Technical (possible computer geek) question
Thread Starter
Race Director
Joined: May 2001
Posts: 14,165
Likes: 9
Technical (possible computer geek) question
First let me start off by saying I f'ing hate internet explorer. I had typed out this whole post, I had one sentence left to go and it just decided to clear the dialog box with no undo feature whatsoever. :smash: :smash: :smash:
Rather than waste my time explaining the whole situation again, I'll skip straight to the point. I need some sort of logical device that can see the sign pulse of an HEI distributor tach signal and put out a 12v constant so long as it is recieving that tach signal. I also need this to be run in parallel so it you could still run a tach.
Simply put I need to be able to use the tach signal to pick up a relay, which will drop out again as soon as that tach signal is lost. It also needs to be cheap or it's not worth doing. Please don't point out that I could use an output of the ECM for the same function, "I" know that, this is for a friend with a carb and no ECM. :cheers:
Rather than waste my time explaining the whole situation again, I'll skip straight to the point. I need some sort of logical device that can see the sign pulse of an HEI distributor tach signal and put out a 12v constant so long as it is recieving that tach signal. I also need this to be run in parallel so it you could still run a tach.
Simply put I need to be able to use the tach signal to pick up a relay, which will drop out again as soon as that tach signal is lost. It also needs to be cheap or it's not worth doing. Please don't point out that I could use an output of the ECM for the same function, "I" know that, this is for a friend with a carb and no ECM. :cheers:
Team Owner
Joined: Mar 2000
Posts: 83,384
Likes: 88
From: Boston, MA
Re: Technical (possible computer geek) question (Nathan Plemons)
Is it for anything critical? Here is an idea if nothing else. Get a MSD RPM window switch and put a super low and super high RPM pill in.
Thread Starter
Race Director
Joined: May 2001
Posts: 14,165
Likes: 9
Re: Technical (scorp508)
Actually it's for the fuel pump, so you could probably call that critical.
The deal is that the guy wants his fuel pump to work like it would have originally. Turn the key on and it primes the system for a second or two and then stops until you actually start the car. Then it would be nice that if the car died the fuel pump would shut off.
The priming feature is easy, you can just get a timed relay. The rest of it is real easy too so long as you have some kind of voltage source that is only on when the engine is running as opposed to just being on with the key. I'm just not real sure where to get a good source for that. On the ECM I would just tap the fuel pump driver, but he doesn't exactly have an ECM to do that with.
I don't know of any sources that would be hot only when running?
The deal is that the guy wants his fuel pump to work like it would have originally. Turn the key on and it primes the system for a second or two and then stops until you actually start the car. Then it would be nice that if the car died the fuel pump would shut off.
The priming feature is easy, you can just get a timed relay. The rest of it is real easy too so long as you have some kind of voltage source that is only on when the engine is running as opposed to just being on with the key. I'm just not real sure where to get a good source for that. On the ECM I would just tap the fuel pump driver, but he doesn't exactly have an ECM to do that with.
I don't know of any sources that would be hot only when running?
Team Owner
Joined: Mar 2000
Posts: 83,384
Likes: 88
From: Boston, MA
Re: Technical (Nathan Plemons)
Not sure about your LT1, but the L98 has a backup method of providing power to the fuel pump. It has a fuel pressure switch by the oil pressure sending unit. This works in parallel to the fuel pump relay. As long as there is decent oil pressure it provides current to the fuel pump. If the fuel pump relay ever died while the engine is running this little thing would continue feeding power to the pump. In this case if the engine died and the oil pressure dropped this would cut off the fuel pump.
Team Owner
Joined: Aug 2000
Posts: 40,156
Likes: 45
From: San Pedro CA
Re: Technical (scorp508)
Not sure about your LT1, but the L98 has a backup method of providing power to the fuel pump. It has a fuel pressure switch by the oil pressure sending unit. This works in parallel to the fuel pump relay. As long as there is decent oil pressure it provides current to the fuel pump. If the fuel pump relay ever died while the engine is running this little thing would continue feeding power to the pump. In this case if the engine died and the oil pressure dropped this would cut off the fuel pump.
As long as the oil pressure switch reads 4psi, it will fire the fuel pump.
Thread Starter
Race Director
Joined: May 2001
Posts: 14,165
Likes: 9
Re: Technical (scorp508)
Well I guess I should specify that this is for a carb'd 350 in a 3rd gen F-body. Right now he's just got the fuel pump to come on with the key, but that tends to run it a lot more than needed should you ever need to just sit with the key on.
