I was so excited - an hour ago I finally had everything done from my TPI to carb swap - manifold, carb, distributor, new fuel lines hooked up, etc,- and then I turned the key and...nothing - the fuel pump didn't come on - was there something hooked up to my TPI system that controlled the fuel pump? I seem to remember reading something about an oil pressure check switch...any thoughts as to why the pump would stop working after a TPI to carb swap?

 

Did you tamper with the ECM at all? I think the ECM is required to operate the factory fuel pump relay.

 

The FP relay is on the firewall on the drivers side. There's an oil press switch that needs to sense pressure before your fuel pump will turn on, that's at the back of the motor by the dissy, it needs to be connected.
The fuel pump will run for a few secs when you turn your key on, but then shut off again if there is no signal from the oil press switch.
It's possible that if your carb bowls are dry, the fuel pump did come on momentarily, but it didn't put enough fuel in the bowls to get it to start.
There's a FP test terminal on the ALDL (I can't remember which one) it should say something about it in your manual if you look up FP pressure test.
If you use the test terminal you can pressurize the system, fill your bowls, check for leaks, set the float level, all without starting the motor.

Hope this helps

 

OK, now I'm scared because I sold my ECM along with the rest of the TPI system (based on advice I got here that I didn't need the ECM for anything after the swap). I do have the oil pressure switch connected (single brown wire going to a silver canister at the back of the block right next to the distributor), but when I turn the key - nothing. I would have heard it come on. Would the ALDL test work without the ECM in place?

 

double

 

orrrrrrrrrrrrrrrr you could bypass the realy and the oil pressure switch..run a wire to the FP realy to a switch...key up flip the switch fuel pump is pumping...

you could also run a wire from a 12v on/off in the fuse block to a switch then to the grey wire under the back seat for the fuel pump...

Either way will power the pump and youll be golden


The fuel pump will come on for a few seconds to pressureize the rails...when the injectors pulse (motor fires) is when the fuel pump and oil switch work together to fire up the pump

 

There's the oil press sending unit, which is connected to your gauge. And there's the oil press/ FP switch which is something entirely different.
I can't remember how to tell them apart, but you need to be sure they're both connected.

 

f-crazy - what did you mean by "Double"?

Do I still want the oil pressure switch involved in a carbed setup?

"orrrrrrrrrrrrrrrr you could bypass the realy and the oil pressure switch..run a wire to the FP realy to a switch...key up flip the switch fuel pump is pumping... "

OK, you'll really have to elaborate on that one...from what point/wire on the relay to what point/wire on the FP? (I'm a total newbie with this stuff - I almost need a diagram ..hint)

How can I troubleshoot what I have now?

 

Where would the oil pressure/FP switch be located? I guess I just have the one to my guage connected - the one next to the distributor..

 

The oil press switch is good to have cause it shuts off your FP if the engine is not running.
Such as if the engine dies and you forget to turn the key off... or if you crash. If you think about that for a minute, you'll see why you want to keep it.

 

On my 85 both the oil press sender and the FP switch are connected to a T at the rear of the motor.
the sending unit has 1 wire and the switch has 2 wires... I'm pretty sure. One of those wires (orange on mine) goes to the relay.

 

There are some wiring diagrams in Tech Articles, If you don't have one.

 

the factory had a redundant fuel powering circuit on your car. The ECM and the oil pressure switch are run in parallel to power the pump. I believe they had the ecm power the fuel pump relay so that it could pre-prime before starting and shutting down. I'm not sure why it was wired the way it was, because even if you lost oil pressure, the ecm could keep the pump running.

anyway, if you still have your wiring intact, the fuel pump relay should be controlled with a green wire that went to the ecm. You can connect that wire to an ignition source, and the fuel pump will come on as soon as the ignition is on, or you can leave the wiring alone, and the pump should come on once you get oil pressure. I would wire the relay control, so that the pump will prime the carb before the engine is even started, but its personal preference.

remember, that pump is a high pressure pump, you NEED to plumb in a regulator to knock the pressure down to the carb friendly 4-6 psi. I would recommend a bypass regualtor, so that the pump doesn't have to work too hard, and hopefully, the return line is still in the car, and would make the hook up easy. Good luck!

 

Isn't that a chicken and egg scenario? How can I get oil pressure without fuel? Fill the carb manually somehow? ( If the answer to this is painfully obvious - forgive me, I was up reeeally late last night trying to get this working....)

And yeah I put in a Holley regulator with 1 line back to the tank...

 

The priming feature of the FP circuit (through the ECM) is timed to come on momentarily when the key is initially switched to run (or start?)
That's to pressurize the fuel rails before starting. But then after that the oil press switch will open or close the circuit, in the event of the engine shutting down or otherwise losing oil pressure.
The priming feature is unnessecary with a carb, cause your float bowls will be already filled before starting.
It's good to have a manual priming button wired in to pressurize the system for checking the fuel press, or to prime the system after it's been worked on.

