Moaning sound after shutting engine off - Problem solved!

7982X

So much fun it MUST be illegal!
82 fuel injected engine.
Finally have engine running and now getting bugs worked out. Fuel pressure is around 35 PSI and holds when engine is shut down.
When engine is shut down (after running for several minutes), you can hear a "moaning" sound for 3-5 seconds and then it stops. So far, I haven't been able to nail down exactly where it is coming from. (It almost sounds like some air conditioning units I have heard when they shut down.)
Any ideas?
cooling system not properly bled?
 
There's a fan in the trunk on the drivers side that blows air into the engine compartment. It's normal for it to cycle on & off for a short period of time after you shut it off.
 
Our car doesn't have the fan as it was originally carbed, but thanks for the idea. I had an 81 35 years ago and never heard that fan run. (We didn't install that particular fan in this car. We decided to try other options to keep the fuel rails cool.) I've never have had cooling system issues either but thought maybe it hasn't run long enough yet for the coolant to flow through the entire system.
 
Thanks for the input.....today I will check cap tightness (new cap) and run it for a while longer. We are also running a stainless tank which may resonate more than a plastic one, although I couldn't hear anything through a stethoscope.
 
came here to suggest the same - I had a defective cap that was making the same sound. Changed the cap, all good! :)
suggestion appreciated. I can see by the car that you drive that you are a "man who knows who I am" (play on words).
 
We are also running a stainless tank

Ah! ok, so - I may be mistaken, but I recall that the neck length was different between plastic and stainless tanks?? Am I right? I can't recall - meaning you may not have the right cap on there?
 
Ah! ok, so - I may be mistaken, but I recall that the neck length was different between plastic and stainless tanks?? Am I right? I can't recall - meaning you may not have the right cap on there?
There is a short neck cap and a long neck cap, IIRC the stainless tank takes the long neck cap. Looking at our vendor sites, the long neck version appear to be a lot harder to come by than the short neck cap.
 
Fuel pressure bleeding down is my guess. I believe there is supposed to be a check valve in the system somewhere to reserve fuel pressure for the next startup. Check valve is missing or malfunctioning?

Edit: Oops, missed the part about fuel pressure holding after shutdown. Never mind!
 
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Ah! ok, so - I may be mistaken, but I recall that the neck length was different between plastic and stainless tanks?? Am I right? I can't recall - meaning you may not have the right cap on there?
Like you said, the necks do indeed appear to be about .100" different, with the stainless unit being longer. Our caps appear to be the shorter ones.
 
Fuel pressure bleeding down is my guess. I believe there is supposed to be a check valve in the system somewhere to reserve fuel pressure for the next startup. Check valve is missing or malfunctioning?

Edit: Oops, missed the part about fuel pressure holding after shutdown. Never mind!
I did look for a check valve in the diagrams anyway as I didn't remember installing one when we converted to a F.I. engine except in the fuel vapor system. That one was the only one I found in the diagrams as well.
Worth looking at though. Fuel pressure bleed down and coolant pressure bleed down were the only 2 things we could think of and the fuel pressure could have been bleeding down in a place that the gauge doesn't show. Our gauge is between the second filter and the fuel rail. Next time I will put a stethoscope on the charcoal cannister and see what we hear.
 
IIRC, the FI fuel pump incorporates a check valve on the outlet.
Correct.

OP, is it possible the noise is happening when running but is only audible when shutting then engine down, or are you sure it only happens after the engine stops spinning?
 
Check valve on the pump outlet makes sense. That may be why it doesn't show up on the diagram OR in our bunch of parts.

I thought that I may have heard the noise 1 time while running, but like you suggested, it MAY be masked by the engine running. I will recheck that tomorrow as well.

On the cap, I am waiting for an answer from MWB. Our tank is an OEM Fiat tank.

AGAIN, THANK YOU ALL FOR YOUR INPUT, SUGGESTIONS, & IDEAS.
 
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