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Discussion Starter #1
Hi,
I've got a Spica fuel pump fed by an electric pump near the fuel tank. My question is about the latter. I'm used to noting the sound of the pump because it is often the first thing I listen for if the engine won't start. It also lets me know by irregular changes in the pitch of the sound on those rare occassions when I'm very low on gas or when the tank filter is dirty.

However, here is a new one. After my car warms up (but not before) the pitch of the pump wavers up and down in a very regular pattern (maybe one cycle per second). The pump was replaced about 2 years ago with one from IAP. The fuel tank filter has about 1K miles on it. This all seems to have started shortly after changing the front fuel filter and the oil filter in the Spica pump.

I have not noticed any effect of this on performance and the rhythmic sound is not associated with any change in rpm at idle (which is about 800-900 rpm).

Any ideas?
 

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Check:
1. All electrical connections clean and tight.
2. Filter clean
3. Your front fuel filter has a pressure relief valve in the front fuel filter. Try pinching the OUTLET fuel line from the front fuel fitting of the injection pump momentarily and see if the pitch of the pump changes.
 

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Discussion Starter #3
Check:
1. All electrical connections clean and tight.
2. Filter clean
3. Your front fuel filter has a pressure relief valve in the front fuel filter. Try pinching the OUTLET fuel line from the front fuel fitting of the injection pump momentarily and see if the pitch of the pump changes.
Well I did some of what you suggested (#1) and will get yet another gas tank filter (#2) but before I do, are there any adjustments needed to the pressure relief valve? Does the spring go bad? I may have tampered with this when trying to remove/replace the fuel filter housing, because I think I had trouble getting to the nuts holding the filter housing to its backing plate.

I did the pinch test and this resulted in an increase in pitch (really a scream), but I believe this sound was coming from the Spica injection pump. I had my son pinch it while the engine was running and my head was near the rear pump and did not notice any change in sound. This made me realize there are actually 2 sounds--the steady hum of the electric pump by the gas tank, and then a hum with changing pitch coming from the engine compartment. I do, however, feel a vibration in the gas line leaving the rear pump that is in sync with the changing pitch.

If it makes any difference, after the car is warmed up, I get this changing pitch with the key in the "on" position even without the engine running.

Also, I have no noticable effect on performance but I suspect that is because I may just be in the early stages of something that, if not fixed now, will eventually come back and bite me.

John
 

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The PRF is not adjustable and really pretty rugged. If the spring was broken, you wouldn't get any pressure in the system.

Is the fuel pressure warning light behaving normally?

Can you hear the return fuel returning to the fuel tank?
 

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Discussion Starter #5
My fuel pressure light is out so I'll add that to my list along with a new rear fuel filter.:D I couldn't hear gas dripping into the tank so I disconnected the return hose and turned the key to the on position for a fraction of a second and the pan I'd placed in the trunk to catch anything that came out was covered with a spray of gas so I guess at least some gas is returning.

I'm ashamed to admit that this is the first time I have changed the front filter and I keep thinking it has something to do with that process. Is there any way air can be trapped in the system? I would think it would be pushed through the Spica pump and then back into the gas tank but maybe not?
John
 

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Changing a front fuel filter shouldn't cause any problems and any air will be purged back to the fuel tank. Confirm that you hooked the hoses up correctly when you put it back. If you mis-connected them, that could cause a significant problem.

No sense in trying to do any more diagnostics until the fuel low pressure light is working. If the dash light is out, you can use an ordinary test light with alligator clips directly on the pos terminal of the battery and the spade terminal on top the fuel low pressure sending unit. That fuel low pressure warning light is very important. Consistently running a Spica injection pump on low fuel pressure can seriously damage it. For the want of a 50 cent low pressure light and the laziness to repair it, you can ruin a $750 pump.
 

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Discussion Starter #7
The plot thickens

OK John,
I checked my fuel pressure light and it works. I have continuity in the circuit because when I ground the wire to the pressure sender unit my dash light goes on. However, I never see the light go on, even for a few seconds, when I initially turn the ignition key to the "on" position prior to starting the car. Nor does it go on when I hear the pump pitch change. This is also the case when running a wire with a light directly from the sensor to the positive battery terminal. I even pinched off the line going into the front fuel filter housing and no light goes on. Collectively, this tells me I need a new pressure sensor. Are there any other tests I should run before replacing?

