95 LT1 PCM replacement problems. newbie
10-22-2004, 07:19 AM
#1
2nd Gear
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95 LT1 PCM replacement problems. newbie
I recently purchased a remanufactured PCM for my 95 at. ACDELCO P/N 88961148. I thought my existing PCM may have gone bad. (cooling fans were not coming on) I will go into the details of that later.
I purchased the new ECM from my local Corvette shop thinking that I just had to pull the chip out of my old PCM (16181333) then place it into the new PCM and I should be good to go. This was not the case, the does not start with the new PCM installed. Now as I read through the forums it appears that the Remanufactured PCM must be re-programmed and if I would have purchased an OEM PCM- 16181333 it would not have to be reprogrammed. (Is this true???).
So at this point I spent $165.00 on a new PCM that now keeps my car from even starting. I put the old PCM back in place and am now back to where I srarted. (The car runs normally except the cooling fans do not come on.) The part is not returnable so either I need to return the remanufactured unit as the core or pay more to get the unit programmed.
I am looking for advice as to what I should do next.
Is the shop screwing me for selling me a non-returnable part that they know is useless to me without a re-programming? How much goes into reprogramming? What is a fair price to get this done?
(I'm thinking I can user TunerCat to connect to the OLD PCM, perform a "Read PCM", save that file. Put the new PCM in place, then using TunerCAT perform a "Program PCM" using the same file. Is this true??? What about the chip I need to pull out of the old PCM and put into the new one. Will that screw anything up. What is the point of the removable chip if the PCM has to be programmed anyway?
I am not adverse to building or buying my own interface cable and programming it myself. (I have a computer/electrical engineering backround, but have no experience with PCMs yet.) I only have 30 days until the core return deadline and I lose my $425.00 on top of the original $165.00 I spent on the PCM I may not even need.
Because then once this is all done I still do not even know if this will resolve my cooling fan problem.
**************
About the cooling fan problem:
The car started overheeating a few weeks ago. It took a little time for me to realize that the fans were not coming on.
I verified the fan functionality by putting the PCM in diagnostic mode by shorting pins 5 and 6 on the OBD-II connector. (From what I've read I think it's an OBD-II connector on a OBD-I PCM.) In diagnostic mode the fans come right on. I believe this verifies that the: fans, fan power, relays, and relay ->PCM connections are all good.
Neither fan runs when I turn on the AC. Neither fan runs when I disconnect the high-side pressure sensor.
The temperature has gotten upto 250 degrees and the fans did not turn on.
I think this is telling me that either - the PCM is bad or (that at the same time the temp sensor is bad and the wiring from the high-side pressure sensor to the PCM grounded out.) I assumed that the PCM was the more likely cause and was easier to fix but now I am starting to lose faith.
This is the first problem I've had with my vette in the 5 years I have owned it. I never plan on selling it so I guess I need to start figuring out how to keep it on the road.
Any help or guidance would be greatly appreciated.
I purchased the new ECM from my local Corvette shop thinking that I just had to pull the chip out of my old PCM (16181333) then place it into the new PCM and I should be good to go. This was not the case, the does not start with the new PCM installed. Now as I read through the forums it appears that the Remanufactured PCM must be re-programmed and if I would have purchased an OEM PCM- 16181333 it would not have to be reprogrammed. (Is this true???).
So at this point I spent $165.00 on a new PCM that now keeps my car from even starting. I put the old PCM back in place and am now back to where I srarted. (The car runs normally except the cooling fans do not come on.) The part is not returnable so either I need to return the remanufactured unit as the core or pay more to get the unit programmed.
I am looking for advice as to what I should do next.
Is the shop screwing me for selling me a non-returnable part that they know is useless to me without a re-programming? How much goes into reprogramming? What is a fair price to get this done?
(I'm thinking I can user TunerCat to connect to the OLD PCM, perform a "Read PCM", save that file. Put the new PCM in place, then using TunerCAT perform a "Program PCM" using the same file. Is this true??? What about the chip I need to pull out of the old PCM and put into the new one. Will that screw anything up. What is the point of the removable chip if the PCM has to be programmed anyway?
I am not adverse to building or buying my own interface cable and programming it myself. (I have a computer/electrical engineering backround, but have no experience with PCMs yet.) I only have 30 days until the core return deadline and I lose my $425.00 on top of the original $165.00 I spent on the PCM I may not even need.
Because then once this is all done I still do not even know if this will resolve my cooling fan problem.
**************
About the cooling fan problem:
The car started overheeating a few weeks ago. It took a little time for me to realize that the fans were not coming on.
I verified the fan functionality by putting the PCM in diagnostic mode by shorting pins 5 and 6 on the OBD-II connector. (From what I've read I think it's an OBD-II connector on a OBD-I PCM.) In diagnostic mode the fans come right on. I believe this verifies that the: fans, fan power, relays, and relay ->PCM connections are all good.
Neither fan runs when I turn on the AC. Neither fan runs when I disconnect the high-side pressure sensor.
The temperature has gotten upto 250 degrees and the fans did not turn on.
