5.9 Magnum Troubles

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NateKerr

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1994
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5.9 Magnum
So as a new member I'll start out by saying that this forum is fantastic! It's helped me fix multiple problems in the past, but now I'm having to start this thread for my current issue. I've got a '94 1500 5.9 V8, and I can't figure out what's wrong with the darned thing. It starts up just fine in the morning, but as I drive it the truck gradually gets worse. It's very similar to tps issues (revs jumping up and down at idle, tries to die, etc.). I've actually gotten that code in the past, and have been through at least 4 of those suckers. In the past, this has fixed the problem. Naturally, when the truck started acting funny again, I replaced the sensor twice (to no avail). Anyways, after driving for a while, (maybe 35-45 minutes of run time, combined with multiple ignition cycles), if I try to start it after shutting it off for a short time (up to 15-20 minutes), no dice. She just keeps cranking, doesn't even try to start. This is especially annoying when I have to get gas. The strange part is that when I try to get codes with the key trick, the check engine light doesn't even come on. When I turn the key and the light comes on, that's how I know it'll start. My best guess is the crank sensor, however i'm not certain. As a high school student who dumps all his money into gas, insurance, phone, etc. and seeing as I'm trying to sell the truck, any amount of money I spend on it is important. So before I go ripping it apart changing parts trying to figure out what's wrong with it, does anybody have any idea? Thanks!
 

Meatball12

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From what I've read. These trucks don't like third party IACs or TPSs. So you may have to buy one from the dealer. That may be your issue but I yield to anyone with a better idea.

Sent from my SM-G930P using Tapatalk
 

DodgeTx

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If you have a buddy with another dodge try swapping the computers make sure its a 5.9l though and pre 95. sounds to me like your pcm is wacky.
 
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NateKerr

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5.9 Magnum
I never thought about o2 sensors, my only problem with that is that I'm not getting any codes. As far as the pcm, I don't have anyone to swap with but I could probably get a junkyard one. I changed the crank sensor, but that didn't do anything. I'll probably do the cap and rotor just because I didn't at the last tune up, and if that doesn't fix it (I doubt it will), I'll just change the cam sensor, o2 sensors, and if none of this works, the pcm. Does it look like I've covered all the bases?
 

Yeret

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You might want to consider heading to your local parts store and have them scan the computer even if you don't have a CEL. Most places will do it for free.

One thing to remember is that if the computer detects a fault, it will set a "pending" code. This will NOT activate the Check Engine Light. If the detected fault persists, the computer will change said code to "active" and will turn on the CEL. If the detected fault corrects itself, the computer won't set a CEL, but it will still store the code which can be found with a scanner.

Back when my truck had random misfires, the computer would usually set a CEL but there were a couple of occasions when it didn't, but a scan revealed misfire codes anyway.
 
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NateKerr

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5.9 Magnum
Well the problem is that the truck a '94, so I'm stuck with obd 1. I did the key trick multiple times, always get the same codes: Battery disconnected within last 50 ignition cycles (duh), and trans temp sensor (I was gonna change it but I figured it wasn't hurting anything). The part that I can't wrap my head around is that when the truck doesn't start, the key trick doesn't work. The check engine light doesn't flash out codes because it never turns on. When I turn the key and the check engine light turns on, that's how I know the truck will start. That's why I think DodgeTx is on to something, I've never heard of the check engine light doing this. Also the oil and air bag lights still come on, so it can't be any fuses or dash electronics.
 

joepizuro

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ok so we have to figure out what signals for CEL ON key on...
 

Yeret

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Hmm, could indeed be an issue with the computer itself. A non-functioning CEL, intermittent or always, could indicate an issue with the computer's diagnostic module.

I'm not positive, but such a thing might be repairable, though I don't know the first thing about fixing electronics other than try the Russian Repair method (kick it a few times until it either works again or breaks, then you have no choice but to replace it, LOL).

I'm gonna go with DodgeTX and suggest swapping in a different computer and see if the issue repeats itself.
 
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NateKerr

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Well I'll take a good look at it and see if there's anything I can fix, but yeah, I'll probably replace it. As far as replacement goes, it's a direct swap? I know on newer cars and trucks, the computer needs flashed to match up to the new vehicle. I assumed that 2nd gens were fairly primitive in terms of the pcm and therefore wouldn't require this, am I right with my thinking? Anyways, I'll try my local junkyard for the computer, but I doubt any of their rams are '94s and 2wd. When this doesn't work, I guess I'll just buy the pcm on ebay.
 

dudeman2009

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The PCMs are non serviceable, you have to replace the whole unit if its acting up. Just match the year and engine size when looking for one at a junkyard, I don't think the added displacement would cause a problem for testing purposes, but the 5.9s are so common I dont see why you wouldn't be able to find one.
 

