[V8] RPM Sensor / Ignitition Timing Sensor - How To

[Jeremy Ward]

Have you ever had a hot-start problem with your V8? You drive home in 
traffic, stop into the grocery store that is a block away from your house, 
grab a gallon of milk, come back out and the car won't start? Do you notice 
that the Tach doesn't bounce as you are cranking it (stays at zero)? You 
have a failing RPM Sensor!
 Have you ever had a problem where your V8 is driving along just fine, but 
when it warms up the engine dies? If you let it cool down it fires right 
back up and then dies again after you drive a few miles? You have a failing 
Ignition Timing Sensor!
 Your V8 comes with these two sensors mounted to a plate attached to the 
bell housing. From the factory, the only difference between these two 
sensors is that they are color coded; grey - RPM Sensor, black - Ignition 
Sensor. They are actually the exact same sensor and are interchangeable. 
Some parts counter list one or the other as NLA (no longer available) and as 
always, the V8 parts fetch a pretty penny (~$200 IIRC). You can purchase the 
same sensor off a 5ktq (which is what I did) for under $100; the only 
difference is the 5k sensor is longer. They grey one I bought from SJM was 
cheaper than the black one ($92.75 vs. $157.39).
 It is a pretty easy job if you have patience and small hands. If not, I 
think a buddy said the dealer charged him $200 for the part and $200 for the 
install. As I am broke, I went with the $100 option ;-)
 You start by jacking the car up to give you room to work. I took extra time 
in doing so as my life is worth a few extra min. I have a buddy who lost a 
friend when his car (on jacks) fell and crushed him. Don't buy cheap jacks / 
jack stands. Find 2 good spots to place the jack stands and bump the car 
with your weight once it is up to make sure it doesn't move or seem 
unstable. I also leave the jack extended as a fail safe if something was to 
happen.
 Next remove 2 10mm bolts, unhook 2 connectors, and swap out the bad sensor 
(1 10mm bolt per). Re-installation is the reverse of removal. You are done! 
Well... I did leave out the yoga-like positions, the swearing, the endurance 
required... It is really not bad, but I would give yourself a few hours.
 Here are the pics:
http://198.107.18.114/V8Q/pics/RPM-Sensor.jpg - A view from the bottom
http://198.107.18.114/V8Q/pics/RPM-Sensor(Closeup).jpg - Here are the 2 10mm 
bolts. I used a open-end wrench to break them loose, and then just used my 
fingers to get them out. Reinstall was helped with a swivel head socket and 
a fine toothed ratchet.
http://198.107.18.114/V8Q/pics/RPM-Sensor-Conector(Bottom).jpg - Here is a 
view from the bottom of the connectors. My camera was able to squeeze in 
there (unlike my big head), but I unfortunately don't remember any reference 
points to give you. Tip: The connector spring-clips used on German cars 
don't have to be removed to unplug the connector - just squeeze the spring 
into the body of the connector and pull the plug loose. You probably already 
know that, but I figured this out on my own after several months of 
ownership ;-)
http://198.107.18.114/V8Q/pics/RPM-Sensor-Top(Closeup).jpg - Here is a view 
between the last 2 headers on the driver's side. Note that the sensors are 
mounted to a plate that can now be removed (once you unplug the connectors).
 Lastly, it has been suggested by some that you want to replace both 
connectors at the same time. This is not a bad idea considering it takes a 
few hours (not to mention the wear and tare on your knuckles), but again I 
am broke. I would rather have a temperamental RPM Sensor than a vehicle that 
dies once it warms up. One will get you to work in the morning, the other 
will not. I chose to put the new sensor as the Ignition Timing Sensor and 
moved the old one to the RPM Sensor spot. I haven't had any problems with 
the other sensor, but Murphy says I will now! :-)
 Hope this helps,
 - Jeremy
 BTW, could someone upload this to the KB for me? TIA