andrewallan95

My 1993 UrS4 has been not starting, I'm fairly certain its the engine speed sensor because I got the 2111 fault code for it but my engine was running while I got it, so its not one of the false codes for the engine being off. But I cannot find one anywhere, called the dealership in town and they said theres 2 engine speed sensor in the country for sale at dealerships in L.A. But when I search the item number for my engine speed sensor the only thing that come up are crankshaft position sensor, so I was curious if any of you know if these sensors work the same and could be interchangeable. As in if I purchase the CPS with matching product numbers as the engine speed sensor would the CPS work in place of the engine speed sensor. If any of this didnt make sense just tell me to re-phrase it, really need to settle this because I start my job on friday.

UrS4boy

I think you will be taking the bus to work. Not enough info for us to pin-point your exact problem.

For starters (pun not intended), read THIS

But really, you should start with this, found with a search:

https://www.audiworld.com/forums/sho...ential+reasons

andrewallan95

I apologize, the car does crank and will start usually once a day. Ive already replaced the crank position sensor and want to replace the engine speed sensor but I cant find one anywhere. Also, I tried unplugging the maf and the car would start but immediately die, so I plugged it back in and it started. But I tried to re-create that and the car didn't start at all. When the car starts in runs fine, no misfires or fuel cut or anything, pulls hard. But it just will not start, I'm currently reading the link you posted and I'm pretty certain my problem is the 4.3 section of it. Because I dont hear the fuel pump priming or anything and a bad g28 sensor causes that. The only problem is I cant find one anywhere and I was curious if the CPS can double as a engine speed sensor, I know they're both magnetic sensors so I figured I would ask.

UrS4boy

I really doubt that your issue is the G28 engine speed sensor. That said, find it, and clean the end (it might have debris on it). The G4 and G28 are physically electronically identical, the only difference is the color of the end connector so you (or others) don't screw up the firewall connections.

UrS4boy

You will NEVER hear a C4 UrS4/S6 fuel pump prime with the ignition key to "ON" unless the car has been converted to VEMS. Normally, the Motronic ECU needs the engine to be turned over at at least 13 RPM to get enough G28 signal to allow the ECU to energize the J17 Fuel Pump relay. A weak battery that doesn't spin the engine fast enough = a non-starting engine.

For more J17 info, click on the J17 label in the upper right corner of this live link AAN engine bay device map:

http://members.shaw.ca/speedtek/UrS%...ice%20Map.html

andrewallan95

What makes you doubt it being the G28? I got the fault code for it while the engine was running after many 3rd gear pulls. Are there other things that can make it think the G28 is at fault?

UrS4boy

I have been on UrS4/S6 forums since 1998 and I can NOT think of an actual G28 failure. False positives, yes. But no actual failures that I can think of. As a suggested, pull the G4 and G28 pair (on a single bracket on the driver's side of the transmission). Clean the ends and replace. Check the connections at the firewall (grey and black as per the annotated photo). Clear the codes (pull the ECU fuse) and try again.

andrewallan95

I'm going to go try taking the bracket off, I've only taken the sensors out individually and cleaned them. Will post results

andrewallan95

Sorry for taking so long to get back I had to finish paperwork for my job, but I took out the engine speed sensor and cleaned off some black dirt or metal pieces that were stuck to it and still no start, replaced all the fuses above the ECU, changed the relay that powers the fuel pump (next to the battery) and still no start. I tested the cam position sensor as well with an led and its still in working order.

UrS4boy

If you have a fuel pump relay by the battery, then either you installed it or somebody installed an 034 fuel pump relay kit (probably based on the DIY instructions I did in 2004). Two things:

1. There is still anothe fuel pump relay, the OE J17 fuel pump relay under the driver's side knee bolster. It needs to function. You need to test for 12V going into the second fuel pump relay while the engine is cranking. The trigger signal should be a green wire with a yellow stripe.

2. Since you have an aftermarket relay you have to check that there is 12V at the top of the fuel pump (under the plate on the hump in the trunk). No 12V, no working fuel pump. Aftermarket wiring harness could be fubar

You might have shared that with us a bit earlier.