GM TBI Schematics

[BadDog]

I gotta say, I'm in the "keep the stock harness" camp on this. As stated, the ECM/TBI harness is pretty much stand alone anyway. There are some cross overs, like VSS and Neutral/Park, but that's about it. I kept it all on mine. Up side is that commonly available parts work, diagnostics like WinALDL or hand helds work, I get "closed loop" which improves longevity, performance (I really like how changing altitude by 7000 feet has minimal effect), and fuel efficiency, and so on. As far as the low oil pressure switch goes, I have yet to see it become a problem. Mine has required physically cutting it off each time I've gone over, and I've never had it abandon me on a climb or off-camber, even when the oil pressure got too low to read.

 

[jac6695]

The problem with the fuel pump relay in my donor truck/harness is that there isn't one. The fuel pump in this truck is wired straight to the coil and has been since I got it. The fuel pump relay is M-I-A and I'm not putting it back.

Now that is a different problem. I would check and see if some of the wiring is can be salvaged to install a relay using the ECM as the power for the relay.

 

[dyeager535]

Supposed cutoff for the oil pressure switch is 5PSI, but I can still see what others are saying about being on the side and losing pressure.

I wondered about the off-camber stuff anyways...even with a sump, you can only run so long before it runs out, and if the truck turns over, the sump will go dry instantly, and the engine should die instantly as well from fuel starvation.

 

[84_Chevy_K10]

Now that is a different problem. I would check and see if some of the wiring is can be salvaged to install a relay using the ECM as the power for the relay.

A relay is not necessary for the kind of current that a fuel pump draws in my opinion.

 

[dyeager535]

If I understand all that a relay does, it seems to me that the relay in the fuel pump circuit is SOLELY so that it can be controlled with the key and oil pump switch, and perhaps the ECM.

The way that the fuel pump relay is situated in the TPI harness of mine, the relay setup doesn't shorten the overall batt feed wire length at all, which is TYPICALLY (again to my understanding) why relays are used. The 12V batt feed in injected setups is already protected by a fusible link as I recall, without looking at a manual to confirm.

Again though, if running the fuel pump switched in any way, the simplicity of the GM relay system is pretty tough to beat. Even then, if you wanted to strip the stock relay wiring down you could, to what, 4 wires total? (switched source, ground, batt in/batt out)

 

[BadDog]

Yeah, the only purpose is so the ECM can control the fuel pump based on ECM inputs (including oil pressure, key, etc) without having to run that current through the ECM. All the ECM does to trip the relay is drop a very low current to ground. If the oil pressure drops (or whatver needs turning off the fuel pump) then it removes the ground.

 

[dyeager535]

Ahh...just clicked in my head. The relay also allows the *ECM* to turn the pump on to prime the system when the key goes to run.

 

[jac6695]

Yes, the ECM pressurizes the system for faster starts. The only way I can see that the oil pressure switch on a TBI system would shut down the engine is if the fuel pump relay drops out of the circuit after startup, which I have never heard of before. Otherwise, it is wired in parellel to the relay and is only a "backup" to the relay.

 

[eagle mark]

Here's a link to pin outs of the 1227747 ECM used with TBI. There is also a link there to the DIY site for the diagrams your looking for.
http://www.justinternationals.org/Binder-Bench/showthread.php?t=1291

If you decide to buy a harness or chip there is an ad in the vendors section for links to both. And a CK5 discount.
http://coloradok5.com/forums/showthread.php?t=121747

Ditch the knock sensor, ESC, EGR and VSS. Then have them turned off in the chip. If whoever does the chip correctly then you will pick up on performance as well.