92 k1500 with 4.3 TBI 5 speed stutters and no top end power.

[wibednaroski]

Have a 4.3 that on cold start idles like a dream, I let the rpm drop, and it drives good with plenty of power to maintain 75 on the highway however after a while it slowly starts to loose power and won’t maintain speed in fifth gear on a level road and starts hesitating while driving through stop and go traffic if I get on the throttle she studders a bit and takes off but when I shift into 4th at 45mph she starts loosing power and studders and becomes a pain to drive I have new plugs and wires, new distributor cap and new o2 sensor. The truck has no cats and the exhaust is run through a flow master muffler. Could it be possible I got a dud on the o2 sensor?
The spray pattern off the tbi looks even and solid and when I unplug the o2 sensor it runs better but still hesitant in stop and go. I’ve checked ignition timing running 3* advance and it seems like the motor is solid. 208k on the odometer. I’m not very experienced with the tbi motors.

 

[Schurkey]

What is the fuel pressure after it starts losing power?

Connect a scan tool, look at the data stream. Verify all the sensors.

Warm up engine so that it's got reduced power. Shut off engine. Pull the coil wire out of the distributor cap, connect it to a spark tester calibrated for HEI ignitions. Crank engine. Does the coil fire the spark tester reliably?

 

[LC2NLS6]

Absolutely check fuel pressure at idle and under load first. These are simple EFI setups, but still need the basics, fuel air spark and compression. If I had to just throw parts at it without diagnosing, I'd upgrade the fuel pump to a vortec one.

 

[steveed]

I had similar issues with my 4.3 along with it dying at idle after it was warmed up. I ended up replacing the fuel sending unit (pump and all) and the coolant temperature sensor (the one that feeds the ECU not the gauge). Never had any issues after that, of course I only had the 4.3 in it for another year. I did drive from Texas to California and back though.

 

[evilunclegrimace]

it is only a 4.3 . But seriously have you changed your fuel filter lately? Your truck is exhibiting all the symptoms of a partially plugged filter