David Trimble

Well my 1984 T/A died on me the other day- was not getting any fuel to the carb. I thought that the mechanical pump had died so I replaced it but it didn't do any good. Then in doing searches here I found some T/As had electric pumps installed, and sure enough I looked at my fuse box and found a fuse in the 'E. PUMP' slot.

Now I've got a '01 Firebird and I know that replacing the electric pump on that is a pain involving dropping both the rear axle and tank to get to the pump- is it pretty much the same procedure on a '84 T/A? The FSM wasn't very specific about replacing the pump. Has anyone replaced their pump and if so how much work is involved?

Thanks!
David

camaronewbie

Same procedure as the '01 car.

David Trimble

Anyone know where the fuel pump relay would be located? The FSM says it's in the engine compartment, on the firewall driver's side - but that's with a L4. Doesn't say where it would be for a carbed 305 - on my car, the L4 location actually has the relay for the cooling fan. Any ideas? I'd like to first check to make sure the relay is working before I go tearing into the fuel tank....

Ozz1967

iTrader: (4)

ON my carbed 84 with the mechanical and electric pump, while I have the spot in the fuse box for the electric pump, there's nothing actually going to that spot, it's empty, won't even hold a fuse in it.

I believe that relay is on the drivers side by the firewall. However, your mechanical pump should pull through that electric pump with no problems, mine did for years until I put in a motor that wasn't drilled for the mechanical and I had to swap the electric pump out.

Disconnect the fuel line and crank the car, should create suction at the pump and push fuel out the line...are you getting any fuel out? If so, hook a fuel pressure gauge up to it and see what you are running..should be 5-6psi.

IROCtheRoad

The fuel pump relay is near the brake booster with your other relays. Since the dealership did the install you have have 5 wires going into a 4 wire relay.

Find your Oil Pressure Sensor (has a single tan wire coming from it). Attached to the OPSU "arm" is another sensor with 2 wires coming from it. Trace those wires to a relay = fuel pump relay.

David Trimble

First of all, thanks guys for the replies...

I remember shortly after I got the car it developed that fuel percolation problem, and the dealer installed the factory fix for it. I know they had installed the carb heat shield, and removed the electric fan with a belt-driven fan. Now the dealer may have installed a electric fuel pump as part of the fix- I don't remember for sure, but from what you tell me they may very well have done that. Now the spot on my fuse block definately has a fuse in it- I even pulled it out and checked it to make sure it hadn't blown. I also disconnected the mechanical pump from the fuel line coming from the tank and cranked the engine while checking the suction and... well it sucks However I've disconnected the mechanical pump to carb line and I get nada from that while cranking.

I'll also find the OPSU 'arm' and see if I can trace down the pump and pump relay's location and report back.

Thanks again!!
David

PS. @Ozz1967 - from what you say about your car being able to run with a dead electric pump, I'm wondering if mine failed in such a way that it blocked the fuel line.. If I can find the relay at least I can tell if it's getting juice or not, and if it is then it's definitely dead...

Ozz1967

iTrader: (4)

The mechanical pump is strong enough to pull "through" the old factory pusher pump. Mine ran that way for 8 years before I swapped motors.

If for some reason your car has a normal electric in-tank pump, it won't be strong enough to pull through it. So far as the relay, most often, it's the pump that's dead, but the relay is a good starting point.

IROCtheRoad

When you trace the 'arm' to the relay let me know if I wire runs to the interior through the steering column from the relay. It might be a grey/brown wire. I'm assuming on my 84 that it's the wire to the fuel pump, but I would like a confirmation.

David Trimble

An update: I did confirm that on the 'arm' I have not one sensor but two. The FSM shows that there should be only one sensor- either a gauge sensor or a pressure switch. I've got one of each apparently- one big honking unit that must be the gauge sensor, and a smaller unit that must be the pressure switch. I need to clean the wires but it looks like the pressure switch has the right colors shown in the FSM as being part of the electric pump circuit. One thing I notice though on the pump wiring- they've been tucked into the wiring convolute, so if this is a dealer install they did a pretty damn good job of installing. If they did do it, unfortunately it makes my job harder since I'll have to trace wiring runs using the FSM and the wire color codes...

