Bought an 87 with lots of upgrades. Had been sitting on blocks for 12 years, long story short finally have most issues sorted out. Had to replace fuel pump and when I pulled tank found two fuel pumps. Replaced both and after following wires to 2nd pump found them hooked to a solenoid installed in fuel line then to a switch in the vacuum line. Is this something that boost in the vacuum line kicks on under certain boost to activate the pump as it is not working and what is the purpose of the solenoid? Any one with knowledge of this as I realize it is older tech as this car was built in the 90s If it is a switch where can I get a new one? I know it is not working because when I go to full throttle fuel pressure drops considerably and motor shuts down. The person that owned this car passed and I bought it from an estate sale so no history known! When I run a hot wire to pump fuel pressure goes to 63 lbs can I just hook a switch to it and manually activate it and does it cause a problem creating that kind of pressure for any length of time I am a newbee but I have really fell for this car but it is completely different from all my other cars as I was a pretty good carb guy!
auxilary fuel pump
- Thread starter chethejet
- Start date
ScottHeidinger
Active Member
- Joined
- May 2, 2015
Second pump should be on a boost activated relay. The pump will probably only come on at higher boost levels 12-17 using the Hobbs switch on the vacuum line. You don’t want both pumps running all the time as the stock fuel return line can’t handle that much and there is no need for the second pump until you are at a point that one pump can’t provide enough fuel. It’s probably working like it should but to test it I would apply air pressure to the switch on the vacuum line to make sure the second pump activates. Don’t put 80 plus psi to the switch. Start low and by 20 psi it should activate.
HTH
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HTH
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salvageV6
Daily Driver
- Joined
- May 25, 2001
Napa has hobbs type switches boost activated.
Plenty of other sources such as ebay as well.
Assuming that's the part you need.
https://www.napaonline.com/en/p/BK_7011609
Plenty of other sources such as ebay as well.
Assuming that's the part you need.
https://www.napaonline.com/en/p/BK_7011609
michael evans
Well-Known Member
- Joined
- Feb 27, 2008
63 pounds is to much for at idle (needs to be 40-42 pounds).
There is a couple reasons for that.
You should not have to "jump" to get fuel pressure as soon as you turn the key to the run position the computer will run the pump form two to five seconds to prime the system then after the engine has oil pressure, it will turn the pump back on.
There is a couple reasons for that.
You should not have to "jump" to get fuel pressure as soon as you turn the key to the run position the computer will run the pump form two to five seconds to prime the system then after the engine has oil pressure, it will turn the pump back on.
I notice that the switch is after the check valve in the vacuum line is that correct I would think that is not right , I had the vacuum lines off and I might have put them on wrong as I did not make a diagram before I took them off! Thank You so much for your tips!!! I notice when I click and look at switch you gave me the link to that it has a threaded end my switch is in the vacuum line and it is a pass thru switch are you familiar with that type?
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The fuel pump hooked to the stock wiring harness does put fuel pressure to 43 pounds at idle with vacuum line off but pressure drops when I go to wot! That is why I feel auxiliary pump is not working as it should. The car has 80 lb injectors and turbo tweak chip to 18 lb boost!
Thank You!!!
Pronto
Believe nothing you hear and half of what you see.
- Joined
- Dec 9, 2002
Post a full list of the mods. After sitting 12 years I would be thinking it's time to start fresh with either a high volume single or a new dual pump setup with a fresh hot wire kit for the setup. You need proper reliable fueling or you'll be picking up pieces that were once your pistons.
michael evans
Well-Known Member
- Joined
- Feb 27, 2008
Sounds like one of the connections is not letting amperage pass.
Can be something simple like the relay by the MAP (most likely) or complicated.
Try temporary passing each one.
With our cars getting up there in age, the wiring is starting to fail. I had to replace the engine wiring harness in my low-mile T
Can be something simple like the relay by the MAP (most likely) or complicated.
Try temporary passing each one.
With our cars getting up there in age, the wiring is starting to fail. I had to replace the engine wiring harness in my low-mile T
1986 Buick GX1
GX1 #001 [The One and Only]
- Joined
- Apr 24, 2015
I believe the Hobbs switch should be between the vacuum block and the check valve. Maybe this is what savageV6 means, I just thought I'd try to clarify.
The check valve prevents boost from going beyond it, so if the check valve is between the vacuum block and the Hobbs switch the Hobbs switch won't see boost and won't activate the second pump.
As mentioned you can check the Hobbs switch by applying air pressure. Start low and work your way up to see when the switch has continuity. Most double pumpers activate the second pump at 15 psi. (where the first pump starts to fall off)
Verify the switch works, then verify the switch is getting boost and go from there.
If you put a jumper wire across the Hobbs switch terminals and the pump runs you know your wiring is good. (maybe this is what you did when you said you ran a hot wire to the pump)
salvageV6
Daily Driver
- Joined
- May 25, 2001
I was thinking the check valve would only allow boost through and not vacuum which might damage the Hobbs switch? Depends on how the check valve is plumbed in there and all of them should be checked for proper operation on a car that's been sitting for sure.
I think the O.P. had better learn a lot about how the car was built and what's on it before trying to go under a lot of boost.
Most double pumper setups are on higher HP built motor cars.
Time to take a lot of pics. including the double pumper setup as far as wiring and vacuum lines.
I'd make sure it's got a street-able pump gas chip in it first before going WOT.
I think the O.P. had better learn a lot about how the car was built and what's on it before trying to go under a lot of boost.
Most double pumper setups are on higher HP built motor cars.
Time to take a lot of pics. including the double pumper setup as far as wiring and vacuum lines.
I'd make sure it's got a street-able pump gas chip in it first before going WOT.
michael evans
Well-Known Member
- Joined
- Feb 27, 2008
The check valve being bad or on backwards will cause problems but not what he is seeing.
I also have had to learn things the hard way.
If you can not get someone to ride with you to watch any gauges then install some type of data logger.
The first gauges to get is a fuel pressure and O2. Then boost pressure.
I also have had to learn things the hard way.
If you can not get someone to ride with you to watch any gauges then install some type of data logger.
The first gauges to get is a fuel pressure and O2. Then boost pressure.
michael evans
Well-Known Member
- Joined
- Feb 27, 2008
The check valve is there to protect and allow the air conditioning control valves to work correctly and another, larger one if it has vacuum brakes that is seperate.
It has nothing to do with the hobbs switch.
The hobbs switch should be before the check valve in the vacuum line. It will see both vacuum and boost.
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