 

Also Cra-Z, do you have a gauge on the fuel line?

 

You don't really want to run the stock TPI pump anyway. I tried to way back when, I even bought the correct regulator, but I couldn't get the psi below 15 psi. regardless of what I did with the regulator. it just wasn't happening. plus, once the pump is regulated down, it will not supply enough volume of fuel to support serious motors. your best bet is too swap in a mechanical pump, or an electric pump that is more suitable for a carb. sorry to say that means your stock pump has to come out, which requires removing your tank, which requires more less dropping the rear end. which is why I'm glad i no longer own a third-gen. trust me, your never going to be able to properly tune your car with that pump. you might just as well do it the right way.

 

Just because youve ahd issues with a pump does not mean he has to yank his. There are at least a few members on this board who run it [carb setup] on a TPI pump. Youre absolute best bet is a pump with a return such as the Mallory 4309.

As for the relay, mine took a crap on me once and i had to get it on the road so i just spliced into the pumps power supply wire and got a radio shack relay and went from there. Theres a power constant hot, acc wire (for now, its acc), ground, and power out to the pump. Ive spliced a flip switch into the acc wire. It seems to be working.

 

thats the regulator I used. it didn't work at all. maybe I got a lemon, but I had no luck whatsoever. even at 15 psi, there is no volume. I was advised by a very reputable mechanic to do a volume test with the regulated pump, and it wasn't even up to par with the stock mechanical pump. it will not support a serious motor.

 

I used the BG afpr on mine, the instructions were hard to figure out cause it isn't originally designed for TPI/ carb swaps, but it's working wonderfully right now.
Another tip.... don't buy a liquid filled pressure gauge.

 

Holley makes a safety switch that powers the pump while cranking & it works very well in carbed applications. Wiring the relay to the start side of the ignition switch would accomplish the same thing. Definitely don't bypass the safety feature of the oil pressure switch. A friend of mine completley destryed his V-8 S10 by starting it up one cold morning & going inside while it warmed up. It stalled out & the pump kept running. The fuel ignited & burned the truck & woods next to it to the ground. Fortunately it was not too close to the house or garage.

 

I'm sorry to be so dense but I'm still not sure how to do this -

What exactly does the FP relay look like (color, how many wires in/out, exactly where is it on the firewall, etc,)

Also, is there a separate oil pressure sensor somewhere other than the one next to the distributor that activates this relay, or is the one next to the distributor supposed to be connected to the relay as well as the guage?

Once I establish that everything is hooked up in the engine bay, is there ever going to be a way to get it to do the "3 second prime" now that the ECM is gone?

Pretend like you're explaining this to a 10 year old...

 

the relay is black, located on the firewall between the master cylinder booster, and drivers fender. The 4 wire colors listed in the 89 vette schematic I have are Red, Orange, Black and Green. I forget which relay it is exactly though.

The oil pressure sender(to the dash guage) is the big dopey thing with one wire, usually located by the distributor. the oil pressure switch is the smaller one, located down by the oil filter, with two wires, I think the harness connector is a light brown color.

the oil pressure switch turns on at like 4 psi, so if the engine cranks over, thats usually enough to close that switch. The best way to do it is to just use the pressure switch, as RickTPI pointed out, if the car stalls and the carb needle and seat don't shut off, the pump would keep going using the relay. Ideally, with the regulator plumbed in correctly, and the needle and seat right, all that would happen would be that the fuel would recirculate back to the tank, but it could be an issue.

the 3 second prime won't happen without the ecm in place.

 

My car is an 85, there are 5 wires on the FP relay. It's on the firewall on the drivers side. It's a little squarish box.
On my car the FP oil press switch is located right next to the sending unit at the rear of the engine. It has 2 orange wires on it.
With a carb the 3 sec prime won't be nessecary, cause the fuel bowls on the carb are a reservoir that holds enough fuel to get the engine started.
It's a good idea to rig up a pushbutton that will power your pump for testing and for a manual prime, if nessecary. Possibly you can make a jumper that you place across the 2 terminals of the oil press FP switch that will prime your system.
But on my own, I found 2 other wires that I used for that.
First find the oil press FP switch tho, and try jumping those 2 terminals. Maybe on your car that switch is in a different location than mine.
The wiring diagrams that are in the Tech Articles are good, but they're only shown for 85 and 86. but maybe the 86 diagram is the one you need.
Try checking those things out and study it til it makes sense.
Too bad your ECM is gone, cause it's complicating the prablem right now, but you don't need in the long run. But there are some needed wires that are within the ECM harness that would be easier to trace with the ECM plugged in, so if you could get it back for some tests it might help.

