll see how soon we can get our hands on this baby.
According to their return policy I've got 30 days to return the product for any defects and then it's got a lifetime warranty - but only for one return. I'm curious if a return in the first 30 days would count towards the lifetime...?
Hopefully it just works - still kind of worried/paranoid though. Haha!
Well, the parts store never called so I called them and they said that the won't be able to get a hold of a PCM for me...
Found another refurbishing site that has a PCM available - they're a little more expensive than the first one I ordered from, which is why I didn't' order for them in the first place.
Put in an order for a PCM and gave them my VIN and put in a request for a refund with the other site.
We'll see how soon we can get our hands on this baby.
According to their return policy I've got 30 days to return the product for any defects and then it's got a lifetime warranty - but only for one return. I'm curious if a return in the first 30 days would count towards the lifetime...?
Hopefully it just works - still kind of worried/paranoid though. Haha!
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From: Iowa
https://dodgeforum.com/forum/2nd-gen...pcm-bad-4.html
I've been continuing to do research to try and figure out if there's anything left to do on my part to not mess up a new PCM and fou d this thread...
I don't know if you remember it - but what he said something I found interesting....
[QUOTE=Dan11288;3572912]Did some research last night about 5v reference signals. I read that if connector at sensor is unplugged or open signal wire the pcm will read that there is a problem and output 5v to trigger CEL. ..../QUOTE]
Which makes me wonder.... since I've been testing everything at the connector with the key on - connector unplugged - am I always going to get 5V on signal return...? I have NOT been backprobing the connectors - though last night I ordered needle-like probes to be able to keep connectors plugged in and stab into the wire.
And then his fix....
He must've cut a small big of the shielding off to get these readings? Or stabbed into the wire?
None of it explains my "no 5v on MAP" code but might explain what we've thought is a bad PCM all this time? Or am I misunderstanding completely?
I've been continuing to do research to try and figure out if there's anything left to do on my part to not mess up a new PCM and fou d this thread...
I don't know if you remember it - but what he said something I found interesting....
[QUOTE=Dan11288;3572912]Did some research last night about 5v reference signals. I read that if connector at sensor is unplugged or open signal wire the pcm will read that there is a problem and output 5v to trigger CEL. ..../QUOTE]
Which makes me wonder.... since I've been testing everything at the connector with the key on - connector unplugged - am I always going to get 5V on signal return...? I have NOT been backprobing the connectors - though last night I ordered needle-like probes to be able to keep connectors plugged in and stab into the wire.
And then his fix....
.... I plugged in harness and solinoid outside of transmission and still 5 volts on signal wire. I pushed down the plug as hard as I could and voltage dropped to .38 on signal wire I let go of plug back to 5.17 volts. So it's the connector from the main harness to the transmission, changed it out and all good. Was a nightmare to troubleshoot especially because the wires were all ringing out perfectly from connector but I guess the connector was not seating completely down.
None of it explains my "no 5v on MAP" code but might explain what we've thought is a bad PCM all this time? Or am I misunderstanding completely?
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I was also wondering if there was something we're missing that would make 5V "normal" on the return side
Anyway HF has a surprisingly nice backprobe kit
https://www.harborfreight.com/back-p...ece-70614.html
Anyway HF has a surprisingly nice backprobe kit
https://www.harborfreight.com/back-p...ece-70614.html
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From: Clayton MI
Wouldn't surprise me if it wasn't there...... Ok, it's "diagnosis and testing" in the fuel and ignition section. See if there is anything worthwhile there.
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Okay so note to all - or maybe I'm the only one that didn't get this - DO NOT unplug your sensors to test the signal return wires. You gotta back probe them 
I got home and my back probing needles had somehow already arrived. So I got excited and ran out to the shop to do some testing.
I confirmed on the MAP, Crank and TPS that the sensors must be connected in order to see proper voltage at the connector - or at least NOT 5v.
Also learned the low fuel light/sensor works - popped on as I turned the key for the first time to check voltages. Gonna need to go get some fuel for this baby....
So back to the "No 5V on MAP" code... I plugged everything back in and back probed the MAP 5V pin and cranked the truck. BANG! MASSIVE backfire.
I sat for a little bit thinking about what could make it backfire like that and decided to try again.... It instantly started - ran like crap and died. My eyes were glued on the MAP and never got a loss or even a slight change in voltage - 5.22V. I was wondering if maybe there would be a loss in 5V at some point in cranking since after clearing the code I would get it when cranking the engine if it didn't start for long enough. Cranked again - took a few seconds but fired right up so I gave it a little gas to keep it alive with my eyes glued to the multi-meter and still the 5.22V never changed.
This time when the truck ran you'd honestly never be able to tell that there was something wrong as long as I kept it above 1K RPM - sounded and felt really smooth. If I'd try and give it gas it'd pick up smooth though I couldn't go too fast or it'd kind of stumble. But the second I let it go below 1K it'd be really rough like it was choking out and would try to die on me.
Got something to hold the gas pedal at 1K-ish so I could get out and wiggle connections - and I wanted to back probe the MAP return wire. I was getting about .77V on it with the engine at roughly 1k RPM. Live data showed it at "22". Though when I'd give it gas and bring the engine speed up the MAP signal never seemed to change? This is on a brand new MAP sensor...
Gonna have to look into the troubleshooting steps and what-not here in a bit. Got excited and went out to test the back probing wonderings before I came inside.
Tonight's reading material, I suppose.
I got home and my back probing needles had somehow already arrived. So I got excited and ran out to the shop to do some testing.
I confirmed on the MAP, Crank and TPS that the sensors must be connected in order to see proper voltage at the connector - or at least NOT 5v.
Also learned the low fuel light/sensor works - popped on as I turned the key for the first time to check voltages. Gonna need to go get some fuel for this baby....
So back to the "No 5V on MAP" code... I plugged everything back in and back probed the MAP 5V pin and cranked the truck. BANG! MASSIVE backfire.
I sat for a little bit thinking about what could make it backfire like that and decided to try again.... It instantly started - ran like crap and died. My eyes were glued on the MAP and never got a loss or even a slight change in voltage - 5.22V. I was wondering if maybe there would be a loss in 5V at some point in cranking since after clearing the code I would get it when cranking the engine if it didn't start for long enough. Cranked again - took a few seconds but fired right up so I gave it a little gas to keep it alive with my eyes glued to the multi-meter and still the 5.22V never changed.
This time when the truck ran you'd honestly never be able to tell that there was something wrong as long as I kept it above 1K RPM - sounded and felt really smooth. If I'd try and give it gas it'd pick up smooth though I couldn't go too fast or it'd kind of stumble. But the second I let it go below 1K it'd be really rough like it was choking out and would try to die on me.
Got something to hold the gas pedal at 1K-ish so I could get out and wiggle connections - and I wanted to back probe the MAP return wire. I was getting about .77V on it with the engine at roughly 1k RPM. Live data showed it at "22". Though when I'd give it gas and bring the engine speed up the MAP signal never seemed to change? This is on a brand new MAP sensor...
Gonna have to look into the troubleshooting steps and what-not here in a bit. Got excited and went out to test the back probing wonderings before I came inside.
Tonight's reading material, I suppose.