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Discussion Starter #1
Starting at the beginning.../ Bought my '73 Spider a year ago, and wanted everything Right, so installed a new IAP fuel tank, and front and rear filters to protect the Spica injection. The fuel pressure light goes off a split second after ignition sw. turned/ fuel pump started. Engine runs well, except when high ambient temps- 90-100F. Then fuel light will come on during accel., climbing hills, etc. Engine will occasionally buck, as though starved for fuel. Have been told that there was a problem with vapor lock in Spica cars with in-line fuel pumps, and that weak fuel pumps would also show this characteristic. I replaced the fuel pump with the latest avail from IAP ( bought from Wes), changed the filters again, and put heat reflective covers over all the fuel lines, the fuel tank, muffler, and pipe, where they are close. Took the car on a quick mountain run- 60-70 miles at good speed, and everything was fine till I stopped for fuel, then the pressure light would come on every time I stepped on the throttle. Checked the filler cap; it was tight. Drove home, engine running fine, except the light coming on with any throttle. That evening I found that there were loose/old hoses at the vapor canister, and replaced them. I took off the fuel return fitting on the Spica block, filled the passage in the fitting with silver solder, and drilled a 1/16" hole. I replaced the pressure sender sw., and cleaned the relief valve in the filter housing. I have previously measured the pressure on a gauge 17 PSI running(prior to adding the solder to the fitting). Also have replaced the little plastic vent near the vapor canister, that prevents vacuum. I have noticed a bit of fuel on the fuel level sender, and what appears to be looseness of the electrical connections where they go through the bolted cover. I have not changed the fuel lines beyond the fuel pump and before the front filter. I have not traced any of the vapor return lines outside of the trunk area. Current situation is the fuel press. light comes on with any throttle, and my head is frazzled with thinking about it. Should the filler cap vent air with an audible sound after running? Is the entire fuel system to be at some pressure? Thoughts on this will save my sanity.
 

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Have you removed the metal tube inside the plastic vapor tank in the trunk and made sure that it's not rusted shut? That can cause the tank to create a vacuum.

Also, have you measured the voltage at the fuel supply pump itself, battery only and with the alternator running? If the wiring is creating resistance and not delivering full voltage and current, that will significantly affect the pressure output.

Why you would get a pressure light after putting in fresh fuel is a mystery. Usually putting in cold fuel improves fuel pressure.
 

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Did you experience a loss in performance of the engine with the fuel pressure light coming on? I f so you will have a problem with fuel pressure.
If not you have a problem with the fuel pressure sending unit or the wire. If the wire is coatless somewhere it might get contact with ground thus illuminating the fuel pressure light.

Good luck

Bernhard
 

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Where is the fuel discharge on the new fuel tank; lower right front like the original tank or through the fuel sending unit?
 

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Discussion Starter #6
Answered in reverse order: I removed the pressure sender, and replaced it with a 0-100 PSI gauge / the fuel discharge is as original, at the bottom right front corner of the tank / there is no immediate fall off in engine performance, but if a mountain pass, or 4000 RPM for 10 minutes uphill, I may experience choking or bucking as per fuel starvation / wires are in good shape. Further info; The fuel light will start out dim, and progress to steady bright with continued throttle. I had alternator failure on a trip to California two months ago, and replaced with OReilly Auto rebuilt unit (exact physical clone to Bosch original unit) and electronic voltage regulator. First rebuild failed two weeks ago, and was replaced ( with the voltage regulator ) last weekend. Voltage at the alternator measured 13.8 engine running, and 13.5 with engine,wipers, lights, and blower fan running. Voltage at the battery ( in the trunk) measured the same. Voltage regulator is non adjustable. Should I try an adjustable unit?
 

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With the fuel pump running (engine off), if you remove the tank filler cap and listen, can you hear the fuel return line returning fuel to the tank. My point here is the system needs to recirculate. For instance, if the outlet restrictor was blocked and the pressure side of the system was being deadheaded, after a while the fuel will heat in the fuel supply pump and eventually cavitate with associated pressure loss.
 

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Discussion Starter #9
I put it in the trunk when the body welding was going on...better for snow driving-hah. I can't hear fuel returning, so tomorrow I'll get some fuel line and a union, and see if it's returning. May also get it on a rack, and check the voltage to the pump. It's great having input on this!
 

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Discussion Starter #10
I think you nailed it with the voltage question. Measured 11.1 to 11.7 volts at idle. Checked for fuel returning, and have a nice flow, but voltage across the terminals, and + terminal to ground are the same at 11+ volts. Now to the fuse block ? does the pump need the full 13.5 V ?
 

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Discussion Starter #11
Found the pink wire coming out of the secondary fuse block (terminal 11) and got 12.7 to 13 volts with the engine turning about 2000 RPM. Alternator doesn't put out over 12.6 unless some throttle, so my measurement of voltage at the fuel pump was really just battery. Hard to troubleshoot alone. Alternator voltage direct at this RPM is 13.9 volts, so the drop through the ignition sw., and the fuse block, to the secondary pump fuse connection is 1 to 1.2 volts. What does the pump need to be happy? I have cleaned all the fuse block terminals with 320 grit wet or dry, and wiped dialectric grease on all the connections. Does the pump wire go through anymore connections on the way to the pump? I don't see colors well enough to tell faded pink from white, red, or grey.
 

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Discussion Starter #12
Another question, if I rewire this, is there an inertia sw. in the system? I don't see one in the diagram; should I add one?
 

