Newbie question regarding Red/Blue PCMs

[buddrow]

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

[57 Handyman]

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.

[buddrow]

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

[57 Handyman]

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.

[buddrow]

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

[57 Handyman]

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

[buddrow]

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