[iPODFAN11]

Normal. LV3, L83, L86, LT1 and LT4 are on the engine list for this PI (all those are Gen V small block engines).

#PIP5179B: Extended Crank Cold With DI (Direct Injected) Engines

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern

DI (Direct Injected) Engines with concerns of extended or long crank time during cold ambient airtemps

Recommendation/Instructions

Direct Injection engines may have slightly longer cold crank times than that of port fuel engines.

Direct Injection systems run at higher pressures, and the mechanical pump on the engine must buildup the required pressure before the first injection event occurs.

The below are typical Direct Injection engine crank times on GASOLINE

Start up Coolant Temperature Crank Time

Above 10° C up to 1.5 sec

Between 10°c (50F) and (- 10°c 14F) up to 2.5 sec

Between (-10°c 14F) and (-20°c -4F) up to 3.5 sec

Between (-20°c -4F) and (-25°c -13F) up to 5 sec

Between (-25°c -13F) and (-30°c -22F) up to 7 sec

Below -30 deg. C -22F, the recommendation is to perform an assisted start (such as use of a blockheater).

Note: For ETHANOL fuel see #PIP5174: Extended Engine Crank Times When Using E85

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

[ChevyRules]

If the LT4 is like the LT1, the high pressure fuel pump needed to build the fuel pressure to the levels needed for DI is driven by the camshaft. Where most other HPFP for DI engines are electric. Since the pump is mechanically driven, needs a few seconds to turn over to build that pressure before light off.

[Ryephile]

^^^it's a nice official sounding excuse, just keep in mind that no other OEM has long-crank issues that's related to DI.

A datalog of the rail pressure, and ultimately injector pulsewidth, would prove this.

[Kanine]

Mine does the exact same thing. I think its normal, although I did think it was odd initially as well.

[Blown67]

There's like a million posts on this apparently as I was told to use the search when I posted the same thing about mine a couple months ago. It's normal on the first start of the day or if the car completely cools down between drives. Mine does it every time, sounds just like mlee's video. That first hit is always the loudest and I usually forget that I'm in an apartment with the valves in track mode. Has to do with the high pressure pump being run off the cam, or so I've read from research.

[ChevyRules]

Originally Posted by Ryephile

^^^it's a nice official sounding excuse, just keep in mind that no other OEM has long-crank issues that's related to DI.

A datalog of the rail pressure, and ultimately injector pulsewidth, would prove this.

And as I mentioned, other DI engines use an electrically driven high pressure fuel pump so the pump is up to speed the moment you press the button. The engine has to be turning in order for the Gen V small blocks high pressure fuel pump to work.

Not sure how that is hard to understand. It's not a DI issue as others tend to say, but how GM decided to power the high pressure fuel pump that is needed for DI for the Small Blocks.

[mlee]

Originally Posted by Blown67

There's like a million posts on this apparently as I was told to use the search when I posted the same thing about mine a couple months ago. It's normal on the first start of the day or if the car completely cools down between drives. Mine does it every time, sounds just like mlee's video. That first hit is always the loudest and I usually forget that I'm in an apartment with the valves in track mode. Has to do with the high pressure pump being run off the cam, or so I've read from research.

^^^This... I just went out and did my 1st cold start of the day.

Same as in the video.

And really sorry someone told you to search. That's not the way we operate here.

[1967RS327]

Originally Posted by Ryephile

The long crank times has nothing to do with DI or push-button in general, otherwise every other DI and push button on the market would have the same "issue".

My hunch is it's priming the oil system prior to actually going into the crank fueling state. The crank times appear to be coolant and/or oil temp related. A warm LT1/LT4 engine fires much quicker than a cold one, and that's all in the calibration.

Until I do a datalog to prove or disprove this theory. You can rest assured however it's not a rule of thumb issue for DI or push button. This is a very intentional calibration by GM.

This is my theory also..

[Hammerli]

Originally Posted by ChevyRules

And as I mentioned, other DI engines use an electrically driven high pressure fuel pump so the pump is up to speed the moment you press the button. The engine has to be turning in order for the Gen V small blocks high pressure fuel pump to work.

Not sure how that is hard to understand. It's not a DI issue as others tend to say, but how GM decided to power the high pressure fuel pump that is needed for DI for the Small Blocks.

I appreciate this thread, was wondering if the long start times I experience were an issue. Interesting on their pump choice. In my 911 when I walk up to car in my garage, even before I touch the car I hear the whine of the fuel pump, the proximity key must trigger it, so is there a reason for the cam driven fuel pump in the LT4?

[ChevyRules]

Originally Posted by Hammerli

I appreciate this thread, was wondering if the long start times I experience were an issue. Interesting on their pump choice. In my 911 when I walk up to car in my garage, even before I touch the car I hear the whine of the fuel pump, the proximity key must trigger it, so is there a reason for the cam driven fuel pump in the LT4?

Not sure if you're hearing the high pressure fuel pump or the normal fuel pump that is in the fuel tank.

As for why GM chose a mechanically driven pump vs electric, going to have to ask them. I believe GM uses electrically driven HPFP's for their other DI engines( the LFX in my dads ATS starts right up).

[mkorgan]

Just so everyone know, my response was what I was told when I picked up my Gen6 ZL1 from the dealer. It has an extended cranking scenario (took longer to crank than my Gen5) to which I asked the mechanic in the shop to review. The mechanic who was their main guy for the Vette's said it was normal for the LT4 to take a bit longer to crank due to the fuel system pressure needing to build to support the DI. This is not me or my opinion, this is what I was told by the dealer.

[Ryephile]

Originally Posted by ChevyRules

And as I mentioned, other DI engines use an electrically driven high pressure fuel pump so the pump is up to speed the moment you press the button. The engine has to be turning in order for the Gen V small blocks high pressure fuel pump to work.

Not sure how that is hard to understand. It's not a DI issue as others tend to say, but how GM decided to power the high pressure fuel pump that is needed for DI for the Small Blocks.

I'm sorry but you're mistaken. Every OEM GDI HPFP I'm aware of is mechanically driven, usually off a camshaft. Feel free to link me to an electric HPFP, but what you're probably thinking of is the low pressure pump in the fuel tank, those are always electric.

I do agree this "issue" doesn't make sense to be DI related, but a conscious GM calibration decision. Have you done any datalogging to observe the lack of injector pulsewidth during cranking?

[ChevyRules]

Originally Posted by Ryephile

I'm sorry but you're mistaken. Every OEM GDI HPFP I'm aware of is mechanically driven, usually off a camshaft. Feel free to link me to an electric HPFP, but what you're probably thinking of is the low pressure pump in the fuel tank, those are always electric.

I do agree this "issue" doesn't make sense to be DI related, but a conscious GM calibration decision. Have you done any datalogging to observe the lack of injector pulsewidth during cranking?

Yep, you're right. My bad. Yeah the ones I found are also mechanical including the LFX's pump and as mentioned, it starts right up in my dads ATS.

So interesting...... Either way it's normal operation for these engines. Nothing wrong.

[Ryephile]

Ok cool.

The only reason from a calibration side I would allow for long crank is to prime the oiling system.

If someone can datalog rail pressure and injector pulsewidth during cranking, that would put a lid on the situation really quick. I'm away right now so it'll be a bit before I can get back to my car and datalog it myself.