UrS4boy

In a quest to solve my minor (but annoying) hot/warm restart issue on my RS2'd 93 UrS4, I decided to take some time yesterday and investigate the G4 Crank Position Sensor and G28 Engine Speed Sensor under the intake manifold, at the junction between the engine and the transmission. Here they are:



They are held to the bracket by 5 mm Allen head socket bolts. The bracket is held to the block with similar 5 mm Allen head socket bolts. You can't get much in there so I used my little 3/8" drive stubby rachet and a 5 mm Allen socket. I started with removing the G28 speed sensor. Make sure that the hex hole of the Allen head bolt is clean and get the 5 mm socket in as far as you can before you attempt to get the bolt off. I pushed the socket and stubby into the Allen head with my left hand while pulling up on the rachet. Took some effort until the little bolt loosened with an audible "SNAP". (Probably never been off the 214K km engine).

I was concerned that I would find something like this (which would block the sensor and create a bad signal to the ECU):



Here is my G28 Engine Speed Sensor off the bracket (I twisted it slightly while pulling it out of the bracket to get it off).



I didn't take a photo but the end of the G28 was covered in a thin black oily film that was easily wiped off. Not even a hint of metal swarf on the end.

Next up was removing the G4 Crank sensor. I got the retaining Allen head bolt off but I could not get the sensor itself to move via twisting or pulling. Okay then, on to Plan B: remove the bracket. I put the G28 back into the bracket and then removed the entire bracket (2, 5 mm Allen head bolts). The result is as shown below. Note the "window" into which the G4 Crank Position Sensor is located in order to detect the crank position pin. Also note the teeth on the flywheel ring gear that impulse the G28 Engine Speed Sensor that the ECU uses to count the number of teeth flying by in a given time period to calculate RPM.



I then flipped the bracket over to expose the end of the G4 (and G28). The G4 was basically clean but I gave it a wipe anyway. This is the result:



After that, I reinstalled the bracket and the G4 bolt and tightened all the bolts to "goodandtight". Can't do much with a stubby rachet.

On to the next phase: Checking and cleaning the connectors at the connector rack:

Here is the connector rack:



I got smart and used large long-nosed needlenose pliers to push in the spring bales that hold the two connector parts (harness and device) together. I inspected all 6 connectors (they were clean with no corrosion). To help ensure that there won't be future issues, I applied a drop of Stabilant 22A VAG electrical contact cleaner and stabilizer to each of the three female pins in the harness connectors before I pushed the connectors back on, making sure that they were seated fully.

Here are the details of Stabliant 22A (originally bought around 1992 for work on my 1986 Jetta Carat):



Regardless of whether this cures the hot/warm restart issue, it was a deed well done and it gives me peace of mind that the connectors are not the issue and that the G4 and G28 are nice and clean. 

Crank Position (G4) and Engine Speed Sensor (G28) Info from the Engine Bay Device Map

Engine Bay Device Map - live label version

sciroccosven

I plucked mine out somewhat recently before going to a coilpack conversion. The conversion fixed all of my issues.


It was easier for me to break the bolts free and then remove the bracket before pulling the sensors.