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Author Topic: ECU doesn't read MAP  (Read 492 times)

Offline slow-n-steady

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  • Model: Alhambra Mk1
  • Spec: 01 TDI 115 AUY+EHH
  • First Name: Steve
  • Region: South West
ECU doesn't read MAP
« on: January 07, 2019, 07:02:13 PM »
Hi,

Alhambra 1.9 PD AUY
My question will sound random without the background. 

I noticed intermittently lack of acceleration above 60.  It got their in its own sweet time. 
Nothing else obviously wrong.  I lived with this for 1000 miles, simply mulling it over in my mind and was convinced that the turbo vanes required freeing & cleaning. 
Finally, on starting I heard an unusual rasping noise but engine appeared happy.  Things got worse.  Within two miles engine seemed strangled and simply refused to pull, but would rev with no load.  I was outside a local garage, so left it with them. 
It took them three weeks and replacement of MAF sensor and duct, and to discover a shredded paper towel in the inlet to the intercooler, used by a previous garage to exclude debris when replacing right strut. 
Having now replaced the MAF and intercooler, the engine ran happily.  I paid the bill and removed the vehicle from their tender care as soon as possible.  The proprietor assured me I would notice a marked improvement in performance and mpg.  In fact there was nothing wrong with the mpg previously but is now considerably worse.  The connector to the MAF had been ‘glued’ in place with silicone because they broke the plug during dismantling.  OK, it only cost me another couple of £ to fix that, but I shouldn’t have to.   
In my own time I checked the inlet air duct to the turbo, and the function of the vane actuator by applying a vacuum (OK).  While in the mood I checked EGR and ant-shudder valves.  Neither functioned as the diaphragms were perforated.  Replaced combined unit, both now operate correctly.  Good not to have the engine shudder to a stop when I switch off. 
Now I get to the point. 
While the weather held I decided to see if my Autel MS508 could identify any other problems.  (Sad to say, I don’t have anything better.  Never got round to TDI VAG COM.)  It showed me that the MAP (BPK 0 281 002 399) reading was a constant 255kPa.  With sensor plugged in, Key On, Engine Off, I back probed and found the following voltages relative to earth:-
Lead 1, obviously zero volts. 
Lead 2, reads 3.16 volts, varies with temperature.
Lead 3, reads 5.00 volts never changing with variation in temperature or pressure. 
Lead 4, reads 1.91 volts, falls with vacuum, rises with positive pressure, returns to 1.91 volts when vacuum/pressure released. 

It looked OK, but as I didn’t know what to expect (and couldn’t find on the internet) I fitted a replacement. 
All back probe voltages followed a similar line, but at a lower voltage.  I won’t proceed with this as I feel it is a red herring. 

Returning to the original MAP, as it appears to function correctly, is it likely that the ECU is not recognising the output from the pressure pin (pin 4)?  I do not understand why the ECU doesn’t set a fault.  There is nothing displayed on the dash or recoverable with the MS508.   

I found this forum that speaks about a ‘stuck’ MAP sensor.  Presumably destroyed by overload, rather than stuck.  http://www.vwaudiforum.co.uk/forum/archive/index.php/t-18347.html
But my problem appears not to be with the MAP sensor, and my turbo actuator rod moves freely enough, starting and stopping at the correct vacuum values.  My problem appears to be either with the loom between MAP and ECU or with the ECU itself. 
Should I back probe at the ECU before proceeding?  I only have Haynes manual, so don’t have a wiring diagram for engine management.  Can anyone tell me which cable colour or pin number is the MAP pressure input on the ECU please? 

Regards, Slow-n-steady

Offline johnnyroper

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  • Spec: 02 tdi 115 ghia
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Re: ECU doesn't read MAP
« Reply #1 on: January 07, 2019, 07:57:48 PM »
So the turbo is functioning ok now,is it boosting normally and not going in to limp mode?

Personally I would obtain vcds and check the map readings as generic ones don’t always give the correct data.

Offline slow-n-steady

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  • Model: Alhambra Mk1
  • Spec: 01 TDI 115 AUY+EHH
  • First Name: Steve
  • Region: South West
Re: ECU doesn't read MAP
« Reply #2 on: January 07, 2019, 10:26:46 PM »
Thanks for that johnnyroper.
It certainly doesnot fall into limp home mode.  Without a signal to my MS508 I can't be sure what the turbo is doing, except I know the actuator moves appropriatly.  I will jury-rig a vac/pressure gauge to share the MAP mounting point and take someone with me to watch the readings under load. 
There is no lack of acceleration. 
Next step VCDS it is then. 
Regards, Slow-n-steady

Offline johnnyroper

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Re: ECU doesn't read MAP
« Reply #3 on: January 08, 2019, 06:11:51 AM »
If it is running right and no lack of acceleration it certainly sounds like ecu is happy and receiving the correct readings, vcds will definitely be the best to hook up and then do a log of boost etc to see what map is reading