A new symptom I just noticed is that the undulating sound from the Spica is coupled (only sometimes) with a small dip in my gas gauge (but no other gauges that I can tell). So could this mean the pump is varying in electrical power delivered to it or that pump demands are changing with fuel pressure, requiring more/less power in an undulating manner?

Unless someone has a better idea, I'll start by getting a new fuel pressure sensor.

John
 

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Discussion Starter #8
correction

John,
One correction. I did have the light go on once this morning when going over a bump in the road and figured the spade connector was just loose. I re-connected it and thought I was right because when I revved the engine with the car stationary, the light did not come on. Went upstairs, had some coffee, and then for the hell of it, started the car again (now cool) and all of a sudden the light on the dash went on! I revved it a but and the light did not go out. I turned the engine off, the light went out. I started the car again and within a second or 2, the light went back on. So I think the sending unit works but that the problem is intermittent.

Sorry to keep pestering you but any help would be appreciated.

John
 

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When you first turn the key switch to "ON" the light should come on for a second or two, then go out. If the light is not coming on initially and the dash light illuminates when you manually ground the wire, then the pressure switch is bad. You can also confirm it by getting an inexpensive fuel pressure gauge from the local auto parts store (about $10). Make a "T" fitting and install it in-line between the front fuel filter and the injection pump. This will help diagnose both the sending unit and the fuel pump.

With regards to the gauge dipping in conjunction with the fuel pump pitch change . . you might want to chase some wires and make sure that the connections are clean and tight. These cars are almost 40 years old need to have some preventative maintenance to the wiring.
 

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Discussion Starter #10
The light never goes on when first turning the key. What is more, right after submitting the last post I started the car again and the light didn't come on, even after warm up and about 60 seconds of maintaining 4500 rpm and ddespite the fact that I could hear the changing pitch.

I guess this is an old refrain on this BB but the most frustrating thing is the intermittent nature of the problem!!!:mad: I'll take your advice and order a new sending unit and in the meantime, I'll see about an in-line temporary pressure gauge.
Thanks,
John
 

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Yea, it sounds like that sensor is shot, but a pressure gauge will confirm it. A changing pitch of a fuel pump won't necessarily mean that the pressure is low. A 69 does not have an in-tank boost pump. You might want open the fuel tank and check that the sump in the bottom of the tank that the exit fuel pipe goes to isn't partially clogged up. Once you're sure that the system is clean and the low pressure light is working normally, the more I think the fuel pump could be the culprit.

BTW, what kind of fuel pump is installed right now. Is it a Bosch pump that has the inlet and outlet in an "L" shape or are they straight through the pump?
 

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Discussion Starter #12
You might want open the fuel tank and check that the sump in the bottom of the tank that the exit fuel pipe goes to isn't partially clogged up.
Aside from draining the tank, I'm not sure what you are suggesting here? I do worry about stuff in the bottom of the tank. I had it coated inside many years ago and now that we are using ethanol-gas, I worry about it eating away at grundge in the tank.

BTW, what kind of fuel pump is installed right now. Is it a Bosch pump that has the inlet and outlet in an "L" shape or are they straight through the pump?
It is of the straight through variety. My original died 2 years ago and so I bought the less expensive replacement alternative sold by IAP. It can't have more than 3k miles on it. Of course that doesn't include the hours of running the engine in the driveway. Sometimes I think Alfas should have a gauge like those in boats for engine hours, rather than an odometer.:eek:
 

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The pump is probably an L-jet supply pump which are pretty reliable.

By opening the tank, I mean removing the gauge level sending unit and looking down into the tank to determine if there's a lot of junk down there near the pickup. Of course, all the standard safety precautions should be observed when opening a tank.
 

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Discussion Starter #14
update

The pump is probably an L-jet supply pump which are pretty reliable.

By opening the tank, I mean removing the gauge level sending unit and looking down into the tank to determine if there's a lot of junk down there near the pickup. Of course, all the standard safety precautions should be observed when opening a tank.
John,
I checked inside the tank and found no junk in the bottom-most part where fuel is drawn. I have replaced the fuel lines between the front filter housing and the spica, replaced the rear fuel filter and the pressure switch. The pressure switch now flashes when I turn the key to "on" and it remained on for the few seconds it took to re-pressurise the system after replacing the lines/rear filter. So I think the light now works. However I still have the sound even though the light does not go on when the car is running. I have not gotten a pressure guage yet.

However, my gut feeling is that this sound has something to do with replacing the front (main) filter.

Is it possible for this filter to not seat properly?

Another possibility. Is it possible I'm using the wrong filter and that is the cause?