As such he's not gonna have any of the cool sensors. F'n carbs, I hate em.
As such he's not gonna have any of the cool sensors. F'n carbs, I hate em.
Thread Starter
Race Director
Joined: May 2001
Posts: 14,165
Likes: 9
Re: Technical (scorp508)
He might. I'm not sure what vintage block he's actually gonna end up with. I know my LT1 has 2 sensors there on the back of the block, right behind the intake. He should be able to make one clear his distributor.
Using a timed relay as mentioned wouldn't even require that it make enough oil pressure while cranking. Turn the key on, it'll prime, which since it's a carb would keep enough fuel in the float bowl to start it. Then after it fired it would pick up enough oil pressure to activate said switch.
That's a really good idea Scorp, I didn't really see what you were getting at at first, but it might just work. Now I wonder how much the sensor costs....
Using a timed relay as mentioned wouldn't even require that it make enough oil pressure while cranking. Turn the key on, it'll prime, which since it's a carb would keep enough fuel in the float bowl to start it. Then after it fired it would pick up enough oil pressure to activate said switch.
That's a really good idea Scorp, I didn't really see what you were getting at at first, but it might just work. Now I wonder how much the sensor costs....
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
5 Best & 5 Worst Corvette Daily Drivers
Joe Kucinski
The Headlights of Every Corvette Generation Explained
Joe Kucinski
5 Best & 5 Most Overrated Corvette Track Packages of All Time!
Joe Kucinski
Every 2027 Corvette Engine Explained
Joe Kucinski
Designer Imagines A Corvette That Looks More Like a Corvette Than the Corvette
Verdad Gallardo
10 Ugly Corvettes That We Still Kinda Love
Joe Kucinski
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
Le Mans Master
Joined: Jan 2003
Posts: 8,596
Likes: 19
From: Portland Oregon
Re: Technical (scorp508)
NAPA has them for about $7. Just go there and check out their oil pressure switch catalog. I used a NAPA part number OP 6118. I wired in a relay system that latches with the OP switch. During cranking the fuel pump gets its power from the Starter S terminal through a 4 amp diode so it can be powered just during cranking. Once started the OP switch closes which activates the relay to power the pump. This was done on an old 69 Camaro that I installed a 502 carbed engine.
[Modified by tjwong, 8:16 AM 5/5/2004]
[Modified by tjwong, 8:16 AM 5/5/2004]
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Re: Technical (possible computer geek) question (Nathan Plemons)
I've blown the circuit in my ECM that primes the engine and runs the fuel pump. Don't ask. I installed a push button under my dash, jumping terminals "A" and "G" on my ALDL for priming purposes. You're buddy could install such a push button to fill the carb, if necessary and rely on the oil pressure switch to keep the car running. Then, unlike our cars, the pump will shut off when the oil pressure drops. If his ALDL lacks the "A" & "G" function, the button could be simply wired to the oil pressure switch. Simple and cheap.
RACE ON!!!
RACE ON!!!
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Re: Technical (possible computer geek) question (Nathan Plemons)
PS. With the reserve fuel he has in his float bowls, he will probably have to use the push button or any other device he chooses, very rarely.
RACE ON!!!
RACE ON!!!
Thread Starter
Race Director
Joined: May 2001
Posts: 14,165
Likes: 9
Re: Technical (CFI-EFI)
Well he lacks the ALDL connector period, so you can't do it that easily. It would be easy like you said to prime the pump using a pushbutton. My dad mentioned that last night. Using a timed relay though the prming function is really easy with the on with the key.
Like you say, he probably doesn't even really need it unless his carb sits for a long time and it evaporates.
Like you say, he probably doesn't even really need it unless his carb sits for a long time and it evaporates.
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
Re: Technical (possible computer geek) question (Nathan Plemons)
You could use a logic probe connected to the tach output from his distributor to operate a relay to power the fuel pump. The circuit for a logic probe is pretty simple and surely available from a search on Google.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Re: Technical (Nathan Plemons)
I was corrected recently in another post about jumping "A" to "G", but since he doesn't have an ALDL, that is moot. If he just connects the push button to both terminals of the oil pressure switch, he'll be done... for cheap and simple.
RACE ON!!!
RACE ON!!!
