MAP-sensor going ape?

Alex B · Post by **Alex B** » Sun Jan 06, 2013 12:24 am

Car: Saab 96 with V4 engine

Finally I found a way to get a clear film og the MJ-screen in action, so the URL leads to the film. It is longish, but it shows a problem I don't know how to solve. The MJ seems to register full load the moment I barely touch the accelerator. The way the needle moves from low KPa to atmosferic puzzles me. Anyone for a good explanation? Because the MJ thinks vacuum is almost constantly at minimum the engine runs with little advance. Afaik the carb does not have ported vacuum, which is confirmed by the mechanical vacuum guage that is on the same vacuum line as the MAP sensor. I made the map using one of the spreadsheets in the MAP-section of the forum.

http://www.youtube.com/watch?v=DTHscWD9gc8

The engine is not in optimal shape. I started running it again this summer after a long period of being not in use and it also showed rough running on the mechanical advance. However, I guess that won't be of influence on how the MJ measures vacuum and how the needle of the pressure guage moves from high vacuum to 100 KPa.

Ambient pressure with engine off reads this time 60KPa. Shouldn't that be 100?

Tia for all input,

Alex

Post by **brentp** » Sun Jan 06, 2013 12:25 pm

Hi Alex,

Was this unit ever calibrated for a TPS sensor? if so, that's probably what the issue is. Your best bet is to re-flash the firmware and get the default MAP load configuration back.

Follow these instructions using the latest v3.2.x firmware http://www.autosportlabs.net/MJLJ_Firmware_update

Alex B · Post by **Alex B** » Sun Jan 06, 2013 8:31 pm

Hi Brent,

Not that I know of, I built it straight out of the original packing and it was a MAP version. It is a V4. The link you gave, does that firmware also apply to V4? Could I have downloaded a wrong firmware version in my ignorance to start with?

Alex

Alex B · Post by **Alex B** » Tue Jan 08, 2013 8:11 pm

I managed to come to the line:
"Waiting for HC08 reset ACK..." and then nothing happened for more than 2 hours, so I broke it off. Is it normal that it takes so long or did something go wrong? Will try to make a screenshot.

And then I got the brilliant idea to power up the Megajolt

. "received 0xfc (good)" Hurra!, However, Calibration break pulse just passed 1800. Is this normal or shoud it be calibrated after 1 pulse? Maybe I'll find out pretty soon myself, but if a bigger expert than me knows, please enlight my ignorant darkness. Tia again.

Alex

Alex B · Post by **Alex B** » Thu Jan 10, 2013 7:27 pm

Progress made. With the other computer the download went as meant, but......no change

. Using the data logging function it shows that when the MAP-sensor is sucked down to a about 0 KPA the white indicator line rockets up to 102KPA. With the load guage in turbo mode the same behavior is shown there. The needle is down to almost 0 KPA and then flies up.

Brent, you mentioned to download the latest v3.0.x firmware. Is that to be used on a V4?

Alex

Alex B · Post by **Alex B** » Sat Jan 12, 2013 10:56 am

Brent, help, I am stuck here. Is there a way to check the MAP-sensor for proper functioning? I tried to measure resistance and voltage with the sensor in situ, but didn't get much wiser. Is it possible to check when it is completely disconnected from the board with only + (5 volts?) and ground connected and use of a multimeter?

Alex

Post by **brentp** » Sun Jan 13, 2013 12:46 am

Hi Alex,

you want the 4.0.2 firmware, downloadable from here:
http://www.autosportlabs.net/MJLJ_V4_Downloads

Alex B · Post by **Alex B** » Sun Jan 13, 2013 4:53 pm

Hi Brent,

Those are the files I used. I tried them again, downloading from scratch and here under are the results.
Is there something I overlook? The mljJunior firmware came as a zip-file. I took the file without using Winzip from the zip-casing and tried that file (the size ± doubled and the extension changed form zip into s19), but that was not successfull either.

Alex

Post by **brentp** » Mon Jan 14, 2013 3:46 am

Actually, the firmware is inside the zip file. unzip it first.. it's the .s19 file you want to use when writing the firmware - you don't want to use the zip file directly.

Alex B · Post by **Alex B** » Wed Jan 16, 2013 9:24 pm

Well, I extracted the zip file with Winzip, I extracted manually, the loadings went largely seen just as the screenshot above, but the result after several attempts is still the same

. So I think the way to go first is to check the MAP-sensor. Is there a way to test it by measaring either voltage or resistance, on the circuit board or removed?

Alex

Post by **brentp** » Sat Jan 19, 2013 10:56 pm

It's certainly possible, but unlikely the MAP sensor might be defective.

Try testing the Megajolt with the software, with the unit powered up but engine not running. disconnect the vacuum line. What MAP reading do you see?

Apply vacuum to the MAP sensor using a vacuum pump. Does the MAP sensor reading in the software change smoothly? What if you add pressure? does it change smoothly and linearly?

Alex B · Post by **Alex B** » Mon Jan 21, 2013 10:26 pm

Hope the video shows.

Start is with Mj off, then switched on with KPa on a steady 44. This is atmospheric pressure. Then some pressurizing with a bicycle pump, everything behaving smoothly. Next is pulling vacuum and with a low of 10KPa it's Presto!! with a sudden rise to 100 Kpa. This is repeated a few times and then it's switch-off again. Barometer showed 1015 (miliBar?, old barometer) and 76 something (not a clue what kind of scale).

I will try to get the old scanner up and working and make a scan of the circuit board for checking if everything was soldered on the right place. I am pretty sure I did it right, but one never knows. Is 44KPa a normal value for atmospheric pressure? I don't live at high altitude, just between 200-250 metres above sea level (± 650-810 feet).

Alex
http://www.youtube.com/watch?v=8iseVwbWT0E

Post by **brentp** » Tue Jan 22, 2013 5:17 am

Hi Alex,

Actually, 100 - 103 KPa is normal for atmosphere. Did the MAP sensor ever work correctly?

Yes, pictures could be helpful to see! Also, you may consider a replacement MPX4250AP if it was working correctly and then problems showed up.

Alex B · Post by **Alex B** » Tue Jan 22, 2013 8:58 pm

Hi Brent,

I got wrong readings from the start, it never functioned correct. Reading back the first post of this topic I see that it started with 60KPa and by heart it was about 54KPa in the first recording (all with engine off and MJ powered up of course

).

Alex

Alex B · Post by **Alex B** » Sun Jan 27, 2013 5:06 pm

Picture via the links (couldn't get the pictures visible in the message

)For as far as I could see all resistors are at the right place. I resoldered the connections of the MAP sensor, but no difference. So I really think the MAP-sensor was faulty from the start.

Alex

https://pz1kbg.bay.livefilestore.com/y1 ... JPG?psid=1

https://pz1kbg.bay.livefilestore.com/y1 ... JPG?psid=1