irocdaddy

Hi everyone-

I am having a terrible time with my efi to carb swap. I have some weird fuel pressure things going on and hope someone here can get this straightened out.

I am running a stock in tank efi pump. At the feed line under the brake proportioning valve on the frame, key on, I get a constant 60 pounds of f.p.

I am using a 5 port return style regulator. My feed in line is correct into the regulator. My exit line going from the regulator to the carb is correct. My return to the tank line is in the regulator correctly at the bottom port.

now, my f.p. reading after the regulator, but before the carbs dual feed line is an adjusted amount of 10 pounds. With the key on, pump energized, the reading after the regulator goes to ten pounds, but bleeds down steadily to no pounds. Does the return line to the tank cause this? I did not see the f.p. bleed down when I checked f.p. at the frame rail prior to making it to the regulator.

Also, when I put a f.p. gauge on the end of the dual feed line going into the carb, I have no pressure on the gauge. I take the gauge off, there is some pressure, but not much.

Given there is no pressure right at the carbs inlet line, could I have something wrong within the carb? Is the gas bleeding down within the carb? I have not got this thing running yet, but can put gas in the carb and it will fire.

can someone help here?

fryer1979

well, I got two things right off for you that are more issues you will face once you get running. First off ten pounds of preasure is to much for most carbs, unless yours specifically says ten pounds in the installation manual. Most carbs run on 6 to 8 pounds, and more than that will give you a constant flooding problem. Seconndly the 750 cfm double pumper is a bit big for a 350 engine, and once running you will be burning too much gas and loosing a lot of performance and driveability. Unless you are running high displacement and a huge cam (your details really didn't say), something in the range of 550 to 650 will perform a lot better. But that is more my opinion from my own experience, I've got a 650 Demon on my pumped 350 and it is almost too much carb.

As far as I know about your preasure problem it could be one of two things. First I have been told that when doing this swap from an EFI system to a carb you need to hard wire the fuel pump to stay on permanently while the key is on. Otherwise, once under a load it will read that the fuel is at preasure and shut off. Having not done this myself I am not sure how accurate this is, but as I am getting close to doing this swap on a friends car I too am curious.

My main thought about your problem is the stregnth of your pump itself. Have you put a new one in, or is this still the original pump? If it is old it may not be able to hold up to the load that the full system puts on it. It can show 60 pounds when put on a guage, but when actually loaded with the vehicle system, cannot hold the preasure. Much like a battery can show 12 volts or better on a voltmeter and still not have enough amps to start a motor.

vindeezl

iTrader: (2)

Try hot wiring the pump like fryer is hinting to, you can ground out your OBD1 connector to run it even. Don't know what you did with the fuel pump wiring or whether you left it stock though.

I'm guessing you have it ran down to 10 at the regulator? As mentioned most carbs are set at 6 or 7. You might be better off saving all the BS and putting a mechanical pump on and saying **** it.

HTH irocdaddy, hope to see you at a meet someday

irocdaddy

Great! Some good info here-

1. I bet the 750 is too big. I only have the hotcam and fastburns. I will look on egay for a 650 d.p. mech. elect. choke.

2. my car has 71k miles, and yes, am running the stock in tank pump. I need to stick with the intank pump or possibly put an electric pump on the frame rail after the intake pump but before the regulator? Can I run it this way and just keep the efi pump in the tank? will the new on frame elect. pump pull gas properly thru the in tank pump?

3. I spent huge doe on the regulator and lines, so I don't want to go with a mech. pump.

4. I can't remember how to ground the adl for keeping the pump on...something about a paper clip I remember.... I left the stock pump wiring intact.

5. I am qlueless about carbs.

thoughts?

yes! need to get out to the meets. just got dumped by the ex now g.f., so will have more available time for my first love... the rock-

sweetaq

iTrader: (1)

I have done this swap and I had to wire the fuel pump relay to stay running when the ignition was hot. I had the exact same problem and hot wiring the relay fixed it perfect. The relay is allowing the pump to prime when the key is turned on but there is no working computer to tell the pump to turn back on when the engine is started. It will prime all day but will never stay on until you rewire the relay. If you want to check it out to see if hot wiring it will work...which it will, there is directions on how to turn the pump on all the time through the adl. I think it is terminal h to power but don't quote me on that.

My car is older than your but going from a EFI motor to a carbed motor net'd me the same issue. Also as stated 10 PSI is way too much. I run my holley 750 at 8 but that was working up from 5. at 5 the psi would drop to almost zero at WOT.

irocdaddy

how do I hardwire the f.p. relay?

what color wires etc. ?

1TUF92Z

Easy!!! Actually it's very easy. Do you have test light? Give me a call tomorrow. I need to know exactly what you've done to your wiring.

sweetaq

iTrader: (1)

This is how I did it though your mileage may vary due to, as stated above, we don't know what you did to your wiring or what could have been done to mine prior to me buying it.

I had a orange wire that was running to a constant 12v source into the relay with other assorted wires coming out of the relay including three red power wires. I wired the orange wire to a 12v ignition hot then the orange wire to I believe 2 of the red wires (the 2 that made the pump come on with the key in run). It might have been 1 but the the car is at my sisters right now. I got it fixed but had too many beers afterwards so it had to stay there.

irocdaddy

update: 01/20

I have a 12 volt hot ignition on feed in the area of the f.p. relay from something else I want to use to bypass the f.p. regulator. so out of these three relays on the driver side firewall 1989 iroc, which is the f.p. relay. what color wires will i be looking for to identify f.p. relay. eric? go look at your car for me. and then, which wires get splised into? I have not cut any wires going to the pump or it's relay. i still have my ecm in...

sweetaq

iTrader: (1)

I just unplugged one at a time until the pump didn't prime when the key was turned anymore.

