Anyone have an idea what would cause the tach to jump occasionally? (ie. btwn 2500-3000 rpm). It's as if there a loose contact somewhere. Also I need to tap on the dash a couple of times to get some of the bulbs on the right side to come on while driving at night. Maybe all that tapping made something loose.

Any thoughts appreciated.

Thanks

95' 964 141k

The tach on our 95 964 would occasionally jump at idle with no corresponding change in engine noise/rpm. The engine ran fine. I changed the RPM/crank sensor and the problem went away. Our 98 S90 is now have the same tach jitters at idle. Go Figure

DEWFPO
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1998 S90 066,800 and 1995 964 150,200

Got a chance to look in the engine compartment today for the RPM sensor. Sure looks like a tight spot to work in. I have one or order. Wish me luck.

Thanks for all the posts.

It is a tight spot.

Use a long extension for your ratchet to loosen the one bolt. I had to ask ny wife who has slender arms and hands to reach down and grab the bolt. Then she located the bolt and the new sensor for me and I tightened it from the top. Didn't take long and was not hard. Just snug access.

DEWFPO .... good luck!
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1998 S90 067,100 and 1995 964 150,850

Will an RPM sensor failure prevent the car from running?

Also is replacement a simple procedure?

Thanks again for your insights.

Dear dnice,

Good a.m. I've never had an RPM (Crank) sensor fail. Based on what I've read on this Board, RPM failure stops the car. If no flywhee/flex-plate movement is detected, no fuel is sent to the engine, so engine stops.

The crank sensor is located atop the bell housing, which covers the joining point of engine and transmission. To see it, stand on the passenger side of the car, close to the back of the engine. At rear corner of the engine, look straight down towards the ground. You should see the crank sensor, atop the bell housing.

The crank sensor is secured by one 10mm bolt. While the sensor is visible, it is hard to access. The crank sensor is fragile. Do not twist, bend, or pull hard on the external part of the sensor. If it is handled roughly, it could snap. Then, the tranny will have to be pulled to remove the remainder.In short, be gentle, or leave it to someone, who's done it before.

Hope this helps.

Yours,

spook

Dear dnice,

Good p.m. and may this find you well. I think Park is right. If the problem were in the instrument cluster, the tach would be erratic in general. Even so, in the event that the problem is in the cluster, I venture to offer some guidance.

While I've never removed an instrument cluster from a 960, I just removed one from a 1993 940, cleaned the inside of the clear plastic face, and reinstalled it. Everything still works.

If the 960 is similarly arranged, use the FAQs for the basic procedure. If you're right handed, it is easier to remove first, the right (passenger) side of the aluminum bezel; the left will then disengage.

As the FAQ procedure states, four Torx screws (T-25) must be removed. Then, the cluster has to be moved over two spring clips at the bottom of the opening. This is actually a little harder to do, than anything else in the procedure.

Reach behind the cluster and grasp the wire harness and pull it very, very gently towards you. Do not - under any circumstances - pull on the cluster itself. If at all possible avoid touching the flexible circuit card: it seems fragile.

Once you have some slack in the harness, disconnect the connectors. You will know instantly if that which drives the tach is loose. I do not know how many or what type of connectors are used on the 960 cluster. I do know that on the 93 940 cluster there are several, of different types. On the 1995 940 cluster, there are three of the same type, plus a single spade connector.

On the 1993 and 1995 940 cluster, the bulbs are in a row at the bottom of the cluster. Each bulb is separate. I doubt you could have shaken them loose. It is, though, possible that the tach connector has worked loose.

If you want to clean the inside of the face of the cluster, you should remove the phillips head screws around the cluster's perimeter. There may be two more screws - in the lower third of the flexible circuit board - that must be removed, to get at the face of the cluster from the inside.

On the 1993 cluster, these two additional screws are located at positions 8 and 16. On the 1996 cluster these screws are at positions 7 and 16. Once these screws are removed, the circuit board and instruments will come free of the cluster face. You can clean the inside of the clear plastic lens with a soft cloth and window cleaner.

Re-assemble in reverse order. As the FAQs state, put a little grease on the spring clips that secure the aluminum bezel. That will make it easier to remove the cluster, if there's a need to do so.

Hope this helps.

Yours,

spook

I think you should change the rpm sensor, yesterday!