Truck wont start suddenly

[yukon06]

Can't say it's the fuel pump until you check the pressure. Even if you suspect the fuel pump, electrical like fuses and wires/grounds would be the next steps... sanitary checks, you know.

Fuel pressure should be around 52-54 psi "ish" with key on, engine off, it depends on engine. Someone may post a spec on actual required minimum pressures...Pressure should also hold steadily for a few minutes.

I will admit that I have never replaced a fuel pump myself, but you have to drop the tank, so yes, it's a big deal.

I will tell you this though: fuel pressure gauge has saved me several times from chasing suspected fuel delivery problems. For example, on my 99 Silverado with the 4.3 I had a persistent crank-no-fire. Fuel pressure always checked okay. I discovered that it was related to damp/rainy conditions. I eventually swapped the engine to a 5.3 and my the fuel pump on that truck is still the original. I'm currently at 270k.

Thank you

 

[yukon06]

Gas or flex fuel different pumps and pressures, but not by much. Just relieving pressure at that valve did not fix anything. You could have just as easily kicked a tire and the same thing happened and started. You may have intermittent no spark and it chose right then to have spark. You need 4 things to start an engine. Fuel, spark, compression and timing/air. You were missing one of those at that particular time.

Thank you.....should i not bother with the pressure gauge?

 

[OR VietVet]

Thank you.....should i not bother with the pressure gauge?

Yes, do the fuel pressure test and know if you have a gas system or flex fuel. You can also rent the pressure gauge at some parts stores. If you get a gauge, rent or buy, get one with long enough hose or adaptors to allow for it to come out back of the hood and tape to windshield and watch while you are driving.

Bear in mind that you may have no fuel delivery problem and have an intermittent spark problem. Crank sensor....cam sensor....etc.

 

[Fless]

Which engine?

You should be able to "rent" a fuel pressure gauge at your local parts store; essentially you pay for it with a credit card, they hold the funds until you return it in the timeframe allowed (usually days), then the funds are returned to your credit card. Free fuel pressure testing. If you don't return it in time, you bought it.

Initial test is to connect the fuel pressure gauge to the Schrader valve on the passenger rail, then turn the ignition key to the ON position without cranking. Read the fuel pressure; V8 spec is 55 to 62 psi; if it's a Flex Fuel engine (VIN Z) it's a little lower, 48-54 psi.


Next time you go to start it, roll down your window and turn the key to the 'on' position without cranking. You should hear/feel the fuel pump run for a few seconds. Get that sound in your head.

Then next time it cranks but won't start, cycle the key and listen for the pump to run. If you don't hear it, well, then you know something's wrong with it or the circuit. But even if it does run, there's no guarantee that it's really pumping fuel.

If it doesn't run, as @89Suburban recommended have someone reach underneath and bang the bottom of the tank a few times. Sometimes that's the attitude adjustment needed to get out of a jam. If that works to make it run, you're probably looking at a fuel pump replacement.

 

[Doubeleive]

Thank you.....should i not bother with the pressure gauge?

it's not something you need will all the time, however they are only $20-30 at harbor frieght, amazon, online, etc and at some auto parts stores' you don't need a $300 tester if you are not using it at a shop for making money.
it can certainly rule a problem in or out without a tow or paying a "diagnostic fee"

 

[Doubeleive]

In the meantime, I would carry around a rubber mallet or hammer that's already mentioned just in case. A smack on the bottom the gas tank might save you a tow
*Pressing the Schrader valve 99% likely had no effect on anything and was probably just dumb luck

 

[dps01]

I will echo leaning towards a fuel pump. Had one fail when my 03 was still under factory warranty.

The wrecker driver showed up to tow it to the dealership, crawled underneath and beat the tank bottom with his fist a few times. That was enough to mechanically agitate the fuel pump to a position where it allowed the truck to start so it could be driven onto the flatbed vs. winched.

Releasing the fuel rail pressure may have allowed just enough rotation of the pump to allow the vehicle to start… just a hypothesis….

 

[Matthew Jeschke]

You say cranks but won't start... As in it fires over but won't keep running? Or just cranks? FYI ~ VATS will produce a similar issue if it glitches and thinks you stole your own truck. It'll fire over but not keep running.

Otherwise, if it's JUST cranking, then you need to make sure your computer is booting. Turn igition to ON but NOT START. Does the check engine light illuminate? If not, your computer fuse maybe bad or an issue with the computer.

Another note, I'm not sure what the pressure range is but I believe nominal Gen III Small block fuel pressure is 58 PSI for NON flex fuel trucks. It's a lower if memory serves me right for flex fuel setups, 45psi?? If you need I can lookup in FSM.

Neighbor kid asked me to help him change his pump... But he assumed it was the pump and didn't check anything else. It's fuse was blown PCM fuse due to shop removing fender liners... I guess they thought he didn't need them. It soaked his under hood fuse block and blew a bunch of fuses. He had bought a pump and his issue was a little fuse.

 

[yukon06]

Can't say it's the fuel pump until you check the pressure. Even if you suspect the fuel pump, electrical like fuses and wires/grounds would be the next steps... sanitary checks, you know.

Fuel pressure should be around 52-54 psi "ish" with key on, engine off, it depends on engine. Someone may post a spec on actual required minimum pressures...Pressure should also hold steadily for a few minutes.

I will admit that I have never replaced a fuel pump myself, but you have to drop the tank, so yes, it's a big deal.

I will tell you this though: fuel pressure gauge has saved me several times from chasing suspected fuel delivery problems. For example, on my 99 Silverado with the 4.3 I had a persistent crank-no-fire. Fuel pressure always checked okay. I discovered that it was related to damp/rainy conditions. I eventually swapped the engine to a 5.3 and my the fuel pump on that truck is still the original. I'm currently at 270k.

thank you

 

[yukon06]

Gas or flex fuel different pumps and pressures, but not by much. Just relieving pressure at that valve did not fix anything. You could have just as easily kicked a tire and the same thing happened and started. You may have intermittent no spark and it chose right then to have spark. You need 4 things to start an engine. Fuel, spark, compression and timing/air. You were missing one of those at that particular time.

thank you