I have an AEM analog boost gauge and I've been having a problem with it at the track since it was new where it will be fine most of the time and then be off by a lot (e.g. 15psi). I finally saw what happened - when I lift at the end of the straight, I'm occasionally seeing a vacuum spike that hits the stop on the vacuum reading (-30 inHg). This causes this gauge to do a full sweep and apparently re-calibrate so that it reads incorrectly until it is power cycled. I have never had a problem off of the track and it appears to read correctly other than this - of course I don't lift from full throttle near redline when DD. Car idles around -20inHg with AC off and will normally read -24/-25 when coasting in gear.

I'm planning to give AEM a call this week but wanted to see if anyone here had seen this or had any ideas. BTW - gauge is T'd from the vacuum line that runs from the intake manifold to the BOV.

 

what is your power source and ground?

 

I used fuse 3 for constant power, 12 for switched power, and grounded to one of the ground lugs near the driver's door (can't remember exactly where). It is calibrating correctly and reads right on what I expect all of the time - as long as I don't hit the negative stop. I've only seen that happen on the track. Pretty sure at this point it isn't a power/ground issue.

 

If I were you, I would try taking the fuse out, cut the end of the wire back on the power source wire and try reconnecting it. If that doesn't work, then its a function error withe the gauge and its time to send it back. Heard of gauges doing some funky stuff having to do with power and ground source so its worth a whirl.

 

Thanks for the suggestion. I believe it is an intended feature of the gauge that it responds that way when it hits the negative stop, but I haven't had a chance to call AEM to confirm. If not, then I will definitely reterminate the wires and see what happens.

 

yea you should definitely give them a call cause that would be a weird feature.

 

I gave AEM a call today. They assured me that the gauge and sensor are working as expected. The needle doing the full sweep is the gauge response to an error condition and below -30inHg it interprets that the sensor is failed. I did run a test where I disconnected the sensor and got exactly the same response. It wouldn't be an issue at all if it came back to the right value, but it has to be power cycled to re-calibrate after it has been out of range. They did have a fair point that I'm seeing values outside the specified range of the sensor/gauge....I was surprised to see that much vacuum. I'm sure it could be addressed by a software filter on the error since it is only that low very briefly, but they wouldn't have much incentive to make that type of change.

Looks like my choice is to continue to live with it doing that occasionally or find a different gauge. For now I'll continue to live with it since it doesn't happen very often.

 

have you try hooking the constant power wire directly to the battery?

 

Good to know! My AEM digital doesn't do this so I guess it is just with the analogs. Though I don't think most cars go into 30vacuum levels either

 

I have same prb , thanks awhitesti

 

[quote=Car idles around -20inHg with AC off and will normally read -24/-25 when coasting in gear. [/quote]

Sorry to bring this thread back, but is that part normal? because mine does exactly the same. -19/-20inhg at idle, then -24/-25 changing gears. just wondering if those numbers are right.

 

Yes