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Discussion Starter · #1 ·
Hello. I was just using the search to determine the compatibility for a 1994-1995 OBD1 PCM. I know the years were limited and I couldn't find much info on it. Could I get one from a 1994 that has the newer electric IP (not the older mechanic unit)

I did a search and it *appears* the same PCM was used in a variety of vehicles (burbs, C trucks, Vans, etc). So I'd wondering if someone might know if I can buy any PCM that is OBD1 and meant for the electric IP.

I have a 1995 C2500.
My vin: 1GCGC29F1SE280574

Thanks for the insight!
 

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just check the number on your current ecm, if anything you may get lucky and just need to change the prom/calpack

i have a ecm from a 94 gasser, that i can check to see if those had the same ecm with a different chip
 

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Discussion Starter · #3 ·
Thanks for the reply. So you're saying ONLY the exact same PCM model number will work? I know in other circumstances, a different model number (such as one from a suburban or 1994 instead of 1995) might work just fine even though the number on the PCM is different.

Also, what is a "prom/cal pack"

I'm unfamiliar with those terms.

Thank you
 

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Thanks for the reply. So you're saying ONLY the exact same PCM model number will work? I know in other circumstances, a different model number (such as one from a suburban or 1994 instead of 1995) might work just fine even though the number on the PCM is different.

Also, what is a "prom/cal pack"

I'm unfamiliar with those terms.

Thank you
the pcm # you want to be the same, the prom/calpack is the chip inside that gives the ecm the info needed for each particular motor, like the ecm i have for a 94 is a 7427(last 4 digits)

some years are interchangeable like 87-90 used the same 7747 ecm
 

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Discussion Starter · #5 ·
Okay. looks like I'll pull mine out and see what the number is on it. By the by...how does one go about checking the prom/calpack if that was the problem?
 

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only way to check it is to replace it, usually the ecm goes bad and not so much the calpack
 

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Discussion Starter · #7 ·
Is there a way to replace the ECM or calpack without replacing the entire PCM? Where could I get the parts. A quick search didn't net much info. Would it just be easier for me to replace the entire PCM?

Thanks so far for the insight.
 

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You can get a new chip from the dealer, but like i said before it is pretty rare for the chip to fail, 98% of the time it is the ecm that fails.

the chip is under the cover on the ecm, it has 2 screws holding the access cover on
 

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The PCMs from 94 and 95 diesels are the same, you dont need exact same #. PCM doesnt usually go bad. From a junk yard might get one for $50 if they have any from the diesel trucks. Online can find them for $150. I have a few and chips.
 

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Discussion Starter · #10 ·
Ok, so I can get any PCM from a 94 or 95? Obviously OBD1 and electric IP. To be honest there *might* not be anything wrong with mine...but I just installed a frshly rebuilt IP pump(with warranty). It worked perfect for two weeks and started having issues again. I'm getting another IP pump from the rebuilder sent out and also wanted to get a PCM just in case to prevent the downtime. The truck was properly diagnosed. It is either a PCM or injection pump. Everything else works just like it should. Thats why I'm trying to figure out what PCM's I can use on my ride.
 

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Yes, you can, and put your EPROM in it. There is a removeable EPROM in a compartment on the back of the PCM.

Who diagnosed the truck? If dealer or garage did it by the manuals, they are often not detailed enough and lead to a lot of unnecessary part swaps, PCM usually always being one they insist in error.
 

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To continue what 94C1500 said, it will turn out not to change your no start conditions. I have read a lot of thread like that here and other 6.5 diesel forum.

If you have an IP issue with rebuild IP, where did you get the rebuild? Did it have all new components like PMD, OS, Stepper Motor. There are a lot of not so good rebuilder. Also make sure that your LP and OPS are 100% good. Better yet, search for an LP/OPS relay mod. When changing IP, you may want to change the injectors also, especially if you don't know how old is the current injectors.

Last but not least, make sure all the electrical connectors (battery positives and grounds) are good. Cables are good (not corroded inside) and there are no loose connections.

See, you need 2 components, fuel and electric. Both are needed, if one is broken, it will not start.
 

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Discussion Starter · #13 ·
Thanks for the response guys. I have checked the fueling side of things. While the truck was running with the new injection pump, I had about 2 PSI at WOT on the pump, about 4-5 PSI steady at idle. OPS works.

The grounds are awesome. I'm certainly most board members would be jealous of them. I pulled the injection pump harness and triple checked all individual wires for cuts, problems, loose connections, continuity etc.

I'm positive in my diagnosing (both the 1st time and now) that the problem is either the PCM or my rebuilt injection pump. Everything else is working correctly. I looked through the forums long and hard checked out everything electrical and fuel wise before I condemned the pump.

It also didn't skip a beat for 3 weeks or so. Then it stated having issues again. I have the GMTD software and by looking at the software, it seems the pump isn't giving the PCM any optical sensor readings. Such as any of the TDC learn readings, timing etc. It would appear that when it will start it's always in limp mode and running off of the crank sensor.
 

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Did you use any type of fuel additives?
 

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Discussion Starter · #15 ·
A lil' bit of power service just to give the ULSD some lubricity. Nothing outside of that. There isn't a chance bad fuel is causing what I'm experiencing. I know bad fuel can cause hard starts, bad MPG, poor power and smoking. This is different.
 

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Bad fuel and air leaks can cause OS problems, and mimic IP or PCM failure.
 

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Discussion Starter · #17 ·
Very True, but I've checked for air leaks already. I even replaced all the fuel lines just for the piece of mind since I didn't know when they were last replaced. The truck ran perfect for 3 weeks and then start acting up again. Very bizarre.
 
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