Replacing Carrera RPM and Crank Position Sensors

[2.7RACER]

I recently decided to replace the original sensors on my 170,000 mile '85 Carrera. Along with this is a new fuel pump and DME relay.
I felt it was better to do this proactively rather than find myself out in the middle of New Mexico with a problem.
So I jacked up the driver's side, propped up with a car stand, pulled the rear wheel and began to look around with my light. Sure enough there were both sensors held in place with a allen cap screw. Removed the first cap screw with my trusty 5mm allen drive on the end of my 18inch extension. A little tugging and out it came. Since both sensors are identical I figured I needed to mark one so as to not mix them up. A little red tape on the end took care of that.

Back in the engine compartment, remove the heat blower and duct work to improve access to the connectors. With the area opened up, I marked one of the connectors, pulled the bracket and wire holder and followed the wires to the rear of the engine tin (towards the driver). The position sensor and CHT wires go through a rubber plug stuck in the engine tin. The rubber plug must be removed to get the sensors and connectors out.

I ended up punching out the rubber plug from the bottom with a long screw driver. Tried first from the engine compartment but no go. With the plug out I fished out the first sensor from the bottom up through the engine tin.
I marked both ends of the new replacement and fished it into place.

The second sensor was close to the engine tin so I needed a small 5mm allen wrench, my 5mm allen socket on the end of the 18inch extension wouldn't fit.

I lightly greased the both sensor bodies to slip them back into the mounting holes, very lightly.

Passed the connectors through the now open engine tin. Reinstalled the allen head cap screws. Since one sensor was marked, no problem getting them reversed. Put things back together and fired up the engine before replacing the heater blower and duct work, just in case.

Probably 2-1/2 hours start to finish.

Oh, the rubber plug is in my tool box waiting for an engine drop to stuff it back in. I wrapped the wires heavily with rubber electric tape where they pass through the engine tin. Access with the engine in place just isn't sufficient for me to reinstall the rubber plug.

Tomorrow the fuel pump gets replaced. Better on my schedule than to be stuck on the roadside unexpectedly.

I now feel a bit more confident taking a longer weekend trip.

[sig_a]

You mention 170000 miles, not part failure, as adequate reason for replacement of crankshaft sensors. My '87 Carrera has somewhere around 26000 miles, but is also 21 years old. Age might have a negative effect on these parts, so I might check mine and replace if necessary. Maybe they are causing engine sputter at RPM below 3000. Seems to come and go with change in outdoor temperature. Any comment?

[2.7RACER]

sig_a,
These parts rarely give much warning of failure. 50 miles between towns here. Parts are a minimum of 24 hours away. I'm not interested in towing and $75 per hour to fix my car. I do almost all my own work. Cell phone coverage in NM can be iffy.
A Ford or Chevy could be fixed just about anywhere. Decent Porsche mechanics in Albuquerque, anywhere else, better to tow home.
I'd be less concerned about a car with 26K miles, unless it's driven or stored in the weather.
Nothing beats putting it on a lift and given a careful PPI type examination once a year.
Wires and some rubber parts get brittle with age. Even sitting in your garage.

[KTL]

These sensors are very simple in their operation but the wiring itself is the failure point. The sheathing becomes brittle from the constant heat cycling and exposes the braided wiring. Wiring develops corrosion and intermittant problems ensue.

Don't even look at these the wrong way. If you're willing to replace them, go for it. But don't play with the wires if you're not ready to replace. By the way there's a thread on this forum that indicates a BMW sensor is a direct replacement for a substantial cost savings. One of my local friends installed the BMW sensors and they work perfectly.

[Wil Ferch]

I thought one of the sensors was particularly sensitive to setting the "gap" between it and the flywheel teeth. With the access problems Doug mentioned..... how did you manage that ?

[2.7RACER]

Hi Wil,
Yes, I'm aware of the gap between the sensor and flywheel.
The bracket holding both sensors is adjustable. Removing the sensors does not require moving the bracket.
The sensors are mounted to the bracket with one each allen head cap screw.
Used my 5mm allen wrench. Don't know the metric size for this screw.
I suppose if one was to use a different brand or part number it might be necessary to reset the gap.
I would compare the length of the sensors to be sure they are the same.
It's a dirty job working on the floor, even with the carpet pieces I use.

[KTL]

The BMW sensors are a direct replacement- no dimensional difference in the sensor body. So if one is lucky enough to be able to get the sensors out of the mounting sleeves (they typically get stuck in there and must be destroyed to remove them) without the need to remove the bracket, then you are correct that there's no re-setting of the air gap between the sensor and flywheel teeth.

[Wil Ferch]

Thanks gents....

[buttjoint]

I just did this and used the bmw sensors made by bosch . $130.00 total and two hours/ 2 beers.

[ChrisBennet]

In my experience, those sensors do not want to come out of the bracket without some persuasion.
If you need to adjust the gap with the engine in the car, glue a 0.8 mm thick washer on the old sensor and use that to adjust the bracket.
-Chris

[Dolle_dries]

Originally Posted by buttjoint

I just did this and used the bmw sensors made by bosch . $130.00 total and two hours/ 2 beers.

Hello which type bmw bosch sensors for flywheel porsche 911 3.2 ltr carrera de 1988
I need the two sensors DG and BG

[Dolle_dries]

Replacing Carrera RPM and Crank Position Sensors
I recently decided to replace for my Carrera 3.2 ltr
The two flywheel sensors
Witch type replace Bmw sensors can I used ?
I read it on the forum please can some one give me a link witch is compatible porsche 911 3.2 1988

[Techno Duck]

Originally Posted by Dolle_dries

Replacing Carrera RPM and Crank Position Sensors
I recently decided to replace for my Carrera 3.2 ltr
The two flywheel sensors
Witch type replace Bmw sensors can I used ?
I read it on the forum please can some one give me a link witch is compatible porsche 911 3.2 1988

Use BMW part # 0261210002 or 12141708619

Functions the same with a slightly longer harness. Significantly cheaper than the 911 specific one. Can be found for less than $65/ea.

[KTL]

I have used part number 12-14-1-708-619-M14 here on Pelican and they work just fine. They are identical to the Porsche part and much much cheaper

DG and BG are the same exact sensor. The letters just describe whether the sensor is the timing sensor or the starting sensor (which reads a set screw in the flywheel). If the engine doesn't start after installing these sensors, you connected them wrong and need to switch connections.

[john walker's workshop]

FWIW, the bottom sensor goes to the middle hole in the engine bracket and top one to the bottom.

[GH85Carrera]

Originally Posted by john walker's workshop

FWIW, the bottom sensor goes to the middle hole in the engine bracket and top one to the bottom.

Yea, that is real important. I mark one of mine with a dob of paint on one of the the connectors. After it gets ready to be connected, double check which one has the paint blob.

[KTL]

Why is it really important? No harm done if the male sensor plugs from the engine are not connected to the proper female plugs in the engine bay. You simply unplug and reconnect accordingly and the engine starts/runs.

I say this only because over time the sensors can be changed and the male plugs not installed back into the same location within the bracket. Plus at this stage in life the original DG and BG stickers have usually fallen off the wires and people don't bother to put a replacement label on the wires.

[john walker's workshop]

That's the way the factory did it and if someone was going to check resistance on one specific sensor it would be good to have them in their original position. Right?

[KTL]

That's what I suspected was being implied. Just wanted to be sure I wasn't missing something. I getting slow in my old age lately.............

[88911coupe]

Just to add to this these sensors can fail intermittently, which can be confusing and frustrating. Thanks it ischmitz I checked mine and depending on the day (heat maybe?) they would test fine and then way out of spec.