Delayed Starting and Fuel Smell After Engine Shutdown in 2008 Trucks with 5.7 Engines: Causes and Diagnosis

When a truck starts acting up, it has a way of making everyone second-guess themselves–owners and techs included. On a 2008 truck with the 5.7, a long crank after a short sit (say, you run into a store for 10–20 minutes), paired with a strong gasoline smell out of the exhaust once it finally fires, is one of those maddening problems that *feels* like it should be simple… but rarely is. And it’s even more frustrating when you’ve already thrown real parts at it–injectors, a fuel pressure regulator, even a fuel pump–and the issue still hangs around.

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What’s supposed to happen (when everything is healthy)

Here’s the basic idea: when you turn the key on, the fuel pump primes the system and builds pressure in the fuel rail. The injectors then spray a measured amount of fuel, the engine lights off, and life is good.

After you shut the engine down, the system is still supposed to hold pressure for a while. Not forever–but long enough that the next restart doesn’t feel like the truck has to “relearn” how to get fuel again. If that pressure bleeds off too quickly, the next start often turns into an extended crank because the system has to rebuild pressure before the engine can run normally.

Now add the fuel smell from the exhaust. That usually means the engine is getting *too much fuel* during that restart (flooding/rich condition), or raw fuel vapors are ending up where they shouldn’t. Either way, it’s a clue worth taking seriously.

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What usually causes this in the real world

A few common troublemakers can produce this exact combo of symptoms:

• Fuel pressure bleeding down after shutdown

This can happen from a leaking injector, a seep at the fuel rail, a check valve issue in the pump, or a leak somewhere in the supply line. Even if the injectors are new, that doesn’t automatically clear them–parts can fail out of the box, and installation issues happen.

• A small EVAP leak (especially with a P0456)

That P0456 code points to the EVAP system–the stuff designed to trap fuel vapors and keep them from venting into the atmosphere. A tiny leak can be as simple as a weak gas cap seal, a cracked hose, or a valve that isn’t sealing like it should. And yes, EVAP problems can make the truck smell like fuel even when nothing is visibly dripping.

• Temperature and “hot soak” effects

After shutdown, heat from the engine can cause fuel to vaporize more aggressively. If the EVAP system can’t manage those vapors properly–or if fuel pressure is doing something it shouldn’t–you’ll notice it most during that short sit window.

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How a good technician typically attacks it

This isn’t a “guess and replace” situation. The clean way to approach it is step-by-step:

1. Look and sniff first (seriously)

A careful visual inspection around the injectors, fuel rail, and lines can reveal damp spots, staining, or that unmistakable fresh-fuel smell.

1. Do a fuel pressure test–then watch what happens after shutdown

It’s not just about hitting the correct pressure while running. The key is: *does it hold?* If pressure falls off fast, you’ve got a direction to chase.

1. Treat the P0456 like a real lead, not background noise

A smoke test on the EVAP system is often the quickest way to stop guessing. It can expose tiny leaks you’ll never find by eyeballing hoses.

The important part is understanding that fuel delivery and EVAP vapor control are separate systems–but they can absolutely “stack” symptoms and make the whole situation feel more confusing than it really is.

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Where people go wrong (and waste money)

Two big traps show up all the time:

• Assuming hard starts automatically mean bad injectors or a bad pump

They’re common causes, sure–but without pressure testing, it’s still a gamble.

• Treating the gas smell as “definitely a fuel leak”

Sometimes it is. Other times it’s EVAP vapors escaping because the system can’t seal properly. The smell is real either way, but the fix may be totally different.

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Tools and parts that usually come into play

To diagnose this correctly, you’ll typically see:

• A scan tool (for codes and EVAP monitoring)
• A fuel pressure gauge (and ideally a way to check leak-down over time)
• An EVAP smoke machine (the gold standard for finding small leaks)

And depending on what the tests show, repairs might involve EVAP hoses, a gas cap, purge/vent valves, or addressing fuel pressure bleed-down causes.

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Practical takeaway

That mix of “long crank after a short sit” plus “gas smell from the exhaust,” especially with a P0456, usually means you’re dealing with *pressure loss, vapor control problems, or both*. Replacing injectors, pumps, and regulators can help–but without confirming what the system is doing after shutdown, it’s easy to keep swapping parts and never truly fix it.

The smartest next move is simple: test fuel pressure (including leak-down) and smoke-test the EVAP system. Once you know which system is actually misbehaving, the repair becomes targeted–and the problem finally stops coming back.