How to test a MAP sensor?

AdzCM · February 22, 2015, 10:35:05 PM

Got a larger [250kPa] MAP sensor fitted to my G40 and fitted larger [310cc] injectors. Bought a chip from Andy to suit, but the car will not run right at all. Not even off boost...

It has symptoms that point in the direction of faulty MAP sensor. Blip the throttle and it wants to cut out. Try to drive forward and it bogs down and cuts out.

I figured a test for the MAP sensor would be to remove the vacuum hose to the MAP sensor connection on the ECU [and obviously clamp it to prevent a vacuum leak for the rest of the system] then start the car and see how it runs. If it runs the same then surely the MAP sensor is at fault?

I did this, and the car runs the exact same. Would you say the MAP sensor is duff then?

Adrian

hayesey · February 23, 2015, 10:04:27 AM

what map sensor have you got?

I'm not sure what running it with the map sensor disconnected would do, I'd expect it to run like crap in that case as the ECU needs this sensor to work.

AdzCM · February 23, 2015, 03:29:00 PM

Quote from: hayesey on February 23, 2015, 10:04:27 AM
what map sensor have you got?

I'm not sure what running it with the map sensor disconnected would do, I'd expect it to run like crap in that case as the ECU needs this sensor to work.

Its a 250kPa one from maxrpm.de

I noted the way it ran with the vacuum hose connected, then disconnected it and there was no change to the way it ran. Surely the map sensor can't be working right?

Is there any way to test with a multimeter.

Don't suppose anyone with an uprated map sensor that works wants to disconnect the vaccum hose to their ECU and start it up with a few revs to see if there is much change?

Adrian

Andy · February 23, 2015, 07:56:58 PM

You can test it on a bench if you've got a spare wiring harness, but not so easily on the car. If your mapping guy can get hold of an EPROM emulator it's very easy to see if the MAP sensor is working, as the ECU will trace across different load sites as the MAP value changes.

You could open up the ECU, plug it back in to the wiring loom and turn the ignition on (but don't start the car). Then with a multimeter you can read the output voltage of the MAP sensor and check it's sensible - you're looking for circa 2V with a 250kPa sensor at atmospheric pressure. Be bloody careful if you do this, as you're exposing the PCB - so you need to keep it away from anything metal so you don't short stuff out. If you're not sure, don't do it!

I replied to your email from the weekend BTW. You need to check what your ignition timing and CO pot are set to. If your mapping guy changed these from stock to get the car back from the aborted mapping session, they could be way out.

AdzCM · February 23, 2015, 08:05:52 PM

Hey Andy, just read your mail. The co pot and ignition timing were not touched at all. Will I still mess with the co pot to see if there's a change?

I'll try tomorrow with a multimeter n I'll make dam sure It touches nothing.

Cheers for that buddy.

I take it the 'test' I suggested by disconnecting the MAP sensor vacuum hose is not a test?

Thanks mate.

AdzCM · February 24, 2015, 01:49:34 PM

Got a reading of 3.18v ... This is a little high with key on/engine off?

Adrian

Andy · February 24, 2015, 03:33:23 PM

Is that measured from the signal pin to the ground pin on the MAP sensor?

Andy · February 24, 2015, 03:37:48 PM

Signal pin with respect to ground pin on the sensor should be between 1.5V and 2.2V ish depending on how far above sea-level you are etc. Make sure you have the +ve lead (usually red) of the meter on the signal pin, and the -ve lead (black) on the MAP sensor ground.

3.18V corresponds to about 165kPa - or 0.65 bar of boost!!

You got a pic of the MAP sensor and how it's soldered in?

AdzCM · February 24, 2015, 09:35:41 PM

It looked a lot better than this. He tried to remove it again to fit the standard map sensor...

This is the little pcb that maxrpm.de give you to make soldering easier.

In the first picture, which of the bottom 3 prongs do I test?

Adrian

AdzCM · February 26, 2015, 01:58:35 PM

Not getting a voltage between 1.5 and 2.2... I got a -(ve) 1.65 ... Reverse the red/white multimeter cable and it reads 0v

Andy · February 26, 2015, 03:25:39 PM

Stick the positive meter lead on the bottom pin (the one with the notch in the leg of it), and the negative meter lead on the pin above. Then you're looking for around 1.5-2.2V.

Andy · February 26, 2015, 03:27:45 PM

You also need to check ignition timing and CO pot values are set to standard.

From there you may need to tweak the CO pot significantly to get it driveable, as that chip isn't intended for such a big turbo!

AdzCM · February 26, 2015, 06:27:57 PM

Quote from: Andy on February 26, 2015, 03:25:39 PM
Stick the positive meter lead on the bottom pin (the one with the notch in the leg of it), and the negative meter lead on the pin above. Then you're looking for around 1.5-2.2V.

Thanks andy. Got 1.71v ... Map sensor all good then? Ill try the copot tomorrow. Just screw it all the way out both ways in increments and rev it to see if it gets better?

Thanks mate

Would aftermarket management be my only hope after this? Or is there any way I could buy an eprom emulator for my mapper. Or is the software really expensive?
Adrian

Andy · February 26, 2015, 07:54:49 PM

Get your mapper to buy himself an EPROM emulator! If he has the rest of the kit they're not expensive on their own - I'm assuming he's already got all the software etc.

AdzCM · February 27, 2015, 05:19:01 PM

Hey Andy, I messed with the co pot today. Kept screwing it clockwise in intervals. Got it to run half way decent

thanks bud.

Is this a sureway fix or is there an underlying problem that needs to be sorted so that I can screw the co pot back to its original position?

Or is it ok to leave the co pot the way it is now?

Also, does the co pot keep turning or will it eventually stop?

Hopefully get it mapped now. Least I'm a step closer.

You've been a great help bud

Adrian