Crank No Start After Driving

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

jrdecat

TYF Newbie
Joined
Oct 28, 2018
Posts
26
Reaction score
10
Location
coloRADo
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!!!
 
Last edited:

corvette744

2004 Z-71
Joined
Jul 11, 2017
Posts
739
Reaction score
768
Location
Northern illinois
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.
 
OP
OP
jrdecat

jrdecat

TYF Newbie
Joined
Oct 28, 2018
Posts
26
Reaction score
10
Location
coloRADo
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

2004 Z-71
Joined
Jul 11, 2017
Posts
739
Reaction score
768
Location
Northern illinois
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.
 
Last edited:
OP
OP
jrdecat

jrdecat

TYF Newbie
Joined
Oct 28, 2018
Posts
26
Reaction score
10
Location
coloRADo
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

Full Access Member
Joined
May 14, 2017
Posts
1,819
Reaction score
1,654
Which scanner/app? Some can do live data that may help you. A 194 bulb works for noid lite also.
 

rockola1971

Full Access Member
Joined
Dec 29, 2016
Posts
2,426
Reaction score
3,089
Location
Indiana (formerly IL)
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.
 
OP
OP
jrdecat

jrdecat

TYF Newbie
Joined
Oct 28, 2018
Posts
26
Reaction score
10
Location
coloRADo
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

2004 Z-71
Joined
Jul 11, 2017
Posts
739
Reaction score
768
Location
Northern illinois
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.
 

Forum statistics

Threads
130,041
Posts
1,825,402
Members
93,475
Latest member
JustinCole

Latest posts

Top