57 replies to this topic

[pete l]

Hi all,

 

I have a BIG problem that is doing my head in !

 

I have 3 MAP sensors here with me for my MPI that runs really badly (problem MAP diagnosed with my T4 machine)

 

I have searched the internet and youtube on how to test a MAP off the car and tested all of mine, and they are all dead !!!

 

Does anyone know if I'm doing something wrong ?

 

I apply 5 volts to the MAP sensor and measure the output on the signal wire. then with a vacuum pump I suck on the sensor and measure the voltage. I am getting no voltage change whatsoever.

 

Please any help will be much appreciated.

 

Am I really that unlucky and only received dud MAP sensors ??? 

 

Pete.

 

 

[Allrounder]

What does the live data say with it on the car??

Think there should be 3 wires to the MAP sensor. 5v, earth and signal to the ecu. If youve got 5v and a good earth then probe the sensor wire, think it should be 1.5v at idle.

Hope this helps.

[pete l]

I agree with you, I have 5 volts and ground. Engine off I am getting 2.3 volts. Engine running I am getting 2.3 volts !!!!!

 

Live data says 76 kpa engine off (should be near 100kpa) , and 76 kpa engine running (should be around 40kpa) 

[Steve220]

Pete, is it worth checking the wiring to the ecu? Or have I been dumb and not read you've already done that?

[Allrounder]

Does sound like a sensor. If your getting the same readings for engine on and off. If you can find the right ohm resistors you can substitute the MAP for them to test the wiring back to the ecu just to be certain.

[Bat]

Hi,

Most ECUs will guess at something, especially a map sensor, if it's unplugged. If it runs better with it unplugged you're on the right track. With the ignition on, sensor unplugged, and looking at the live data, bridge between 5v and signal and then ground and signal, you should see the map pressure changing. Also while unplugged check the voltage on the signal wire there should be voltage on that too. Check resistance between the ground wire and a known good ground point, another check would be with the sensor plugged in the ground wire should read 0v to your known good ground.

Cheers 

Edited by Bat, 23 May 2018 - 10:27 PM.

[pete l]

Pete, is it worth checking the wiring to the ecu? Or have I been dumb and not read you've already done that?

 

I have had the engine loom out, unwrapped and checked, all is well.

 

Does sound like a sensor. If your getting the same readings for engine on and off. If you can find the right ohm resistors you can substitute the MAP for them to test the wiring back to the ecu just to be certain.

 

I like this idea, thanks for that, i might even try a variable resistor.

 

Hi,

Most ECUs will guess at something, especially a map sensor, if it's unplugged. If it runs better with it unplugged you're on the right track. With the ignition on, sensor unplugged, and looking at the live data, bridge between 5v and signal and then ground and signal, you should see the map pressure changing. Also while unplugged check the voltage on the signal wire there should be voltage on that too. Check resistance between the ground wire and a known good ground point, another check would be with the sensor plugged in the ground wire should read 0v to your known good ground.

Cheers 

 

Here's another strange thing, I thought also that MAP unplugged or dead would cause limp mode, but the engine won't even start with the MAP unpluged.

 

 

But, all the MAP sensors I have are not changing value when I bench test them.

 

I have another 2 on the way from the UK, this time it's the MHK100490 version, not the MHK100600.

 

Pete.

[pete l]

This is the kind of test that I'm doing with my MAPs 

 

[Steve220]

Pete, is it worth checking the wiring to the ecu? Or have I been dumb and not read you've already done that?

 
I have had the engine loom out, unwrapped and checked, all is well.
 

But have you actually checked for continuity over the length of the loom from sensor plug to ecu plug?

[pete l]

I have yes. 

[Bat]

Hi,

Is there any voltage on the signal wire with the map unplugged?

Cheers 

[pete l]

I must admit, I haven't checked, should there be ?

[Bat]

Hi,

I think so, fhough I'm not running a standard ecu anymore so I can't check.

Cheers 

[Sprocket]

 

Pete, is it worth checking the wiring to the ecu? Or have I been dumb and not read you've already done that?

 

I have had the engine loom out, unwrapped and checked, all is well.

 

Does sound like a sensor. If your getting the same readings for engine on and off. If you can find the right ohm resistors you can substitute the MAP for them to test the wiring back to the ecu just to be certain.

 

I like this idea, thanks for that, i might even try a variable resistor.

 

Hi,

Most ECUs will guess at something, especially a map sensor, if it's unplugged. If it runs better with it unplugged you're on the right track. With the ignition on, sensor unplugged, and looking at the live data, bridge between 5v and signal and then ground and signal, you should see the map pressure changing. Also while unplugged check the voltage on the signal wire there should be voltage on that too. Check resistance between the ground wire and a known good ground point, another check would be with the sensor plugged in the ground wire should read 0v to your known good ground.

Cheers 

 

Here's another strange thing, I thought also that MAP unplugged or dead would cause limp mode, but the engine won't even start with the MAP unpluged.

 

 

But, all the MAP sensors I have are not changing value when I bench test them.

 

I have another 2 on the way from the UK, this time it's the MHK100490 version, not the MHK100600.

 

Pete.

 

 

What value would you use to substitute in limp mode for MAP sensor that will not cause damage to the engine?......................... none, because any fixed value would eventually cause damage, or, the engine would run too poorly to be worth running at all.

 

Best action is to prevent engine running.

[Sprocket]

 

 

Pete, is it worth checking the wiring to the ecu? Or have I been dumb and not read you've already done that?

 
I have had the engine loom out, unwrapped and checked, all is well.
 

But have you actually checked for continuity over the length of the loom from sensor plug to ecu plug?

 

More importantly, are the right wires going to the right terminals on the sensor?