Tbi 350 dies at half throttle

[Loganwayne]

Finished up Robby’s rig last night truck idles fine but keeps dying at half throttle.
Any ideas on what to look for truck sat for unknown amount of time before he got it

also doesn’t have exhaust yet will be getting that this morning.


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[Jody Treadway]

Fuel supply
Timing
Test with vacuum guage

 

[drkelly]

I believe the ignition modules are known to be problematic on those motors.

@a_kelley seems to always have good insight.

 

[Loganwayne]

I believe the ignition modules are known to be problematic on those motors.

@a_kelley seems to always have good insight.

I think that’s on the list of parts to grab after he gets exhaust finished
He had 4/5 sensor type stuff he was gonna grab.
Throttle position sensor had twist lock nuts on it [emoji15] so that’s getting fixed as well


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[Fabrik8]

Don't even bother troubleshooting until you know the sensor wiring is done properly (no more wire nuts).

If it doesn't have an exhaust, where does the exhaust stop? This could be causing bad O2 sensor readings.

 

[Tim C]

Get all the sensors and wiring straight first, but don't just go replacing sensors for no reason, the parts cannon can get expensive. If all the sensors are wired right and it has no codes then start with the basics like @Jody Treadway posted.

Definitely check fuel pressure AND volume. I don't remember the volume spec off top of my head but pressure is 9-13 psi stock, I prefer to see the high side, 11-15. Both volume and flow make a difference on these. They can idle great at 5 psi but die if you touch the gas pedal. If it has good volume but the pressure is low, pinch off the return line to see if it will spike higher, if so the pressure regulator spring may be broke. That's a common problem too.

Also use a bright light or even a timing light flashing after checking the timing to look at the injectors spray pattern. It should be a full cone that widens to nearly match the throttle blades at the bottom. If it's been sitting for even a few months injectors and/or fuel pumps will varnish up on these and cause all sorts of issues.

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[ckruzer]

Park ground

 

[a_kelley]

Tps, fuel pressure/flow, injector spray (though usually it's the reverse problem, sticks at low injector dwell, flows somewhat at higher dwells).. definitely check the ignition module .. if you remove it, advance, etc can run it on their tester, also check ig coil, rotor button & dizzy cap. That generation doesn't care too terrible much about o2. It'll run fine unplugged.

 

[C.Berry]

If no exhaust it’ll still run but like straight ass, shouldn’t be dying after half throttle tho I’ve never heard of that happening bc of o2 but is plausible bc it could be sending lean reading and floods when crappy tps send throttle reading!? Any smell of extra fuel In the TB? Also Check the cts bc it will if faulty or on the way out not allow engine to run with throttle applied heavy but will idle and run if unplugged so easy check to mark off list!

 

[a_kelley]

I doubt it's the o2, it doesn't use the signal except at cruising and idling, but is ignored WOT.

 

[Tim C]

I doubt it's the o2, it doesn't use the signal except at cruising and idling, but is ignored WOT.

And even when the o2 is getting used it only tweaks the fuel map slightly rich or lean. Not nearly enough to cause it to die out.

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