Crank No Start After Driving

[jrdecat]

Hooked up a noid light to the injector harness and spark tester. I have both spark and injector pulse. I'll pick up a fuel pressure gauge later today and start logging fuel pressure readings.

Any other ideas now that I've ruled out injectors not firing or no spark?

 

[jrdecat]

Ok, so now I have a fuel pressure gauge hooked up to the port on the injector rail. 2 Attempted starts under identical conditions with different results. I had just returned from AutoZone to get the gauge and let the beast sit for about 15 minutes.

1. Turn key on, 50 psi. 179* engine temp, 57* ambient temp. Turn key to crank and it fires right up. Fuel pressure at 42 psi. Let it run for 5-7 sec, turned off, and waited for 10-15 sec.
2. Turn key on, 50 psi, 181* engine temp 58* ambient temp. Turn key to crank and it just cranks and cranks for about 5 sec. Turn key off, crank again and it fires right up.

I'm stumped. I have spark, I have injector pulse, but I guess I can't confirm fuel is getting there.

I have not replaced the MAF sensor, but I cleaned it recently with MAF cleaner. I'm leaning towards the fuel/air mixture. How do I test for that without a super expensive scanner?

Thanks in advance!

 

[jrdecat]

9:53am
Fuel pressure at 0.
Key on and pressure jumps to 50, then down to 48.
Crank engine an it starts with water temp of 48* and air temp of 35*.
Let run about 15-20 sec at 40# fuel press and then turned off.

Waited about 30 sec. Fuel press still at 40.
Key on and pressure jumps to 50, then down to 48, just like before.
Cranked engine for about 4 seconds with no start.
Turned key off, waited 5 seconds, key on (pressure back to 48).
Crank engine and it starts perfectly with water temp at 57* and air temp at 35*

 

[jrdecat]

Fuel pressure varies from 42# when coasting without pressing on go faster pedal to 50# when I get on 'er like a rat on a cheeto. Here's my log from today with conditions.

12:01pm
FP: 40
Water Temp 55*
Air Temp 35*
Successful start on first crank

12:08pm - turned off - had been driving since 12:01pm
Water Temp 190*
Air Temp 31*

12:11pm
FP: 45#
Water: 188*
Air: 49*
No start on first crank, started great on second

12:27m - turned off - had been driving since 12:11pm
Water: 190*
Air: 42*

12:58pm
FP: 46#
Water 165*
Air: 73*
Successful start on first crank

1:06pm - turned off - had been driving since 12:58pm
Water: 190*
Air: 46*

 

[Fless]

I don't necessarily think it's a fuel problem; I'd lean more toward an intermittent electrical issue. Maybe a loose/dirty fuel rail ground or a connector. Just a SWAG.

It looks like you're swapped, but is the original pump for Flex Fuel? Those pressures run lower than non-Flex, but the pumps can push more volume.

KOEO specs for NBS V8 engines:
Non-Flex: 55 to 62 psi
Flex: 48 to 54 psi

Would be interesting to have a noid light on it when it happens.

 

[jrdecat]

I don't necessarily think it's a fuel problem; I'd lean more toward an intermittent electrical issue. Maybe a loose/dirty fuel rail ground or a connector. Just a SWAG.

It looks like you're swapped, but is the original pump for Flex Fuel? Those pressures run lower than non-Flex, but the pumps can push more volume.

KOEO specs for NBS V8 engines:
Non-Flex: 55 to 62 psi
Flex: 48 to 54 psi

Would be interesting to have a noid light on it when it happens.

I did put a noid light on it. I have injector pulse (noid light flashes) and spark from the plug wires while cranking with no start condition. It is the original flex fuel pump and flex injectors which flow at a higher rate. That was taken into account with the tune...or so I'm told.

 

[ivin74]

I don't necessarily think it's a fuel problem; I'd lean more toward an intermittent electrical issue.

I agree w @Fless
You need to check the wiring to the cam and crank sensors.
How many miles are on the current fuel pump? Is this pump spec'ed out for the 6.0?

