350 tbi flooding

[don]

this is a problem i have been working on for months. my truck is a 1987 chevy 4x4 with a 350 with tbi. when the engine is first started it floods bad for about 3 minutes then like turning on a switch it quits flooding and runs great. the truck was doing this when i bought it and i have not been able to fix it. i have had the truck to 3 garages 2 of the garages were dealership garages. they kept the truck over night so they could scan it while it was flooding and all 3 garages said nothing is showing up on the scan tool. this is what i have done to it with no change with the flooding problem.

1.rebuilt engine
2.changed computer 3 times
3.changed chips in the computer
4.changed all sensors several times
5.new distributor,wires, plugs,cap,rotor,coil,module
6.new holley throttle body
7.new fuel tank and pump
8.pulled the engine wire harness out and checked all wires from the ecm plugs to the sensors. all had a circut.

i have ran out of ideas and to the point of changing it to a carb which i dont want to do because the tbi is why i bought an 87 model. the only thing i havnt changed is the engine wire harness but i did check it and didnt see a problem and all sensors are picked up on the scan tool. any ideas would be appreciated. thanks

 

[bucket]

Assuming you changed the coolant temp sensor in the intake manifold? Did the Holley TB come with new injectors?

 

[89Suburban]

Oh Jimmy.....

 

[don]

it came with new injectors and all sensors were replaced several times. also the fuel pressure is 12 lbs.

 

[bucket]

Do the injectors have a good spray pattern on start up? Does it have the problem on a hot restart too?

 

[don]

has a good pattern just too much fuel. after warming up for about 3 minutes it runs and starts very good. the only problem is at start up when engine is cold.

 

[bucket]

So it probably clears up when the ECM goes into closed loop, which from my understanding, is mostly determined by the O2 sensor warming up.

Hopefully Jim has some ideas.

 

[don]

that is what it seems like. i have tried a heated o2 sensor and that didnt help at all.

 

[Jims86]

Hi Don,

1) could you measure the voltage at either the white or red fuel injector wires while the engine is running?
2) Have you checked the fuel return line for blockage?
3) 12 PSI IS within spec, but most run at 10 from the factory.
4) Can you hook up a vacuum gauge and let us know what vacuum it pulling while its warming up?
To your knowledge, is this a stock engine? Cam? Heads?
I know some of you may be thinking, why would those 2 things cause a rich condition on startup only?
Open loop on startup does ignore the o2, and the factory settings command 14.7 fuel ratio, but the ecm doesnt know if its running rich or lean until closed loop, therefor can't lean it out to correct the situation.
It could still be running rich when warm too...just not as bad beacause the ECM is able to thin things out a bit.

 

[don]

the voltage at the red and white wires is 14.6 volts
the vacuum at the intake is jumping between 14 and 16
the holly throttle body has an adjustable fuel pressure regulator. i have had the pressure as low as 8 lbs. it floods less but not enough pressure once it warms up.
the engine is .30 over with new crankshaft, rods and pistons. it has a comp cam made for this engine with tbi. its basically a factory cam. everything else is stock. it had this flooding problem before i rebuilt the engine.

return line is not restricted

 

[Jims86]

the voltage at the red and white wires is 14.6 volts
the vacuum at the intake is jumping between 14 and 16
the holly throttle body has an adjustable fuel pressure regulator. i have had the pressure as low as 8 lbs. it floods less but not enough pressure once it warms up.
the engine is .30 over with new crankshaft, rods and pistons. it has a comp cam made for this engine with tbi. its basically a factory cam. everything else is stock. it had this flooding problem before i rebuilt the engine.

return line is not restricted

Ok, the vacuum is supposed to be steady, and 16 even seems a little low.
You may want to go through and check your valve adjustments...jumping vac could be a mis adjusted valve, and may take care of the flooding issues.
I just dealt with a rich running issue with mine, due to a cam from Comp that is supposed to be TBI TPI safe.
When the vacuum goes low, the map sensor commands more fuel.
And since you are 30over, 12 psi is just fine.

 

[don]

the unsteady vacuum is due to the engine loping from the flooding. vacuum is steady at 17 when the engine warms up.

 

[Jims86]

the unsteady vacuum is due to the engine loping from the flooding. vacuum is steady at 17 when the engine warms up.

Do you have a scan tool, or did it belong to one of the shops?
The speed density system is extremely sensitive to performance upgrades, and I think that a combination of cam, and the overbore are calling for some ECM tuning to be done. Does it smell rich at all once its warmed up?
Also, could you take a look at your ECM, and Tell me what the 4 letter bcc code is?

 

[don]

it is slightly rich when warm. it flooded before the cam was changed. nothing changed after i rebuilt the engine.
i believe the code you are asking for is akaj

 

[Jims86]

How about system grounds? Thermostat housing, engine to Body/Frame?