Voltage at AAV terminal

[That]

I cleaned my AAV today and it seemed to be working ok. However, when checking voltage , with car running, I get 13.5 on one leg ( using engine ground as the other) but nothing going across the two wires in the connector?? Is that normal? Thanks to all you tech people

[76was124]

The ground side of the AAV is switched through the ECU. Was the engine cold when you did the test? If so, I am guessing the ECU only turns on the heating element in the AAV after the engine is up to temperature..

[That]

Yes, it was cold. Thank you so very much for the explanation. So much to learn about these little cars. Again, my thanks.

[bradartigue]

Sorry but that's not how it works.

The full FI diagnostic is scanned in here: http://www.njfiats.org/joomla/images/st ... BoschL.pdf

With the motor running the AAR should have power. If not then you have a wiring break, a bad temp sensor, a bad relay set, or all of the above, or some of the above.

[spider2081]

I get 13.5 on one leg ( using engine ground as the other) but nothing going across the two wires in the connector?? Is that normal? Thanks to all you tech people

I think your test is valid and the results could be good for a correctly operating system. What I have not been able to find is a document stating if or when the ECU removes the ground from the AAR.

Power for the AAR comes from the FI dual relay set. Simply stated anytime the fuel pump has voltage the AAR has voltage. I believe your measurement from the AAR connector to ground confirmed this. You found one of the pins had voltage when measured to the engine ground. The other pin in the AAR connector connects to pin 34 of the ECU. I don't think the ECU supplies a continuous ground to the AAR. I believe that is why when you measured between the pins of the AAR connector, you did not measure voltage. The voltage was still present on one pin but no ground was present on the other pin 34 of ECU. I also believe the AAR has to be physically mounted to the coolant neck because it is partly the engines heat being conducted through this physical connection that closes the ARR window. The electrical connection assists or speeds up the closure.

Like I said I could not find a document to support this but looking at the wire diagram this is what I think.

[bradartigue]

Engine heat does indeed open the aar - but relying on engine temp alone is inadequate; therefore the thing is self regulating.

In this case his aar fails the test; it isn't powered when it should be. I'm fairly certain they receive power at all times, every l jet I've seen (and k jet for that matter) it's a constantly powered device

[76was124]

With the motor running the AAR should have power.

@Brad, So that makes me ask the question, "Why take the ground connection back to the ECU?"

I am not challenging your statement, as I really don't know and do trust your answer..I am just curious why use the ECU ground? Normally, if you have a sensor that you are monitoring, you run the ground back to the same place as the sensor voltage is measured. However, the AAV is not a sensor, it is an output device? Seems odd, but there must be a reason.

Also, does this mean the heater in the AAV has a somewhat time delay effect, having to be on long enough for the Bi-Metallic actuator to switch, which coincides with the engine warming up? Or is to help overcome outside temperatures when in a cold climate?

[RRoller123]

The heater element helps accelerate the closing of the AAV, it would take too long to react if it just moved by surrounding temp alone. I think the issue is that the engine heats up faster than the unaided bimetallic AAV can close.

[bradartigue]

With the motor running the AAR should have power.

@Brad, So that makes me ask the question, "Why take the ground connection back to the ECU?"

I am not challenging your statement, as I really don't know and trust your answer..I am just curious why use the ECU ground? Normally, if you have a sensor that you are monitoring, you run the ground back to the same place as the sensor voltage is measured. However, the AAV is not a sensor, it is an output device? Seems odd, but there must be a reason.

Also, does this mean the heater in the AAV has a somewhat time delay effect, having to be on long enough for the Bi-Metallic actuator to switch, which coincides with the engine warming up? Or is to help overcome outside temperatures when in a cold climate?

I don't know and it's a common question of L-Jet owners across marques. These components are really simple - the AAV is just a strip with a resistor on it. Resistor gets hot, metal strip moves. Engine temperature does not appear to be a variable in its operation; the test procedure is simply if the fuel pump is on so should be the AAR. In terms of the FI components, nearly everything has a connection back to the ECU. I think this just goes with the bolt on design of L-Jet.

Keep in mind though the design isn't really to overcome cold air temperature or even cold engine temps per se - it is only to increase idle speed during the period of time when fuel is being lazy and condensation is forming during the intake cycle. I've never tested the theory - and maybe I should, it would be interesting - that the AAR only comes on after the CSI has shut off. In other words, during cold start (when the ECU ignores everything and just goes full force on all five injectors for a few moments) perhaps the AAR is not powered because it would be pointless, it is wide open anyway.

Something to do this winter!

[76was124]

..Keep in mind though the design isn't really to overcome cold air temperature or even cold engine temps per

Sorry, I didn't make it clear, I meant was the AAR heater/resistor to help the bi-metallic overcome cold ambient temp ( not the AAR functioning was related to ambient temperature itself.). The rest of your reply answered that for me. Thanks!

[bradartigue]

Yes because otherwise there would be an opening while the motor is internally warm enough to maintain good idle speed

[wizard124]

http://www.fiatspider.com/f15/viewtopic.php?f=5&t=22898

My thread showing the inner workings of the AAV.

Sounds to me that you have a break in the ground wire.

[spider2081]

Found this on the web, double click on the schematic in the middle of the page to open the diagrams.
It is not for a Fiat however it appears to me it is very similar. http://www.team.net/TR8/tr8cca/wedgelab ... tr7ecu.htm

The + voltage is applied to one pin of the AAR when ever the fuel pump is supplied + voltage. The - voltage or ground is supplied by the ECU all the time the ECU is plugged in.

I then took the cover off a spare ECU I have and looked. Pins 16,17, 34, and 35 are all connected together . So for our Spider ECU's pin 34 should be grounded as long as the ECU is plugged in.

So I now believe you should measure voltage between the AAR connector pins as long as the ECU is plugged in and the fuel pump is running.

Referring to your first post it appears the ground wire to the ECU is not completing the circuit.

Sorry if I led you astray with my first post.

[Turbofiat124]

For what it's worth.

The AAV seems to be the most common component to fail on an L-jet system. I suppose due to it's design (using the bi-metallic strip of metal). I always wondered if there was a time delay built into the system. Kind of like modern rear defoggers that shut off after 10 minutes or so. I assume having power going to it at all times would eventually burn it up.

The original AAV on my Spider was bad (idle speed remained constant). I confirmed it by placing it in a freezer and it did not open. I replace it with one from an X 1/9 parts car. Not the same part number but worked fine for awhile. At some point in time it stopped working.

The idle speed remains the same when cold as it does when warmed up. But unlike some of my carbureted cars with manual chokes, my Spider does not seem to struggle when cold. I installed a manual choke on my Yugo and the idle speed is very lumpy until it warms up. It sounds like it has a racing cam in it when it's cold!

Is there any real reason to get this valve working? Or is this one of those emission control devices that is simply there to help get the engine hotter so it burns cleaner?

[bradartigue]

Is there any real reason to get this valve working? Or is this one of those emission control devices that is simply there to help get the engine hotter so it burns cleaner?

It is not an emissions control device. It increases idle speed by passing more air into the manifold during cold running.