It seems the main filters changed from 69-74 to 75 onward. I believe I may have been using the former with a 75 Spica pump. I have Wes Ingram's book and the Alfa Bible so I know the pump model ID#s but can't find them on my pump (at least the numbers on the little Spica plaque don't seem to correspond with any of Ingram's numbers). The photo of the 1750 pump in the Alfa Bible on pg 46 (figure 2-33) shows no temperature setting lever (which I thought was standard on the older pumps, but also shows no fuel cutoff solenoid). Mine has no temp/altitude lever but does have the fuel cutoff solenoid and microswitch--both characteristics of newer pumps according to Ingram.

Do you know what the difference is between the fuel filters for 69-74 versus later pumps and what might happen if I'm using the wrong filter?

To make matters more confusing, the filter I installed in the spring (purchased from Centerline and specified for 69-74) is different from the one I just received from IAP (also specificed for 69-74). The latter is encased in metal with perforations while the former just had metal top and base with the currigated filter in between (no perforated metal cylinder on the outside.

Bofore I replace the main filter I want to make sure I'm using the right one.

Oh yeah-one more thing. I have a 2 litre engine because the 1750 had a massive coronary and it was, at the time (1990) much more expensive to rebuild a 1750. The spica pump was sent out to be rebuilt but I don't know if it is the pump I had in my car originally (69 1750) or whether it came from the car (1975 Alfetta) that supplied the donor engine.

Any ideas?

Thanks,
John
 

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Take a picture of your front fuel filter, fuel pump and injection pump for me so I can see what we're dealing with. Sounds like you have parts from several different years there. Also, look on the side of the injection pump placard and see what the "T" number is. It should say "T260" in the upper right part of the placard if it's a 1975 model pump.

Now that you have the fuel low pressure warning light working correctly, it seems that your fuel pressure is normal. Now, we're just trying to hunt down the cause for the noise . . . right?

The difference between the filters on the early and mid models is the incorporation of a pressure relief valve. The mid models had a 3-port supply pump that had it's own pressure relief, and therefor didn't need one in the front filter. The late 70s models went to the L-jet style 2-port pump without a dedicated pressure relief valve (although in reality there is an internal pressure relief, but it's MUCH higher than the 17 psi that the Spica system should have. Normally, the PRV never actuates anyway, so it can sit dormant in the system for years. You can force-activate it by pinching the outlet hose of the injection pump and cause the pressure upstream to go above 17 psi and open the PRV. The visual differences in the front fuel filters with and without the PRV is that the non-PRV filters only have two fittings . . an inlet and an outlet. The PRV filters have the return line from the injection pump go throught another set of fittings on the pump (4 total). When the PRV actuates, it vents the excess pressure into the return line to the fuel tank. Hope that makes sense to you.

Even a tiny leak in the PRV would probably cause a severe drop in fuel pressure.

Have you downloaded the guide at HP PUMPS?
 

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The difference between the filters on the early and mid models is the incorporation of a pressure relief valve. The mid models had a 3-port supply pump that had it's own pressure relief, and therefor didn't need one in the front filter. The late 70s models went to the L-jet style 2-port pump without a dedicated pressure relief valve (although in reality there is an internal pressure relief, but it's MUCH higher than the 17 psi that the Spica system should have.
John,

Great advice as usual, but I think you should define early/mid/late by year as you've got me a little confused. Also, it may be helpful when discussing "late" to specify if it's Spider or Alfetta as there were some differences.

Joe
 

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Discussion Starter #17
Found the Pump ID which is T 260/1. Thanks for pointing out where the nearly impossible to see number is.

Yes, as I mentioned, I've not had any performance problems, just the unusual sound which may be nothing or may indicate unusual strain somewhere in the system.

Here are the pictures. Sorry if they are blurry. The filter pictures are of both types. The left one is what I put in last spring and the right one is waiting to be installed, if correct.
John
 

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Ok. You've got a '75 injection pump with an L-jet type supply pump and a 69-74 front fuel filter. This is a good workable setup. The fuel low pressure warning light is acting normally, so there's good fuel pressure. Check the voltage/current at the pump to ensure you're getting a good consistent 12v+. Perhaps the supply wiring/ground is loose or dirty or broken.
 

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John,

Great advice as usual, but I think you should define early/mid/late by year as you've got me a little confused. Also, it may be helpful when discussing "late" to specify if it's Spider or Alfetta as there were some differences.

Joe

I'll try. The following is generally true. Keep in mind that Alfa often would change configurations within model years sometimes.
 

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