Warm Start Problems

[mcsc1]

Good afternoon all. I’m hoping someone here can guide me in the right direction. It’s a long one, but I’m gonna give all info and things I’ve tried.

My issue is I’m having difficulty starting when warm. When it’s cold, it fires right up. When I put my foot down to clear flood mode it will sometimes fire, usually it “may” help it start.

I’ve replaced fuel pump, all 8 injectors, coolant temp sensor, evap purge solenoid, 8 spark plugs.

Checking pressure on a snap-on scanner, we saw it fall from 42-43 at idle to (key on engine off) down to lowest of 16. Key on to prime, it got to 24 roughly.

I’ve pulled all 8 injectors still attached to the rail and put paper towel underneath to see if any leaked, and none are.

If it’s not injectors, but clear flood mode helps start it…what in the world is going on?

 

[Fless]

Tell us more about what the vehicle is: make, model, engine, etc.

 

[OR VietVet]

It's a "secret".

 

[mcsc1]

My apologies. It’s a 09 Yukon SLT, 2wd. 198k miles. 5.3, vin code 3, flex fuel.

 

[Foggy]

Look at your IAT when cold, driving and hot restart...
The sensor or circuit if screwed up could cause an issue
You'll need a bidirectional scanner to get live data

 

[Doubeleive]

Good afternoon all. I’m hoping someone here can guide me in the right direction. It’s a long one, but I’m gonna give all info and things I’ve tried.

My issue is I’m having difficulty starting when warm. When it’s cold, it fires right up. When I put my foot down to clear flood mode it will sometimes fire, usually it “may” help it start.

I’ve replaced fuel pump, all 8 injectors, coolant temp sensor, evap purge solenoid, 8 spark plugs.

Checking pressure on a snap-on scanner, we saw it fall from 42-43 at idle to (key on engine off) down to lowest of 16. Key on to prime, it got to 24 roughly.

I’ve pulled all 8 injectors still attached to the rail and put paper towel underneath to see if any leaked, and none are.

If it’s not injectors, but clear flood mode helps start it…what in the world is going on?

that pressure it too low, koeo should be 50-65, running it should be minimum 43 (i think) mine runs about 44
i would try what foggy suggested otherwise I might be batting a eye at the fuel pump or fuel pump control module, module may be getting hot and failing, you can pull the harness off and check it for corrosion or water intrusion as that has been known to happen before. the module is mounted under the spare tire area under the frame.

 

[mcsc1]

Look at your IAT when cold, driving and hot restart... The sensor or circuit if screwed up could cause an issue You'll need a bidirectional scanner to get live data.

I’ve seen IAT on a scanner at idle and key off engine warm. It read 107 when outside temp was 81. Where does it get IAT at? The MAF sensor?


D, I’ll check that out. I was curious about the module, but wasn’t certain. The pump did have a broken bowl which I rigged with my old bowl. That may or may not be my issue but it’s under warranty.

 

[Doubeleive]

I’ve seen IAT on a scanner at idle and key off engine warm. It read 107 when outside temp was 81. Where does it get IAT at? The MAF sensor?


D, I’ll check that out. I was curious about the module, but wasn’t certain. The pump did have a broken bowl which I rigged with my old bowl. That may or may not be my issue but it’s under warranty.

either maf or map pulls double duty, I think it's the maf, after 160k miles they are always suspect in my book, they can just go goofy after that

 

[mcsc1]

either maf or map pulls double duty, I think it's the maf, after 160k miles they are always suspect in my book, they can just go goofy after that

So my wife has a 2011 Denali, I swapped her MAF with mine and it made no difference in starting. Hers runs perfectly normal so I assume it’s a working MAF.

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

You are already receiving sage advice from the knowledgeable folks on this Forum.