2006 6.0 Cranks but won't run after new oil pressure switch installed

[Black02Silverado]

His is a 6.0 and I don't think it has a screen since it doesn't have AFM.  I'm under the impression that AFM and the screen go hand in hand.

[davester]

4 hours ago, Black02Silverado said:

Check all those connections.  The fuel pressure should be 52psi.  You can get a test gauge loaned to you from Auto Zone.  That is where I got mine when I had hard starting issues. Turned out to be a bad fuel pump on my 02 Silverado.  Which is a known issue on the GMT800's.

 

I forget the exact correct value, but it's right around 60 psi.  52 psi is definitely too low (the truck will still run, but the injectors won't be able to spray the fuel right because they are designed for 60 psi, and they will spray slightly longer to make up for it).

 

And when checking fuel pressure, check both at idle and when you hit the gas and rev the motor up to 3K.  The FP should only drop for a short period of time, then quickly return to full pressure, when you hit the pedal to speed up the motor.

[Supreme Pizza]

22 minutes ago, Black02Silverado said:

His is a 6.0 and I don't think it has a screen since it doesn't have AFM.  I'm under the impression that AFM and the screen go hand in hand.

 

   You are probably right, but it only takes a few minutes to find out for sure. From what I was reading, some of the engines were originally fitted for AFM, but those parts were removed and the system was disabled in the factory, maybe the screens were left in? Not sure why they fitted them and then removed them. Anyway, I think it would be worth having a look, especially since he has been removing the oils sender anyway. 

[BanoChris]

I can feel and hear the relay throw when the key is turned to the run position. I swapped it with the headlight relay and the headlights still worked and the relay still clicked when the key was turned to run.

 

I was also able to hear the fuel pump prime when the key was turned to the run position. It lasted about 3 seconds.

 

I put a fuel pressure test gauge on the left fuel rail and bled the line. When the pump primed it jumped to 60lbs and then dropped to 55lbs. I bled the pressure off and then when the key was turned to start, the pressure jumped to 60lbs then down to 55 and stayed there. It turned over but did not start. I did this several times to ensure the pressure was consistently reading the same.

 

I'm still not seeing a code. After priming, the fuel pump shuts off. When does it turn back on? What controls the injectors and allows them to open and spray fuel?

 

I'm still going through all the connectors and making sure they are all good.

[davester]

The ECM(alternately known as the PCM) controls the injector firing, both when they fire and their duration.

 

55 psi is a little low, but it's fine for starting and running the engine, assuming it can maintain that pressure once the engine starts.

 

As a comparison, when I bought my truck, which had a failing pump, it could get up to 58 psi when the key was turned on, drop to about 45 psi and stay there at idle, and then drop to 20 psi and stay there at speed.  The engine would run, but didn't have a lot of power and the fuel trims were WAY out of whack.

[BanoChris]

If the ECM is malfunctioning, will it throw a code?

[davester]

4 hours ago, BanoChris said:

If the ECM is malfunctioning, will it throw a code?

If it is malfunctioning, then you can't really count on anything about it working right.  But it failing is at the end of the GM full-service manual checklists for fixing problems...

[BanoChris]

If there is 60lbs of fuel pressure at prime, even if the fuel pump was hosed, shouldn't I at least be getting a sputter? The odd thing is that I'm not getting any codes.

[txab]

20 hours ago, Black02Silverado said:

His is a 6.0 and I don't think it has a screen since it doesn't have AFM.  I'm under the impression that AFM and the screen go hand in hand.

Correct. 6.0 of that  year no AFM, nor screen

[BanoChris]

Thanks for the clarification. That's one less thing to troubleshoot. :-)

[davester]

15 hours ago, BanoChris said:

If there is 60lbs of fuel pressure at prime, even if the fuel pump was hosed, shouldn't I at least be getting a sputter? The odd thing is that I'm not getting any codes.

If everything else is working right, yes, the engine will start.

 

I would first check that the spark plugs are firing, as that's relatively easy to check, maybe check compression at the same time with the plug out, and if those check out, then test if the injectors are getting power (a noid light or something else that can test for intermittent power), then if they are getting power (more of a hassle), I would get one bank of injectors out just enough to see if they are actually squirting fuel (or see if the plugs are wet with fuel after trying to start the engine).

 

When I bought my truck, it could get up to about 60 psi turning the key on, but the pressure would rapidly drop when there was any demand on the engine (to below 20 psi and stay there).  The ecm could kjnd of compensate for this, but it wasn't great.

[BanoChris]

Is it normal for the starter to run for only about 5 seconds when trying to start the engine?

[davester]

You don't want to run the starter for an extended period of time, because it gets really hot and starts melting things inside.  But that's long cranking, like more than 20-30 seconds.

 

Does your starter just stop after 5 seconds, even with the key still turned to keep it going?

[BanoChris]

Yea I would never keep the starter running for that long. My ol' man drilled that into me a long time ago. :-)

 

Yes it stops after about 5 seconds even if the key is still turned to keep it going. Is that normal?

[davester]

I would say no, but I don't recall having to crank my truck over for more than a second or two.  It surprises me when it doesn't start with a very short blip of the starter.

 

It might be a save-the-engine thing, like no oil pressure, but I don't know.

 

I'm not sure what cranking it longer would do, long crank times were only needed way back with mechanical fuel pumps, if the line was empty, it took awhile to pump the fuel from the tank to the carb, but now with electric fuel pumps, that's not a problem...