Fuel pump relay issue with msd
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Joined: Jul 2012
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Fuel pump relay issue with msd
Hi!
I'm trying to install a VW Rabbit fuel pump on my 1975 Corvette with msd ignition.... But without success.
No matter how I do the wiring, the fuel pump runs directly on ignition on without the motor running. And it's not the priming...it runs forever.
My fuel pump relay has the pinout with 30,87,15,31 and 31b.
And my issue is problem howto wire the 31b signal.
I tried to connect it to:
1. Tach out on coil
2. Coil - on the coil
3. The msd unit Tach out signal
But my problem is that the relay starts at full directly on ignition without engine running. Anyone that are able to help me with the wiring?
Seems as the tach out signal at coil shows signal even without motor running. Is it possible to add some kind of pulldown resistor or something?
I really need all the suggestions I can get. Please!!
Thanks
Marcus
I'm trying to install a VW Rabbit fuel pump on my 1975 Corvette with msd ignition.... But without success.
No matter how I do the wiring, the fuel pump runs directly on ignition on without the motor running. And it's not the priming...it runs forever.
My fuel pump relay has the pinout with 30,87,15,31 and 31b.
And my issue is problem howto wire the 31b signal.
I tried to connect it to:
1. Tach out on coil
2. Coil - on the coil
3. The msd unit Tach out signal
But my problem is that the relay starts at full directly on ignition without engine running. Anyone that are able to help me with the wiring?
Seems as the tach out signal at coil shows signal even without motor running. Is it possible to add some kind of pulldown resistor or something?
I really need all the suggestions I can get. Please!!
Thanks
Marcus
Melting Slicks
Joined: Sep 2004
Posts: 2,655
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The oil pressure (Hobbs) switch comes with normally open and normally closed terminals. Wire the normally oppen to the keyed ignition, normally closed to the starter solenoid. That way the fuel pump runs while cranking.
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Thanks for the replys. Unfortunately I dont have the oil pressure relay. But my relay is intended to do pretty much the same.
My fuel pump rela has an tacho inpu that indicates that the engine is running...pretty much the same as the oil pressure switch does.
But now I need help from someone who has installed this type of relay and howto get the correct 31b/tacho signal.
One extra feature with this relay is that it also primes automatically on ignition.....
My problem is that the 31b signal suppose to be a pulsed tacho signal to gnd. But during ignition this signal is gnd already....
My current idea is to add a pullup-resistor 1K between coil tacho signal and 12v and then wire it to the fuel pump relay 31b ??
Anyone who worked with this type of relay....please help!!
/Marcus
My fuel pump rela has an tacho inpu that indicates that the engine is running...pretty much the same as the oil pressure switch does.
But now I need help from someone who has installed this type of relay and howto get the correct 31b/tacho signal.
One extra feature with this relay is that it also primes automatically on ignition.....
My problem is that the 31b signal suppose to be a pulsed tacho signal to gnd. But during ignition this signal is gnd already....
My current idea is to add a pullup-resistor 1K between coil tacho signal and 12v and then wire it to the fuel pump relay 31b ??
Anyone who worked with this type of relay....please help!!
/Marcus
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Joined: Jul 2012
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Yes! Here are some wiring example and a pic of the fuel pump.
and...
The 31b or in some diagrams 1 is the signal i don't get right.
Some says to connect to Tack, some says Coil-. But I tried both and the pump runs even when the engine not running.
Thanks
Marcus
and...
The 31b or in some diagrams 1 is the signal i don't get right.
Some says to connect to Tack, some says Coil-. But I tried both and the pump runs even when the engine not running.
Thanks
Marcus
Melting Slicks
Joined: Sep 2004
Posts: 2,655
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I think I see what they're trying to do. Is this on a points ignition?
If so, the negative post on the coil connected to the tach and points triggers the relat by grounding it. If your points are closed with the engine off, the relay will continue to run the pump.
A complicated solution to a simple problem. Buy a $10 oil pressure switc and $3 relay and wire it up the standard way.
Figure 3
http://www.jegs.com/InstallationInst...0/650-4110.pdf
If so, the negative post on the coil connected to the tach and points triggers the relat by grounding it. If your points are closed with the engine off, the relay will continue to run the pump.
