prepping for a swap

**conwaymuddy** · 07-12-2013

Getting ready to swap a tbi into my 93 gmc k1500. Currently running a carbed 454 and th400. Picked up a tbi setup from a late 80's 454 and this is where it gets fun. The guy gave me a 7747 ecm that he thought was for the motor and tbi. Looked up the bcc (ASDU) and its for a small block. So i pulled the original pcm from the truck and its an 8625 with bcc BHAS which i cant find. Truck has tbi wiring from another 93 or 94 i dont remember. So im wondering which ecm/pcm im better off using? I really only need it to run the tbi. I know most use the 7747 but i dont know why. Thoughts or opinions?

**EagleMark** · 07-12-2013

If the truck came with 16168625? Then use it! Don't worry about BHAS, it was superceded twice to BLCR which we may have here:

http://www.gearhead-efi.com/Fuel-Inj...Information-E6

But that is still a 5.7L bin, can be tuned for 7.4L or just start with an $0D bin, most of them work with that PCM, if not a 16197427 will plug into your harness.

**conwaymuddy** · 07-12-2013

Thank you. I had been leaning toward the 8625 since it will require less modification to use. I figure it will be best to reflash the prom to some sort of stock 7.4 tune and work from there. I seem to recall seeing something here about dual fuel and spark tables as well, cant really complain about that.

**conwaymuddy** · 07-13-2013

Best i can tell since i havent heard from my friend yet, looks like the wiring harness is for 94 5.7 auto trans gm based on the pinout. So do i repin the plugs to the 93 pcm or do i have to do something else as the harness and pcm will be running a 7.4 tbi from the late 80's? Im assuming just repin to the pcm but i dont want to start and then redo.

**EagleMark** · 07-13-2013

Unless I'm missing something? No! No repinning, your origanal PCM will work as is, you just need to change the chip/Memcal inside the PCM.

**conwaymuddy** · 07-13-2013

Ok thanks. Was looking through the wiring diagram in the haynes manual for a 94 5.7 4l60e and it matches the harness i have perfect for the pinout. There was nothing specific for 93, just 88-95. Found the 93 diagram on here but its hard to see on a smartphone. Just want to make sure im headed in the right direction.

**conwaymuddy** · 07-20-2013

Just how bad will an engine run without a vss? How hard is it to tune out? I run turbo 400 trans and there is no vss. I know i can put one in but i tend to go through a trans a year and dont want to have to deal with it every time i blow one up. The swap is going in a mud truck. It sounds like without the vss it may have a high idle or a jumpy erratic idle.

**bentrod** · 07-21-2013

By "tune it out" do you mean get the engine to run the same as if it had a VSS? I don't think that is possible because the VSS provides input for how the motor should act after say, a prolonged run at above idle RPM.

Maybe a cheap hax way around it, you could write something and sneek it in there like "if rpm>2000 for xxxxx cycles, then increase idle up pulse width by xx% and fuel pulse width xx%", you could give that a go? It'll probably be 200 lines of assembly... maybe 100 bytes assembled?

Keep in mind you could do all that work and have it not be effective.

**ony** · 07-21-2013

some trans and pcms need a vss sensor to shift right,could be why you are blowing 1 a year.

**conwaymuddy** · 07-21-2013

Th400 has a vacuum modulator to control shift points. Truck only sees park, neutral, reverse, and first. I think my driving style is why i blow up transmissions. Hopefully at some point ill get a trans built to withstand my kind of abuse but its a ways down on the list. More or less wondering if anybody has run without one and how bad it was? Its strictly offroad for this truck but id like it to not be fighting to run at idle or like garbage under acceleration/ WOT. i know it wont run tip top without the vss but dont know just how bad it could be.

**EagleMark** · 07-21-2013

I've never liked any that I have tuned without VSS... they were all better with.

**conwaymuddy** · 07-25-2013

Try this again after the site logged me off and this disappeared.
I think these should be all the wires/ pins i need to run the engine

A5,a4,f11,b2 - distributor
E15,a16,a9 - injectors
A10, f15 - O2 sensor
F6,b12, e16 - fuel pump relay
E6 - check engine light
F9,a14 - data link
B4,b13,e14 - map sensor
F14, a15, b3 - throttle position sensor
B8 - engine coolant temp sensor
A1,a2,a12, - ground
A7,a8,a3,a6 - IAC

Wires/ pins im unsure of
B15 - knock sensor, dont have but could always add later
E13 - brake switch, serve any purpose?
F12,f13 - V.S.S. buffer, do i need this if i run a V.S.S
F2, f3 - V.S.S, any harm in leaving these in unconnected at the sensor end until i decide on running V.S.S or not?

I think that should get the engine running minuse the smog garbage and e-trans control. Let me know if im missing anything or what else can be removed.
Thank you

**Nasty-Z** · 07-25-2013

Originally Posted by conwaymuddy

Try this again after the site logged me off and this disappeared.
I think these should be all the wires/ pins i need to run the engine

A5,a4,f11,b2 - distributor
E15,a16,a9 - injectors
A10, f15 - O2 sensor
F6,b12, e16 - fuel pump relay
E6 - check engine light
F9,a14 - data link
B4,b13,e14 - map sensor
F14, a15, b3 - throttle position sensor
B8 - engine coolant temp sensor
A1,a2,a12, - ground
A7,a8,a3,a6 - IAC

Wires/ pins im unsure of
B15 - knock sensor, dont have but could always add later
E13 - brake switch, serve any purpose?
F12,f13 - V.S.S. buffer, do i need this if i run a V.S.S
F2, f3 - V.S.S, any harm in leaving these in unconnected at the sensor end until i decide on running V.S.S or not?

I think that should get the engine running minuse the smog garbage and e-trans control. Let me know if im missing anything or what else can be removed.
Thank you

Just a quick scan through of your Pin #'s looks like you have it pretty well figured out , although there are many wiring diagrams on this site under the '8625 , '6395 and '7427 PCM headings to help you out.

Be careful of the IAC wiring with the 454 TB unit, it is wired different than a 350 IAC valve , that and the TPS plug could be different depending on the year of the 454 TB unit you are using .

Thats about all I can think of off the top of my head , I would try my best to run a knock sensor , brake switch input and a VSS , it will make idle quality and driveability much smoother than without .

HTH

TOM

**conwaymuddy** · 07-26-2013

Thanks. I still have the wiring original to the tbi set up so i can always steal the plugs from that if they are different. Wasnt sure if the brake switch really did much other than the canister purge solenoid. Do i need the v.s.s. buffer for the v.s.s. to function? I would assume so but im trying to cut down on random wires/ plugs floating around until things get installed. Similar to the knock sensor, dont have one but will eventually like to get one in there. I used the diagram on here for the 8625 and one from a chilton manual. Easier to see than on my phone and spot on..

**conwaymuddy** · 07-26-2013

Wheres my V.S.S.? chilton shows f2- red/black and f3 - dark blue/ white to v.s.s. I dont have those in this harness. What i believe is the plug for v.s.s. has purple/white , green/black twisted to a plug. The wiring diagram on here shows a brown wire from pin f12 to v.s.s. buffer (DRAC) that wire i have, comes from same plug as the twisted pair to the pcm plug. Ill see if i can figure out pics and post.