Crank No Start After Driving

[jrdecat]

Well it's time to bring out the big guns (that's you guys). Last year I swapped in an LQ4 into Fat Konnie (Yukon XL). Specs are in my sig. I have a very strange, but not unheard of, starting issue. When I did the swap I put in all new AC Delco sensors on the motor) with the exception of the MAF, which I cleaned with MAF cleaner. One odd thing was that when BlackBear did the tune with the data logging, I was told I needed to clean my throttle body, which I had done prior to putting it back on. I cleaned it again and still have the same problem.

When starting the vehicle from sitting overnight it starts right up about 65-70% of the time. The remaining 30-35% it will just crank and crank if I continue to hold the key down. Yes, I've tried the flood clear procedure to no avail. If I turn the key, let it crank, let off the key, then try again it fires up like it's supposed to. If I try to start after the engine has run AT ALL, then I have the same non-start issue on the first key turn 97% of the time. For example: yesterday, after sitting overnight, I started Fat Konnie on the first key turn and moved her over to the other side of the driveway. The engine ran about 30 seconds. I looked under the frame rail to find the fuel composition sensor and filter, went inside to grab my wallet, then hopped inside to head out for a filter. It took maybe 2 min, but when I went to leave I had the same no start on the first key turn.

Fuel pressure does leak down to about 20psi after a couple hours. Cycling the key 1-50 times before starting has no effect on the starting problem. I have also pulled the fuel rail off and pressurized the system and there are no dripping injectors. FPR seems to work fine (no gas smell, no gas dripping) and I have tried to run it with vac line to FPR uplugged with same results.

I don't want to spend the money that mpope2 did here with his rig: https://www.tahoeyukonforum.com/threads/delayed-crank.125739/#post-1557535

We've been messaging and the one thing we can identify as being the same is that our vehicles sat for an extended period before the problem started. Varnish?

So let's throw out some ideas please! But let's also try and give a helpful explanation as to why. Simply saying "Fuel Pump" doesn't help. It would be nice to have a logical explanation as to why it starts the majority of the time correctly after sitting, but poorly after being started.

Thank you in advance for your insight!!!

 

[corvette744]

The 3 things i would have hooked up for an intermittent no start would be fuel pressure gauge-scanner and something as simple as a screw driver in spark plug boot to ground looking for spark when its happening.You didnt mention what your fuel pressure was when trying to start only that it drops over time.If its easy to duplicate alot faster to find your problem.No codes in the system at all??Narrow down if its fuel or spark then attack those spots.

 

[jrdecat]

The 3 things i would have hooked up for an intermittent no start would be fuel pressure gauge-scanner and something as simple as a screw driver in spark plug boot to ground looking for spark when its happening.You didnt mention what your fuel pressure was when trying to start only that it drops over time.If its easy to duplicate alot faster to find your problem.No codes in the system at all??Narrow down if its fuel or spark then attack those spots.

Good points. I did have a fuel pressure gauge hooked up and don't remember the exact readings, but that that they were "in spec" from my understanding. I will borrow the gauge from AutoZone again and get an exact reading.

No codes.

 

[corvette744]

Obviously you want the reading when its not starting if its within spec then -no fuel pump required.I would have a scanner on it for checking injector pulse or if you have a noid light to plug into injector.Also scanner will read crank and cam sensor operation.Should be able to narrow it down within an hour.Spark or fuel find that out first.

 

[jrdecat]

I found an email that had some numbers from my last fuel pressure test...

With key on engine off, the fuel pressure pops right to 52. After running it drops to 15 within a few hours and to zero overnight.

If it was a fuel pump losing prime, then I wouldn't have a problem starting right after shutdown. I can go for a drive, shut it off, and try to start again within 5 seconds and it won't start the first time....but every time on the second time.

I watched the security light yesterday and it comes on with the key, then shuts off after about 5 seconds.

I'll have to dig to the depths of my toolbox and see if I still have a noid light around. I don't have a proper diagnostic scanner, just a cheap one that will pull and clear a code.

 

[exp500]

Which scanner/app? Some can do live data that may help you. A 194 bulb works for noid lite also.

 

[rockola1971]

I also would not rule out loss of spark before I chased fuel system problem. Easy check once you get a fail to start symptom.

 

[jrdecat]

Which scanner/app? Some can do live data that may help you. A 194 bulb works for noid lite also.

Scangauge II. Definitely not a high end tool...like myself.

 

[jrdecat]

Sooooo close! After finally getting the fuel filter changed, O2 sensors replaced (with OEM), and 2 cans of seafoam in the 1/2 full tank I took Fat Konnie for a test drive. The first start took two bumps like normal, but for the next 2 hours I made 5 stops of about 5-11 minutes in duration and she went off on the first crank every time! I thought my problem was solved. I didn't care if it was the fuel filter or O2 sensors...she started like she was supposed to.

Fast forward a couple more hours and I had to go back out and run some errands. EVERY start after sitting has been just like it was before...crank crank crank crank...let off key...turn key and everything is great.

Waiting to hear back from blackbear about what they did with the fuel composition sensor when they did my tune.

 

[corvette744]

If its that easy to duplicate the problem-start troubleshooting now.Spark or fuel-get your gauge from autozone and ground a spark plug wire when its doing it and go from their.

 

[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."
View attachment 359542

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.