Fuel pressure
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Instructor
Joined: Feb 2007
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From: CRYSTAL RIVER FL.
Fuel pressure
1992 LT1. Fires right up for about five seconds stumbles and dies. It seems to be fuel related. I replaced the fuel pump about two years age during a fuel gage sender replacement. I've did a vacuum check on the fuel regulator. It holds. Was going to check fuel pressure and can't find the schrader valve. Traced the supply and return lines up to the fuel rails. No valve. Is there something unique to the '92?
Got me stumped
TIA Dave
Got me stumped
TIA Dave
Thread Starter
Instructor
Joined: Feb 2007
Posts: 132
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From: CRYSTAL RIVER FL.
Hooked up the fuel pressure gauge (thanks to Kimmer) starts up, runs a little rough for about five seconds, and dies. Zero indicated fuel pressure. Did this several times. What's it running on residual fuel/pressure in the lines? Is it common for the fuel pump to die after a couple of years and a few thousand miles?
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Could be the small rubber line from the fuel pump to the hard line in the tank, they swell and get lose over time.
Thread Starter
Instructor
Joined: Feb 2007
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From: CRYSTAL RIVER FL.
Problem solved. Kinda. I replaced the sender/pump assembly about 3 years ago due to a failed gas gauge sender. Turns out the dealer sold me a ZR1 unit that has two pumps. The primary or bottom pump and secondary pump above that that tee together to a common outlet pipe.
Here's the perplexing thing. When the car died I could switch on and hear a pump run for about 5 seconds and shut off. Normal. This tells you the relay is good, and you have power to the pump. With a pressure gauge on the fuel rail and switch on, zero pressure? Car would start right up run for 5 seconds and die.
After removing the assembly I bench tested each pump. Primary lower pump dead. Secondary upper pump runs strong. Having just found out you can by just the pump on the after market, the ads always say "If ZR1 order two pumps".
So. If the pumps are both the same why would the car not run on the secondary upper pump with almost a full tank of fuel when the lower pump failed, and the LT1 is designed to run on only one pump?
And note that the upper pump is starved out below 3/4 empty mark.
Your thoughts; discuss.
Here's the perplexing thing. When the car died I could switch on and hear a pump run for about 5 seconds and shut off. Normal. This tells you the relay is good, and you have power to the pump. With a pressure gauge on the fuel rail and switch on, zero pressure? Car would start right up run for 5 seconds and die.
After removing the assembly I bench tested each pump. Primary lower pump dead. Secondary upper pump runs strong. Having just found out you can by just the pump on the after market, the ads always say "If ZR1 order two pumps".
So. If the pumps are both the same why would the car not run on the secondary upper pump with almost a full tank of fuel when the lower pump failed, and the LT1 is designed to run on only one pump?
And note that the upper pump is starved out below 3/4 empty mark.
Your thoughts; discuss.
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From: Lacey WA RVN 68-69
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The ZR-1 uses two pumps because it has two sets of injectors. The primary pump is used for normal street operation and the secondary pump is used for cold engine cranking and high RPM operation From what my '92 FSM says about the fuel pumps, the ZR-1 tank has a separate pump that insures fuel is always available to the regular fuel pump (section 6C2-3).
But I'm curious how a single relay could run both pumps. The ZR-1 uses two relays and also has two separate fuses (INJ1 and INJ2).
And why did that dealer install a ZR-1 pump in the first place? AC Delco pumps are available at many parts wholesalers. You can even get them on flea-bay. I would suggest getting the correct fuel pump and remove the ZR-1 pump.
But I'm curious how a single relay could run both pumps. The ZR-1 uses two relays and also has two separate fuses (INJ1 and INJ2).
And why did that dealer install a ZR-1 pump in the first place? AC Delco pumps are available at many parts wholesalers. You can even get them on flea-bay. I would suggest getting the correct fuel pump and remove the ZR-1 pump.
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Thread Starter
Instructor
Joined: Feb 2007
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From: CRYSTAL RIVER FL.
The ZR-1 uses two pumps because it has two sets of injectors. The primary pump is used for normal street operation and the secondary pump is used for cold engine cranking and high RPM operation From what my '92 FSM says about the fuel pumps, the ZR-1 tank has a separate pump that insures fuel is always available to the regular fuel pump (section 6C2-3).
But I'm curious how a single relay could run both pumps. The ZR-1 uses two relays and also has two separate fuses (INJ1 and INJ2).
And why did that dealer install a ZR-1 pump in the first place? AC Delco pumps are available at many parts wholesalers. You can even get them on flea-bay. I would suggest getting the correct fuel pump and remove the ZR-1 pump.
But I'm curious how a single relay could run both pumps. The ZR-1 uses two relays and also has two separate fuses (INJ1 and INJ2).
And why did that dealer install a ZR-1 pump in the first place? AC Delco pumps are available at many parts wholesalers. You can even get them on flea-bay. I would suggest getting the correct fuel pump and remove the ZR-1 pump.
The dealer didn't install it. I did. So, either it was the wrong pump three years ago, or I just didn't notice. The factory pumps are Delphi and are available at NAPA. I replaced the lower pump and went on. Also the factory body harness is a four wire end. The LT1 pump harness end is a three wire and the LT5 pump harness end is a four wire. I haven't checked but perhaps the LT1 has both relays as well.
Thanks for the feedback. Dave