Low Fuel Pressure

azchevy99 · September 24, 2008

I have a '99 Silverado 1500 with 4.8L. I just checked my fuel pressure and it's at 50 psi when idling. I know that it should be around 55-62, but is 50 low enough to cause hesitation problems when the engine is cold (which I've been having)? I guess my next step was to block the fuel return line to rule out the fuel pressure regulator. I've already replaced the fuel filter, so I know that's not the problem. Thanks for the help!

95Sierra2500 · September 24, 2008

Generally, the pressure is controlled by 2 things: the regulator and the pump. Granted there's the possibility of leaky injectors causing the pressure to bleed down a bit, but it's not usually that much. If I were you, I'd consider just replacing the regulator (cheaper and easier) and if the problem goes away, you found it. If not you'll need a pump.

And yes, low fuel pressure can cause hesitation.

abracadabra · September 24, 2008

Your fuel pressure is low.

From a post I've saved:

Pressure is low.
Go threw the complete fuel pressure test.

And do not forget the voltage and ground test.

The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.

A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.

But do not run the pump at full pressure very long.

Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes

until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold and fuel pressure testing guide line.

Check cold start fuel pressure.

Check engine running fuel pressure.

Check engine running on the road fuel pressure.

Then shut it off and watch for fast leak down.

Pinch off at rubber part or block off return line and check full pressure.

If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.

Later V6 and V8 gm engines should have 60-66 fuel pressure.

Cold start should be 64-65 lbs of pressure.

If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.

Do not leave home without it.

Engine running should be 60-66 lbs pressure depending on engine load.

Full pressure with return pinched off should be 75-85 or more.

And if it has a fast leak down after shut off you have a leak in system.

Post back fuel pressure readings.

azchevy99 · September 24, 2008

Your fuel pressure is low.

Thank you, but I already know my fuel pressure is low. It reads at 50psi with key on and at idle. My question was whether 50psi would really cause noticable issues since it's really not that much lower than recommended pressure (55-62).

C6Racer · September 24, 2008

Well, until 2 weeks ago, my fuel pressure was at about 20 psi for about 3 weeks. It idled and drove just fine... as long as I didn't floor it. The MIL(Malfunction Indicator Lamp, which is the PROPER term) came on, so I checked the codes and they said the engine was running lean(surprise surprise), but, again, the engine idled and drove just fine as long as I didn't put a considerable load on it. To put it simply, at 20psi, a 1975 Honda Civic could leave me in its dust completely stock. When the MIL came on the fuel pump lasted about 3 more weeks.

Moral of the story is that 50 psi won't affect it much, but it means the fuel pump, if that's the problem, is on its way out. I wouldn't push it, however, because a lean condition will cause misfires and that is hell on the catalytic converters. Just avoid flooring the throttle until you can get the problem fixed.

By the way, stay far, FAR away from Airtex fuel pumps. I'm on my 4th pump. The 2nd and 3rd were Airtex and both of them took a dump within a year(about 15k miles). I didn't have $250 to spare for another pump from a parts store, and I REALLY needed my truck, so I got one off of eBay for $80, which also has a 1-year warranty just like the Airtex pumps and they claim it's made in the USA. It didn't say "Made in China" anywhere on the pump so it's probably true. My truck has been running awesome for 2 weeks so I'm hoping this will last me at least a year.