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Thread: Newbie question regarding Red/Blue PCMs

  1. #1
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    Newbie question regarding Red/Blue PCMs

    Are the internals (processors, connector plug wiring, etc.) of Red/Blue PCMs the same? I have both a 16168625 BBMX and a 16195925 BHRJ. The 8625 is from a '93 Chevy Sierra 4.3L (I believe) while the 5925 is for a '94 Olds Bravada 4.3L. I have seen a bunch of write-ups on the 8625 and, therefore, my plans are to use the 8625 in my '92 4x4 S-10. On the other hand, I can find nothing about the 5925. I am wondering if the only difference is the chip and not the physical internals.

    I ask this because I am running into the same "no start/run" problem when I install both PCMs. In so doing, I am trying to determine if the issue to the no start/run is the PCM or the adapter that I have constructed as I learn about tuning.

    Lastly, is it possible to turn the 5925 into the equivalent of an 8625 by reprogramming and installing a PROM?

  2. #2
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    I've wondered how much hardware difference there is as well.
    .
    1994 Chevy G30 Van "Big Blue"
    5.7 TBI, Vortec Heads, Summit Intake, Thorley Short Headers with dual 2.5" exhaust, 4L80E transmission

  3. #3
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    One would think that GM would not design separate pieces of hardware to accommodate the various makes, models, and engine/transmission configurations. In the absence of an authoritative/definitive response from someone, and once I get more comfortable with and know what I am doing with these PCMs, I will perform a test to validate or invalidate my hypothesis regarding common PCM hardware.

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    To somewhat answer your question, they are different beasts in a few ways. First the 8625 will run the TBI engine just fine, with 2 injectors, blah blah blah. The 5925 is meant to run the CPFI(spider injector) style of multi-port injection. Is the wiring at the red/blue connectors different between the two, you betcha! Stick to the pcm that "came with" the engine you are trying to run. The 5925 likely will never start your engine in its current state.. HTH

    Buddrow
    If it don't fit force it, if it don't force fit f&%@ it!

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    buddrow, thanks for providing input to this thread. So, based on what you are saying, the 5925's red/blue connectors will NOT fire the 2 TBI injectors because the BCC (which includes the .bin, .xdf, and . adx are different plus the red/blue connectors are wired differently. Interesting...

    With regard to your recommendation of sticking with the PCM my engine came with, all my research/readings online say that it is possible and likely worth the effort to upgrade to the 50x's faster 8625 PCM rather than stick with the slower 4288 ECM that came stock in my '92 4.3L S10.

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    It's not so much the connectors themselves as the hardware internal to the pcm as well as the software that runs everything is different.

    The '4288 is a direct replacement for the '7747, provided they are both from the same engine size, 4.3,5.0,5.7... The '7747 may not be the best choice for performance applications, but for simplicity, it would be an easier swap than the 8625 since it's a direct swap, no pin swapping. I know this because I have done such a swap in a friends '92 with the '288. The 8625 will run the 4.3L, you will just have to do some pin swapping at the pcm connector. There are wiring diagrams available on this site, or if necessary I may be able to provide you with wiring diagrams for both pcms.

    The BCC(broadcast code) is the calibration code name/designation.
    the .bin is the actual calibration file
    the. xdf is used by tunerpro to organize the .bin file for human viewing, modification, etc.
    the .adx is solely for datastream interfacing, datalogging, etc.

    These are all different from one pcm to the next, but are the same between different calibrations/.bins of the same pcm number, if that makes sense.
    Just food for thought.

    Buddrow
    If it don't fit force it, if it don't force fit f&%@ it!

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    Buddrow,

    Thanks for your offer to assist me with tuning/reprogramming the 4.3L in my '92 S-10. If the 7747 is a direct swap to my stock 4288, are there benefits to making the swap? Is the internal processor speed higher or the same 160 baud in the 4288?

    I am aware of the repining required in switching from the black 4288 connectors to the red/blue for the 8625. I guess my preference for the 8625 is tied to the benefits I've read about on the site and, more so, the amount of work others have already done with the 8625. While I have seen and found a few wiring diagrams, I would appreciate seeing a listing which you have used with success and what your recommendations you'd make regarding sensors, such as O2 and knock sensors. Both of these are the stock pieces and I was wondering if I should be using different ones.

    Again, thank you for helping.

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    The main benefit to swapping to a 7747 over 8625 is plug-and-play. The 7747 doesnt require any modifcations to the connectors or anything else, its a direct replacement. The 288 has limited support versus the 7747(which is very heavily supported on this site) in regards to xdf, adx, bins, etc. The 7747 is inferior to the 8625 in a couple of ways depending on your perception of things. The 7747 is 160 baud(yuck) vs 8625 which is 8192(9600)baud, this is only noticeable during datalogging/data aquisition though. The 8625 has higher resolution fuel and spark tables which is a benefit, but not a ncessity in my opinion. Ive been running a modded 7747 in my 90 Chevy and to the unaware, you couldnt tell the fuel and spark maps stop at 3600rpm. When it comes to tuning these ecms/pcms, hardware required to do so comes into play. How are your soldering skills as some are required to make updating the bin possible. Time for coffee...:-)

    Buddrow
    If it don't fit force it, if it don't force fit f&%@ it!

