Map sensor failure symptoms.

AnotherPerson

Veteran Member
Joined
Oct 24, 2015
Location
New Orleans
TDI
1999 Beetle
Trying to judge a couple things on my car and this is kinda a 2 part question. When a map sensor is failing has anyone ever had it report higher boost than it's getting?

Second part, if the map sensor is saying to the ecu I'm getting 20lb of boost does the ecu fuel for 20lb of boost? I know newer cars can adjust but didn't know if the alh based fueling on sensors or if it was just set throttle position and rpm maps for fuel.


Sent from my iPhone using Tapatalk
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis (where it's safe)
TDI
There are just too many to list....
Never seen a MAP sensor fail on an ALH. Ever. So I could not tell you the symptoms.

Obviously if it is plugged in and the circuit is complete, you'll have no DTCs, so that much is OK. The question is, is it reading the correct value? The only way you could verify that would be with a manual boost gauge.

Depending on the software, the ECU which is controlling the boost, will fuel accordingly but a tuner would be better to answer that question.

Perhaps some context to your question is in order. Are you trying to fix a problem that doesn't exist, or are you just curious how the system works in general?
 

AnotherPerson

Veteran Member
Joined
Oct 24, 2015
Location
New Orleans
TDI
1999 Beetle
Still trying to figure out my bad mpg. Vcds shows requested and actual almost spot on. Before my tune, lots of smoke 30mpg. After tune. Much less smoke 30mpg. Just cleaned the turbo because vanes were sticky from before I replaced the injectors and a pretty old and dirty air filter,30mpg. We have gone through almost everything and the only thing left is the map sensor. At upto like 3k rpm the car seems to be fine. Above 3k it blows a lot of smoke. Which is why I'm thinking maybe it isn't actually getting the boost it should for the fuel. Vanes this time we're at the point where sometimes it would do that little chirp when it would break loose.

Wish someone would have made a steering wheel pod for my car and I would have a boost gauge. But the only ones I come across out there are so expensive it's a joke for a piece of plastic.


Sent from my iPhone using Tapatalk
 

eddieleephd

Top Post Dawg
Joined
May 27, 2012
Location
Asheville, NC
TDI
2002 jetta Wagon
Haven't read checked timing.
I find that advanced is necessary for efficiency and EGT's.

Timing needs to be played with to get right.
 

Shoveltrev

Well-known member
Joined
Feb 11, 2015
Location
Hutchinson ks
TDI
2002 new beetle deceased, 2003 jetta . 2002 jetta , 2012 sportwagon
had one fail on the 2002 bug at 200000 miles . it was easy to diagnose it showed boost before you started the engine. when i changed it out it was full of oil. was kinda slutty to change on the bug as its mounted in the intercooler
 

AnotherPerson

Veteran Member
Joined
Oct 24, 2015
Location
New Orleans
TDI
1999 Beetle
Have had the map off previously so I know it's a pain. What vcds groups to compare with engine off for baro and map?. Timing is good. Even my brake drag issue is 100% fixed now. I know people will always look back on that one lol. I feel like maybe the map is showing High at boost and more normal at idle.


Sent from my iPhone using Tapatalk
 

Enabled

Veteran Member
Joined
Apr 23, 2013
Location
Houston, TX
TDI
2003 Jetta TDI Manual, BMW 328d SW
No, the ECU does not add extra fueling if there is more air. It's only negative feedback.

Does your intake manifold have carbon deposits/buildup?
 

AnotherPerson

Veteran Member
Joined
Oct 24, 2015
Location
New Orleans
TDI
1999 Beetle
Intake is clean. So it wouldn't fuel for 18lb of boost even if it's actually getting 14? I would have figured if it was calling for 18lb of boost it would fuel for it if the car said it was getting it. The n75 doesn't have set levels for boost correct? Like it will adjust pressure for what psi is requested based on map?


Sent from my iPhone using Tapatalk
 

turbocharged798

Veteran Member
Joined
May 21, 2009
Location
Ellenville, NY
TDI
99.5 black ALH Jetta;09 Gasser Jetta
It fuels based on MAF, not MAP. Yes it will adjust the N75 based on MAP but to a point. It compares it to a set value and adjusts it as needed.

Just scroll though the VCDS groups, one of them will be the baro and MAP readings.
 

