Kevin in Atlanta

87 S4.

Been knee deep in this for a couple of days.

What we know:

Holding the key in the start position the car starts and immediately dies. Hold the key in the start position after the car dies we have determined that the injectors (as gauged by the fuel pressure gauge not twitching) and the spark (holding a spark plug to ground the spark plug stops firing) stop at the same time the the engine no longer is trying to fire up.

We suspect a bad CPS. Of note is that repaired the CPS connector on the harness. We will circle back to that later this week.

Has anybody had a CPS with this failure mode?

Mrmerlin

is the CPS new? or the connector?

Frankly if you are touching the crank position sensor and it looks old ,
then you should be touching it to be replacing it ,
and this usually is done with an intake refresh

Kevin in Atlanta

CPS is two years old. Replaced the harness connector.

andy-gts

I replaced mine when the computer told me it was bad after 2 yrs of rebuild....boy what a tough position to get to....ugh but mine acted rough and random died....the next yr the hall sensor gave out....!!!!

Mrmerlin

If your repair work on the car side CPS connector is not suspect then put in a new CPS.

make sure to use Bosch parts.
the FAE units dont work like the good parts,
and its usually a recipe for rework

Kevin in Atlanta

Swapped in a spare used CPS I had and and it fired right up!

Don't know if this adds anything to start and stall diagnosis, but when spark and injectors stop when the engine no longer trying to start it likely is the CPS.

Kevin in Atlanta

The unit that failed has a very long lead - the one I used successfully is shorter. FAE vs Bosch?

Mrmerlin

Bosch parts usually have Bosch stamped on the part if its a long lead then it could be a FAE

worf928

I don't know why anyone trys to 'fix' these connectors. If you take enough time to properly deal with the shielding and your time is worth anything you've just about paid for a new CPS.

Fixing the harness-side has different associated economic math though.

I've been using the 944 part for the CPS, for years, exclusively. I've had zero issues. It's got the long lead. Comes in a bosch box.

Simon928

Interesting. I plan on doing an intake refresh over the winter and this is one of the things I plan on replacing. What is the part number for the 944 CPS if you don't mind me asking? Is there a significant price difference between this and the 928 CPS?

Wisconsin Joe

That's interesting.

I have an '83 944 that has been 'acting up' for a while. Narrowed it down to the CPS.

Placed an order with Roger over the winter, and when talking, asked if he carried the CPS for a 944.
He said that the CPS for both cars was the same. Checked part numbers and everything.

When it arrived, it was exactly the same as the one that was in there (purchased and installed by the Porsche stealership). Solved the problem too. Price was ~$77. Don't have a part number, just Roger's in house stock number.

So the answer to the question: "What's the part number?" Would be:

Call Roger.

worf928

Years ago, the short-lead 928 specific CPS was - IIRC - 2x the price of the 944 part.

I suspect - would be willing to wager a beer - that the original 928 part has superseded to the 944 part and only a very ancient version of PET would show the original's part number.

Kevin in Atlanta

The part that failed is a Bosch part made in Germany.

polecat702

When I return home, I have to replace the CPS, and the Hall sensor, along with a new EZK relay in my 89.

Connectors are falling apart on the sensor side.

outbackgeorgia

The sensor itself probably has not failed, just the connector. There are no active parts in the sensor, just a coil of wire. Quick fix/test, skip the connector, solder the wires, shrink wrap. Connector is there for ease of assembly. Sensor itself will likely outlast the engine. Reliability is eliminating points of failure. Eliminating the connector makes the car more reliable.
Dave