ruddyrid

iTrader: (8)

Well I have a very strange issue that to me doesn't make much sense. I have an AEM EMS-4 w/ a standard GM 3-Bar MAP sensor.

I found from my data logs that I was boosting some 8-10 PSI w/ an open wastegate on my U-Trim S5 Hybrid Turbo. I thought initially this made sense since I have a free flowing exhaust and turbo inlet, and I didn't know what to expect from a hybrid.

The issue came up though when I compared the data logs from my AEM WideBand Fail Safe. It showed that I was only boosting 4-6 psi. So I started thinking that maybe I had a faulty MAP sensor, bad wiring, or an incorrect sensor calibration.

I also double verified that I was only really boosting about 4-6 PSI by keeping an eye on my AEM Boost Gauge, and it was dead on.

So I went ahead and made a little pressure tester from a Cylinder Leak Down Tester and hooked up the AEM FailSafe boost reference hose and GM MAP Sensor hose together and added pressure. They were both very close to each other and only off by a maximum of 2 PSI at 25 PSIg.

So I guess the only thing that may be throwing off these readings is where I have the MAP signal coming from. For the GM MAP Sensor, I have it off the little nipple off the passenger side of the UIM, pretty much right under the BAC valve. I would think this would be the best place to hook it up but I may now try to hook it up to one of the lines by the fuel injectors on the LIM.

I'll be trying this out possibly this weekend, but in the mean time if anyone has experienced this please feel free to chime in!

ruddyrid

iTrader: (8)

Anyone? :o

Vicoor

First, make sure you have the proper calibration loaded into the EMS for the particular MAP sensor you are using.

Next you said you are tapping off the UIM for the MAP sensor, that's good. But you didn't mention where you are hooked up at with your boost gauge.
Really that should be hooked up to the same location.

You say that when you pumped them both up there was a 2psi discrepancy, that's too much. 10% variation between sensors is nuts, and is yelling that you are not accurately measuring boost.

Get them both hooked up to the UIM and check if they read different. If so check the mechanical connections, hose integrity, and such.

If that's ok look at the electrical connections. Differences in reference voltage and ground offsets will make them read differently as well.

Hope this helps.

ruddyrid

iTrader: (8)

I do have the correct MAP sensor calibration loaded onto the EMS. Being that it's off by a few PSI I don't think it matters much, as long as it's consistent. Just my gauge pressure and EMS pressure wont be dead accurate to one another.

In any case it does bug me a bit, being I sometimes feel a bit obsessive about small details.

But last night I swapped the reference ports for the EMS MAP sensor and the FailSafe. So I now put the WBFS on the side port of the UIM and the MAP sensor on the little nipple that sits in-between the two oil injection valves on the LIM.

Sure enough, now I'm reading some 8-9psi on the FailSafe and only 5-6 PSI on the EMS MAP Sensor. So tonight I will try hooking the MAP sensor up on the UIM where it was and the WBFS to the other port that sits in-between the Secondary Injectors. Hopefully this will get me solid readings on both units without having to T into anything, I hate T's!!!

bumpstart

restriction within the lower reading port nipple ?

ruddyrid

iTrader: (8)

Possibly, I spoke w/ my co-worker about this also and came to the conclusion that it could be some kind of restriction or due to the angle of the port, it could be causing some type of venturi effect.

I went back and hooked up the GM 3 BAR MAP sensor to the side port of the UIM and then hooked up the WBFS to the port on the LIM between the secondary injectors, T'd w/ the FPR.

Here is a pic of a log how they compare now. I think I'm ready for le dyno tune.

Vicoor

I think you are asking for problems if you are reading manifold pressure anywhere other than the plenum.
If I understand what you are saying that you are take a pressure measurement in the runner of the LIM, the Velocity and associated pressure drop will prevent an accurate static pressure reading .
Check out this link
http://en.m.wikipedia.org/wiki/Bernoulli's_principle

I'd suggest making a vacuum manifold and connecting it to the plenum portion of the UIM and connecting everything to that.

ruddyrid

iTrader: (8)

Damn, yea that just sealed it for me. Close this thread lol. For now I'll just leave it as is since all the sensors and gauges seem to be reading consistently and very close to one another. Maybe if I go with the V-Mount and FD UIM next year I'll apply what I've learned to that setup.