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I don't think a drop in one volt will cause a fuel supply issue unless the pump itself is starting to fail. You can also pull the pump in the tank and make sure the filter screen on it is clean and un-restricted.

Have you checked the inline pump under the car? Make sure it too has 12V's supplied to it.

Also check the fuel pressure before the large fuel filter canister under the hood. I don't know what the exact pressure should be, but it should be well north of 20psi to provide adequate fuel to the injector pump. Just word of caution, don't dead head this pump. As a point of reference, my '79 has 40psi measured pre-canister with new in tank and inline pumps.
 

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... Does the pump wire go through anymore connections on the way to the pump? I don't see colors well enough to tell faded pink from white, red, or grey.
First, you clearly have a mind for troubleshooting - well done, I'm sure you will find it!

The pink wire goes from the fuse to the large rear harness connector that is under the dash on the driver's side near the hood release (usually). There may also be a spade connector as it emerges from the driver's fender routing near the tank.

What you might try is running a decent gauge wire directly from the battery to the pump which, with the battery in the rear would only be a couple of feet. This would be absolutely temporary for obvious reasons but it could tell you if this is the root cause. Frankly I doubt it but worst case you could eliminate that from your list of suspects.

Inertia switch: I don't think they had them in '73 but if it does, it is mounted on the firewall, passenger side near the heater hose. It is usually a gray plastic cylinder about 3" tall and an 1"OD.

Good luck!
 

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I think the comments below apply to later Bosch L-jet rather than your Spica.

I recommend you buy Wes Ingram's book on Spica maintenance. He discusses all of the stuff others have mentioned here, in a well organized way.

Voltage has a significant impact on Spica electric fuel pump output. Voltage at idle is likely insufficient for good testing. You'll want to confirm various voltage points with engine making some above-idle rpm. Check all grounds as well. Using a VOM meter between, for instance, the fuel pump power wire and the chassis will not test the ground connection of that pump.








I don't think a drop in one volt will cause a fuel supply issue unless the pump itself is starting to fail. You can also pull the pump in the tank and make sure the filter screen on it is clean and un-restricted.

Have you checked the inline pump under the car? Make sure it too has 12V's supplied to it.

Also check the fuel pressure before the large fuel filter canister under the hood. I don't know what the exact pressure should be, but it should be well north of 20psi to provide adequate fuel to the injector pump. Just word of caution, don't dead head this pump. As a point of reference, my '79 has 40psi measured pre-canister with new in tank and inline pumps.
 

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Discussion Starter #17
As a master of monkey-motion and overkill, I have installed a relay in the trunk, between my battery and the fuel pump, activated by the pink wire that formerly went to the pump, and will connect pump direct to pos on the battery. Relay is continuous rated, draws .2 amps, takes 8 volts to draw in, and holds down to 4 volts. Battery is charging at 13.8 volts, and this should cure any under voltage problem at the pump. Too late tonight to put the fuse panel back together and try it, but tomorrow will see that done and tested.
 

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Let me correct some posted mis-information.

1. The line pressure should NOT "be north of 20 psi." The pressure relief valve in the front fuel filter is set at 17 psi. 7 psi turns on the fuel low pressure light. I like to see 10-15 psi under normal running conditions.

2. The fuel supply pump IS very sensitive to under voltage. Old corroded wires, kinked wires, etc. all contribute to line voltage loss.

3. '73 models did NOT have an inertia switch installed as OEM. But installing one is a very very good idea, unless you like the idea of after a collision of having a breached fuel system pumping fuel all over the place. I consider this a mandatory safety upgrade.

4. '73 models did NOT have an in-tank boost pump. The fuel outlet up thru '74s was out the bottom of the tank, not through the top fuel level sender flange.
 

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Discussion Starter #19 (Edited)
I have cured the under voltage condition of my fuel pump with the rear mounted relay, but I still have a ghost in the machine. Pressure light goes out immediately on turning the key. The engine runs almost flawlessly to my ear. The fuel light stays out on full pedal acceleration, and steady throttle running, but now comes on in partial throttle acceleration. The light will go out if partial throttle become full. Am I getting some sort of turbulence at the pressure switch that lowers the pressure? I don't understand why the fitting exiting the filter canister to the Spica is designed as it is. Still scratching my head, but I think that unless this new pump is marginal capacity, I may have a sensing flaw that means nothing. John, I agree with all you have said in your last post.
 

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Is there any evidence of actual fuel starvation in the engine at any time now?

Have you inspected the fuel low pressure warning light wire for any chafing or bad insulation that at a certain resonance might ground the wire? You could bypass the car wire, add a temporary one out the hood and into the passenger compartment.

1. Get a test light and tap power from the cigarette lighter and hook the sensor wire to the neg terminal of the test light. Effectively bypassing the car's wiring. See if it exhibits the same symptoms.

2. If yes, and you're confident that the car's wiring is good and the indications are accurate, bypass the PRV in the front fuel filter by disconnecting the return lines to the front fuel filter and hooking them together with a short length of pipe. Cap off the front fuel filter return line fittings. See if it exhibits same symptoms.

3. Lastly, if still getting a LP light, get a new fuel low pressure sending switch.

Hooking up a dampened mechanical fuel pressure gauge and seeing how it relates to the LP light would be very useful. There are a lot of pulses in the pressure side of the fuel line due to the pumping action of the injection pump, so a dampened gauge is much more useful than an undampened one.
 
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