5.7 Vortec won't crank cold, exhaust smells rich

[redfishsc]

1999 Suburban 5.7. 250k miles

After a flawless 2,000 mile drive the week of Thanksgiving, now she doesn't want to start when cold. {EDIT: FOR CLARITY: Engine cranks over, but seems to get no combustion until 10-20 seconds of cranking. Then it spits, misfires, and knocks for a brief while, then suddenly runs perfectly.}

When warm, starts great, runs flawless.

Starter itself works fine.

Exhaust always smells rich. I've owned other 5.7 Vortecs that didn't smell this strong. Not quite "raw gas" but still smells strong to me.

It has seemed strong to me for a year or two, so maybe this isn't directly related to the non-start.

Injectors are upgraded MPFI, replaced when i redid the cylinder heads a few years ago (all stock)

Fuel pressure... 55psi with key on, engine off. Once running, it's 50 psi.

Fuel filter is probably 4 years old and WILL be replaced soon but I'm suspicious that this could be the issue since it runs great at wide open throttle.

The only engine code is EVAP. I don't smell raw gas around the truck.

O2 sensor front bank, both report an average of 0.7v once engine warmed.

Coolant temperature sensor (OBD2) is giving accurate readings (can read via torque pro app) and matches what's reported on the dashboard by the other sensor.

I'll report back later what the fuel pressure does after sitting for a while.

If I end up replacing the fuel pump, is there an additional sock filter I should be buying?

 

[Schurkey]

I don't understand how it "won't crank" but "the starter itself works fine".

There are two possibilities:
CRANKS but won't START, or
WON'T CRANK

You need to explain which is actually happening.

 

[stutaeng]

Probably a crank-no-start based on what was described.

55 psi with key on engine off should not be a problem for the MPFI. I'm guessing the fuel pressure regulator also changed?

You can try pinching the flexible return fuel hose down under the truck near the transmission to see how much pressure your pump can deliver. They make some pliers for doing this.

When I was messing with my truck thinking my fuel pressure was too low, I capped the return hose temporarily and pressure shot up to like 70 psi, so I knew it wasn't my pump.

 

[redfishsc]

I don't understand how it "won't crank" but "the starter itself works fine".

There are two possibilities:
CRANKS but won't START, or
WON'T CRANK

You need to explain which is actually happening.

Yeah sorry for the lack of clarity. Cranks, won't start.

It will spit, sputter, and stumble for about 10 seconds when it finally does start

 

[redfishsc]

Also, no I didn't install a new fuel pressure regulator when I did the cylinder heads and injectors. Heaven only knows how old it is

 

[stutaeng]

Yeah sorry for the lack of clarity. Cranks, won't start.

It will spit, sputter, and stumble for about 10 seconds when it finally does start

So the truck does manage to fire then? I thought it would crank, but not fire...

Do you have the service engine soon light on? How cold is it when it happens? Only in the mornings it does this? Or time of day doesn't matter? Is your weather damp or humid?

 

[redfishsc]

So the truck does manage to fire then? I thought it would crank, but not fire...

Do you have the service engine soon light on? How cold is it when it happens? Only in the mornings it does this? Or time of day doesn't matter? Is your weather damp or humid?

Yes, obviously I posted this too close to bedtime last night. I just realized how vague my post was so I edited it. Engine cranks over, but seems to get no combustion until 10-20 seconds of cranking. Then it spits, misfires, and knocks for a brief while, then suddenly runs perfectly.

Engine light doesn't work. The only OBD code showing on a scanner is EVAP.

Temperature has varied from 40f to 80f, so definitely not icy weather.

Does this after sitting for a day or so. Seems like it's always easy to start as long as she's been started successfully once that day.

Weather here is mostly humid but average 50-80q humidity, certainly not more humid than usual

 

[stutaeng]

Ok, thanks for the clarification.

Does your fuel pressure hold with key on engine off? Should only drop a few psi after 10-15 minutes. If it falls more, your FPR is probably leaking and that floods the engine when you try to start it.

Another thing to try is putting a hair blow drier pointed to your distributor cap. Let it run for about 15-20 minutes. If it fires right up after that, it's likely moisture inside the cap.

50-80% relative humidity is pretty humid...

Cranking with gas pedal fully pressed I think cuts fuel to the fuel injectors. Try that, it may help trying to get it to start faster if it is in fact flooded.

I hope this helped.

Good luck!

 

[redfishsc]

Ok, thanks for the clarification.

Does your fuel pressure hold with key on engine off? Should only drop a few psi after 10-15 minutes. If it falls more, your FPR is probably leaking and that floods the engine when you try to start it.

Another thing to try is putting a hair blow drier pointed to your distributor cap. Let it run for about 15-20 minutes. If it fires right up after that, it's likely moisture inside the cap.

50-80% relative humidity is pretty humid...

Cranking with gas pedal fully pressed I think cuts fuel to the fuel injectors. Try that, it may help trying to get it to start faster if it is in fact flooded.

I hope this helped.

Good luck!

Hmm. I hadn't thought about the fuel leaking INTO the intake via the regulator and flooding it. I was thinking maybe the fuel was draining back into the gas tank and it had a lot of air in the fuel line to burp out. Thank you for that tip.

So, yes the fuel pressure drops a little after turning off the engine, down to maybe 50 psi in a few minutes.

Overnight it dropped to nearly 0. I didn't try to start it this morning because I was on a tight schedule (and the Sub isn't my daily driver for now) but I suspect you're on the right track, the FRP probably has flooded the intake.

I'll probably just replace the FPR soon, it's pretty easy compared to a cylinder head job, I think I still have an upper intake gasket sitting around too.

 

[redfishsc]

For what it's worth, the Fuel Pressure Regulator has to be somewhat recent. When I installed the new MPFI injectors a couple years ago it should have come with a new FPR.

Well since I've noticed it smelling kinda like it's running rich, maybe the FPR is malfunctioning. It's not throwing "running rich" codes so maybe it's not a giant leak (yet).

I'll get a new FPR ordered soon. I hate that they buried it under the upper half of the intake but at least I don't have to remove a f'n wheel just to do an oil change or rip out the back seat to replace a battery