Primetime91

iTrader: (15)

Like the title says, I want to wire a toggle switch to control my fuel pump. Reasons: It would make a nice anti-theft device, and secondly the fuel pump only runs for the 2 sec prime period. I just replaced the oil pressure sending unit when I did my engine swap, I can't believe that would be the culprit. That leaves the relay I guess, but I think this is the perfect opportunity to install a switch. (I have been wanting to do this)

I was thinking I could splice into a switched power sourch such as the ignition, so it would still turn off when the key comes out. Any problems with doing it this way? I'm open to suggestions.

BigBadLou

iTrader: (3)

Two problems for doing it that way:
1) why reengineer something that has already been designed to satisfaction and probably just needs a simple fix?
2) for safety reasons, the electric pump should not be tied to power via a toggle switch.

To elaborate on 1)
- If your fuel pump primes, the relay is good, no need to replace it.
- If the fuel pump does not continue running when the engine starts up, you have a deeper problem, most likely the ECM.
- The FPOP (Fuel Pump Oil Pressure) switch bypasses the relay completely so if that one is good, you shouldn't even need the relay.
I recommend troubleshooting your fuel pump circuit real quick to identify the faulty component which can be then easily fixed/replaced: http://www.austinthirdgen.org/index.php?pid=35

As for 2), the main safety reason NOT to operate the fuel pump manually via a toggle switch is fire hazard. If you get hit by a lady in a minivan and you are knocked unconscious while fuel is spewing on top of the hot engine and exhaust manifolds because even though the engine isn't running anymore, your switch is still powering the fuel pump. It would be sad to lose a member due to a manual override switch.

Hope this helps.
Lou

Primetime91

iTrader: (15)

Point taken Lou. Thanks for the link, that should help.

BigBadLou

iTrader: (3)

Let me know if you have any more questions about troubleshooting the F/P circuit, I know it like the back of my hand. Or the front?

Lou

Primetime91

iTrader: (15)

I have a feeling that it has something to do with my V6 to V8 swap. Does knowing that change anything? I went from an '88 2.8 MPFI, to a carbureted 350. The only sensors I kept were: Oil pressure and water temperature (I went to a mech. fan, no need for the fan switch.)

Am I missing something I need? I was under the impression that the oil pressure switch/sender would take care of the fuel pump, but apparently not. I have had this issue since the first start up, and attempted break-in.

deadbird

Uh... yeah... this is VERY relevant information you would have wanted to include in you initial post.

FlyDoc

do you have an ECM at all with a swap to a carb?
if you want a toggle for anti theft then wire it to the ground side of the relay. that way you will still have the safety and the ability to over ride the relay.

BigBadLou

iTrader: (3)

Oh yes, that information is very pertinent.
Should we assume yuo kept the V6 ECM since you said that your fuel pump primes when you turn the key?
But if the ECM is not connected to the distributor, then it does not detect the distributor pulses and does not turn on the fuel pump (via the relay) once the engine is turning.

However, you only need the F/P prime from the ECM and if the FPOP switch is wired properly, it should take care of the fuel supply once the engine starts up. I would check the orange wire on the FPOP switch for power which comes from the single-fuse holder on the fender by the battery. That fuse is likely good since it powers both, the F/P and the ECM.

Hope this helps.
Lou

Primetime91

iTrader: (15)

Yes, I still have the ECM connected. I didn't want to remove any wiring until I confirmed that everything was working like it should.

I don't have access to my car right now, but I'm pretty sure the FPOP switch is operating correctly, as the instrument panel showed correct oil pressure when the engine was running.

If I read what you said correctly, the fuel pump "should" still turn on if the FPOP switch is hooked up, even though the ECM is no longer hooked up to the distributor?

deadbird

That is correct.
Keep in mind though, the oil pressure switch was not meant to be primary power for the fuel pump, only a backup in the even of relay failure. The wiring to the OPS is thinner gauge than what it running to the relay. Granted, it just enough to bypass the relay.
If you are wanting to keep this permanent, I would use the OPS to control the relay. You then could use a toggle to the other side of the relay to turn it off (security) as you please.
I hope you're running some sort of fuel pressure regulator with that pump as well.

Primetime91

iTrader: (15)

I'm using a Mallory #4309 for a regulator.

Deadbird, when you say you would use the OPS to control the relay, what exactly do you mean by that? How would you wire it? I'm sorry if it seems obvious, wiring is not always the easiest for me.

BigBadLou

iTrader: (3)

The F/P relay is actuated by positive voltage from the ECM. Deadbird is suggesting that the FPOP switch is wired to actuate the relay the same way. (instead of the FPOP supplying power directly to the F/P as it does now)

You can actually remove the ECM completely (you don't need it to run the carb and you don't need it to control the electrical fans since you removed them) and just use a momentary button to prime the carb bowls (if necessary at all).

Lou

Primetime91

iTrader: (15)

Oh....ok, that makes sense now. (I think).

Are you suggesting removing the ECM wire on the relay, and then putting the OPS wire in its place?

deadbird

Lou 'hit the nail on the head'.

Ignore the crudeness of the diagram (ms paint has its limits)..

Primetime91

iTrader: (15)

Thanks, the diagram definitely helps. I might be back with more questions once I actually get a chance to work on it though. Thanks, both of you