Is fuel pressure flow chart wrong?

[_rgk]

I am trying to diagnose a no-start condition on a 98 K1500 using page 6-1734 of the FSM. Here is how it goes:

Step 2: Is fuel pressure within specified value with fuel pump running? Yes, go to step 3.
Step 3: Does fuel pressure hold steady? No, go to step 4.
Step 4: Install fuel feed shutoff at fuel filter. Does fuel pressure remain constant?

I don't have the valve yet, but if yes, go to step 12: replace fuel sender.

How can the fuel pump be bad if you valve off flow between the pump and injectors? Wouldn't it be the opposite, that if you cut off flow at the feed line, and get good pressure, that you have ruled out the pump as being bad, and the injectors or regulator might be leaking?

Edit: Never mind, my slow brain got it. The pressure gauge is located after the shutoff and is showing that the injectors and regulator are not leaking.

 

[kennythewelder]

On a Vortec, you need over 60 PSI for the engine to start properly. Anything less than that, and you will have hard stating issues. It takes that much pressure, to force fuel through the injectors. The 60+ PSI, is pre start. When you first turn the key on, the ECM cycles the fuel pump for something like 2 or 3 seconds. This is where you need over 60 PSI. Once the engine starts, the fuel pressure will fall into the 50s PSI range. If you rev the engine, the fuel pressure should come up, then fall back into the 50s once the RPMs drop again. If this is not the results your having, then your fuel pump is weak, and need to be replaced. Just because you have pressure, that doesn't mean it's enough pressure. Anything less than 60 PSI, prestart, just isn't enough pressure.

 

[_rgk]

I'm right at 60 at ON (car not running) when the pump is running. As soon as the pump stops running it drops to 52.

When cold it runs ok for about a minute, then dies. Then tries to restart, but refuses to. Seems like it's flooding because it will run for a minute again the next day.

Just replaced fuel filter. No change. Pressure drops slowly after the test.

It should be either a bad pump, FPR, or injectors. The shutoff valve should tell me which one to replace.

 

[_rgk]

Pressure bleeds off with valve closed upstream and downstream of fuel injection assembly. Ordered MPFI upgrade. Poppets are probably toast.

 

[Orpedcrow]

Pressure bleeds off with valve closed upstream and downstream of fuel injection assembly. Ordered MPFI upgrade. Poppets are probably toast.

That’s what it sounds like to me. They’re stuck open or not closing fully. It’ll run better after the upgrade anyway.

 

[_rgk]

Dang. Installed new injector assembly and car is doing the same thing. Starts hard, runs for a minute or so (engine sounds weak) and then dies and does not restart. Pressure with the new assembly is now 58 psi when the pump runs, drops to 54 psi or so after pump shuts off, and slowly bleeds off. I thought the pump was OK because the pressure bled off with the valve closed in place of the fuel filter. Engine starts with starting fluid but dies right away.

 

[Schurkey]

Verify that you have spark after the engine dies.

Connect scan tool, look at the data stream.

 

[east302]

Dang. Installed new injector assembly and car is doing the same thing. Starts hard, runs for a minute or so (engine sounds weak) and then dies and does not restart. Pressure with the new assembly is now 58 psi when the pump runs, drops to 54 psi or so after pump shuts off, and slowly bleeds off. I thought the pump was OK because the pressure bled off with the valve closed in place of the fuel filter. Engine starts with starting fluid but dies right away.

If you put the supply valve back in, does pressure now hold with the valve closed?

Meaning, you could have had both leaking injectors and a pump issue.

Might as well add one on the return to make sure that you don’t have a defective (new) regulator.

 

[_rgk]

Yep, I have to do all of these things before ordering the pump. I considered the possibility both the pump and injectors might be bad. I just didn't have the heart to take it on last night.

I am also concerned it might just be bad gas, because I bought the car last winter and never stabilized it. I don't honestly know how long prior to that the previous owner filled it up, because he had a knock and hadn't driven it much. If so, that will be a major pain.

I'm hopeful it's not that because of the obvious pressure issue. Also, when I first started it just after the rebuild it ran fine for a good few minutes. I pulled it out of the garage and it died. The next day I was able to start it and run it and it ran good, I got it up to temp. I was able to get it back in the garage. But now it won't run for more than a minute, and sounds 'weak.'

Based on this I am hopeful the gas is ok. Also, the previous owner already had hard starting issues last year. He also had battery issues. I was able to trickle charge the battery and it shows a decent voltage, but it is suspect. I do have a good spark though and the starter cranks great, so I'm still going in the direction of fuel delivery. Oh, and the fuel pump does sound kind of loud. This is my first Chevy and none of my other cars have a fuel pump this loud, but then again I don't think any of my other cars are meant to deliver 60 pounds.

That's all to say that I'll test the pressure today and go from there. Maybe I'll remove the bed and just inspect the pump, maybe find something obvious.

Before you guys ask, the security light does not blink.

 

[RichLo]

Might be worth it to drain the old gas out of the schroeder valve with the pump and purge the line with some fresh stuff too. Then you can also visually see how well the pump is flowing and smell the old stuff coming out.