map sensor (in)accuracy

diesel_guy86 · **Posted:** Sat Aug 02, 2014 6:38 pm

Was playing around today doing some full throttle pulls now that the turbo has loosened up. I have a boost and egt gauge and I like to use torque pro. I've noticed the map sensor being off but didn't really think much of it, for instance it reads 2lbs of boost at idle, when its actually 0. On one full throttle run I buried the 30psi boost gauge, while torque pro was telling me that the sensor was only detecting 22-23 lbs. Anyone else ever compared there's? That's a big difference, and means the engine isn't taking advantage of all the air.

I should add that yes its clean, I got it off GDE's bench when the original one was found to be faulty (from the machine shop not taking it out when they hot tanked it)

flash7210 · **Posted:** Sat Aug 02, 2014 8:11 pm

I dont have a boost guage. I only use torque pro to monitor turbo boost.

It seems that torque pro is slow in adjusting sensor readings. At best, what you see on the
display is an "average" over short period of time.

Other factors to consider are:
1. how accurate is your boost guage? Has it been properly calibrated?
2. Where in the intake path is your boost guage sensor/port in relation to the MAP sensor?
The MAP sensor is in the intake manifold and pretty close to the intake valves, which sould be
the most accurate placement.
3. The MAP sensor is sensitive to temperature changes. Now, I dont know the exact correlation
between intake temp (taken from MAP sensor) and turbo boost (taken from MAP sensor) but I
have observed that when intake temp is high (100+ deg F), turbo boost is lower. And when
intake temp is low (below 80 deg F) turbo boost is higher.

Using torque pro, the highest boost I have seen is 22.5 psi with my stock turbo setup.
And that was under ideal conditions like:
clear and cool morning weather
straight, flat road with no traffic
planets in perfect alighnment, etc

diesel_guy86 · **Posted:** Sat Aug 02, 2014 9:17 pm

My sensor is only 2 months old and is a higher end unit, it matches the torque pro within 2-3 psi in normal driving. I have observed the lagginess, but it isn't that bad and I can hold 30 psi long enough that it should have picked up a higher reading than 22-23 psi. Its also tapped in right above where the fcv bolts to the cover.

The anamoly you mentioned with boost vs temp is called density, and is why people are obsessed with lowering charge air temp. I seen 160°f intake temp on one of the 30psi runs today. A better intercooler would help along with water/ meth injection. The lower the temp, the higher the density, the less boost you need to make the same power.

For the record I'm no longer using the stock turbo in case anyone is wondering why my boost is higher.

CATCRD · **Posted:** Sat Aug 02, 2014 11:48 pm

I question whether it is the right sensor at all, if it was found laying on a bench. i.e. 2.5 bar max vs 3 bar max sensor.

user113 · **Posted:** Sun Aug 03, 2014 12:03 am

Just try pinching your CAC hose while your engine's idling and tell me that is zero psi. (Compare to when the engine is not running, for a true 0 reference.)

diesel_guy86 · **Posted:** Sun Aug 03, 2014 12:50 am

I'll try it, but it can't be much, thermorex had to install a snubber in his gauges boost line because he was picking up the vacuum from the valve overlap.

viewtopic.php?f=5&t=79402

flash7210 · **Posted:** Sun Aug 03, 2014 9:08 am

I have no doubt that your custom turbo setup is pushing 30psi.
But if your MAP saw 30 psi dont you think you would get an overboost code?
Maybe GDE did something to your tune to limit MAP readings?

diesel_guy86 · **Posted:** Sun Aug 03, 2014 9:26 am

Yes he did have to do something to keep from throwing the over boost code. I figured he just "deleted" the code/ limp mode feature. But maybe he did just limit the max psi the sensor would see. A new sensor is only $25 so might order a new one and see.

mass-hole · **Posted:** Sun Aug 03, 2014 10:12 am

Just thinking out loud:

In the Jeeps ECU there is a Driver wish map that determines the required torque(fueling) vs throttle % and RPM. There is also a boost map which controls the desired boost based on how much fuel is being requested, this map obviously is not used anymore since you no longer have a VNT turbo. The third map is a smoke map. As the name suggests this map is supposed to override the drivers wish map and prevent the engine from too rich by limit fueling based on the manifold pressure. So basically if the turbo is not where it is supposed to be when you mash the throttle, the fuel will be limited until it is. I suppose you don't NEED this map to properly tune the engine. If the Drivers Wish map is tuned right it could be ok other than you might get some smoke while the turbo is spooling up.

diesel_guy86 · **Posted:** Sun Aug 03, 2014 12:11 pm

OK, I understand that, but the sensor isn't even reading the correct pressure. I'll compare some more today, have you messed with ecm tuning much? I'd love to be able to tweak things myself but afraid I'd mess something up.

mass-hole · **Posted:** Sun Aug 03, 2014 1:09 pm

diesel_guy86 wrote:

OK, I understand that, but the sensor isn't even reading the correct pressure. I'll compare some more today, have you messed with ecm tuning much? I'd love to be able to tweak things myself but afraid I'd mess something up.

