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Hi All,

Proud owner of a '78 Spider here. Bought it about a year ago and its running great! During the last few drives (over the last couple of weeks) I've noticed its developed a bit of a growl or grinding sound upon deceleration right before the fuel cutoff. If I hold the accelerator right at that point and keep the RPMs there (around 1750 rpm) the grind/growl sound will continue but the car operates as normal. If I raise RPM, sound goes away. If I lower RPM, fuel cuts off as normal and sound goes away.

I'm starting to think maybe my fuel pump is going bad, so I thought I ought to poll the crowd to see if I should just go ahead and replace it now or wait out the sound until something gives way?
 

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Check that there isn't anything being affected by your engine moving around on acceleration / deceleration.
Alfa engine mounts are soft and the engines move around a lot based on the physics involved with a car in motion.
I learned this with my rusty but trusty Alfetta GT.
Some how, the throttle cable was getting pulled as I slowed down and the engine would rev up as
I approached a traffic stop because the engine was tilting forward and stretching it.
Worn motor mounts, exhaust mounts and driveshaft mounts may be the culprit.
Put on your detective hat...
 

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'66 Sprint GT, '67 Duetto, '70 BMW 2800CS
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I'm starting to think maybe my fuel pump is going bad, so I thought I ought to poll the crowd to see if I should just go ahead and replace it
I'm not sure what could be causing those symptoms, but a failing fuel pump would be pretty low on my list. I like 1978alfa's theory (soft engine mounts) better.
 

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I don't think that's the fuel cutoff solenoid, but to confirm . . pull the wire off the Fuel Cutoff Solenoid and tape it out of the way and retest. If you're holding the rpm at 1750, the fuel cutoff is not engaged. For the FCS to energize, the throttle has to be closed in idle and the rpms above 1300-1600 or so.

Does it make any difference if the clutch pedal is pushed in? Sure it's not just a interior vibration from something loose?
 

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But Mad North-Northwest
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I had a vibrating heat shield once that did something similar. Doesn't sound like a fuel pump problem.
 

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'66 Sprint GT, '67 Duetto, '70 BMW 2800CS
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I had a vibrating heat shield once that did something similar.
I really like that theory. These late '70's cars had a heat shield tack welded to the downpipe. With time, a few of the tack welds would fatigue and fail, leaving the shield to vibrate against the pipe at certain RPM's.

The simple solution is to remove the pipe, chisel off the remaining welds, remove and discard the shield, and get on with life. I don't think the heat shield performs any essential function.
 

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Also, check that your fan isn't hitting your radiator fan shroud, if you have one.
This is a common indicator that your motor mounts have retired.
 
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