08 Silverado 5.3 cold start exhaust smoke and engine stall

Question

For some time now I've been getting a considerable amount of dark smoke from my tailpipe on cold starts which I believe to be an oil burning issue. I have an oil consumption test in progress, so far it seems to be about a quart every 1k miles.

Typically in the morning the engine starts fine, but then immediately sounds like it is struggling to stay running. This is when the smoke starts coming out of the tailpipe. Usually the engine and smoke clear up after 10 seconds or so. This morning, however, the engine completely stalled during this ignition phase. This has never happened before.

There is no engine light and everything runs fine otherwise. I have a clean MAF, clean throttle body, brand new spark plugs and cables, and several bottles of techron through the tank for the injectors within the past few months. Mileage is about 81k.

Any ideas?

Answer 1

Oil consumption in the LM7 engines is pretty common. The L33 in my '06 Silverado is around the same amount, maybe a little less. What you are talking about sounds more like a stuck/leaky injector. Oil smoke will usually last longer than 10 seconds, if that were the issue. And it would be distinctly blue, not black/dark.

The way you could tell if this was the issue is to put a fuel pressure gauge on the fuel rail. Ensure the fuel pressure is good (I don't remember off the top of my head, but believe it should be in the 53-60psi range). Then, shut the engine off and allow the vehicle to sit overnight with the fuel gauge on it. If there's no leak, you should get a minimal amount of fuel pressure loss ... maybe 10-15psi, but if there is a leak, you'll get a much more dramatic drop or all of it for that matter. This doesn't mean it is specifically a fuel injector leak. It could also mean that the fuel pump anti-drain back isn't working right, but if the anti-drain back weren't working right, it wouldn't start up as easily as you describe.