mj1pate

There are numerous threads concerning both of these topics, so this is a summary plus personal experience.
1) Access to the Crank position Sensor (virtually) requires removal of the fuel hose to the Fuel cooling unit. Since there is an access relationship, I would suggest replacing the CPS when its tiime to replace the fuel lines, and vice versa.
2)When performing either task, the old vacuum lines are available, routed behind the intake manifold. This is a good time to identify kinked or open vacuum lines and advisedly replace vacuum hoses with silicon equivalents.
3) When removing fuel lines, I advise purchasing a set of flare-nut wrenches (line wrenches), so as to better clasp the inline nuts on the fuel lines. No better way to hopelessly round off inline nuts than with open ended wrenches. Flare nut wrenches won't fit on every fuel line nut, but will for most. In removing one very stubborn fitting. I had to fabricate a cheater, consisting of a flarenut wrench, clasped by an oversized channel lock. If an open wrench had been used, damage to the inline nut would surely have resulted. Naturally, secure the nut's adjoining line with a suitable wrench, while loosening the line nut.
4) I took advise from Rennlisters concerning hopelessly stuck CPS, that break off, requiring way out of proportion work to extract them. I began spraying the CPS base and retaining hex bolt with penetrating oil 3 times a day, 5 days in advance. After removing the hex bolt, firm back and forth hand twisting freed the sensor. The SOB portion of this job turned out to be the easiest.
5) Check all electrical sensor connectors and wires for (yes, I'm saying it again) CHAFING. Do any repairs while you''re in there.

Best of luck;

Mike

mj1pate

BTW: Thanks to those who gave advise on CPS removal. You made my weekend!

Regards;
Mike

mj1pate

What a difference.
Right off; the old cross-over fuel line on the front side was worn and cracked by being (saying it again) severely CHAFED under the oil filler inlet. The cracks ran deep. Thanks Rennlisters and Rog for the heads up in suggesting giving this attention!
In the test run today gains were made as follows:
1) Cruise control now works
2) shifting is smoother
3) this car accelerates faster
Reasons for this is as follows: old vacuum lines were kinked and one was loose. Repaired severely CHAFED MAF electrical connector, so that bare wires were insulated.
Life is good, for now. Well, it usually is better than I deserve...
Carrry on,

Mike


.

H2

I guess it makes sense to replace the crank position sensor every time you replace rear fuel hose/s (every 20 years?) but it's not a high wear item is it? I replaced it in one of my cars but the old one looked near new still and it's a simple mechanism. But, just to be safe I guess it's a good idea. I'd hate to do this on the side of the highway 50 miles from Resume Speed, Nevada.

Harvey

SteveG

The '85 doesn't have a CPS. I wonder what MY Mike is working on?
Does anyone else wonder what MY cars have a CPS . . . like Mike's MY which we don't know BTW.

sharkmeister85

I put one in my '85 recently.
https://www.928gt.com/pc-1792-9-timi...-jetronic.aspx
Glenn

mj1pate

Hey....
Sorry, my MY is 86.5. CPS failures at particular mileages are notorious in some makes/models. I don't know if that applies to Bosch parts. The condition of the CPS cable and particularly the connector were frightful. I ended up picking little bits and pieces of the CPS connector out of the harness connector with a dental tool. Advise given to me was to avoid breaking off the sensor terminal (the only thing you can put a hand on), at all costs. Penetrating oil worked for me. I would have tried some kind of ultrasonic vibrator applied to the sensor if that failed. Just wasn't ready to pull the bell housing off last weekend ;-)

Oh, I don't know specific differences between 85 and 86.5, but I thought they were identical except for brakes and some suspension upgrades.....

soontobered84

Now you tell me.

Okay, I had a gorilla helping me remove my Crank Sensor this time, and while this is the third one I have replaced on various 928s, this marks the first time that I have broken off the sensor terminal. Crap. How do I get the SOB out now?

I tried drilling it, but magnets don't drill so well.

Shoot fire Heck and shucky darn (just adding more expletives here to mitigate my disgust)

Am I gonna have to remove the exhaust system and the lower bell housing and drive it out from underneath? I wonder what I can F up while I'm under there? I'm sure that I can find something. This may end up being a day long job for what shoulda been a 10 minute replacement.

Mrmerlin

yes all of that plus remove the flywheel if it wont budge, Warning dont try to turn the flywheel if you have driven the sensor into the housing you could damage the flywheel sections

Bertrand Daoust

Ok here we go!
I had the exact same problem (broke the CPS in 2 in the bell housing) about 1 month ago while doing my intake job. I did remove it from the top.
By the way, you can't easily reach it from under as the flywheel is the way!!!
I did't want to remove the flywheel either! To mutch work.
Also, don't try to push it out from under as you will probably bent it and have more problem removing it from the the top. Ask me how I know!

Anyway here's how I did it.
1) I put alot of penetring oil on top of the CPS.
2) from the top, I used a Dremel tool to remove as mutch plastic as I can inside the CPS on top and around the magnet. About 1/4" below the top of the magnet worked fine for me.
3) I used a pair of long nose plier and pull the magnet out. It did come out quite easily.
4) Now that the magnet is out, you can tap the hole and use a long bolt, nut and a spacer (a 1/2" small pipe work well for me) and take it out!

When I pull the CPS out, the lower metal part separated from the top plastic section and stayed stuck inside. Now another problem. As I could't remove it from the top, I push it from the top and picked it from under on the top of the bell housing.

It took me about 5 hours to do it but at least I did not have to remove it from under - moving the trans./ torque tube, removing the flywheel etc.

As it did work for me, it should work for you too.
Good luck.

Lizard928

This is incorrect information.

ALL 1985+ cars (and the 84 EURO) have CPS.

The 85/86 cars do not have a hall sensor for reading the positioning of the camshaft.

I have replaced a few of these now and am finding that these cars are coming to an age that most of them are going to start failing more and more. Though I normally just pull off the airbox and that is all I have needed to do to have enough access to remove it.

The front hose starts to chafe as either they were made shorter before or as it ages it shinks bringing it into contact with the filler neck.

soontobered84

Thanks for the information Bertrand.
I believe my cat is plugged and I have MSDS headers to go on the car, so although I was planning to remove the doggone thing from the top, I decided to get to it from the bottom and do the headers at the same time. I got everything loose last night, and am thinking hard about removing the flywheel at this point. ( I may have no choice from this direction).

mj1pate

Mine is a 86.5. As you have stated, it has no cam position sensor; only the crank position sensor. Some Bosch Hall devices are notorious for failure. Bosch BMW 540i cam position sensors (another Hall device) are notable. My son's 540i had its third cam position sensor by the time it hit 120k miles. There is no external indication that the device has failed. I assume that the bonding between the pickup and the harness develops an out of tolerance resistance, but the net effect is that you stop dead somewhere. The 928 crank position sensors are relatively cheap, and with careful removal, a needless towing can be avoided.


I made the after-purchase trip home, between San Francisco and Maryland in the 86.5, right after picking it up from the PPI. No issues at all. But a subsequent inspection of the fuel hoses revealed the dangers. That hose under the oil filler was dry, brittle and badly chafed. The replacement hose is buffered by an insulating tube, and I check it regularly.

TRA

Hey Folks,

Looking at my CPS on my 86, It doesn't appear to plug into anything? The wire from the CPS runs up to a clip on the intake manifold, and terminated to an unused 3-pin round plug.

Am i missing a connection or did a Previous owner make an "epic fail" here?

soontobered84

That's not the CPS you are looking at. That's a test port. The CPS is more forward of that.You would not have spark if your CPS wasn't plugged in.