84 S10 runs good then quits

[mdh250]

I have an 84 S10 blazer with an upgraded 3.0L and a external electric fuel pump which hooks up through the oil sending unit? It runs really good then it will die at varied times but will start back up in a couple of minutes. I've just had the distributor rebuilt and bypassed the oil sending unit to hot wire the fuel pump still same problem. Anyone else had this happen?

[OverBoardProject]

Welcome to Automotive Forums!

What did you get a 3.0L from?

I knew that Chevy mad a 2.8l, 3.1L, and a 3.4L. All of which are basicly the same. But I've never heard of their 3.0L.

Do you still hear the fuel pump when it dies?

Personally I would never consider running the fuel pump off either source.
You can use them to triger a relay and have the relay run the fuel pump. But it uses to much energy to run in your set up.

A head light relay should work fine, and only cost about 10 - 15 bux here in Canada. This might solve your problems
They're a 3 wire setup, and it should only take you about 1/2 an hour to install.

[mdh250]

Thanks for your reply. Sorry for the typo the motor is an 3.4 crate motor from chevy that they installed before we bought it. The last time it quit I shut off the key just long enough to coast to a stop got out and open the hood I turned the key back on enough to get power to the pump and it was running, so I got back in and it fired right up and ran fine but you never know how long it will go before it quits it could be a 1/4 mile or the next day before it acts up again. Any tricks on the head light relay or just straight forward. Because I was told and learned through the other posts that the pump is wired that way to shut off at no oil pressure for safety reasons.

[OverBoardProject]

Those are the best motors for your truck. I wish that I had 1 in my Blazer.

It's pretty straight forward with the relay.
It's a 4 wire unit, with a map for which wire goes to the switch, ground, and then the other 2 go to your power supply and the fuel pump

[MT-2500]

The oil pressure switch for a fuel pump is not a saftey set up. It is used as a helper in case the fuel pump relay quits.
If you are running fuel injection on this engine you should have a in tank fuel pump setup.
The external puel pumps are short life and are not real dependable.
Is this a carb or fuel injection setup on the engine?

[OverBoardProject]

84 is still carburated, which is why mdh250's truck was set up that way.

The 3.4L was always fuel injected, wheic is the only reason why they used an electric fuel pump.

I think that it's a pretty good idea to use the oil sending unit just to trigger a relay. It'll only be energised while the truck is running and will kill the motor if there is a sudden loss in oil pressure (depending upon how it's wired in)

I believe that newer fuel injected models partly rely on the same setup, to shut their engines off if there's no oil pressure.

[MT-2500]

Originally Posted by OverBoardProject

84 is still carburated, which is why mdh250's truck was set up that way.

The 3.4L was always fuel injected, wheic is the only reason why they used an electric fuel pump.

I think that it's a pretty good idea to use the oil sending unit just to trigger a relay. It'll only be energised while the truck is running and will kill the motor if there is a sudden loss in oil pressure (depending upon how it's wired in)

I believe that newer fuel injected models partly rely on the same setup, to shut their engines off if there's no oil pressure.

On the oem systems that use a oil pressure switch with the fuel pump relay.
The oil pressure switch is only along for the ride. The fuel pump relay does the key on prime and turns on fuel pump when the pcm starts firing the ign and injectors.
The oil pressure switch is only there to keep the engine running in case the relay fails.
It could be wired all together threw the oil pressure switch but you would need a primer switch or button to prime up the fuel pump pressur for starting untill the oil pressure comes up.
The primmer button and fuel pump running off of the oil pressure switch was used on a lot of older large trucks when they started putting fuel pumps on the gas tank.
On the posters external fuel pump a in tank high pressure fuel pump would work a lot better than external fuel pump system.
Just like a old house type well or deep well water pump a water pump can push a lot better than it can pull.

[mdh250]

The Blazer is carburated and was an upgrade from the original 2.8 thats why it has an external elec. pump. The pump only has two wires one from the oil sending unit and a ground. It sounds like I'm looking at a new pump and relay just which way is best? And I've looked for the relay from the manual but can't seem to find the same looking thing. I don't know what they did at the dealer when they changed motors.

[MT-2500]

The external add on electric fuel pumps were always short life pumps.
The oil pressure switch running/wired off of fused ign should run the fuel pump ok.
Make sure the elecric pump is mounted as close to the tank and and as low on the frame as you can get it. Keep in mind it will push fuel a lot better than it will pull it.
Aso for easier starting or to get the fuel primed up in to the carb. You could put a push button for a fuel pump primer on it.
And if oil pressure switch ever quits it would help you get back home.

[mdh250]

Thanks for all your info. I really appreciate it, since I became disabled a couple years back it's difficult to help my teenage sons work and learn to keep their vehicles going.
The elec. fuel pump is now mounted on the drivers side front wheel well next to the brake line jct. block. If I mount the pump near the tank and use a headlight relay per "OverboardProject" should I mount the relay in the rear also and run it off the hot wire to the lights or ? or put the relay up front and run all new wires back to the pump?

[OverBoardProject]

Leave it with me until tonight, and I'll make up a drawing of what I would do. Then the other members might also have something to add or change.

I'll post the drawing on this thread.

[mdh250]

Thanks again.

[OverBoardProject]

I haven't forgotten about it.
I've got the pic made up, but I want to describe what to do, and take a pic of where to run the power wire (it was pouring out here today so I didn't want to take the digital camara out)

With the exception of the the photo I'll have it on a web style page tonight with a link

[OverBoardProject]

I'm happy with it now.
What are your opinions on the setup
http://mypage.uniserve.ca/~kvsbt/scr...mp%20wire.html

After a bit of remembering your oil pressure unit only has 1 wire going to it. So it's fully energised whenever the key is on. This means that the S10 won't shut off with no oil pressure, but you won't need a primer button with this setup.

[mdh250]

I know this is a dumb ? but where does this switched source come from? I'm not to familiar with the elec. part on vehicles.