ssr345

Ok, so what the difference between these:

http://www.collectorcarsforsale.com/...0406950367.jpg

and

http://www.google.com/imgres?imgurl=...t:429,r:16,s:0

I cant get power to my fuel pump and I cant figure it out? But I'm confused about the relays. please help

mantaguy

iTrader: (5)

That first relay is either your MAF power relay or MAF Burn off relay,it is used for either one their the same.That second one I don't know what that is.

ssr345

I mean I replaced the first one on my fuel pump relay but I'm still not getting power to my fuel pump?? I have new fuses as well, new pump, new fuel tank, so I don't know what else? any ideas? thanks

camaronewbie

Are you sure it's the fuel pump relay you replaced? In alot of these cars, there several relays, and many of them all look the same. You have to go by the colors of the wires to the relay to know which one your replacing.

Did you check the connector for scorch marks etc.? Alot of times it's not the rel;ay but the connector.

Did you hold the relay in your hand and feel it "click"? If the relay is clicking, it's working, and your issue may be elsewhere.

Did you test the wires to the relay and make sure they are doing what they need to? Should have one ground (usually black), a relay signal wire (usually green with white stripe), the fuel pump wire (usually tan with white stripe or gray), and a battery power wire (usually orange). Green/white wire will get 12v+ when key is on, orange will have 12v+ always, black needs to have a good ground, and if you run a jumper wire in the connector from the orange wire to the tan/white (or gray) wire, the pump should run.

ssr345

Ok I was checking the wrong thing. But anyway the only wire i'm not getting power to is the green wire?? I don't get it? Any help. Also I get no power to where the fuel pump connects to the tank and everything, I don't know which wire I should be getting power to in the back tho? Thanks again

ssr345

Ok, I jumped it by using a paper clip and sticking it in the green one which wasnt having power and the red one to give it power but still no prime on the fuel pump and still not starting

camaronewbie

The green/white wire gets 12v+ from the ECM. This "activates" the coil inside the relay, which is already grounded, and thus the relay connects the red (or orange) battery wire with the grey (or tan/white stripe) fuel pump wire. Jumping the red (or orange) with the gray (or tan/white) wire should make the pump run. That red (orange) wire should have 12v+ always - jumping puts that 12v+ to the fuel pump.

There will be no 12v+ on the green/white wire EXCEPT in two situations:

1) the key is turned on, then the green/white wire gets 12v+ for only 1-2 seconds to "prime" the pump
2) the ECM reads a constant ignition signal from the distributor

So - if the car is not running, you only have a 1-2 second chance of ever seeing the 12v+ on the green/white wire - that's why you can't see it.

Between the battery and the fender, there is a 20amp fuse in it's own little weatherpack. It has a red wire into it, and a orange wire out of it, with the fuse connecting the two. Make sure it's not blown - that feeds 12v+ to the ECM.

The wire color differences are because they changed in certain years - that's why I have different colors in parenthesis. What year is your car, and what induction (carb, TPI, TBI)?

GanymedeElegy

iTrader: (1)

So, that relay and the prime is important then? I was just gonna hard wire a fuel pump in with a standard relay to only run when the key is in start/run. I just swapped a 1990 5.7 TBI into my 83, as Im sure you probably know, and I havent got to work on swapping the fuel tanks and running wires for the pump yet.

camaronewbie

Well, yes and no. The priming is important if you desire an easy quick starting of the engine. As the car sits for a while (even just 10 minutes), the tiny amount of fuel that is at the injector evaporates, leaks back to the tank, whatever - and thus the injector has no fuel to initially fire. Unlike a carb that has fuel bowls inside the carb that hold enough fuel for the car to start and run for several blocks even before it 'runs out'.

The reason GM made the "prime" function was so that as soon as the key is turned on, the pump sent fuel to the injectors immediately - so they'd have fuel to fire on startup - thus the car would start quickly, without having the pump constantly pumping fuel between the time you turned the key on and when you actually started the car.

Like for instance, you are driving in the rain, and leave the wipers on but turn the key off - your wipers are now stuck midway on the windshield, so you turn the key back on so that you can allow the windshield wipers to return to their perch (bottom). Having the pump wired directly means that the pump is running the whole time you are screwing with the wipers.

