AEM Digital Boost Gauge inaccuracy.

[SCREAM]

I swapped out my old electronic Greddy analog -30/30 boost gauge for a new AEM -30 /35 digital boost gauge today and I noticed some inconsistencies between the two. The AEM unit seems to be reading 6-7 psi below what the Greddy unit was reading. I am more inclined to believe the AEM to be more accurate, however it is displaying my idle at -17/-18 inHG and max boost only hits 21 psi. My Greddy unit would read -10/-11 vacuum and max boost was 27 psi, which is what I was tuned for using the Greddy unit. Having a 2.3 and Cosworth M2 cams, -10/-11 seems to be a bit more realistic after doing some researching, it seems to be consistent with others with similar builds. And the previous power levels I made at 24 psi seem to be consistent with EVOs with similar builds.

There are no kinks in the vacuum hose and it is tapped into the same location, off of the fuel pressure regulator, but the vacuum hose length went from 6 inches from the Greddy electrical wired sensor to about 2.5 feet to the AEM wired sensor.

The AEM unit is using the same ground as my AEM UEGO wideband and they are both tapped into the same power source, off of the ignition. This is exactly how my Greddy unit was wired. I'm not sure if this could be causing a problem for the AEM unit, but I'd like to be sure before I have to cut and re-solder my connections. For what it's worth, I ran my old AEM Tru Boost and AEM UEGO wideband off the same power source and ground on my previous EVO without a problem.

Something else I noticed was that the AEM unit sort of stops at 0 psi for a split second before climbing into positive numbers. With the analog gauge, it would gradually increase without an issue. Digital boost gauges are generally more accurate than analog gauges, but a difference of 6-7 psi seems rather excessive. Unless I've just been wrong this entire time and the Greddy gauge was just that far off. I'm just not sure which one to believe.

Any thoughts?

[silverbullet2010]

I thought my boost gauge was correct for a very long time. Then I installed a jdm map sensor and was reading boost from the manifold and my gauge was wrong. Maybe installing a Jdm Map to see what the actual boost is and go from there?

[SCREAM]

I thought my boost gauge was correct for a very long time. Then I installed a jdm map sensor and was reading boost from the manifold and my gauge was wrong. Maybe installing a Jdm Map to see what the actual boost is and go from there?

How far off was your gauge and what type were you using?

I will most likely have to go that route, unless I feel like trying to toss in a 3rd boost gauge I have laying around. I'm getting a full retune shortly with a GrimmSpeed instead of this Forge UNOS MBC, just trying to sort all of this out before then. Everything I keep researching says to trust the AEM unit, but I'll see if I can locate a MAP sensor to toss in.

[silverbullet2010]

I have a cheap ass glow shift Gauge. Its consistant just not accurate. It was off by 3-5 lbs.

[SCREAM]

I've always had great results with AEM digital stuff, and always heard the same. I just couldn't imagine another electrical gauge being off by 6-7 psi displaying numbers that seem more accurate than the AEM unit. I'll see if I can locate a MAP sensor to use.

Someone else suggested that it is possible the AEM unit is better suited to handle atmospheric/temperature changes which could explain the discrepancy. I'll just have to test via MAP. I always just used the boost gauge as a reference and adjusted tunes via load. I would just increase the boost and tweak the tune to get around knock and eventually leave it at whatever psi I was able to reach, which was 27 on my Greddy electrical. It's been a while since I've been able to log, well over a year, since my friend lost my tuning cables so hopefully I'll just settle everything when I get a full re-tune. So well see then I guess.

[BlackIXMR]

My aem boost gauge, i didnt even get to use. The sensor was broken right out of the box, So i traded it for a defi blue racer gauge. That I have never a problem with.

[Dsmolition]

as mentioned. I always log my map sensor and the boost gauge to check for inaccuracies
using a AEM tru boost / 35-30

[awdboost]

I have a AEM boost gauge with the 5 bar senor and it only off 1 or so psi to my EMS logs. I've always trust my AEM EMS logs over anything else, because they factor in more then just psi.

[SCREAM]

I had the car tuned and boost logs were taken off of load and the map sensor. The AEM gauge was actually accurate within a psi. So the Greddy unit was about to 5-6 psi off. Which means the entire time I was running with the Greddy tuned to 24 psi, I was probably running more like 19-20 psi, and when I tuned to 27 psi I was closer to 22-23 psi. I'd love to get the car on a dyno to actually get a more accurate portrayal of the power it now makes since I am now running 32 psi. For a good reference, the 24 psi I ran previously on the Greddy gauge (more accurately 19-20 psi in reality) the car put down 390~ on a mustang dyno (lost the dyno sheet, but it was within that range).