I also noticed on the driver's side firewall, up in the corner there's another relay hidden behind the relays that I had accounted for. I haven't checked the wire codes or ran a continuity test yet but I suspect this may be the fuel pump relay.

More to come...

PS. @Ozz1967 - because of the wiring looking factory, I'm beginning to wonder if this is a factory install. If so then the pump will probably be in the tank But at least it'll account for why I can't run on just a mechanical pump. But yes while I'm hoping the relay had gone out (my cooling fan relay did) it'll be my luck that it'll be ok. But I have to check anyway...

David Trimble

My FSM shows that the wire running from the relay back to the pump should be tan/white, changing to tan before it gets to the pump. But I'll keep a lookout as to where the run goes and let you know.

IROCtheRoad

The tan wire on the arm is the signal for the oil pressure gauge. The other sensor is part of the fuel pump circuit. In order for the fuel pump to work, there must be oil pressure (it's a fail safe thing; no oil pressure = kill pump = kill engine). The additional sensor runs directly to your fuel pump relay.

IROCtheRoad

PS

Look at a 1986 wiring diagram from austinthirdgen, or whatever the site is called. It has the FACTORY installed pump circuit in the diagram. The wire's colors even match the dealer installed pump circuit.

David Trimble

Cool- thanks!!! This is SO much better than my FSM wiring diagrams I grabbed the '84 diagrams while I was at it. But yes this'll help a lot- right now I"m having trouble matching up the wire color codes, but I'll hopefully figure this out by the weekend...

HawkZ28

iTrader: (2)

IIRC, my 86 has a weather pack connecter that's accessible from under the car that makes the transition from interior to exterior wiring. I think it was behind the back seat rest under the carpet.

At least an easy location to test for power.

David Trimble

Just a FYI- I hit a snag in this- my multimeter took a dump on me Thursday. I think the batteries died on it (well they ARE pretty old). I'm hoping I can find a set cheaper than the $6/each Radio Shaft wants- I should be up and running in a few more days....

Ozz1967

iTrader: (4)

84's never came with normal "electric" pumps from the factory. They only came with the pusher pumps but I haven't been able to find out if they were dealer installed options or factory installed options. The pusher pumps on ly pushed about 2-3psi, just enough to keep the fuel going forward to help with vapor lock and they used something of a worm-gear. This gear allows alot of free flow when the mechanical pump pulls the fuel forward if it's dead. more modern pumps aren't built like this and the mechanical pump can't pull through them.

That said, you may have sucked up debris from the tank that caused it to clog up the line at the electric pump in the tank. Use an air compressor, blow air back into the line from up by the fuel pump and have someone listen near the fuel tank, do you hear bubbling in the tank?

David Trimble

Sorry that it's been a while, but I haven't had time to look further into this until now. And I finally got a working DVM, too (turns out that after replacing the batteries the old DVM was DOA :/ )...

@Ozz1967 - you're probably right in that it's a pusher pump - I wouldn't expect to find anything very powerful in the fuel tank- certainly not for a carbed engine. And I hope you're right in that it's just junk in the fuel tank causing my problem. However, I don't have access to a air compressor (well at least nothing more powerful than those cheapie tire inflators that plug into a cigarette lighter), so I can't really blow it out like I would like to....

As an experiment, I'll probably rig the mechanical pump to siphon gas from a fuel canister just to see if it can draw fuel and start the engine. If it does then at least it verifies that there is something going on back in the fuel tank, or that I got a clogged line somewhere...

David Trimble

As another thought - I haven't gotten under the car yet to take a look around the fuel tank, but are the fuel lines completely metal from the tank running up to the engine compartment, or does the tank have lengths of rubber hose connecting the tank to the metal lines that run up to the front? If so, a idea had occured to me- possibly those hoses had split on me from age and they're not letting the mechanical pump draw a vaccuum. I would think though that if the electric pump was running I'd see a fuel leak around the tank from the fuel being pushed thru where the hose had split. But then again if my electric pump is dead then such would not be the case. Any ideas on this?