Yeret

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If you stick with a different ECU, the only reason why you have to reflash it is so the VIN stored in it matches the VIN tag on the truck. Me, I wouldn't bother with it since if I need my VIN for whatever reason, I'm just going to read what's on the tag rather than bother with trying to scan the computer, LOL.
 

codered

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magnum 5.9/360
Well the problem is that the truck a '94, so I'm stuck with obd 1. I did the key trick multiple times, always get the same codes: Battery disconnected within last 50 ignition cycles (duh), and trans temp sensor (I was gonna change it but I figured it wasn't hurting anything). The part that I can't wrap my head around is that when the truck doesn't start, the key trick doesn't work. The check engine light doesn't flash out codes because it never turns on. When I turn the key and the check engine light turns on, that's how I know the truck will start. That's why I think DodgeTx is on to something, I've never heard of the check engine light doing this. Also the oil and air bag lights still come on, so it can't be any fuses or dash electronics.
there is no trans temprature sensor. It's there to send you to the dealer and they get more money from you. i've been under there to confirm it and i've had a trusty mechanic tell me the same thing.
 

codered

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magnum 5.9/360
Well I'll take a good look at it and see if there's anything I can fix, but yeah, I'll probably replace it. As far as replacement goes, it's a direct swap? I know on newer cars and trucks, the computer needs flashed to match up to the new vehicle. I assumed that 2nd gens were fairly primitive in terms of the pcm and therefore wouldn't require this, am I right with my thinking? Anyways, I'll try my local junkyard for the computer, but I doubt any of their rams are '94s and 2wd. When this doesn't work, I guess I'll just buy the pcm on ebay.
hey nate man shoot me a private message. i can get you a brand spanking new PCM for about $100. I work in an auto warehouse and i get parts cheap. i looked for a PCM myself and the one i found was about $104 94 5.2 2wd. just tell me the info on your truck, i'll call my local dodge dealer for the PCM number, then i'll ask about it at work and then we'll have to find a way to ship it and pay for it. Also this PCM is from cardone so no chinese ********. i found cardone 79-7277 on Autozone that is for the 5.9 that retails at 253.99 Cardone Reman/Engine Control Computer 79-7277- ReadReviews onCardone Reman #79-7277
Ok, now you see the PCM for my truck is cardone 79-6669 for my 5.2 it retails for 234.99 on the advance auto website. Buy Cardone Engine Control Computer - Remanufactured 79-6669 at Advance Auto Parts
I can get that same PCM for $104 from my parts guy in the warehouse. If you are interested man just shoot me a PM i'll be happy to help. You'll pay the shipping and part cost. no mark up or tax from me. I'm just a common man, drive a common ram, my dog ain't got no pedigree. :crazy:
 

Pntyrmvr

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The part that I can't wrap my head around is that when the truck doesn't start, the key trick doesn't work. The check engine light doesn't flash out codes because it never turns on. When I turn the key and the check engine light turns on, that's how I know the truck will start.



It's the computer. My 93 did that and I didn't even bother trying to check for codes. New puter all good.
 
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NateKerr

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I waited a few days to reply since I wanted to see if this really did fix it, and strangely enough it did. A few days ago I changed the cap, rotor, and ignition pickup and now it runs like new. It doesn't rev up and down at idle, starts right up after a long day of work, throttle is much snappier, even the oil pressure is noticeably higher and it even shifts better. When I used to go full throttle (on rare occasions), it would shift around 4300 rpm. Now it goes all the way to the redline again, which it hasn't done in around half a year. I'm assuming it was the ignition pickup as I've seen that it can be culprit with cranking but not starting when hot. It was actually really nasty and gunked up. I'm still a little wary, as I still think the pcm is messed up. I'll keep driving it, and I'll probably report back in a few weeks or if the problems come back. I (and my truck) appreciate everyone's help, thanks!
 

joepizuro

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Magnum v10
there is no trans temprature sensor. It's there to send you to the dealer and they get more money from you. i've been under there to confirm it and i've had a trusty mechanic tell me the same thing.

Some come with trans temp sensors. It requires a different trans line with the temp sens plug... I've been wanting to drill a hole in my pan and run a sensor to a gauge..

TO OP:

It was ignition related. You're fine..
 
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