TBI Help please :

[conoverbandit]

Hello,


I have a 87 Chevy R-30 crew cab, it has the 7.4 engine, I bought the truck spring of this year and haven't gotten it working right since. The problem I have is the TBI won't let the engine idle, it's as if it had a "choke" and it's stuck. I've talked to local guys around here and done everything they told me to do but no luck. You can crank it up and it's loading up bad, black smoke, it would drive at least, but you'd have to stand on the brakes to get it to stop.To date I've replaced : gaskets on top and bottom of TBI base, fuel pressure regulator, coolant sensor,new plugs,wires,cap, button, all these to no avail. I had one guy tell me that gm injectors were interchangeable and that others would work. I took the ones from my mom-in-laws caprice (5.0) TBI engine, and put them in the truck, it cranked and ran but had a terrible "surge" to it like it was running out of gas or something, called local parts house and they said probly bad idle air control (iac), so I go buy a $70.00 IAC put it on and still does it, so I put old injectors back inplace and it idles but black smoke rolling from back.....Put old IAC back in today with caprices injectors and it still surges. I need some help here, I'm about to see if I can get what I got into this thing and let some one else worry with it. It is not throwing any codes,nothing , I took the cluster out and replaced all the bulbs and put it back in, the light comes on when engine is cranked, but goes out about one or two seconds later. Thanks for any help you can give me.

[twoodson]

I am not TBI expert but here are some other things to check. Check the PCV valve, and the rest of the other sensors that are on the TBI as well as the idle screw on the front of the TBI as well as any vacuum lines. I am not for sure about the black smoke. Also post the question on www.thirdgen.org. They may have other suggestions as well. I know quite a few guys on this forum will have other suggestions just give them a little time

[Russell]

Ok, I'd guess either your MAP sensor is toast, causing the engine to run extremely rich (black smoke is fuel, blue smoke is oil, white smoke is coolant) or else your 7.4 injectors are done. While the injectors will interchange between the throttle bodies, your truck's computer programmed to think that is has injectors that are from a 7.4, so thats why the 5.0 Caprice injectors do not work.

[conoverbandit]

HE He,

Silly me, I guess I should have included the part that the guy I got it from tried to crank it after sitting in back yard for a year or better, it backfired and toasted the injector wires. I had no idea about that, but I drove the truck home like this, and upon inspection and going over things a bit, guess what I found under the air cleaner! fixed that first, also, if the o2 sensor is bad could this effect the fuel dumping thing?

Thanks,
Wayne

[Russell]

yes, the 02 sensor also has direct control over the mixture just like the MAP sensor