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    Buddrow,

    You've just about got me convinced regarding pros and cons for switching to a 7747. I'm re-evaluating my needs in light of what I've experienced in getting my truck to run smoothly and dependably. At present, it maybe a whole bunch of problems, i.e., vac leak, possible sensor, need to rebuild the TBI again, fuel relay/pump, etc. on top of the internal engine mods I've made...marine cam, .020-in overbore, higher compression--flat-top pistons, 96 Vortec heads, etc. Also, since I wanted to keep the TBI (vs change to a carb), some of these mods resulted in no EGR--the Edelbrock 2114 intake does not have a place for one. Is yours a 4.3L or V8 in your '90 Chevy?

    As for soldering skills, I'll be able to do the ones described on this as well as other sites. Now, I also need to find a 7747.

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    If it were me, I would swap in the 7747 and be done. Maybe a few tweaks here and there to the cal/bin. When swapping ecm/pcm's, always make sure the net resistor matches the engine family, i.e. v6-v6, v8-v8. Also, you mentioned sensors, you can retain your factory '288 sensors as they are the same as 7747 hardware. You can find the 7747 in most 88-91 Chevy/GMC trucks at most salvage yards fairly cheap(under $50) at pull-a-part places. Pulling it yourself insures what you get, full size trucks had the 7747 in v6 and v8 trim, if in doubt, run the .bin/BCC against the list for the 7747's. And don't fret too much if the truck you get it from is a manual trans and your is auto, you can change between the two in the .bin file with Tunerpro.

    Installing the Moates adapter in the 7747 is pretty straight forward and easy to do even with minimal soldering skills.

    But before you embark on the swap, verify all mechanical issues are squared away, otherwise you can chase your own tail for days, weeks...:-)

    Buddrow
    If it don't fit force it, if it don't force fit f&%@ it!

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    Buddrow,

    I am leaning toward doing what you suggest about using a 7747. With respect to verifying the mechanical issues before making the ECM to PCM swap, that is exactly what I have been trying to do, especially, with regard to the EGR. I have been focusing on the EGR because it is the one sensor that I eliminated. However, that being said, I don't exactly know how significant an impact the EGR has on my 4.3L running smoothly and dependably. Additionally, I don't understand to what extent the engine modifications I've described above contribute to the issue of smooth and dependable performance.

    Up to this point, I have been unable to take any action on what you've suggested in this thread because I am currently away from home attending Hot August Nights in Reno and will return home in Hawaii on Tuesday. While here in Reno, I have been searching online for a 7747 and have found several candidates. As you may realize, the availability of parts in the islands is very limited. I will get back to you shortly. Again, thanks for your help.

  12. #12
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    The only time you may experience an issue where EGR is causing a driveability concern would be if the egr valve is being opened by a misplaced vacuum line maybe, if the pintle valve is stuck allowing exhaust gas to enter the intake, causing rough running and such. But just eliminating the egr shouldn't cause any ill effects. You can "eliminate" the egr in the .bin so the ecm doesnt even look for it. It isnt electrically connected to anything in the ecm other than the vacuum control valve so the ecm will never know its gone until its commanded and the ecm looks for a change in MAP sensor signal. If it doesnt see the change it expects, it'll set an egr code, but still have no adverse effects on engine performance.

    As far as the mods you have made, do you have specs on the "marine" cam? Also, you may have head-to-intake mating issues, but I can neither confirm nor deny that at this point, ill have to investigate that. Do you have the casting numbers on the heads you're using by chance? I know the intake port is slightly higher(raised roof) on the v8 Vortec heads which can cause mating/sealing issues between the head and intake, the v6 may be a similar situation.

    I can only imagine how scarce parts are on the island, that's gotta complicate things. Have fun in Reno.

    Buddrow
    If it don't fit force it, if it don't force fit f&%@ it!

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    Hey Buddrow,

    Got back home the other day but couldn't and can't get to the truck until an hour from now. The Navy Hobby shop where I have my S10 has limited hours.

    The one thing that is interesting about the EGR is the ECM has NOT set any codes. Also, glad to know the absence of the EGR has minimal impact on how motor runs. Unfortunately, that means the cause of my idle problems is something else.

    With regard to the Marine Cam Specs, I did have that information some place...just need to find it. As for the casting numbers for my Vortec heads, I will remove the valve covers and get those to you.

    Since I've been away from working on and messing around with the truck for a week or so, that absence will allow me to have a fresher perspective rather than a mindset. Also, I know your insights will help. I'll get back with more info soon. Thanks

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    Sounds like its time to hook up(if not already) the correct pcm, a vacuum gauge and a timing light and have a look at things. Also check for any vacuum leaks around the intake ports. Spray some brake cleaner around the port area, listen for a change in idle.

    Buddrow
    If it don't fit force it, if it don't force fit f&%@ it!

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    Buddrow,

    After doing some digging, I was able to find these cam specs...Elgin Pro E-1033-P:

    Valve lift: .403 Intake/.410 Exhaust
    Lobe centers: 108/116
    SAE duration: .271/.284
    .050 duration: .202/.213

    Valve springs are stock.

    I'll get the head casting info today and additional efforts to find vacuum leaks.

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