I hope what I've told you is correct,
if it isn't someone correct me.

 

I did a search on the Electrics board "fuel pump relay" I think, and found some info on how to test the pump.
Unfortunately when you ditched your ECM, the ALDL connections went with it.

 

It dawned on me that the problem could be that you or whoever replaced your block might have lost or left out the oil press FP switch.
Might that be it??

 

Don't think so, because it ran (very poorly) with the TPI on it, the only thing that's changed since it was running is the TPI is gone and the ECM is out (minor mods, no?)

I'm leaving work now (finally) to go and track down that switch- wish me luck!:lala:

 

I just finished the installation on my completely rebuilt 350 and rebuilt 700R4. Today was the big day. We started it, and it ran, for about 5 seconds. The fuel pump shut off, therefore cutting the fuel supply to the carb. I'm running the stock electric pump in the tank to the Mallory 4309, then to the carb. It sounded great for those 5 seconds, but then i ran into the same problem as Cra-Z. This thread has helped me a lot, I'm gonna try to work it all out tomorrow, i'll let you know how far I got. The only question I have is the colors of the two wires for the oil pressure switch, and do I just directly connect that to the FP switch?

 

I can't speak -

Good news - I found the FP switch (thanks for all your posts today guys, they really helped) - it had been installed near the back of the block on the drivers side - I unplugged the harness, and shoved a peice of wire between the connectors - sure enough, the pump came on and I could hear the bowls filling - I was almost giddy....I turned the motor over a few times and it almost wanted to start .

Bad News - I went back to the engine compartment to check the choke was open and I knocked the FP harness with the bare wire sticking out of it against the block where it sparked and then the fuel pump went dead....

I checked every fuse (twice) - is there another fuse box other than the one under the steering wheel? Would there be an inline fuse anywhere?

I can't believe I was sooooo close....

 

Oh yeah, and just to make it interesting - as I was leaving work today (Honda dealership) boss says, "how much longer are you gonna be needing to borrow a car?"
"Not much longer, I think the Camaro will be running any day now."
"Good, because after Friday if you're still driving a car, we'll have to charge you for having a demo unit like eveyone else" (taxable benefit of $780/month)

Nice.

 

i do so believe there is an ECM/FP fuse up by the battery/overflow tank. I think its 20A. Perhaps that is blown.

 

That's tragic, CC....
I don't think you toasted the pump tho, the FP relay might be fried.... EZ fix.
On the Electrical boards, if you do a search, I'm sure you'll find a way to do a quick check on that relay.

Good Luck... use an insulated jumper wire next time. And put a pressure ga on there too, too much pressure can force fuel out the carb vents and start your new engine on fire.
And have a fire extinguisher handy, fer goodness sake!

 

You have to run a hotwire to the fuel pump relay to give the pump juice with the key.

Mine primed after I did the TBI-carb swap but it soon ran out of gas. I ran a wire to the fuel pump relay and solved the problem.

 

Steckman - looked around for 10 minutes near the battery and overflow - couldn't find any fuses - there were a couple of relays (I think that's what they are - 4 or five wires going into a black cylinder the size of a WD-40 lid) mounted on the fender beside the battery, but I couldn't find a fuse - am I looking for a glass inline one or....

Streetiron85 - I hope it's something simple like that - I'm going to do a search right after I type this...I do have a pressure guage..regulator is supposed to be preset at a 'carb friendly' rate...and I think I will keep that extinguisher around!

88Camaro 350 - Where on the relay do I attach the hotwire (remember I'm totally new and dumb with wiring) also, I still haven' identified which is the FP relay on the firewall - there are about 4 little black boxes with wires going into them beside the master cylinder

 

The fuse you are looking for comes directly off the positive battery terminal. On mine there was two wires, the big one leading to the starter, and a smaller one that powers the FI system. Follow the small wire a few inches to a black "box" looking thing, this is the fuse holder. There is a weather proof cap on it, so you won't be able to see the fuse without opening it. There should be black and orange wires coming out of the fuse holder.

 

I would connect the fuel pump relay to the starter solenoid terminal (usually a fairly thick purple wire). That way when you turn the key to start the fuel pump runs. As soon as the key is released the relay kicks off. The engine will start and the oil pressure switch will take over from there.

 

heres a pic:

 

sorry....I can't get it to work right now...I'll have to try again later.

what I was going to say was that it looks like you fried a fusible link, either at the battery post, or down by the starter. You'll either have to back probe the wires, or hopefully, the link smoked and left a burnt wire to find. look for one fo the fusible links to be alot more flexible, you can grab both ends and pull, and the burnt one will stretch, hahahha.....

replace that bad boy, throw some tape over that jumper, and get movin' or replace the switch, and plug it back in.

 

Thanks for the info - I worked that problem out - now I have some timing issues - see my other post.....thanks again..