Food for thought
My suv did something similar to yours several years ago with a 1yr old FP and I could not believe it be the pump again. I got tired of diagnosing and took it to a shop. The shop stated that the pump would run good and after running for a while the pump would get hot and would start messing up. When cold it would start every time. Anyways the shop put a new pump on and it's been running since.

 

[corvette744]

The fuel pressure specs are straight out of GM Service Information online service manuals.

"1999-2003 4.8, 5.3, 6.0 all had a fuel rail with 3/8" supply line and a 5/16" return line. The fuel pressure regulator is on the fuel rail, and has a vacuum line to the intake manifold. In 2004, All engines went to a single 3/8" supply line, with NO RETURN LINE (returnless) except 5.3L L59 Flex Fuel vehicles. For 2004, Flex fuel engines KEPT the return line, BUT used a fuel pressure regulator with a lower pressure ratting. 2005 5.3L L59 Flex Fuel engines switched to a single 3/8" supply with NO RETURN line in 2005. Non flex fuel engines, fuel pressure spec is 55 to 62 psi with vacuum line disconnected, fuel pump running. 5.3L Flex Fuel engine 2004 and back, 48-54 psi with vacuum line disconnected, fuel pump running. 2005+ with returnless fuel rail all shared same fuel pressure spec, 55-62 psi. There is no vacuum reference on these, so fuel pressure should remain constant under all operating conditions. The computer is programmed differently for fuel flow rate depending on type of fuel rail. This is important to know when having a PCM programmed."

 

[jrdecat]

I agree w @Fless
You need to check the wiring to cam and crank sensors.
How many miles are on the current fuel pump? Is this pump spec'ed out for the 6.0?

Food for thought
My suv did something similar to yours several years ago with a 1yr old FP and I could not believe it be the pump again. I got tired of diagnosing and took it to a shop. The shop stated that the pump would run good and after running for a while the pump would get hot and would start messing up. When cold it would start every time. Anyways the shop put a new pump on and it's been running since.

I got the vehicle with 105k and now it has 135k. I have never replaced the pump and don't know about its prior history. She's going into the shop for a new front diff in a couple weeks. I'm just going to have them do a little troubleshooting with their fancy scanner.

 

[jrdecat]

The fuel pressure specs are straight out of GM Service Information online service manuals.

"1999-2003 4.8, 5.3, 6.0 all had a fuel rail with 3/8" supply line and a 5/16" return line. The fuel pressure regulator is on the fuel rail, and has a vacuum line to the intake manifold. In 2004, All engines went to a single 3/8" supply line, with NO RETURN LINE (returnless) except 5.3L L59 Flex Fuel vehicles. For 2004, Flex fuel engines KEPT the return line, BUT used a fuel pressure regulator with a lower pressure ratting. 2005 5.3L L59 Flex Fuel engines switched to a single 3/8" supply with NO RETURN line in 2005. Non flex fuel engines, fuel pressure spec is 55 to 62 psi with vacuum line disconnected, fuel pump running. 5.3L Flex Fuel engine 2004 and back, 48-54 psi with vacuum line disconnected, fuel pump running. 2005+ with returnless fuel rail all shared same fuel pressure spec, 55-62 psi. There is no vacuum reference on these, so fuel pressure should remain constant under all operating conditions. The computer is programmed differently for fuel flow rate depending on type of fuel rail. This is important to know when having a PCM programmed."
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Thank you. I have the flex w/regulator on the rail, so 48-54 w/ vacuum disconnected is the target. Of course, I didn't check with the line disconnected this time around. This is the second time farting around with the fuel pressure gauge and I know I did that last time, and that the pressure jumped up when I disconnected the line but I don't remember the exact number.

Other fun data...I found out that my ancient Scangauge II reports air to fuel ratio. Yesterday when I started it up the AFR was 13.6 and after warming up a few minutes it went to 14.1 and stayed there while driving around. Idling, accelerating, coasting, it didn't matter.