I bought the cable needed to pull and flash tunes and identified a lot of the important maps within the stock tune but never did any tuning. Im not confident enough to do it myself.

mass-hole · **Posted:** Fri Aug 08, 2014 11:36 am

CATCRD wrote:

I question whether it is the right sensor at all, if it was found laying on a bench. i.e. 2.5 bar max vs 3 bar max sensor.

What should the stock MAP be, I cant seem to find it listed anywhere? And when someone says a 3 bar map, is that absolute pressure or gauge pressure?

GreenDieselEngineering · **Joined:** Sun Jun 07, 2009 5:10 pm **Posts:** 1111

The MAP you installed was a stock part number.

SargeIndustries · **Posted:** Fri Aug 08, 2014 3:18 pm

my stock MAP sensor pegs at 37.4 when my scan gauge reads it. You would have to subtract 1 atmosphere or about 14.7 to get actual boost reading. It must be the limit of the stock sensor...

diesel_guy86 · **Posted:** Fri Aug 08, 2014 5:00 pm

Are there any sensors that are rated for higher?

diesel_guy86 · **Posted:** Fri Aug 08, 2014 10:57 pm

OK, I'm pretty sure I've tapped out the map sensor. Started thinking about how to find a higher rated map sensor. First thing came to mind was Cummins, and there's guys pushing 40-50+ boost in those engines. After some searching I came up with this: http://www.genosgarage.com/CUMMINS-4921 ... -WKc3PD_qA

Looked it up on Napa online and they have it, so gonna pick it up tomorrow and see if it'll work. Looks identical to ours, just rated higher and costs 2x as much.

If it'll work, I don't know, but I'll try it. Only thing I see is it will bolt on backwards.

diesel_guy86 · **Posted:** Fri Aug 08, 2014 11:33 pm

Found another one, made by Bosch, that is perfect. I just can't find how many bars its rated for.

diesel_guy86 · **Posted:** Sat Aug 09, 2014 9:34 am

Did a bunch of research and reading last night. I'll just note the couple important things I learned.

There's map sensors, and there's tmap sensors. The t designating temperature measuring, which is what the crd uses. Also the "a" means absolute (duh me) pressure, meaning it measures from true 0psi (30" of vacuum).
The stock sensor is a 2.5 bar sensor. For those who don't know a bar is one atmosphere of pressure, 1 bar = 14.7 psi. Measuring from 30" vacuum up 2.5 bar puts us at 22.05psi. It won't read after that.

I found a 3.5 bar (good up to 36.75psi) sensor that will swap right in. Only thing I'm not sure is if the computer will have to be tweaked to read the higher scale. Already ordered it so should be here next week. Kinda excited to see what the jeep does when it can finally see 30psi of boost.

mass-hole · **Posted:** Sat Aug 09, 2014 10:33 am

diesel_guy86 wrote:

Did a bunch of research and reading last night. I'll just note the couple important things I learned.

There's map sensors, and there's tmap sensors. The t designating temperature measuring, which is what the crd uses. Also the "a" means absolute (duh me) pressure, meaning it measures from true 0psi (30" of vacuum).
The stock sensor is a 2.5 bar sensor. For those who don't know a bar is one atmosphere of pressure, 1 bar = 14.7 psi. Measuring from 30" vacuum up 2.5 bar puts us at 22.05psi. It won't read after that.

I found a 3.5 bar (good up to 36.75psi) sensor that will swap right in. Only thing I'm not sure is if the computer will have to be tweaked to read the higher scale. Already ordered it so should be here next week. Kinda excited to see what the jeep does when it can finally see 30psi of boost.

I had read somewhere around here that the VW TDi MAPs work. They have two bolts holding them in but one of the holes lines up with ours and everything else is the same.

For the new MAP sensor to work properly with your boost levels, and have an effect on your fueling, you would need to make sure that the "smoke" map in the ECU is active and properly tuned. I believe the stock one goes up to around 2.2 bar. If the smoke map requests less fuel than the actual throttle position map I believe it will cut fuel at the 2.2 bar level regardless of how much boost you actually make.

diesel_guy86 · **Posted:** Sat Aug 09, 2014 12:00 pm

Gotcha, I'll call GDE and see what they can do. Hopefully there not tired of me yet...

map sensor (in)accuracy

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