350 Tow Vehicle TBI?

[CraigG.]

Hey Everybody,
What causes a 1988 c2500 2wd 350 TBI to flood on tip - in and run fine on all other throttle postions?
I have spent $ - computer, 02 sensor, NEW dist. - plugs wires - etc. checked TBI gaskets but not rebuilt the TBI.
Sorry and let me know if this is not the right place for this post.
Thanks, Craig

[In-Tech]

TPS is probably bad. There is a free scanner program called WinALDL that will allow you to monitor everything, and you can make your own cable for just a couple bucks. The suck is that old computer is only 160 baud on the data rate so it can be a tad tricky to catch a bad sensor, patience.

[Alan Roehrich]

Or, check either the voltage or the resistance across the sensor with a digital volt ohm meter. Usually around 0.46 volts at idle, and 5.00 volts at wide open throttle. It should increase smoothly and consistently, about 0.01 to 0.02 volts at a time as you open the throttle.

Other possibilities include the MAP sensor and the fuel pressure regulator.

[In-Tech]

Alan 100% . VOM grey is +5v, black is analog ground, blue is signal.

[user-612937456]

I have had the EST module (mounted beside the M.A.P. sensor, and E.G.R. solenoid) be a pain in the A** to diagnose It can severely retard the timing at low rpm's causing a stumble, caught, or backfire at take off the harder you accelerate the worse it acts

[CraigG.]

Thanks guys.
It is off idle FLODDING - smoke in all. Will only clean out when past that throttle spot.
The tps checked at .6 idle to 4.36 at wide.
The MAP checked at 4.6 not run and 1.01 when idle.
Both are in spec with my Hayes manual.
I can recheck the tps to check for the .01 increase right at the Fat spot - but?
Thanks Again, Craig

[ijames]

Put the meter on the tps, key on, engine not running, and very slowly crack the throttle and open it. The voltage should rise exactly in step with the throttle opening. You are looking for a dead spot where the voltage drops or jumps suddenly, usually just off idle where the throttle spends most of its lifetime cruising so the sensor gets worn out right there.

[Alan Roehrich]

Also check the coolant temperature sensor, connector, and circuit.

[Mean Racing]

a surging condition when just off idle could be the EGR valve, unplug the vacuum hose to it and if the surging goes away replace the EGR valve.

[Schurkey]

How's that charcoal canister and purge valve?

[CraigG.]

Thanks the Coolant sensor - checks good.
Craig

[900HP]

I had one that did that and the injector wiring had rubbed through and one wire was grounding on the throttle body/air filter spacer.

[CraigG.]

The EGR valve is new.
Thanks, Craig

[CraigG.]

Guys - TPS tests perfectly.
Thanks, Craig

[cpracing639]

Is the intake manifold coated with sludge? I've seen a ledge on the floor made from heavy amounts of fuel/carbon deposits causing fuel to puddle. When the throttle is opened from off idle, it pulls the puddled fuel in causing the stumble , and black smoke. These things can drive you nuts. Just need to keep after it. Good luck.