95 Yukon 350 TBI flooding

[norv struckman]

Yukon (v8 automatic) likes to stall on deceleration a lately has escalated to serious flooding issue. Smoged last month and tech said that “cat” was on it’s way out. Fresh plugs and wires plus ran sea foam in tank and down TBI. Also Techron thru the tank. Advise, thanks, norv.
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[ChevyTech]

The most common problem that causes flooding is the coolant temp sensor.

Check out the testing info in my posts in these two threads.

http://67-72chevytrucks.com/vboard/s...d.php?t=379142

http://67-72chevytrucks.com/vboard/s...d.php?t=322811

[norv struckman]

Originally Posted by ChevyTech

The most common problem that causes flooding is the coolant temp sensor.

Check out the testing info in my posts in these two threads.

http://67-72chevytrucks.com/vboard/s...d.php?t=379142

http://67-72chevytrucks.com/vboard/s...d.php?t=322811

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[special-K]

So that sensor would be a common cause of running rich? I suspect my '95 Suburban is running rich.

[ChevyTech]

Originally Posted by special-K

So that sensor would be a common cause of running rich? I suspect my '95 Suburban is running rich.

Yes

The OBD1 systems are very unlikely to set a coolant sensor code unless the reading is off the end of the possible range.

1995 is still an OBD1

[1976gmc20]

Originally Posted by special-K

So that sensor would be a common cause of running rich? I suspect my '95 Suburban is running rich.

Never thought about it before, but it makes sense.

It's the EFI equivalent of the choke being stuck closed.

[special-K]

How about backfiring when deccelerating, letting off at hiway speed? I have done nothing yet about the rich fuel and now when I back off, at say 70 or so, it will backfire as if I cut the ignition and cut it back on while in gear. Same thing coasting down a steeper hill. I doubt the spark is cutting out and on, seems like maybe raw gas fumes accumulating, but I really don't know. Any thoughts by someone who knows the system?

[kwmech]

Check the vac hose to the MAP sensor. If it is leaking or collapsed it will also create the similar issue

[special-K]

Great. Simple enough. I'll check that. Now that mine needs service maybe I'll learn something. It's my second 350 TBI truck and the other was the '90 Blazer I bought new and put 190k on before selling. Never skipped a beat!

[ChevyTech]

Originally Posted by special-K

How about backfiring when deccelerating, letting off at hiway speed? I have done nothing yet about the rich fuel and now when I back off, at say 70 or so, it will backfire as if I cut the ignition and cut it back on while in gear. Same thing coasting down a steeper hill. I doubt the spark is cutting out and on, seems like maybe raw gas fumes accumulating, but I really don't know. Any thoughts by someone who knows the system?

When decelerating several things come into play

As stated, the MAP sensor should send a high vacuum signal the the computer. This leans out the mixture.

The TPS (throttle position sensor) should show the computer that the throttle is closed and if the computer sees this at high speed then the computer should have the IAC (Idle air control) opening as the engine slows down to act like the dash-pot did on old carbureted engines. The P/N (park / neutral) switch must show the transmission is in gear if the vehicle has an automatic transmission for the IAC the aid in deceleration.

So is short here are a few of the possible causes:
Map (Manifold absolute pressure) sensor
TPS (Throttle Positions sensor)
IAC (Idle Air control)
P/N (Park/Neutral) switch

Somebody experienced with a scan tool can start ruling out potential causes in a few minute.

[special-K]

I'll have to borrow my OBD 1 scan tool back. Thanks for giving me a way to go.