Ahu tdi low boost no faults

alghamedGT

Active member
Joined
Dec 10, 2023
Location
MOROCCO
TDI
GOLF MK3 AHU
Hi folks i have a strange low boost situation boost is always at 1.5 bar in vcds
Things that i checked .
N75 is good i borrowed it from my friend car
Maf from the same friend
Cheked the injection timing
I changed the i injection pump for some noises
I had the low boost before changed it so i dont think i have a fuel situation
I changed the turbo 2month ago because i had a leaking turbo
Now i have no oil consumption and from what i remember when installing it the car was fine 1.7bar when i install it

I even bypass the maf sensor with the diode mode and still had the low boost

Any clues friends .?

Image with maf bypassed

 

thechoochlyman

Vendor , w/Business number
Joined
May 7, 2015
Location
Campbellsville, Kentucky
TDI
1997 B4 Sedan
Check all your boost pipes for leaks. I'd be willing to bet something didn't get clamped up properly. What turbo did you put back on it? May also be good to at least temporarily install a mechanical boost gauge.
 

garciapiano

Veteran Member
Joined
Feb 12, 2018
Location
Southern California
TDI
1997 Jetta TDI (1Z)
Double check your boost sensing hose off the top intercooler pipe (it goes to the ECU under the cowl tray). A small hose in the ECU often cracks and leaks, causing the ECU to see the wrong pressure and that results in limp mode.
 

alghamedGT

Active member
Joined
Dec 10, 2023
Location
MOROCCO
TDI
GOLF MK3 AHU
i just changed all hoses with brand new ones problem still there
and i did more tests
one thing i noticed that when i bypass the maf with diode and when i remove the red hose going to n75 the car pull marginaly better with pressure in vcds 1.7 in 3000 rpm but alot of black smoke
 

garciapiano

Veteran Member
Joined
Feb 12, 2018
Location
Southern California
TDI
1997 Jetta TDI (1Z)
Bypass the MAF with a diode? What

There is no need to do that. Switch it back to how it was.

My guess is you probably have your stuff hooked up wrong. Make sure you have your vacuum lines all connected the correct way:

 

$tututu

New member
Joined
Jan 26, 2024
Location
Ohio
TDI
07/1997 Jetta TDI 1Z
As others have stated, check the small hose that is inside of the ECU. Have to open it up to find it inside. It is more than likely original and cracked.
 

alghamedGT

Active member
Joined
Dec 10, 2023
Location
MOROCCO
TDI
GOLF MK3 AHU
All hoses are fine
I tested the car with another immo off ecm from my friend's car . Same problem
I think maybe a have a faulty turbo or exhaust gases are escaping from some where i dont know
One thing i noticed that turbo is silent now because it doesn't produce the sufficient boost and i remember before that problem occurs you can hear the turbo clearly but now you can bearly hear it

Another thing i changed in the last 2 months is the flex pipe from the exhaust and i cleaned the catalytic converter maybe thats has no relation with my problem but its good to mention it
 

thechoochlyman

Vendor , w/Business number
Joined
May 7, 2015
Location
Campbellsville, Kentucky
TDI
1997 B4 Sedan
The turbo is bad, something isn't hooked up right, or your readings are off. There's also a slim chance your MAP sensor is bad. I'd hook up a mechanical boost gauge, at least temporarily, to see if your VCDS readings correspond with the gauge.
 

alghamedGT

Active member
Joined
Dec 10, 2023
Location
MOROCCO
TDI
GOLF MK3 AHU
I tested with a mechanical gauge always low on boost
The thing i noticed is when i disconect the red hose
So wastegate is always closed (I know its risky but im just troubleshooting) I get better results around 1.7bar at +2300 rpm
So i get boost but i think its late

I have very low smoke and the fuel pump and turbo is recently replaced
 

alghamedGT

Active member
Joined
Dec 10, 2023
Location
MOROCCO
TDI
GOLF MK3 AHU
Yes you are right some times the car goes into limp mode because the requested is 1.8 bar and the actual is 1.5bar
I noticed that when i remove the air filter the turbo sound is weak even when flooring it like it doesn't spool as much maybe i have a weak turbo or i dont have the fuel requered to spool the turbo
 

alghamedGT

Active member
Joined
Dec 10, 2023
Location
MOROCCO
TDI
GOLF MK3 AHU
Hi guys i just found that the turbo was the source of my problem i dont know why the turbo is 4 months old in my engine i remember it had no shaft play at all now it have plenty and the engine start to burn oil
My car has no modification done at all
I dont know what caused that turbo to destroy it self in that short period maybe because it was sitting in the junk yard for to long or maybe oil supply ?
Any i deas guys ?
I need to solve that problem to not have have that problem again when i changing the turbo
Maybe its time to upgrade the turbo
 

$tututu

New member
Joined
Jan 26, 2024
Location
Ohio
TDI
07/1997 Jetta TDI 1Z
Make sure that your oil return line is not kinked or clogged. Many times a compromised return line will blow the seals out of the turbo.
 
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