5th fuel injector disable: 1996 VW Passat TDI
How to disable or remove the 1996 VW Passat TDI 5th fuel injector
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The 1996 Passat was the first year for the VW TDI in North America and have a problem with the 5th fuel injector in the exhaust for emissions.
Volkswagen had diesel powered cars for many years but not the turbo, intercooled, electronically controlled injection pump that distinguishes the TDI from earlier VW diesels, the IDI. There were also other major differences in the engine and engine management.
The 1996 Passat also had a unique to '96 5th fuel injector. See 1000q: mk3 jetta and passat differences to see a list of differences, interchangeable parts, model year differences, etc. The fifth fuel injector injects diesel fuel into the exhaust downstream of the turbo and upstream of the catalytic converter. The fuel was supposed to clean the emissions by heating up the catalytic converter but it didn't work very well and often made the car smoke more. It's recommended to remove or disable the 5th fuel injector to reduce smoke (emissions) and wasted fuel.
The 1996 had a technical service bulletin (not a recall) that replaces the fuel injectors and changes the ECU (ECM, car computer) and 5th injector. Since it was not a recall, it may not have been done to all 96 VW Passat TDI. You don't need to have these changes done to plug the 5th injector, you can just plug it. Also check the ecu hose since this problem always shows up sooner or later. See 1000q: ECU hose for more details.
Below are pictures showing a 1996 (left) vs. 1997 (right) passat TDI fuel line. The 96 has an extra branch off to the 5th injector (note the T below), the 97 does not. If you follow the extra fuel line in the 96, it goes to a solenoid, then to a fitting on the exhaust. In the 1997, both lines go directly from the fuel filter to the injection pump.
-1997 passat fuel line to replace the old line. The part number is VW# 3a0 130 307 e (1z and AHU engine). VW# 3a0 130 307 d is also listed but the parts catalog doesn't say what engine it's for. I recommend an OEM line rather than making your own because of fitment and because it should have a clear section. Do not use standard rubber or vinyl hosing because the line will come into contact with diesel fuel and heat. For reference, the Jetta fuel line is VW# 1h0 130 307 ae.
-paper towel to catch any fuel spills
-rubber or vinyl gloves to protect your hand from diesel fuel
Unscrew the clamps on the old T shaped fuel line and replace with the new fuel line. You will also see the solenoid there. Remove the line and the 5th injector as pictured below on the exhaust. Make sure to plug the exhaust bung so there are no exhaust leaks. Put the new line on and tighten all clamps. Start the car and check for any evidence or presence of fuel leaks, fuel odors or vapors, or abnormal engine performance. This is cleanest method.
A faster method is just to plug the old T with something that will not be corroded by diesel and to replace the T. Some suggest sticking a thin screw to plug the line and then replacing the T so there are no fuel leaks. If you do this, make sure there are no fuel leaks at all since you do not want any exposed fuel in the engine bay creating a possible fire hazard.
Below is a picture showing the fitting on the exhaust. If you want to remove the solenoid and line it won't set a check engine light or make any difference in running. The issue is that you have to make sure that the fuel line is disabled as mentioned above and that there are no exhaust leaks. You can weld over the fitting or remove the union and stuff a ball bearing in there and then replace the union over it but on most cars it will be rusted in place.