05 Silverado 5.3L Hesitation at first start & Fuel Pressure question

[relentless85]

A few months ago I replaced my fuel pump with a new AC Delco fuel pump in my 2005 Silverado 5.3.  I replaced the fuel pump because I was having the symptom of turning the key and the engine not starting on the first try.  I had to "prime" the system by turning the key a few times then the engine would start like "normal".

 

After replacing the fuel pump, the engine now starts on the first crank but I am getting a hesitation on only the first start up after the engine has been sitting overnight.  If i were to shut the engine off immediately after the first start, I could crank the engine over again and it would start with no hesitation.

 

I connected a mechanical fuel gauge to the port on the passenger side of the engine and here are the results:

 

- Key on engine off 64 PSI then slowly drops.

-  Engine on at idle steady 64 PSI

- Engine off right after idle drops to 58 PSI

-Engine off key off for after 2 hours drops to 30 PSI

- Engine off key off overnight 18 PSI

 

The MAF and Throttle Body has been cleaned with CRC cleaner.  Last night i went trough and sprayed carb cleaner on the vacuum hoses I could see and I did not get a fluctuation in idle, so i don't think I have any vacuum leaks.

 

Since my truck is an 05, I don't believe it has a fuel pressure regulator or an idle air control valve.

 

The coolant temp sensor in the driver side of the block has been replaced too, I need to OHM that out to verify it is working correctly.

 

My question is:

 

A) What else do I need to be looking for that will cause the hesitation only on the first start up?  Is there a way to test the MAF or throttle body with a multimeter?

 

B)  is the fuel pressure supposed to bleed off like that, or is it supposed to hold the higher pressure all of the time? Or am I worrying about nothing with the fuel pressure bleeding off?

 

Edited July 23, 2020 by relentless85

[davester]

The pressure can bleed off over time.  GM just specs it to hold for a relatively short time (10 or 15 minutes with a small drop).

 

[Area51]

I had a similar issue with the starting and replaced thr battery...it was better, but not fixed. I've also replaced the ECT sensor at least once. On vacation, I had to replace the ECT sensor and thermostat again, and all they had in stock was the "premium" AC Delco brand. Popped it in, and the truck starts fine now, and idles a bit higher when cool like it should.

[Colossus]

Both the fuel sending module (including filter) as well as the fuel pressure regulator were known issues in earlier model GMT-800s most notably the 99-03s.  But I wouldn't be surprised if the FPR is bad on your truck as well.  Once the FPR is replaced, it might be worth doing a pressure down test. 

[sefiroxx]

Get a good scanner and check the loop and sensor readings. Truck may be getting wrong sensor data.