Buick 3800 V6 starts, immediately stalls

2002 Buick Regal LS, 3800 V6, normally aspirated

Symptom:
Starts, dies within a second or two.

If I disconnect the MAF, it will run poorly, with a little throttle applied, but with crazy high fuel trims (39% LTFT). The exhaust manifold has some smoke coming off it in this condition, but I suspect that's because of the poor running condition.

The 18x and 3x CKPS waveforms look good and as expected.

The camshaft position sensor looks good, *I think*, with a pulse every 720 degrees on the middle-width 3X CKPS pulse.

The MAF sensor wire is clean, and outputs a variable frequency square wave, about 300 hz, at key on engine off.

Fuel rail pressure WAS a problem, but replacing the fuel pressure regulator has it holding 52 psi or so for several minutes once primed. Fuel pump was replaced (possibly a part changer move, but I did have a diagnosis on it), and his great pressure at the pump.

If I pull the fuel pump fuse, the engine will crank and not start. Replacing that fuse gets me the start that lasts maybe a second, which to me suggests that fuel injectors are firing at least once.

The front bank of cylinders (one on each coil) show spark on my light-up spark tester. And, it does start for a moment. Three front plugs (easy to get to) looked fine.

This is the first head scratcher I've run into as a DIYer, so I'd love any suggestions to help me in my diagnostic direction.

GeekPriest

just some quick ideas.


Check for an EGR valve that is opening when it should not ( stuck open )
Check system voltage in a few places ( including at the battery ) when the engine dies
Check for fuel pressure loss when the engine dies
Check for ignition loss when the engine dies
Check ignition timing when the engine dies
Check the condition of the plugs and wires ( if it uses a distro )
If not, check the Coil On Plug units for age and wear ( spark could be jumping to ground )

39% fuel trim?? At idle? What’s it do at 2500 rpm? What are the oxygen sensors reading? Front and rear. But I think the other member is right check for a stuck open egr.

Definately check egr and ect, iat and iac as well as see if throttle body is clean. Need to also check fuel pressure while running as well as maf readings as you said with it unplugged it runs but poorly.