I think this is telling me that either - the PCM is bad or (that at the same time the temp sensor is bad and the wiring from the high-side pressure sensor to the PCM grounded out.) I assumed that the PCM was the more likely cause and was easier to fix but now I am starting to lose faith.
This is the first problem I've had with my vette in the 5 years I have owned it. I never plan on selling it so I guess I need to start figuring out how to keep it on the road.
Any help or guidance would be greatly appreciated.
10-22-2004, 11:22 AM
#2
Le Mans Master
Member Since: Jan 2003
Location: Portland Oregon
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The stock programming for your fan turn on temps is over 200 degrees. I can't remember the exact number but its around 210 or 215. Having the PCM in diagnostic mode does confirm that the circuit and the PCM driver that controls the relay is working. Did both fans come on? If not check the battery feed circuits to the relays, there is a 30amp for the primary and a 40amp for the secondary fan. If I remember right both fans should come on.
There are also two temp sensors in the engine. One is for the PCM and its located at the front of the water pump, the other that is for the gauges is located on the drivers side cylinder head between cylinders 1 and 3. What you may see on the dash is not always what the PCM sees.
Have you checked the cooling system to make sure that it is full? If there is a leak in the system, there could be an air pocket in the system which can cause overheating. This air pocket can cause the system to be air locked and the temp sensor will not sense the correct temperature which will cause the fans to no come on. Turning on the ac does not always turn on the fans immediately, the PCM has to see X high side pressure from the ac system before it turns on the fans. If you just disconnect the sensor then the pressure reading goes low, try jumping pins B and C together, pin B= 5v reference, and pin C= sensor signal to the PCM. Give it a high pressure input and see if the fans come on. In a stock PCM code, the PCM has to see >189 PSI before it turns on the fans.
As for your "new" pcm, a dealer or someone with a GM SPS system has to initialize and program it with the GM calibration to your VIN. Dealers usually charge $85 or so to do this. I don't think TunerCat can do it but I can't say for sure as I have never tried programming a new PCM with it. I always use my TECH2 and the GM SPS programming software to initialize a new PCM.
The chip you are refering to that is under the cover of the PCM is not a chip. It is the knock module, that has to be transfered to your new PCM.
There are also two temp sensors in the engine. One is for the PCM and its located at the front of the water pump, the other that is for the gauges is located on the drivers side cylinder head between cylinders 1 and 3. What you may see on the dash is not always what the PCM sees.
Have you checked the cooling system to make sure that it is full? If there is a leak in the system, there could be an air pocket in the system which can cause overheating. This air pocket can cause the system to be air locked and the temp sensor will not sense the correct temperature which will cause the fans to no come on. Turning on the ac does not always turn on the fans immediately, the PCM has to see X high side pressure from the ac system before it turns on the fans. If you just disconnect the sensor then the pressure reading goes low, try jumping pins B and C together, pin B= 5v reference, and pin C= sensor signal to the PCM. Give it a high pressure input and see if the fans come on. In a stock PCM code, the PCM has to see >189 PSI before it turns on the fans.
As for your "new" pcm, a dealer or someone with a GM SPS system has to initialize and program it with the GM calibration to your VIN. Dealers usually charge $85 or so to do this. I don't think TunerCat can do it but I can't say for sure as I have never tried programming a new PCM with it. I always use my TECH2 and the GM SPS programming software to initialize a new PCM.
The chip you are refering to that is under the cover of the PCM is not a chip. It is the knock module, that has to be transfered to your new PCM.
11-18-2014, 11:40 AM
#3
Yes CATS can flash the PCM this is what I use
There are actually 2 Flash modules.
If the flash transfer is interrupted and stops for any reason!
dash signal noise. AC/DC laptop noise. Virus scan Ect.
It's game over!! You will need to de-solder both A & B flash modules. The best mod is to solder in a ZIF socket. Unfortunately the flash modules are almost extinct!!
As above your factory calibration. the fans due not turn on till 210
deg and above. Unless modified. Via re-flashing.
There are actually 2 Flash modules.
If the flash transfer is interrupted and stops for any reason!
dash signal noise. AC/DC laptop noise. Virus scan Ect.
It's game over!! You will need to de-solder both A & B flash modules. The best mod is to solder in a ZIF socket. Unfortunately the flash modules are almost extinct!!
As above your factory calibration. the fans due not turn on till 210
deg and above. Unless modified. Via re-flashing.
Last edited by THE 383 admiral; 11-18-2014 at 11:55 AM.
11-19-2014, 02:58 AM
#4
Race Director
I suggest getting a scan tool (either hand held or software & cable) and looking at what the PCM is seeing for the coolant temperature and the AC input. That's the only way to really find out what is happening.
11-19-2014, 08:40 AM
#5
Drifting
The coolant temperature sensor is what the PCM gets input from, and the dash gauge reads from a sensor in the head. What is the PCM reporting when the dash gauge gets to 250F? The PCM sends a ground signal to the fan relay typically at a temp above 220F (I only can document 93 and older), so has this wire been tested for proper output? When you jump terminals A & B on the ALDL and enter diagnostic mode, do the fans come on?