Offline slow-n-steady

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  • Model: Alhambra Mk1
  • Spec: 01 TDI 115 AUY+EHH
  • First Name: Steve
  • Region: South West
Re: ECU doesn't read MAP
« Reply #4 on: January 08, 2019, 10:27:54 AM »
Thanks again Johnnyroper,
As a time-served Luddite, I do not own a laptop.  While I wait for a younger member of the family to explain what features I need, I will hook up a vac/pressure gauge in the passanger seat and treat wy wife to a ride in the country!  On second thaughts, maybe a video camera would be more informative! 
Car continues to perform well, except there is a 'whistle' as it passes through 2000 rpm under load. 
I noticed my Autel MS508 tells me the MIL is not set, which is good, but the MIL on the dash does not light during the lamp-check period when the key is furst turned.  Another job. 
Regards, Slow-n-steady

Offline brianh

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  • Model: Galaxy Mk2
  • Spec: 2001 2.3 Ghia LPG
  • First Name: Brian
  • Region: South East
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Re: ECU doesn't read MAP
« Reply #5 on: January 08, 2019, 06:59:21 PM »
It also might be worth testing it with your new maf unplugged - If you notice an improvement it may be a dodgy MAF. New doesn't always mean any good, and cheap pattern MAF units can be problematic. Any idea what brand has been fitted?

Offline slow-n-steady

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  • Posts: 17
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  • Model: Alhambra Mk1
  • Spec: 01 TDI 115 AUY+EHH
  • First Name: Steve
  • Region: South West
Re: ECU doesn't read MAP
« Reply #6 on: January 09, 2019, 05:36:44 PM »
Hi anyone,
False alarm, my Autel Maxiscan OBD11 reader was not, and still is not reading a MAP output from the ECU. 
However, both old and new MAP sensors talk to the ECU and using an old fashioned gauge in parallel with the MAP sensor, I experience up to 140kPa gauge (about 240kPa absolute). 
At one time during this test, on a steep ascent, at a time we would normally change down, I floored it and managed to get it into limp home mode.  Turned off/on, boost back to normal.  I pluged the MS508 in at the first opportunity.  No codes stored, no codes pending.  I'm begining to think it is of very limited use. 
During this exercise I noticed how closely boost pressure follows the throttle position, regardless of engine speed, and then falls off as the rpm catch up. 
Sorry to have wasted everybody's time, thanks for the suggestions, I really must change to vcds!
Regards, Slow-n-steady

Offline brianh

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  • Model: Galaxy Mk2
  • Spec: 2001 2.3 Ghia LPG
  • First Name: Brian
  • Region: South East
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Re: ECU doesn't read MAP
« Reply #7 on: January 11, 2019, 03:52:14 PM »
Unfortunatly using obd2 scanners on earlier vehicles can throw up odd readings - My mk1 showed something like 34v battery voltage when the engine was running, but a multimeter proved that to be incorrect.

Offline slow-n-steady

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  • Posts: 17
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  • Model: Alhambra Mk1
  • Spec: 01 TDI 115 AUY+EHH
  • First Name: Steve
  • Region: South West
Re: ECU doesn't read MAP
« Reply #8 on: January 12, 2019, 02:14:27 PM »
Thanks Brianh, 
I have an appointment with a guy who has both 52 Galaxy and 51 Sharan to establish if the problem is with theMS509. 
In the meantime, I wrote to Autel and asked if it was a known problem, and could they repair my OBD2.  I guess it is small beer to them as they have not bothered to reply. 

Which VCDS do members usualy plump for?  I would be using it on more than 3 vehicles so that rules out one option.  The free version looks very limited.  Any advice please? 
Regards, Slow-n-steady

Offline Mirez

  • Pondering the next mod...
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Re: ECU doesn't read MAP
« Reply #9 on: January 12, 2019, 03:00:59 PM »
Where abouts in the South West are you Steve?

If you are planning on having VAG cars for a whole then invest in the hex-can version, yes it's expensive but will pay for itself over and over in time if you stay with the brand.
03 Ford Galaxy 1.9 TDI 115 Ghia in Spruce Green Metallic
With cream leather interior, Full Bodykit, Remapped at 145bhp, Lowered on 18's
06 VW EOS 2.0 T-FSI 210 Sport in Deep Black Pearl
With red leather interior with full Caractere bodykit, Remapped at 255bhp and sitting on 19's
14 VW Tiguan 2.0 TDI 177 R-Line in Deep Black Pearl
With black leather interior, panoramic sunroof and bi-xenon headlights.
08 Ford Transit 2.2 TDI 115 in Frozen White
With retrofitted everything except another slidey door! :)

VCDS HEX/CAN - Scans/Coding done in Wiltshire in exchange for winegums! :)

 

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