Intermittent hard start

[Sanitarian544]

I have a 97 5.7 C1500. The shop has replaced the starter twice and it doesn’t fix it. It always starts perfect first thing in the cold morning from then on it generally cranks a while to start but not always. I can let it sit at work for 10 hours and it still maybe hard to start but first thing in the morning,perfect start. I have replaced the fuel filter and the fuel pressure appears to be in spec. I hat to just start changing parts. I hope anyone has ideas. Thanks

 

[HotWheelsBurban]

97 so it's a vortec. Here's what I did with my 99 Burb, 5.7 vortec C1500. It was doing something similar.
Check out your battery cables; these trucks are prone to having corrosion down in the cable where you can't see it. I cleaned the negative cable and the shorter positive cable. I replaced the longer positive cable as it had corrosion down inside it. Also check the grounds ( there's a lot of them) and the terminals to be sure they're clean and tight. My truck had a loose terminal on the solenoid. I tightened it up and cleaned everything ( the starter was oily and grungy).
These trucks are very picky about good connections and grounds. If my battery cable bolts are just a quarter turn loose, it acts like it doesn't want to start. And my battery, starter and alternator are all good.
And the starter grounds through the block mounting surface, so be sure that is clean too.
How old is the battery? I used to see a lot of battery and charging/starting system problems when the weather changes, back in my auto parts store days. Cars have gotten muck more complex in 30 years, but if an electrical system has a problem, it'll show up when the outside temperature or humidity changes a lot. If something is marginal, that'll make it act up.
After you check all this out,there's other things to look at too. Is the crankshaft position sensor connection good? The sensor doesn't last forever, and it may be going out. A bad coil or ignition module can also cause a hard start. Also look at the cap and rotor. If they're worn, it takes a little more to get everything going, because the spark is having to jump further.

 

[stutaeng]

So it cranks over just fine, but doesn't fire?

And it always fires ok on first attempt, but doesn't fire after subsequent attempts?

In other words, cranks but sometimes doesn't fire on warm engine?

I'd check fuel pressure regulator and spider injectors. Sometimes they stick open when engine warms up and leak and flood the engine...

 

[Sanitarian544]

Thanks I’m going to check my ground cables but I’m leaning towards a crankshaft position sensor. I just hated to throw money and time at it and it not work.

 

[stutaeng]

https://troubleshootmyvehicle.com/gm/4.3L-5.0L-5.7L/how-to-test-the-crank-sensor-1

 

[Schurkey]

Cranks and starts fine cold.
Cranks but doesn't start warm.

My '97 7.4L does the same thing. I'm told that this is a common symptom of leaky injectors. If the engine sits long enough for the gasoline to evaporate or run down the rings, it starts fine. Otherwise, it's flooded.

I have zero plans to dick with the injectors on mine; so I'm adding Techron to the fuel now and then to hopefully clean the injectors. If that doesn't fix it over the next year or so, I may play with the injectors...later.

 

[stutaeng]

Cranks and starts fine cold.
Cranks but doesn't start warm.

My '97 7.4L does the same thing. I'm told that this is a common symptom of leaky injectors. If the engine sits long enough for the gasoline to evaporate or run down the rings, it starts fine. Otherwise, it's flooded.

I have zero plans to dick with the injectors on mine; so I'm adding Techron to the fuel now and then to hopefully clean the injectors. If that doesn't fix it over the next year or so, I may play with the injectors...later.

I've read if the injectors are stuck wide open it could possibly dump enough fuel to hydrolock the cylinder? If you crank on this condition you can get a bent rod?
I don't know. But I always try to have that in the back of my mind if a gross amount of fuel is going "somewhere." I.e., fuel pressure drop is instantenous?

Edit: not saying you have this condition, just saying to be aware this could be a possibility.

 

[east302]

So it cranks over just fine, but doesn't fire?

And it always fires ok on first attempt, but doesn't fire after subsequent attempts?

In other words, cranks but sometimes doesn't fire on warm engine?

I'd check fuel pressure regulator and spider injectors. Sometimes they stick open when engine warms up and leak and flood the engine...

I’d agree with the above and check the fuel pressure to see how fast it leaks down. There are ways to isolate the supply and return lines to get a definitive answer if that’s the case.

If you have a scanner, also check the coolant temperature sensor (ECT sensor) reading when cold and warm. It should be close to the thermostat setpoint (190 or so) when warm. If not and it’s reading negative 40 degrees or some strange number, the computer will call for too much fuel and flood it out.

Holding the gas to the floor while starting is a workaround as it temporarily stops injector flow but will still yield a pretty lousy start up. Try doing that next time and see if it it helps.


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[someotherguy]

Sounds like we're not effectively communicating what the description of the hard start is, if you're replacing starters and being concerned about fuel pressure in the same post. Those would be two totally different sets of symptoms.

If the hard start is the starter turns slowly and sounds like a weak battery, then I would be looking at the starting/charging system.

If the hard start is the starter turns at normal speed but the engine just doesn't want to fire, then you're concerned with fuel pressure/fuel system/possible spark issues (but more than likely fuel issues.)

Especially since you're a small block Vortec - if it's spinning over normal, the problem is likely marginal fuel pressure. It only takes them getting a few psi low and the poppet valves on the spider don't like to open. It's a crappy setup.

Richard