A complicated solution to a simple problem. Buy a $10 oil pressure switc and $3 relay and wire it up the standard way.
Figure 3
http://www.jegs.com/InstallationInst...0/650-4110.pdf
Last edited by Garys 68; May 26, 2013 at 07:48 AM.
Drifting
Joined: Aug 2010
Posts: 1,839
Likes: 45
From: nassau co. new york
i agree with garys 68 and set up mine exactly the way v2racing did with the momentary prime switch.switch comes with wiring directions and is a no brainer to install.good luck. holley 12-810
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Yes, maybe the oil pressure switch is the only way to go....
But know I wired it up in this configuration and would really like to get it working. But i have just confirmed that it's the msd unit that grounds the coil- terminal directly even on just ignition on. I thought that the coil- / tach signal should be a pulsed gnd signal during engine running and free floating during ignition only...... Hmmm
Anyways.... I found another good picture how the relay works.
But maybe the oil pressure switch is the Only safeswitch that works. It's not really the price of buying the pressure switch....it's just that i already have som many potential leaking sensors on engine (water temp, oil temp, oil pressure to gauge....) I thought this might be the best way for safe fuel pump shutdown.
The oilpressure switch shutting down the fuel pump are known to not save the engines on oil pressure drops anyway because of all the fuel left in the carb.....
Thanks
Marcus
But know I wired it up in this configuration and would really like to get it working. But i have just confirmed that it's the msd unit that grounds the coil- terminal directly even on just ignition on. I thought that the coil- / tach signal should be a pulsed gnd signal during engine running and free floating during ignition only...... Hmmm
Anyways.... I found another good picture how the relay works.
But maybe the oil pressure switch is the Only safeswitch that works. It's not really the price of buying the pressure switch....it's just that i already have som many potential leaking sensors on engine (water temp, oil temp, oil pressure to gauge....) I thought this might be the best way for safe fuel pump shutdown.
The oilpressure switch shutting down the fuel pump are known to not save the engines on oil pressure drops anyway because of all the fuel left in the carb.....
Thanks
Marcus
Melting Slicks
Joined: Mar 2008
Posts: 2,666
Likes: 289
From: Spring Park MN
You don't need a relay that complex. All the diode, resisters, and capacitors just aren't necessary. A simple normally open relay of high enough current rating for your pump with the oil pressure switch. If you have the regular old style solenoid, you can hook into the ign terminal so it pumps while it cranks. I would also put in a momentary normally open switch so you can manually prime the system to make sure the carb is full before you crank it. Easier on starters that way.
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Ok...
Maybe I'll visit the stores tomorrow to what kind of oil pressure switches they have.
My current setup on the left rear side slightly above the oil filter already consists of a T-coupler takeout with the gauge oil pressure sensor upwards and the oil temperature sensor on the other T-output.
Those of you who installed the oil pressure switch, what is the suggestions to put it? Should I buy another T-coupler and add the pressure switch (that makes a quit big and heave sensorlump...
Or are there combo-gauge and switch sensor out on the market that offers signal both to my original gauge and to fuel pump?
Or are there any other standard locations to put the pressure switch?
Then the practical part... The cold engine oil level is located under the sensor positions? So it is safe to remove the sensors without loosing a lot of oil?
Marcus
Maybe I'll visit the stores tomorrow to what kind of oil pressure switches they have.
My current setup on the left rear side slightly above the oil filter already consists of a T-coupler takeout with the gauge oil pressure sensor upwards and the oil temperature sensor on the other T-output.
Those of you who installed the oil pressure switch, what is the suggestions to put it? Should I buy another T-coupler and add the pressure switch (that makes a quit big and heave sensorlump...
Or are there combo-gauge and switch sensor out on the market that offers signal both to my original gauge and to fuel pump?
Or are there any other standard locations to put the pressure switch?
Then the practical part... The cold engine oil level is located under the sensor positions? So it is safe to remove the sensors without loosing a lot of oil?
Marcus
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Joined: Jul 2012
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Ok!
So will this oil pressure switch do the trick? My local dealer has it in store..
http://www.summitracing.com/parts/smp-ps126
It seems to have 2 connection which I suppose connects when there is oil pressure. Therefore I'm able o choose if the high oil pressure should engage to gnd OR 12v depending on what I plug to the other pin.
