Preferred PCM: 8625, 7427, or 6395

[57 Handyman]

Of these three PCM's which is the preferred unit for upgrades and what are the pros/cons for each? Are there any benefits or pros/cons to changing to a 7427 since I already have my 8625 connected and functioning in my S10. I realize these 3 all run at 8192-baud and are faster than the first gen 160-baud ECMs.

I still have my 8625 connected to the installed harness via a self-made ECM-to-PCM adapter. My main reason for making the ECM-to-PCM adapter was for insurance; I didn't want to get stranded on the highway. At the time I began all of this, I wasn't familiar with the limp home mode being built into the computers. I ask this question just in case a new person is thinking of having this kind of assurances available as they contemplate upgrading to a PCM.

[dave w]

I don't know if what I experienced is true on all cases when using the '8625 with a 4L80E. I upgraded a '7747 to the '8625 on a 454 / TH400 vehicle. Fast forward a couple years later, when the 4L80E replaced the TH400. Turns out the 4L80E shifted fine with the '7427, but with the '8625 the 4L80E had shifting issues (using the same Memcal / .bin file in both the '7427 & 8625). I did not try another '8625, because all my spare PCM's are '7427.

dave w

[57 Handyman]

I ask this question...

After re-reading this post, I realized I forgot to state a separate question which was different from the one about PCM preferences. Is it really necessary to make/use an ECM-to-PCM adapter since most computers have a built-in limp home mode?

Dave W, do you think it could be related to the processing speeds since both '7427 and '8625 run 50xs faster than the '7747? Are there any design differences in these 8192-baud PCMs, i.e., early vs later usage/deployment by GM? Lastly, in switching between '7427 and '8625, what kinds of changes regarding the bin/adx/xdf were required?

[dave w]

After re-reading this post, I realized I forgot to state a separate question which was different from the one about PCM preferences. Is it really necessary to make/use an ECM-to-PCM adapter since most computers have a built-in limp home mode? I've done several '7427 without an adapter. A couple advantages to an adapter plug: simple easy installation and no wiring / schematic skills required.


Dave W, do you think it could be related to the processing speeds since both '7427 and '8625 run 50xs faster than the '7747? Are there any design differences in these 8192-baud PCMs, i.e., early vs later usage/deployment by GM? Lastly, in switching between '7427 and '8625, what kinds of changes regarding the bin/adx/xdf were required? I don't have access to the PCM circuit board schematics, circuit trace layout, or the build sheet of components to accurately know what is different between the '8625 and '7427. Likely only the GM Engineers know the "REAL" differences. What I've noticed is the '7427 is used for both the 4L60E and 4L80E. The '8625 is 1993 with 4L60E. $OD & $E6 are for 4L60E. $31 and $OE are for 4L80E. I've successfully used the '7427 with $OD, $E6, $OE, and $31.

If it's the '7427 I'll use it, if it's not the '7427, I WON'T use it.

dave

[57 Handyman]

Ah...so, I guess Dave's PCM of choice is '7427 :innocent2::thumbsup:

Dave, you list bins for '7427 with 4L60E and 4L80E but which bin/adx/xdf would you start/use with a 700r4.

Also, I now see why wiring pin outs (attributed to you) indicate "NOT used on 87 GMC w/454"...:jfj: Thanks

[stew86MCSS396]

Whilst it may not be the exact thread that I extracted the parameters from to make a '8625 control a 700r4, this thread has the pertinent information: http://www.gearhead-efi.com/Fuel-Injection/showthread.php?43-16197427-and-a-700R4

[57 Handyman]

Domo Arigato, Stew...I need to give this a shot and learn how to do this.

[dave w]

Dave, you list bins for '7427 with 4L60E and 4L80E but which bin/adx/xdf would you start/use with a 700r4. A modified $OD .bin / .xdf / .adx works well for a 700R4. http://www.gearhead-efi.com/Fuel-Injection/showthread.php?303-16197427-PCM-Information-0D

dave w

[stew86MCSS396]

A modified $OD .bin / .xdf / .adx works well for a 700R4. http://www.gearhead-efi.com/Fuel-Injection/showthread.php?303-16197427-PCM-Information-0D

dave w

Before I knew any better, I suppose $0D .bin w^^^700r4 mods could be used in a '8625 w less a$$ pain! I went on the premise of "run what you brung" so leaned on modifying the $E6 for 700r4. The screenshots dave w provided in the link I posted ^^^as an fyi I ended up changing 32 parameters in tp locating them with ctrl+f any search term I could think of related to 700, tcc etc. Used compare tool to see what if anything was changed and copied into second tp session w $6E opened. Don't forget Efan control was also added to your $6E, too.

[In-Tech]

Hiya folks, using the search I just found this thread. I am working on a 94 bbc suburban with a 502, still tbi. The first issue was the 02 voltage toggling between ~450 mv to over 1 volt with just the key on. I grabbed a spare red/blue (6395) assuming they are all the same but maybe not, o2 toggling was gone so at least it is not in the wiring. I haven't driven it yet to see if it will control the 4l80e but I was having some weird issues with the electronic IAC so it dawned on me to research a little.
After reading Dave's post I will hunt down a 7427 and try next week when I am back to work and post what I find.

[myburb]

I have 94 burb bb 454, aluminum intake unheated, upped fuel pressure, ported heads, headers and .500 lift cam. It came with 6395 and that is what I use but have swapped 7427 in and no difference. I did a lot of tuning in the beginning but haven’t burnt a chip in two years. It is a daily driver and runs great. I run in open loop with auto iat correction.

[In-Tech]

Thank you for the feedback, much appreciated. I assume your 94 has the 5 wire IAC? From memory it seems I have swapped between the 7427 and 6395's in the past but that could very well have been 350/4l60 stuff with the switched EGR. I have dyno tomorrow on an '03 cammed 5.3 that I just installed a whipple, then hospital up at UCSF on Tuesday so I won't be doing anymore testing on this one till Wednesday but I will post back what I learn. Thanks again.