I could use some advice testing the MAP sensor. I have been troubleshooting a boost problem. My pattern is 10-2-2. The boost just dies when the secondary should kick in. I have tested the Turbo actuator and today tapped into the pressure and vacuum lines that move it. At the 4500 transition i have both pressure and vacuum.

I then thought about the MAP sensor. I took it off to check resistance with vacuum, 0 pressure and pressure. No change in resistance but that may not indicate anything. Then I tested it according to the FSM. At idle, i have 4.96 volts at pins A and B rather than 1.3-1.6. That would seem to indicate that the sensor thinks i'm at full boost and is probably shorted internally. Then when I pulled the the vacuum line off, as the FSM says to do, the motor died. I tried this a couple times. I even turned it off, pulled and plugged the hose so there could be no leak and tried it. But the motor didn't want to start. Does it seem reasonable to conclude that the MAP sensor is bad? Does this fit with my boost issue on a motor that seems to run well otherwise? I appreciate any feedback.

 

The map sensor is relatively linear away from the edges and should give you ~2.63V at zero pressure, close to 5V at 17 psi, and ~1.3V at idle (depending on vacuum). You can pick up a used one cheaply in the classifieds.

 

are you sure the CRV is closing when the CCV in the y-pipe opens at 4500? If the map was shorted i you would also have some idle/power issues

 

No, i'm not sure the CRV is closing or the CCV opening. I can check them static but haven't tried to check them on the road. Any easy way to do that? I could T into the vacuum lines i guess. I too think that if the MAP were shorted i would have other issues, but honestly don't know. Perhaps i am checking the wrong pins although i triple checked!

I'm on the road for the rest of the week so hope to get back at this Sunday.

 

So what would make the engine die when I remove vacuum from the MAP sensor? As I noted, I tried pulling and plugging the vac hose and then starting the engine but it didn't want to start. Doesn't that suggest an issue with the MAP sensor?

Thanks for all the replies! Just getting another perspective helps.

 

The ECU uses the MAP sensor to monitor and adjust fuel. If it's unplugged it will send bad signal and the engine will run like it's blown. The map sensor plays no role in determining the 10-2-2 that you're seeing or 10-8-10 boost you want.

Keep it plugged in and focus on the boost control system.

Dave

 

i can only confirm, my mate has problem with his map sensor, and the car sounded terribly at idle, it was going up and down and doing some crazy ****, if ur idle is fine i dont think this would be ur map sensor..

btw im having the same problem after i done my vaccum job, tested my babes again yesterday and my boost patter is even worse 10-8-0 or 10-5-0 or whatever basically my boost is all over the place, and noone can help me

 

If you were getting better boost before you probably got some hoses crossed or left a connection loose.

 

dont think so...i know how it sounds like mate but i have taken UIM off again couple of weeks ago and checked all the hoses, crossed two but i got them back as they should be and still got the problem, i didnt actually make any difference+ i get this high pitched noise...i have left my car in mazdas dealer...see what they say...


anyway, i dont want to hijack this map sensor topic but i was just wondering, coz people install 3bar map sensors or something, i have seen quite few, but would it make any difference if i got my one working, im running or pretty much stock engine if i changed this map sensor? if so is it just a straight replace? as in take the old one out and put new one back in connecting the same way as the old one?

cheers

 

Uh, oh. They will probably suggest a rebuild and new turbos.

A new type of map sensor will require recalibration, which you cannot do with the stock ECU.

 

To OP it sounds like you may not have tested the MAP sensor correctly, If it is indeed showing 4.96 volts with the throttle shut, then the car would be dumping fuel into the engine. It probably wouldnt even start, and probably flood the engine.

My guess is something is wrong in the vacuum nest.


Sickboy: the high pitched noise sounds like a leak between the UIM and LIM. maybe a wire got pinched in there or the gasket isnt sealing correctly.

Both of you should check for leaks between couplers and all the boost pipes, buy or make a pressure tester for the intercooler piping and pressurize it.

 

yeah..if it only was this simple...

the thing is i have done it twice, checked everything,couplers, i even replaced my ic pipes with aluminium ones..i tried to make(they dont sell them rubber 3" end caps - i swear itried lkike 11 hardware stores!)and buy(they dont sell them over here, i even emailed fighters garage asking if they can ship it to UK and they never replied to me ) a boost tester - i tried everything, and it looks like my only chance was to give it to someone who can actually test it...havent driven thic car for a month because of this so im hoping...they will at least tell me where the boost leak is...

 

Finally figured things out so I thought I'd complete the thread. Turns out that the boost problem was two crossed vac lines. As a resulth the CCV was never seeing boost on chamber A to make it open. My mistake when I swapped engines! Now it works perfectly. Since it works fine i'm no longer pursuing the MAP sensor testing. It must be working correctly or something would not be right. Guess I measured the wrong pins or something. Thanks for all the replies and help.