350 5.7 TBI Fuel Pressure Issues

[joep123]

I have a 1992 k1500 5.7 TBI that's just gone through a frame up restoration, drive train is all brand new, fuel filter, fuel pump, TBI Rebuilt Kit, etc. etc. and all the parts used were AC Delco.

While rebuilding it I installed a fuel pressure sensor post fuel filter and at idle its 10.5~ PSI. When i Rev or load up the motor I notice that the pressure will drop down to 9 and as low as 4 PSI depending how far down I'm pushing the pedal. Just driving the truck around not going in excess of a quarter throttle the truck drives great, it accelerates great, and the fuel pressure stays roughly around 10 PSI. But if i try to really hammer it the pressure just drops and i can't seem to break 3500 RPM.

With all the components being new for the tbi and fuel system I am wondering if I could have A. Damaged the fuel pressure regulator putting it back in or B. Faulty fuel pump?

There are two codes that the truck has thrown during the first 500 mile oil change. One is 32 (Baro sensor circuit error / EGR circuit Error / MAP sensor signal open), and the other is 54 (Fuel pump circuit low voltage / Digital EGR valve solenoid 2 error). I have replaced the Fuel Pump Relay and have a new EGR valve but I am waiting to take everything apart till I get my CFM spacer in as I don't want to take everything apart 3 times.

 

[evilunclegrimace]

1)Verify voltage at the fuel pump connection
2) Verify that the fuel pressure gauge is accurate
3)Dead head the pump and see what kind of pressure it can produce.
4) Map sensor signal open should be a code 33 if I remember correctly.

 

[evilunclegrimace]

Also, check the MAP voltage KOEO. It should be in the range of 3.8V to 5.5V for your altitude.

 

[joep123]

1) Verify voltage at the fuel pump connection. 12.68 volts when I jumpered the fuel pump relay.

2) Verify that the fuel pressure gauge is accurate. T'd a mechanical gauge in with the digital. they are both reading 9 PSI with the fuel pump relay jumpered.

3) Dead head the pump and see what kind of pressure it can produce. Crimped the rubber portion with some needle nose vice grips and jumpered the fuel pump relay to the battery, 9.5 PSI.

4) Map sensor signal open should be a code 33 if I remember correctly. References this list of fault codes for 32 "https://repairpal.com/gm-obd-i-code-chart".

5) MAP voltage KOEO. I got two readings here, one was at 5.023V and the other was around 4.9V.

 

[PlayingWithTBI]

I wonder if the hose that the pump is connected to inside the tank is split? That or your pump is bad. You should have closer to 13PSI at all times - idle to WOT.

 

[joep123]

New sender unit went into the tank without any complications but I guess I can lift the bed up and take a look at it. When I get it out, anyone know what the pumps motor should ring out to?

 

[evilunclegrimace]

1) Verify voltage at the fuel pump connection. 12.68 volts when I jumpered the fuel pump relay.

2) Verify that the fuel pressure gauge is accurate. T'd a mechanical gauge in with the digital. they are both reading 9 PSI with the fuel pump relay jumpered.

3) Dead head the pump and see what kind of pressure it can produce. Crimped the rubber portion with some needle nose vice grips and jumpered the fuel pump relay to the battery, 9.5 PSI.

4) Map sensor signal open should be a code 33 if I remember correctly. References this list of fault codes for 32 "https://repairpal.com/gm-obd-i-code-chart".

5) MAP voltage KOEO. I got two readings here, one was at 5.023V and the other was around 4.9V.

I just pulled a factory Driveability and Emission manual out of the shop. Code 32 is for the EGR system not the MAP system. The MAP system is code 33 and 34.

 

[evilunclegrimace]

Dead head fuel pressure should be in the 13-15 PSI range.

 

[joep123]

I'm leaning towards the pump taking a dump, I'll pull the sender out and take a look at it and see if there are any cracks/tears that might allow it to bypass while im doing it.

 

[joep123]

So I wasn’t willing to pay autozones mark up for a new fuel pump so it’s on order. I did have a cfm adjustable fuel pressure regulator that I installed to see if it
Made a difference. It made the problem more noticeable.

I adjusted the pressure from 10.5 up to 12 and drove it around. Drove fine in the quarter pedal range but if I quickly press down the gas or go to half throttle the pressure falls off to 8~ psi and it boggs down.