Delayed Crank

[mpope2]

Good morning all,
I’m having a little issue with my Sierra that I can not run down for the life of me. It has a delayed crank. For a while it was 2-3 key cycles before she would hit, and now it’s like 3-5 cycles even with pause after turning switch on. It’s like there is an immediate residual prime issue. If it sits for a day or so, it will crank immediately first try. If it’s hot, it’s a PITA to crank.

Here are the truck specs. 2000 GMC Sierra Z71 with 6.0 LQ9 swap. Truck still has T code 5.3 injectors and the swap was done appx 5 years ago. The delayed crank issue began after it was down for a bit last year with a head gasket leak. Along with reman 317 heads, it got new lifters, pushrods, gaskets all the way up. From the time it went back together, the delayed crank has been there and wasn’t previously. The delayed crank was happening with the same fuel pump, pressure regulator combo that had been in it for years prior. Even prior to the 6.0 going in with zero issues after.

My initial thought was a vacuum leak between the intake and pressure regulator or check valve failure in pump. Most components as mentioned were original to truck for years prior. At that point I decided to throw the book at it. I replaced the fuel rails(OE), injectors(aftermarket), pressure regulator(OE), vacuum line to intake from regulator(OE), filter(WIX), and pump(OE). Still exact result as with all the old stuff on there. As mentioned, cold start it hits immediately. Can’t wait to crank actually. While running, there are zero driveability issues. No CEL on dash. Nothing. You stop it to get gas, and royal pain in the a$$ to start. Does anyone have a suggestion?

 

[Fless]

To be sure we understand, it cranks (turns over) right away but doesn't fire? Or is it struggling to turn over?

 

[exp500]

You're Gonna need to put a fuel pressure gauge on it. And you probably have codes too.
Post fuel pressure key on engine off, and how long it holds till below 45. Then start it and give idle pressure, next see if it bounces around while driving. Scanner look for fuel trims and misfires per cylinder.

 

[mpope2]

From dead cold, cranks starts immediately. After that there is a delayed crank issue until cold again. Delayed crank meaning turning switch it turns over but does not start until 4-5 key cycles. Once it’s hot it will still eventually start after the 4-5 key cycles/attempts. Once started it runs fine no matter if started cold or warm.

The issue has been present with old/original fuel pump and fuel pressure regulator, aftermarket standard pressure regulator and aftermarket precision pump, and with new Delco pressure regulator and pump. Three different pump and regulator combinations have yielded the same delayed crank issue. There are no stored or current codes. Once the truck starts cold, or after you finally get it to start warm it runs very well. No driveability issues at all. I plan to put a gauge on it this week and make note of some different PSI numbers. Hopefully it will tell me something I don’t already know. I wasn’t sure if it was one of those duh moments and I’m missing something blatantly obvious.

 

[mpope2]

From dead cold, cranks starts immediately. After that there is a delayed crank issue until cold again. Delayed crank meaning turning switch it turns over but does not start until 4-5 key cycles. Once it’s hot it will still eventually start after the 4-5 key cycles/attempts. Once started it runs fine no matter if started cold or warm.

The issue has been present with old/original fuel pump and fuel pressure regulator, aftermarket standard pressure regulator and aftermarket precision pump, and with new Delco pressure regulator and pump. Three different pump and regulator combinations have yielded the same delayed crank issue. There are no stored or current codes. Once the truck starts cold, or after you finally get it to start warm it runs very well. No driveability issues at all. I plan to put a gauge on it this week and make note of some different PSI numbers. Hopefully it will tell me something I don’t already know. I wasn’t sure if it was one of those duh moments and I’m missing something blatantly obvious.

 

[mpope2]

I think I’m going to try and get my hands on a smoke machine this week as well.

 

[ks03]

When it first starts to run does it have a misfire for a few seconds after running on its own?

When you’re expecting a long crank, try holding the throttle wide open for the clear flood function, do one long crank, and then try to start normally for the 2nd attempt.

whether it’s fuel, fuel vapor, oil, oil vapor, coolant in a cylinder or 2 or in the intake, hopefully it clears it out. If it still is taking 3-5 attempts then look elsewhere, but this may narrow down the issue to look for

 

[mpope2]

When it first starts to run does it have a misfire for a few seconds after running on its own?

When you’re expecting a long crank, try holding the throttle wide open for the clear flood function, do one long crank, and then try to start normally for the 2nd attempt.

whether it’s fuel, fuel vapor, oil, oil vapor, coolant in a cylinder or 2 or in the intake, hopefully it clears it out. If it still is taking 3-5 attempts then look elsewhere, but this may narrow down the issue to look for

It doesn’t seem to misfire or stumble once started. It hasn’t triggered a P0300 or any other particular cylinder misfire code, I’m not certain what the misfire counts are and if there is variance from one bank to next. I’m going to try and get a scanner on it and also see ST/LT trims

I’ll try holding it open like you said when it happens and see

 

[Fless]

I'd probably call it "extended" crank, since it does crank right away, it just doesn't fire.

As @exp500 suggested, do some fuel pressure tests to see if the pressure is correct, and if it's leaking down. One thing that can cause leakdown is a bad injector, one that stays open and dumps fuel into the cylinder, causing flooding. Not saying that's it, just a potential cause.

 

[mpope2]

I'd probably call it "extended" crank, since it does crank right away, it just doesn't fire.

As @exp500 suggested, do some fuel pressure tests to see if the pressure is correct, and if it's leaking down. One thing that can cause leakdown is a bad injector, one that stays open and dumps fuel into the cylinder, causing flooding. Not saying that's it, just a potential cause.

Thanks for the suggestions. I’m going to pick up a pressure gauge tomorrow and make note of readings. The extended crank term is also applicable and probably more accurate one to use