Solved - Crank No Start, Just Floods

Well at this point I feel like I'm just chasing my tail. (5.7 FF) So my new chapter in this truck is trouble starting. Turns over, get a glug glug here and there like it tries, but ultimately nothing. If I pull plug one it's got fuel all over it of course. Every once in a while after many, many, many... cranks it will finally start, poorly though, I'll have to jab the pedal to rev it up so it doesn't just sit and misfire. When this happens there's a nice puff of smoke from the rear of unburnt fuel and a strong smell of it. Once the truck is running everything is fine, good gas mileage, nothing out of the ordinary.

So, the only code I have is a P0420 on bank 1. I've reset the alc density, and replaced the coolant temp sensor. TB, air filter are clean, fuel pump and filter are new. I'm going to do a smoke test to check vacuum shortly, but I don't think I'll find anything. At this point I'm almost ready to give up on it. Let me know if you have any ideas

 

Have you checked the ALC%?

 

Currently at 0%

 

Ran smoke through the brake booster hose, no leaks found.

I did manage to get it to start. I tripped across someone saying that holding the pedal to the floor sets it to a mode where it closes the injectors, aka clear flood mode. It seemed to allow some of the excess fuel to dissipate enough to get it to chug and I was able to rev it to life after that. Checked the ltft/stft while it was running, fine there with -2to-3 on long and 0.7ish on short

 

About an hour and a half later - needed to run to the store, figured I'd try the truck again. Fired right up. Curious because recently it would only take 20-30 of sitting to become troublesome again. When I was in there earlier checking the fuel trims I looked at the throttle position sensor and noticed it was a hair over the max (idle max I believe) so I did a memory wipe on it hoping it would correct. It only changed by about .5. When I left the store (ony there 10mins or so) it fired right up. Fingers still crossed and breath held. The real test will be tomorrow morning on a cold, overnight sit. I'm hoping that after changing the CTS it needed to be run for the ecu to believe it, not likely but hope floats

 

To my surprise it cranked up this morning with a only a little trouble. Drove it about 25 miles, parked it, came back about 45mins later and it started with the same amount of sputter it did earlier. When it sputtered I just tapped the gas and it smoothed out. No idea what that's about, but I think I'll leave it alone for now and move on to the P0420

 

Do you think it might be a leaky injector dripping when off that floods it while parked?
Could run a bottle of techron or other fuel sytem cleaner just in case if you haven't already.
Wouldn't running rich or otherwise having excess fuel going through muck up cats or o2 sensors possibly causing that code?

 

Not likely, I've pulled all of the plugs at different points and all were wet, so the odds of so many dripping aren't high. I am wondering about the fuel pressure regulator diaphragm though

 

Solved - changed out the upstream and downstream sensors on bank 1, seems to be doing much better

 

Sorry, but this is unlikely the solution. When a car starts from a cold state,it runs in what we call open loop mode. The fuel flow rate is set by the default tables, NOT based on O2 feedback. Once warmed up to a certain point, it goes into closed loop mode, where fuel flow is metered based partially on O2 data feedback. O2 sensor data is not used during startup or the following few seconds or minutes, depending upon temps.

 

That's what I thought about it as well, which is why I posted, because I was a bit baffled. But I don't think it's as black and white as that, although it was on all my 80s and 90s 'Yotas.
I actually had a bit of conversation with @shifty` about it and he convinced me, through no small amount of explanation, that this was the source of my issue.
I can also say that as unlikely as it may seem it must be. Between the time I made this post and now, I have only done three things to the truck - 1) replaced downstream sensor, 2) replaced upstream sensor, 3) left the neg battery cable off for a bit to force a relearn. And now after about 60 miles or so and 4 or 5 cold starts it runs perfectly again, mpg is back up around 16.7 as well.
To be even more specific, I first replaced the downstream sensor and did not force a relearn. I let that go for about 2 days. Starting the truck went from nearly impossible(previously had to use clear flood mode method to get it going) to better than it was but still a big issue. P0420 went off and came back. Then I replaced the upstream sensor and did not force a relearn - I wanted to see how it would react first. First crank it came to life with a little hesitation but quickly smoothed out with no interference from me. I then shut it down and left the battery cable off for about half an hour while I did other things. Came back hooked it up and everything is right as rain now.

 

Struggling to see that as more than coincidence, but happy for you. The upstream replacement makes a lot of sense for the mpg improvements, but not the cold starts. Plug your scanner in and go to live data and fint the closed/open loop settings and observe for yourself as you start the engine . If you do some research, you will see that O2 sensors have heaters and the ecu monitors the temps. The ecu will not even look at O2 data until the sensors get up to temp. And this takes a minute or two. Their output is not reliable when below min temp.

 

I appreciate your input and as I said before I agree, in general terms it shouldn't resolve the issue. However two things stand out - 1) it did resolve the issue, and 2) while the interwebz is full of information and comments about O2 sensors not being able to affect starting, there is a also a lot of information that would suggest otherwise, such as people replacing O2 sensors with cheap parts and encountering starting problems, as well as a host of other scenarios. To really contest the possibility I would suggest disconnecting your O2 sensors on bank 1 and then trying to start your truck. In theory you are correct, but I think the fault may lie more in the readiness, pass/fail checks the ecu runs and what each specific manufacturer lines out as a response to a not ready or fail state.