Intermittent flooding issue--Need help!!!

[Lattimer]

I have a 1994 Blazer, 5.7 TBI, 4l60e, 4x4. 217k. Silverado trim, all stock. Had the truck for a little over 2 years. Its always started well no matter the temperature. Now, I'm suddenly having an intermittent flooding condition on cold start. Happened overnight.

Not necessarily cold weather, but engine cold. Every 3rd or 4th time I go to start the truck it tries to pop off like normal and stalls, then floods. Hold gas pedal to the floor and it will start. Strong gas smell the whole time. If I pull a plug its wet and smells like gas.

Once there truck starts, it runs great and drives great. Smooth idle, no issues. Doesn't burn oil or anything. Gets about 14 mpg running 75-80 on the highway. Restarts perfectly after its been running for a minute.

In the last year or so, the truck has had:
New fuel pump/sender/tank/filter
New MAP sensor
New distributor/coil/plugs/wires
New 02 sensor
complete new exhaust (manifolds to tailpipe)
NewCoolant temp sensor
New thermostat
New radiator/hoses/water pump
New starter/alternator/battery/belt/idler/tensioner


What I have done so far to troubleshoot:

Found leaking injector and leaking fuel pressure regulator. Rebuilt a spare TBI unit with all new parts. New reman injectors, new diaphragm and spring, new TPS, new IAC. No change whatsoever in starting, but no longer have leaks. Driving performance vastly improved. Better throttle response and power.

Checked all the vacuum lines and around TBI base and intake manifold with carb cleaner. Can't find any vacuum leaks.

Checked coolant temp sensor with multi meter per info I googled. Tested fine but I decided to change it anyway, even though it was only about a year old. No change.

Replaced EGR valve and solenoid. Both look original so I figured for GP I'd do those as well. No change.

Changed plugs. AC Delco plugs. No change. Had a couple old ones that looked a little fuel fouled but not bad. They had about 16k on them. No visible electrode wear.

Checked base timing, its at zero degrees with the wire unplugged. Seems to advance properly with the wire plugged in.

I've run out of things I know to troubleshoot. SOMETHING is causing way too much fuel, but not all the time. My last guess is something is wrong with the ECM, but I hate to buy one just to find out that wasn't it either.



Anybody got any guidance? Huge thanks in advance!!!!!

 

[Schurkey]

Connect a scan tool, look at the data stream.

Wouldn't hurt to test fuel pressure, cranking compression of all eight, and verify proper spark with a spark tester calibrated for HEI ignitions.

 

[Lattimer]

Connect a scan tool, look at the data stream.

Wouldn't hurt to test fuel pressure, cranking compression of all eight, and verify proper spark with a spark tester calibrated for HEI ignitions.

I don't have the tools for any of that unfortunately.

 

[PlayingWithTBI]

Connect a scan tool, look at the data stream. Wouldn't hurt to test fuel pressure, cranking compression of all eight, and verify proper spark with a spark tester calibrated for HEI ignitions.

^^^X2, I would also check TPS voltage. Which CTS did you change, the one next to the T-Stat (2-wire feeds the PCM) or the one on the left head between #1 & 3 cylinders (1-wire feeds the gauge)? Did you calibrate the throttle body after changing all that stuff? I would normally say your injectors are leaking but, you fixed that right (when shining a light behind them you see even spray cones and no drips)? How's your fuel pressure after rebuilding the "spare" throttle body?

When you push on the gas pedal, the PCM thinks you're in "flooded Mode" and won't give it any fuel so, another thought is maybe you're losing spark causing your flooded condition? Or maybe poor compression?

TBI tuning-website - Tuning the TBI.pdf

 

[Lattimer]

One of the old injectors would have a tiny drip even with the engine off and the key on. New ones don't do that, and the spray pattern looks very good.
I actually did both temp sensors but I know the one on the head is just for the gauge.

I don't have access to a scan tool, so I'd have to pay a shop to do anything more and I'm obviously trying to avoid that. Not sure if many shops have stuff compatible with OBD1?

I was looking for how to test fuel pressure, but with the TBI design I don't see a way to check after the pressure regulator. I could unhook the supply side and use rubber tube to hook up a gauge there maybe. But I wouldn't think low pressure could cause flooding? I know the regulator is supposed to maintain about 12-13 psi, but what does the pump put out?

The only thing I saw in my repair manual for the throttle body was setting base idle, which I did set up at 500 per the procedure. Once it's running with the computer in control it idles at 1000 in park and about 800 in drive.

I also wouldn't think low compression happens overnight---this literally had never happened with this truck in 2 years, then suddenly started to happen. Truck runs like brand new once its started, and after its runs for a minute or 2 will restart with half a crank. I gotta see if I can borrow a compression tester and check though. I have an absolute shitload of tools but have never needed one of those.