Enabled

Veteran Member
Joined
Apr 23, 2013
Location
Houston, TX
TDI
2003 Jetta TDI Manual, BMW 328d SW
In static air to fuel ratio cars (gasoline cars), the ECU will add more fuel when there is more air measured because it has to keep the engine between 12:1 - 14.7:1 afr. Any leaner and it will get damaged.

In diesels, you can go as lean as you want without damage. Diesels do not have a programmed positive feedback. It will fuel the same.
 

eddieleephd

Top Post Dawg
Joined
May 27, 2012
Location
Asheville, NC
TDI
2002 jetta Wagon
Alright, do you know what the variance has to be to throw limp mode?
Sent from my iPhone using Tapatalk
I can't say exactly, however, it's probably in excess of 225 to 300 more than requested.
I have mine set for 150ish over and had a sticky actuator for a while causing a regular overboost that didn't throw it into limp mode.
Something makes me think it's actually more than a set limit of boost.
Over 18psi for a stock car and maybe more than 26psi for my tuned car set to around 26psi.
 

AnotherPerson

Veteran Member
Joined
Oct 24, 2015
Location
New Orleans
TDI
1999 Beetle
Malone emailed me back even though there on vacation. Said its a mix of the map and maf that do fueling. May give it a couple weeks and just let malone send me some new chips for a 3bar than change it to a 3bar.
 

AnotherPerson

Veteran Member
Joined
Oct 24, 2015
Location
New Orleans
TDI
1999 Beetle
Got a new Maf already. Did have it reading low at higher rpm prior. Gonna get some chips from Malone than do the 3 bar. They are on vacation so I got a couple weeks


Sent from my iPhone using Tapatalk
 

AnotherPerson

Veteran Member
Joined
Oct 24, 2015
Location
New Orleans
TDI
1999 Beetle
Here's a question. If the tune was setup for a 3bar instead of the 2.5. Would running the 2.5 cause it to run very rich?


Sent from my iPhone using Tapatalk
 

eddieleephd

Top Post Dawg
Joined
May 27, 2012
Location
Asheville, NC
TDI
2002 jetta Wagon
This is a question for Malone.

They told me that the sensor reads different all together and isn't compatible with stock sensor tunes.

You'll have to keep the original and reinstall to go back.
 

Enabled

Veteran Member
Joined
Apr 23, 2013
Location
Houston, TX
TDI
2003 Jetta TDI Manual, BMW 328d SW
Putting a 3bar sensor on a 2.5bar designed tune will artificially raise the amount of boost. (But no changes in fueling so it will do nothing to power, keep in mind).

These sensors work on 0-5V.
A 2.5bar sensor will be around 2.5Bar at 5V, while a 3Bar will have 3bar at around 5V.

The tune just redefines the pressure definition at 5V.
If the scaling is wrong, the ECU will not know the correct boost level and try to correct (upwards in your scenario), giving you a risk of overrunning the turbo.
 

AnotherPerson

Veteran Member
Joined
Oct 24, 2015
Location
New Orleans
TDI
1999 Beetle
I don't know much on bars. How many psi would that be under where it should be if it was the other way around?


Sent from my iPhone using Tapatalk
 

vanbcguy

Veteran Member
Joined
Feb 22, 2013
Location
Vancouver, BC
TDI
'93 Passat - AHU mTDI with GTB1756VK
1 bar = 1 "barometer" or atmosphere = 14.7 PSI at sea level(ish)

These are absolute pressue sensors, with no boost it should read about 1 bar as it's exposed to the atmosphere. So a 2.5 bar sensor is good for 1.5 bar, or about 22 PSI of boost. A 3 bar sensor is good for about 29 PSI. You actually don't want a tune that takes you right to the edge of the sensor limit though, as once it hits the limit it can't tell if it is 0.001 bar over or 10 bar over. The ECU can no longer act in a proportional manner.

Sent from my LG-H873 using Tapatalk
 

Nevada_TDI

Top Post Dawg
Joined
Aug 17, 2008
Location
Reno, sort of...
TDI
2001 Jetta TDI
Another Person, to answer your last question; yes it is possible running a 2.5 bar MAP sensor on a 3 tune could very likely cause your engine to run smokey.
And historically speaking, MAP sensors don't usually die. But if they never died, why are replacement units sold to fix the bad ones? And they are cheap enough to replace if all other option have been depleted.
 
Top