HawkZ28

iTrader: (2)

On my car there was rubber lines connecting the pump to the hard lines. As for being that way stock, take that with a grain off salt. My car had several idiot POs.

If you did have a split line so bad the pump couldn't draw fuel the gas smell alone would be horribly obvious.

naf

iTrader: (7)

You should have two relays on the bracket next to the brake booster that look the same. One for the engine fan and one for the fuel pump. Instead of chasing down wires, simply jump either relay off. If the engine fan comes on, try the next one. Each of these relays should have a pigtail with four leads. Constant hot, hot in run only, sender lead and power lead to motor (pump or fan). Easy enough to tell which is which with a meter. The sensor lead may or may not have more than one wire connected to it.

You can jump by shorting the constant power wire to the power to motor lead.

With the fuel line to the mech pump disconnected (the larger 3/8 line, rubber), jump the fuel pump relay off and fuel should flow into an appropriate catch can. If it doesn't you may want to test leads closer to the pump, but the pump's probably bad.

David Trimble

@HawkZ28 - true- if I did have a hose split I would be smelling fumes, which I'm not. So that idea is a long shot, I suppose.

@naf - actually I think I already found the pump relay- as you said it's next to the fan relay, which I had to replace recently as a matter of fact (fan would not come on when the temps started to rise- while the relay was closing, it was either not making contact or if it was, the contact wasn't carrying enuf current for the fan to turn over). But in checking the pump relay I did manage to verify that it IS getting +12v. If I jumpered the +12v to the pump, should I be able to hear the pump running, assuming that it's ok?

naf

iTrader: (7)

Yes. You should be able to hear it, if the engine is off.

David Trimble

Ok- I just tried jumpering the pump on the relay header. Long story short, I heard a loud pop from somewhere that I realized sounded like a fuse blowing (rather violently). Found that the 3A Crank fuse went byebye. The wierd part about this is that if a fuse were to blow in this circuit, it should've been the F/P CLTR fuse (which was fine, btw). Using the FSM for reference, I had run a connection from the BLK/ORG line (+12V) to the TAN/WHT line (fuel pump motor lead) which SHOULD have been feeding +12V to the pump directly... this makes no sense - I'm beginning to wonder if the FSM's fuel pump schematic is inaccurate....

naf

iTrader: (7)

Wiring diagram must be off. You may have jumped the 12 volt constant to the '12 volt with ignition in run' lead. Replace the fuse and check that lead to see if it's got 12 volt to it only when the ignition is in 'run'.

The fuel pumps are not all wired the same throughout the years. Yours may also enable the relay through the crank switch until the OPS takes over. It may not have even been a 'factory' installation, as many were wired at the dealership in response to a 'vapor lock' complaint.

Ozz1967

iTrader: (4)

On my 84 L-69 there are short rubber lines connecting the fuel pump assembly to the fuel/return lines in the back and until I ran the electric pump, hoses running from the front of the fuel lines to the mechanical pump. I then had a hard-line set up from the mechanical fuel pump to the carb that I believe is factory but can't verify.

David Trimble

Urg..... I'll just have to trace the wires then it sounds like THis is gonna be fun but it's going to be the only sure-fire way to know how that relay is wired. When I first got the car it did have the vapor-lock issue and supposedly the dealer did the factory-issue fix on it so that may very well explain the diagram inconsistencies.

But anyway I guess I'll have to spend a afternoon tracing them out- and with the holidays, that might not happen until next week :/

David Trimble

The hard-line from the mechanical pump to the carb is definately factory. That's how mine is set up, and I've never modifed it.

Since I'll be chasing wires I'll wind up under the car around the fuel tank, so I might as well inspect the lines while I'm under there. It may not be until next week before I can get to it but I'll report my findings then.