Help! GM TBI crash course

[ford141]

I need some help with a little bit of a mess that we created. Long story short, we had a POS 98 Tahoe with a blown 350 Vortec, a POS 94 2500 with a 454 and serious frame rot, and a POS 79 F250 with a set of 4.10 geared axles. After some creative parts swapping we now have a POS 98 Tahoe with a TBI 454, 4L80E, manual transfer case, a Dana 44 straight front axle, and a Dana 60 rear axle. We are now trying to get the mess working.

So far, I got the 454 to fire, but only by dumping gas down the throttle body. I have spark, but no injector drive. I pulled all of the engine control wire harness from the 2500 along with the PCM. Using a wiring diagram from a Haynes manual, I powered the TBI PCM from the Tahoe, but I can't figure out why I don't have injector drive. All of the original sensors for the TBI are hooked up to the TBI PCM. What am I missing?

[Loren]

Fuel pressure? It'd be nice if it were something that simple, huh.

[smiti99]

Immobilizer possibly? Did a regular flat steel key work in the Tahoe, or did it require transponder keys?

[ford141]

We are running a Holley Blue fuel pump to it at 14psi. The pump is running, but I don't have a gauge on it to see how much its putting out. Does it have to see a certain pressure before it drives the injectors?

We completely bypassed the Tahoe's original computer at this point. We have a push button starter on the dash. I don't think the TBI computer has an anti-theft protection, but I could be wrong.

[SpiderGearsMan]

noid light for injector pulse , run a test light inline on the connector ..fp on a tbi should be 9-12 psi ..was the bbc running when you pulled it ?..injector pulse is triggered by the ignition module ..
a 98 fuel pump on 5.7 r id 60 psi ...

[ford141]

noid light for injector pulse , run a test light inline on the connector ..fp on a tbi should be 9-12 psi ..was the bbc running when you pulled it ?..injector pulse is triggered by the ignition module ..
a 98 fuel pump on 5.7 r id 60 psi ...

Thanks spidey, good info. Yes, the 454 was running when we pulled it. We eliminated the stock Tahoe fuel pump in favor of the Holley electric pump (because of the fuel pressure issue). The ignition module should be in the distributor, right? This is the first GM that I've spent any amount of time on. Since it has spark, I would assume the ignition module is working...

[Matt Cramer]

Are the injectors getting 12 volt power? The TBI ECU just grounds them.

[ford141]

Are the injectors getting 12 volt power? The TBI ECU just grounds them.

Good to know, I will check that. So, you are saying that there should be 12V at the injectors at all times with the ignition on?

[dieselgeek]

Good to know, I will check that. So, you are saying that there should be 12V at the injectors at all times with the ignition on?

Yes. Noid light will be handy, once you know you have 12v then see if you get noid light pulses. They're cheap at auto parts stores.

[ford141]

Yes. Noid light will be handy, once you know you have 12v then see if you get noid light pulses. They're cheap at auto parts stores.

Cool! Good reason to buy more tools!