But it's not really a problem - I mean there's nothing to be damaged by having the pump running the entire time the key is on. The fuel pressure reulator will take all the excess fuel and return it to the tank, thus your just pumping fuel from tank to fpr and back to tank the entire time the key is on - no biggie. But I'm sure that safety reasons (or Uncle Sam's safety reasons) mandated that the fuel pump not run the entire time the key is on, thus the "prime" function programmed into the ECM.

With no priming, and without the fuel pump coming on with the key, the car will still start - it just takes longer cranking time. This assumes that you have a properly wired Oil Pressure Sending Unit. The OPSU on the FI cars also takes over as a secondary backup fuel pump circuit. In the event that the ECM or fuel pump relay has issues, the OPSU will run the fuel pump on an FI car as soon as it "sees" oil pressure. But this of course takles a few seconds (sometimes up to 20-30 seconds) of cranking, enough time for the starter to turn the motor over enough for the oil pump to start pumping up oil and 'set off' the OPSU.

I've long ago swapped to carb, but run the TBI intank pump. And I've had mine wired to run always with key on for years now with no issues at all. Like I said it won't hurt anything - just more of a safety issue.

GanymedeElegy

iTrader: (1)

Well that makes sense. The oil pressure sender for the gauge is on the driver side cylinder head right? and the oil pressure switch is the bronze cylinder behind the distributor? Ive been trying to figure that out. I know quite a bit about the anatomy of an engine but still learning something new every day seems like. I got the mechanics done, and the most of my wiring done too, but just a few unknowns remain.. as in, making sure my oil pressure gauge will work with the new engine and the coolant temp gauge too. I have 8 unknown wires on my new engine harness and I cant seem to find them on the wiring diagrams :/ Eventually tho lol or theyre unnecessary? Ill find out.

So if the fuel pump is wired to run all the time, without the prime then wouldnt there be fuel in the TBI unit ready to start the engine? And I can see it being a safety concern, if you crash, and theres a small fire or something if you got leaking fuel then the pump is constantly pumping fuel into the fire D: bad.

camaronewbie

The driver side head sender is coolant temp for the temp gauge - single wire that factory is green in color.

The china wall sender (distributor area) is sender for the oil pressure guage on the older model cars - a single wire sender that has a black wire.

The unit just above the oil filter is the OPSU for the fuel pump circuit on the FI cars (and maybe the few carbed cars that had an intank pump like late 1986 and 1987) - a two wire sender with orange and either gray or tan/white stripe.

Later in the years, GM combined both the oil sender for the gauge with the OPSU for the fuel pump into one unit, that they located above the oil filter - a 3 wire sender, with black (gauge), orange (from battery), and gray or tan/white (fuel pump wire).

And yes - if the fuel pump is wired to run with key on, then there will be fuel in the injectors to start the car.

GanymedeElegy

iTrader: (1)

They sure make it complicated lol. Ok so I got the green wire hooked on the temp sensor on the driver side head. The brass oil pressure sender behind the distributor has a three wire connector, 1 orange, 1 tan, and 1 tan w/ white stripe. There is a well above the oil filter, but its plugged off because its got the newer style OPSU switch for the fuel relay I can imagine thats how it is. So the unit by the water neck is also coolant temp but for the ECM then I assume, it has 1 black, and 1 yellow wire. You know you just made my life easier CamaroNewbie.

I didnt mean to hijack your thread ssr345! But Im sure that bit of info was useful to you as well. Good luck on yours, I have to kinda build mine from scratch haha.

camaronewbie

OK, so someone has placed the 3 wire OPSU at the distributor location - that's fine.

And yes, the thermostat housing area sensor is coolant temp for the ECM (black and yellow wire).

GanymedeElegy

iTrader: (1)

Well yea, this setup is from a Chevy G20 van lol the old 305 was just worn down and I got a deal on this engine, $100. It was pretty clean, It may have been rebuilt at sometime. the ODO was at 220,000 or close and it ran 4 years ago when they first got it. When I can pull off getting a good job then Ill do a full rebuild. With aftermarket heads, a better Carburetor intake with a TBI adapter plate with a modified TBI. You know, just to get at least 300 horses and keep it California street legal somehow. Thats later, I just want to get this car started so I can find any more problems if there are any.

ssr345

Thanks for all the reply's guys but I finally got it working.

My dumba** didnt check the sending unit it wires and one of them had been cut somehow..idk but any stripped that and connected and the pump is working perfect.