89 gmc lean running condition
 

I have a 1989 GMC 1500 2wd, with A 4.3 L V6 from a 1994 Chevy 1500 4 x 4.
(The version with the counter balance shaft) and a five speed manual transmission. When you start the truck cold it will Idle up normal at first then makes like it wants to die then Back up again and it will do this for a few moments as it is warming up Then will eventually Idle normally. As I start out in first gear, unless I am extremely easy on the throttle it will bog down, Sputter, and act like it is out of fuel regardless of how much fuel is in the tank. Once it does go, if you push on the gas lightly it will accelerate seemingly normal but give it some throttle( 1/3 or more to the floor) it falls flat on its face till i let up just a smidge, it is very noticeable when it fades out. The only code that comes up is code 44 for lean exhaust. Now I literally blasted the parts cannon at this thing. New fuel pump x2(at first pump only, then just yesterday the entire assembly) fuel filter, complete teardown and rebuild of tbi unit including fuel pressure regulator and injectors, removed intake manifold and cleaned it out And reinstalled with new gaskets, new Coolant temperature sensor, new tps, replaced IAC, map, ESC and EGR with ones from a perfectly running truck, new EGR gasket (EGR was checked and vacuum tested as well) new distributor, plugs, wires, cap and rotor, new knock sensor, new o2 sensor and timing is set to factory spec of 0 degrees btdc with timing control unplugged.(also has new timing chain and gears) I have checked hoses for fuel leaks and vacuum leaks. All of which have made little to no difference. Am I missing something? I have tried everything I can think of. Any ideas?

Re: 89 gmc lean running condition
 

I am new to the TBI world, so take anything I say with a grain of salt. Recently I disconnected one of the injector connectors accidentally, and it ran the same way you described yours where it would rev up and then want to die repeatedly. The check engine light came on, but I didn't check the code. In my case, of course, it was fixed by simply pushing the connector back into place. the connector latches were missing, so I ended up replacing the connector housings so this wouldn't happen again. While researching how to replace the connectors, I read an article that said the injector wires are known to fail where they pass through the grommet on the front edge of the throttle body housing. I'm assuming neither of your connectors is loose since you've had everything apart. Maybe one of the injector wires has failed though. You could possibly do some probing of the wires with a multimeter and a pin, along with wiggling the wires.

Re: 89 gmc lean running condition
 

Welcome to the board.

You have covered the bases fairly well.

It looks like it is time for diagnostics.

First thing I would do is test the fuel pressure with it running, which is not as easy because there is no test port on the TBI trucks. Spec is 9 – 13 PSI.

If the fuel pressure is good you should get the system data with a good scan tool or WinALDL.

If you can post data I will look it over and see if I notice anything.

Re: 89 gmc lean running condition
 

What ChevyTech said! Don't just throw parts at it and hope.

I had a similar problem and eventually found out one of my two injectors was clogged. But it took a while to figure it out.

Re: 89 gmc lean running condition
 

My truck had a bad ground. It made the oxygen sensor read lean, really lean. The computer dumped a ton of fuel into the engine, it ran horrible. It's supposed to bounce back and forth between about .3 and .7 volts, mine was in the negative. So I would check the oxygen sensor readings.

Re: 89 gmc lean running condition
 

Thank you for all your great info guy’s, but I finally got it figured after weeks of hair pulling and head scratching it turned out that the place I bought the truck from had used a front end loader with forks to move the truck around their yard and had bent the bottom of the fuel tank so it was making contact with the pump inlet and squashed the strainer causing a fuel restriction. Could have saved a lot of messing around if I had only took the tank out of its shield, but lesson learned
Won’t be over looking that ever again, lol.