with both.
Quick fuel pressure question.
Thread Starter
Safety Car
Joined: Nov 2001
Posts: 4,166
Likes: 2
From: Las Vegas NV
Quick fuel pressure question.
With the key on, car not running, should fuel pressure hold steady or will it pump up and then drop off to "0"?
Searched the archives and didn't really find an exact answer to my question.
Car in question is an 86, all stock.
TIA,
David
Searched the archives and didn't really find an exact answer to my question.
Car in question is an 86, all stock.
TIA,
David
Safety Car
Joined: Sep 2003
Posts: 3,599
Likes: 24
From: Orange County NY
St. Jude Donor '10-'11-'12-'13
Once it pumps up to 40 psi or so, it should hold for a bit. Now comes the question - how long? On my car, it will hold for about 30 minutes. You'll find a LOT of variation to that figure (from 10 minutes to 24 hours 
), but if it is going to zero right away, there is likely a reason (injectors leaking, fuel pump, pressure regulator - fuel is bleeding down somewhere). The factory service manual has a procedure for methodically pressure checking the system.
), but if it is going to zero right away, there is likely a reason (injectors leaking, fuel pump, pressure regulator - fuel is bleeding down somewhere). The factory service manual has a procedure for methodically pressure checking the system.
Thread Starter
Safety Car
Joined: Nov 2001
Posts: 4,166
Likes: 2
From: Las Vegas NV
New pressure reg....new fuel pump......turn key to on position, fuel pump runs for a couple of seconds, goes just over 45 psi but then drops to zero within a couple of seconds.
Looks like I must have some bad injectors bleeding pressure down.....
AnY other ideas / suggestions???
Looks like I must have some bad injectors bleeding pressure down.....
AnY other ideas / suggestions???
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
Fuel pump....bad check valve or pulsator.Cheaper than injectors and easy to check. A misconception...each time the key is turned on the FP pressurizes the system, it does pressurize the system....but if the key is turned on and off and then on again in less than 10 seconds it will not pressurize again the second time unless enough time has lapsed.
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Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
There are a few procedures need to find out where the leak is. With my old stock FPR and with my new Holley AFPR the fuel pressure leaks down within 8 minutes or so. The injectors and cold start valve were not leaking and the new injectors and cold start valve are not leaking. I confirmed they by raising the fuel rail and priming the fuel system to verify. I pinched off the fuel feed line after priming the system and pinched it off and the pressure still leaks down. Same for the return line. My FPR has never had gas in the vaccum, so I really don't know where it's going (no external leaks).
As stated, when the key is turned on....the ECM energizes the fuel pump relay which sends 12v to the fuel pump, but only for 2 seconds. This can be heard audibly. There is a 10 second interval where you have to wait for the fuel pump to be primed again by just turning the key "on".
All this does is build pressure to the fuel rail so there is fuel to start the engine. Once ~4 psi of oil pressure is made, the oil pressure switch closes the fuel pump circuit and sends 12v to the fuel pump.
As stated, when the key is turned on....the ECM energizes the fuel pump relay which sends 12v to the fuel pump, but only for 2 seconds. This can be heard audibly. There is a 10 second interval where you have to wait for the fuel pump to be primed again by just turning the key "on".
All this does is build pressure to the fuel rail so there is fuel to start the engine. Once ~4 psi of oil pressure is made, the oil pressure switch closes the fuel pump circuit and sends 12v to the fuel pump.
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
DaBo, just saw you post before me. You need to get some vise grips and take the gas lid and rubber boot off. You will see three lines. Top right is the fuel feed line, bottom right is the fuel return line, and the left one is the EECS or vapor canister line.
Turn the key "on" and quickly pinch off the top right line...then watch the fuel pressure. What does it do? Do the same for the fuel return line.
If the pressure still drops off, pull the spark plugs and look for signs of gas or wetness and pull the vacuum off the FPR and see if it has gas in it.
Turn the key "on" and quickly pinch off the top right line...then watch the fuel pressure. What does it do? Do the same for the fuel return line.
If the pressure still drops off, pull the spark plugs and look for signs of gas or wetness and pull the vacuum off the FPR and see if it has gas in it.
Team Owner
Joined: Jan 2003
Posts: 20,315
Likes: 245
From: Summerland B.C. Canada