Expert: Stephen Sokol Date: 2/15/2007 Subject: Jetronic Aux Air Valve / Idle Performance
Question My in-tank pump (and sock) was recently replaced with a larger Delco unit for a Volvo, so probably ok there. Q1: If my Alfa were losing resisual fuel pressure when parked, would this explain the "starts instantly-->nearly stalls-->runs perfect..." syndrome? Q2: How do I adjust the valve flap tension? [With these idle adjustments I've been making, I think I'm addressing the symptoms but not the cause.] Q3: What does a buzzing main fuel pump usually indicate? It's always buzzed steadily when the car is running and is only a few years old. Drivability is perfect except for the start-then-stall bug.
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Great info. My Spider's in great shape and running quite well (never quite well enough for me though...) but I'll keep bugging you, for my education.. :) Now that the CSI is working, it starts so fast when I turn the key that I wonder if fuel pressure isn't quite up to speed immediately after startup, causing it to stumble in the first few seconds. Next, I'll fiddle with the screw on the AFM.
I should clarify my description of the first item below - the strange, off-and-on "mooing" noise I hear, often in parking lots in the minutes after startup - it's not the differential, because it happens moving or not, often just idling. It almost sounds like it's coming from the Engine Management Computer (not likey I assume). Definitely somewhere aft of the seats. An odd noise. Doesn't affect running. I'd think it was a fuel pump, but I can hear them too and it sure doesn't sound like it.
When I asked you about the rather loud buzzing my new(ish) main fuel pump has always made, you recommended grounding the fuel pump to the chassis - why? - you must suspect a supply voltage issue. Please note the fuel filter and in-tank pump were recently replaced, so should be ok there. Replacing those parts did not change the buzzing noise.
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Interesting ideas. I appreciate your expertise. I couldn't adjust the timing to save my life. However, I bet they checked it when it was in the shop recently.
I've got the warm idle at a little over 1000 rpm. I adjusted it with the "idle adjustment" nut over by the intake manifold. Also put in NGK plugs. And an MSD coil. It still stumbles and almost stalls on startup. Fuel pressure was checked good recently. It's running GREAT besides this idle issue. Always something! Haven't touched the nut on the AFM yet - afraid I'll screw up the mixture.
You mentioned the fuel pump. I repalced my Bosch pump with a new one just a few years ago, and it has always made a rather loud buzzing sound, all the time. I can easily hear it over the engine when outside the car. Is this normal?
By the way, what is that intermittent "howling" / "mooing" noise I hear over my shoulder when driving it? It doesn't sound anything like the fuel pump buzz, although it seems to be coming from the rear.
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At what temp is the aux air valve supposed to close off completely? Wondering if it's supposed to be a factor when starting up in warm ambient temps (e.g. 75 degrees outside). Should I try messing with the adjustment screw?
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I'm shining a flashlight into my 1984 Alfa Spider's Auxiliary Air Valve. How wide should the opening be at 30 degrees-F? Mine opens like a peice of pie, and less than a quarter of the area of the circle opens at that freezing temp. When hot, it closes completely. Is this how they're supposed to operate?
Reason I'm looking at is, I've been having idle problems. If my Alfa sits out all day in the sun, it starts up instantly, then dies. Over and over. In that case, once I get it running by applying throttle while turning the key, it's totally fine the whole drive home. Starting in a COLD morning, it starts instantly, then ALMOST stalls, then is fine...
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About half the area should be open around 30F. Any Bosch air valve will do so get the best price. You could also try advancing the timing 4 degrees, and make sure the warm idle is 1000rpm. Readjust the idle co screw on the air flow meter to slightly richer (turn in--clockwise).
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You have two problems which is why I gave you the tuning parameters. I have had hit and miss luck messing with the adj. screw especially on units more than 2 years old. The aux. air valve should not be open at 70F. Do the tuning stuff and then you might try loosening the spring tension on the air valve flap, but, only after trying the tuning stuff. Of course. concerning the hot start problem: it might be a fuel pump starting to fail. Bosch pumps seem to not start rather than quit while running.
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Re: the noise. The differential is limited slip type and needs a 75w-90 synthetic oil that needs to be renewed from time to time--now is the time.
Re: the pump. Ground the pump to the chassis and replace the intank pump with a BBK unit for an 86 and above Mustang. (Summit Racing has it).
Re: the pressure check. This is a common error that mechanics make--volume must also be checked.
Re: the mixture. You will only affect the idle mixture.
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I am not there to hear the noise but it must be fuel pump related and there are two ways that noise occurs with a new pump. 1) the ground is faulty so splice a wire into the negative lead of the pump and attach it to the chassis nearby.
2) the intank pump is not sufficient as originally designed and that is why I recommend the higher pressure BBK pump be installed--it always brings an improvement.
Answer 1)Now is not the time to adjust the tension of the air flow sensor.
2)The check valve on the output side of the main fuel pump is required to hold and gradually lose residual pressure for at least half an hour.
3)Volvos with two pumps quite often suffer this malady also because they use a low pressure in tank pump--increasing its volume does not always cure the problem but a higher pressure pump does.
4)The noise of the pump I have always found associated with one or both of the issues I mentioned.
5)Most of the time the need for an intank pump is because of excessive heating of the returning fuel...