Check out he schematics on the electrical board it will tell you exactly which wire will provide power to the pump.

sweetaq

iTrader: (1)

It looks like the orange wire needs to be wired to the tan/white wire then the orange wire to the 12v ignition hot.

here is the link assuming the motor used to be 5.0 TPI

http://www.autozone.com/az/cds/en_us...rInfoPages.htm

irocdaddy

sweetaq-

that looks correct per the schematic reference. i did locate the relay and the wiring. now, i hate too just cut into things...crap. i guess i can make connecter ends on the wires if i want to go back.

1. if this does work out, what should i expect? i would think with key on, i would here the f.p. running constantly. when the desired pressure is met, does the pump keep running as long as 12 volt power is connected? sounds like this would be really hard on the pump to be constantly running-

sweetaq

iTrader: (1)

If you are hesitant to cut the wires make a jumper and disconnect the relay andrun the jumper from the orange wires terminal to the tan/white terminal.

The pump will come one whenever the key is in run. I can't hear my pump from the engine compartment but I just watch the fuel pressure gauge to see if the pump is on.

The pump would be turning anyway in our cars because of the return style system we have. Its not hard on the pump because of the regulator just runs the gas back to the tank when the pressure is high enough which is what happens in the stock setup as well. Just don't forget to turn your key off, I did once and it drained my battery in a couple hours.

irocdaddy

update: 1/25

i took the tan/white wire out of the f.p. relay plug end and put it with 12 volt power ign. on. the f.p. stays on with key, cool, but.........

i have no oil pressure on the dash gauge when running. looking at the wiring diagram, i can't figure it out. the f.p. and oil pressure switch share the same relay, but when i put the tan/white wire back as stock, still no oil pressure. does oil pressure guage run through ecm?

sweetaq

iTrader: (1)

It should not effect it because from what I understand the gauge runs from the sensor at the back of the motor next to the dist and the oil pressure switch runs through the fuel pump relay from the sender at the oil filter housing.

I fhte gauge is not working then check to make sure the gauge sender is hooked up correctly and if it is the get a mechanical gauge to verify pressure and check to see if the gauge in the dash is just bad or the sender could be bad.

irocdaddy

o.k. so the oil pressure switch and the oil pressure sensor are not combined into one.

not sure where the sensor is on a 89 tpi motor...
the older motors I know had the sensor right where you say, next to the back china wall.

who out there know's where this sensor is on my motor?

sweetaq

iTrader: (1)

HAve you looked on the china wall because I am pretty sure you will have a sensor there as well. If not then look at the sensor on the filter housing. Does it have three wires? If so then it is a all in one unit that controls the light, gauge and the fuel pump relay.

87tpi

iTrader: (5)

I believe the one you're looking for is right next to the distributor on the driver side, big one.

sweetaq

iTrader: (1)

Am I mistaken by saying that is where all first gen sbc motors have the oil pressure gauge sender?

Jeremy_84_F41

iTrader: (3)

89 TPI car should have the oil pressure sender on the side of the block, right above the oil filter.

irocdaddy

I think the tpi has it somewhere else, or is in 1 unit.

I have a pipe plug in the hole on the back china wall where I have seen a sensor of some type on like 60's sbc's...
----------
yes, it is there...

I need to count how many wires are going in... I think three are.

The gauge should not be broken or the switch for that matter.

big picture is: how do I manually test for oil pressure? I am super nervious running the engine w/o knowing the pressure.

Jeremy_84_F41

iTrader: (3)

The only way is to connect a mechanical gauge, at the port next to the distributor, or above the oil filter. BTW the oil pressure gauge circuit does not go through the ECM as far as I know.

Jeremy_84_F41

iTrader: (3)

And am I reading that right? You took the white wire out of the fuel pump relay harness and are applying 12V straight to it? So you are applying 12V to the pump without using a relay?? Put whatever wiring you changed back to stock, and then apply a switched 12v to the green/white wire, pin C on the relay. Disconnect it from the ECM harness and wire your switched 12v circuit to that wire on the relay. That way you are just taking away the ECM's control of the fuel pump relay and just making the relay close whenever the key is on. This should also keep the redundant oil pressure switch operational in case the fuel pump relay fails. See attached schematic.

There is no reason to modify any other wiring going to/from the oil pressure switch or the fuel pressure relay.

irocdaddy

RECAP-

o.k.,

1. I am to take the drk grn/wht wire and disconnect it at the ecm.

2. at the f.p. relay, tie 12v switched power into the drk grn/wht wire with out removing it from the relay.

3. make sure relay is wired as stock

is this all correct?

Jeremy_84_F41

iTrader: (3)

Yep. Well, you don't have to disconnect it from the ecm, just disconnect that wire from the relay, and connect a 12v switched power source in it's place. If for some reason your ECM is still hooked up in the car, tape this disconnected wire into the harness so it doesn't ground out on anything.

And after you do that, if your oil pressure gauge for some reason isn't working properly, it's likely that your sending unit is failing. At least I think that is the most common part that fails. I can show you how to test the gauge circuit and gauge but I doubt those are causing your problem.

irocdaddy

cool.

this weekend will give it another try..

fryer1979

Even though I am not the original poster, I just wanted to say thank you to those that have posted with info here. I am staring down the barrel of this same issue with my friend's car in the near future and we had much the same questions. This thread should be very helpful through our project, thanks again.