03 tahoe flex fuel intermittent no start

[Monk17]

So my tahoe randomly wont start at times. It trys to turn over but just wont. It cranks and cranks amd cranks. Sometimes it will start and almost stumble after long cranking. Other times she starts right up. Typicaly if she cranks and wont start she will if i try agian right after it. What can be the cause?

Battery is good i have power she runs smooth oils good etc. Just no turn over speraticaly like maybe 1 in 5 starts or so

 

[OR VietVet]

First, let's get the jargon right. Turning over and cranking are the same thing. You say it cranks and will not "fire off" or "start". I believe you have a fuel delivery problem. I would attach a fuel pressure gauge to the rail and see if you have ANY pressure at that time. Then turn the key to KOEO, key on engine off, and see if the fuel pump is pushing fuel to the rail and also what that pressure is. Then attempt to start the engine, crank it, and again watch the pressure and when it does start what is the fuel pressure at idle? Then shut off and see if the pressure bleeds off and ** fast. Post that info when you can. You can buy a cheap fuel pressure tester at Harbor Freight or rent them at an auto parts store.

If all your pressures are good you likely have a spark problem during initial engine crank.

Welcome to the forum from Oregon.

 

[Monk17]

First, let's get the jargon right. Turning over and cranking are the same thing. You say it cranks and will not "fire off" or "start". I believe you have a fuel delivery problem. I would attach a fuel pressure gauge to the rail and see if you have ANY pressure at that time. Then turn the key to KOEO, key on engine off, and see if the fuel pump is pushing fuel to the rail and also what that pressure is. Then attempt to start the engine, crank it, and again watch the pressure and when it does start what is the fuel pressure at idle? Then shut off and see if the pressure bleeds off and ** fast. Post that info when you can. You can buy a cheap fuel pressure tester at Harbor Freight or rent them at an auto parts store.

If all your pressures are good you likely have a spark problem during initial engine crank.

Welcome to the forum from Oregon.

Thanks for the info that was my plan today but didn't want to throw stuff at it if there was a better thing to test first ill try to get a tester today and update readings

 

[OR VietVet]

Yea, don't throw parts at it till we chime in with some inspections to do to narrow down the problem.

 

[Monk17]

Yea, don't throw parts at it till we chime in with some inspections to do to narrow down the problem.

So its looking like 48 on average with key on no start when i start it jumps to 54 and bounces between 46 to 54 and settles down with in 20 second . Lowest i could get was 40 once it shut off couldn't get it to do the the no start after 10 trys

 

[OR VietVet]

What kind of pressure did it have when you attached the gauge before you turned the key to KOEO? Did the pressure bleed off from 40 psi when you let it sit for 10-15 minutes or more?

 

[Monk17]

I do have a small valve cover leak on both sides but i dont think thats the cause

 

[OR VietVet]

Oil leaks are not related to your problem.

 

[Monk17]

What kind of pressure did it have when you attached the gauge before you turned the key to KOEO? Did the pressure bleed off from 40 psi when you let it sit for 10-15 minutes or more?

46-4 . I didnt let it sit that long

 

[Monk17]

46-4 . I didnt let it sit that long

46-48**

 

[OR VietVet]

So, when you first attached the gauge, before even touching the key, it had 46 psi showing? And then when you shut the engine down and watched the gauge it dropped to 4 psi? How quick did the pressure drop?

 

[OR VietVet]

46-48 when? First attached? Or after you shut off and it held at 46-48? Please be more detailed with your answers.

 

[Monk17]

46-48 when? First attached? Or after you shut off and it held at 46-48? Please be more detailed with your answers.

When i attached it before even putting in a key it was zero. Put in key turned to on position without start it did 46-48 multiple times

Engin on it jumped to 54 and settled down to 48

When i turned off the engine it dropped to 40.
Im currently doing the timed test as requested

 

[Fless]

After it's been sitting for a while, connect the fuel pressure gauge and write down the reading. Make sure the gauge is connected tightly to the schrader valve on the fuel rail. Note any changes over a minute or two.

Now turn the key to ON WITHOUT starting the engine. The NBS KOEO (key on, engine off) Flex Fuel pressure spec is 48 to 54 psi, and it should hold within that range. Note the reading and write it down.

Start the engine and observe variations in pressure; there will be some but check the running pressure at idle and maybe 1,500 or 2,000 rpm. Write them down.

(I think you're doing this now) Turn off the engine and the key, and observe every few minutes over an hour or so what the psi reads. This will tell you how long it takes the pressure to leak down.

If you had zero to begin with, it's apparently leaking down, indicating a faulty fuel pump or a leaky injector, or something else in the fuel line that is allowing leakdown.

 

[Monk17]

After 13 minuets no drop it actually climbed about 3 psi ill check it again in 30 min

 

[Monk17]

The zero pressure to start may have been my fault

 

[Fless]

How many miles on this truck, and do you know if the fuel pump has ever been replaced?

 

[Monk17]

How many miles on this truck, and do you know if the fuel pump has ever been replaced?

Almost 200k no idea if pump or fuel filter has ever been changed

 

[OR VietVet]

https://www.rockauto.com/en/moreinfo.php?pk=356952&cc=1412244&jsn=3423

https://www.rockauto.com/en/moreinfo.php?pk=7056044&cc=1412244&jsn=3454

And 13500114 AC Delco fuel pump relay.

I see these in your future. With that kind of mileage and no history and the fact that the pressure is bleeding off and not knowing how long that old fuel filter has been there causing the pump to work so hard to push fuel to engine, these are likely the culprits, but, and I mean BUT, like Steve said, you may have leaking injector(s) allowing the pressure to bleed off. Before you replace the fuel pump and the other components, try just turning the key to the on position and not cranking the engine, for about 10-15 seconds before you actually turn the key to crank the engine. It may start way easier after you have allowed the fuel pump to build pressure before you crank the engine.

 

[wildcatgoal]

Sort of right behind that little red power junction box on the side of the engine is a small sensor plug. Is that plugged in tight? If it isn't plugged in, you get these symptoms exactly.