Why unhook vacume hose??
Thread Starter
Advanced
Joined: Nov 2005
Posts: 54
Likes: 0
From: Mountain Home AR
Why unhook vacume hose??
When checking fuel pressure today on my stock 86 for the first time, it was 46# with the vac line to the reg. hooked up. Un hooked and pluged, it read 36#. First---is the pressure ok?? Second----with the vac pluged,it took 3 min. to leak down to 36#. Then it just stayed at 36# for another 10 mins, so I unhooked the gauge.Why on the form do you say to unhook the vac line and plug to run this test. Whats the diff.??
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
First off, your fuel pressure is fine, although I usually leave mine attached for about 1/2 hour to watch the bleed off. The second part of the test is for checking the health of the Fuel pressure regulator.
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
The 46 psi with the FPR vac connected it high to me. When the FPR vac is off it should read 5 psi higher than with the vac connected if the vacuum is correct neg pressure. Normal fuel pressure for a 86 is 36-40 psi vac connected and with the vac disconnected it should be in the low/mid 40's. I haven't ever plugged the FPR to check fuel pressure. When you watch for fuel pressure bleed, the engine should be off and no vacuum will be present connected or disconnected.
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
On my 86E, when you first turn the key the fuel pressure goes to 42psi and when the pump is primed (after 2 sec) the pressure stops at 40 psi. After the engine is started the pressure stays at 40 psi. I am on the high side of fuel pressure for the L98. This is the reason I purchased a AFPR, to decrease fuel pressure to compensate for larger injectors I have. My pressure is at 40 psi engine running and when the FPR vacuum is disconnected the pressure goes to 45-46 psi. From what I remember reading...L98 (36-40) LT1 (40-46). Vacuum connected on all. I consider this normal.
I don't have a way to confirm this right now.
I don't have a way to confirm this right now.
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
This is what my FSM for 87 says;
"Ignition "ON" pump pressure should be 280-325KPa (40.5-47 psi). This pressure is controlled by spring pressure within the regulator assembly.
2. When the engine is idling, the manifold pressure is low (high vacumn) and is applied to the regulator diaphram. This will offset the spring and result in a lower fuel pressure. This idle pressure will vary somewhat depending on barometric pressure, however, the pressure idling should be less indicating pressure regulator control".
"Ignition "ON" pump pressure should be 280-325KPa (40.5-47 psi). This pressure is controlled by spring pressure within the regulator assembly.
2. When the engine is idling, the manifold pressure is low (high vacumn) and is applied to the regulator diaphram. This will offset the spring and result in a lower fuel pressure. This idle pressure will vary somewhat depending on barometric pressure, however, the pressure idling should be less indicating pressure regulator control".
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