But this switch hopefully fits into the threads behind the distributor and hopefully that narrow + long so it fits without hitting the intake bevel.
/Marcus
So will this oil pressure switch do the trick? My local dealer has it in store..
http://www.summitracing.com/parts/smp-ps126
It seems to have 2 connection which I suppose connects when there is oil pressure. Therefore I'm able o choose if the high oil pressure should engage to gnd OR 12v depending on what I plug to the other pin.
But this switch hopefully fits into the threads behind the distributor and hopefully that narrow + long so it fits without hitting the intake bevel.
/Marcus
Melting Slicks
Joined: Sep 2004
Posts: 2,655
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No, get the 3 post switch and wire as per the diagram in my earlier post. That relay design is a ridiculously complex solution to a simple problem. No oil pressure switch wil, or was designed, to save your engine in case of loss of oil pressure. They're designed to turn off an electric pump if you crash and the engine stops.
Search oil pressure safety swich on summit, or just get a 3 post locally.
Search oil pressure safety swich on summit, or just get a 3 post locally.
Race Director
Joined: Sep 1999
Posts: 11,361
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From: Plano TX
I actually kinda like it. One self contained unit that does everything. Too bad the MSD tach output doesn't mimic what a regular tach output does when the engine isn't running.
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Ok!
So you recommendation is a dual (nomally open and normally closed) safety switch. But this is to get the function for fuel pump during cranking.
But if my local dealer doesn't have this dual (I live in Sweden with high shipping cost and customs from summit) will my suggestion above work for normal operation.
Maybe I'll skip the "fuel during crank" function and concetrate on fuel at engine running AND adding a manual prime-button for manual prerun?.
Would that be a way to go if I cant get hold of the dual switch?
Thanks
Marcus
So you recommendation is a dual (nomally open and normally closed) safety switch. But this is to get the function for fuel pump during cranking.
But if my local dealer doesn't have this dual (I live in Sweden with high shipping cost and customs from summit) will my suggestion above work for normal operation.
Maybe I'll skip the "fuel during crank" function and concetrate on fuel at engine running AND adding a manual prime-button for manual prerun?.
Would that be a way to go if I cant get hold of the dual switch?
Thanks
Marcus
Drifting
Joined: Aug 2010
Posts: 1,839
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From: nassau co. new york
that would work but don't forget to flip the switch off after start up.one more thing to remember. i got mine through amazon but i don't know how there oversea shipping charges are.good luck
Last edited by billcarson; May 27, 2013 at 06:03 AM.
Melting Slicks
Joined: Sep 2004
Posts: 2,655
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The 3 post would be best. Maybe try ebay for overseas availability too.
A 2 post pressure switch with a momentary switch to prime would work. Just make sure the switch is closed with pressure. Standard dash light oil pressure switches, like the one in your link, open with pressure.
A 2 post pressure switch with a momentary switch to prime would work. Just make sure the switch is closed with pressure. Standard dash light oil pressure switches, like the one in your link, open with pressure.
Last edited by Garys 68; May 27, 2013 at 09:10 AM.
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hehe.... just as I thought. 
I tried to install my new pressure sender unit today.
The plug on engine top under the distributor was stuck as hell. So I ended up with a round allen plug.... still stuck as hell....
So my quest continues. Now I have a new oil pressure switch in a box, but the installation became a lot more complex. (Probably need to drill the plug and drain the engine on oil etc etc...)
Is there any combined oil pressure switch/sensor that works with both my 1975 dash gauge AND as a switch. (might just replace the stock one)
The problem is that on the left engine side I have both stock pressure sensor AND a oil temp sensor on a T-coupling.
Hmmm.. any suggestions ?
/Marcus
I tried to install my new pressure sender unit today.
The plug on engine top under the distributor was stuck as hell. So I ended up with a round allen plug.... still stuck as hell....
So my quest continues. Now I have a new oil pressure switch in a box, but the installation became a lot more complex. (Probably need to drill the plug and drain the engine on oil etc etc...)
Is there any combined oil pressure switch/sensor that works with both my 1975 dash gauge AND as a switch. (might just replace the stock one)
The problem is that on the left engine side I have both stock pressure sensor AND a oil temp sensor on a T-coupling.
Hmmm.. any suggestions ?
/Marcus