Lizard928

CPS = Crank Position Sensor.

The factory manual refers to it as the reference sensor.

UKKid35

Apparently the CPS is not easy to change, and has to be removed destructively. There's a guy on the UK list who has spent the last week trying to remove the old sensor...

Volla

Ok, thanks for all responses. Good news is I think I found the culprit. Will test for few more days just to be sure.

The CPS is not difficult to get out. You remove the air filter and air box, then remove the MAF (you ca do it without removing MAF if you have one of those fancy bend-at-any-angle ratchet set that can fit in there).

Then it is one (if i remember correctly 6mm) allan bolt that keeps the CPS in there. A spray of penetration fluid and a few bloody knuckles then the CPS comes loose (i have pics if anyone is interested)

The CPS is in 100% condition, with a perfect connector housing, I cleaned it all up in anyway and reinsterted.

Unluckily that didnt fix the problem!!

I have a scope image attached of the CPS signal at the EZK connector while cranking a non starting motor, note that the voltages in the pic is half of the actual voltage (i have a voltage divider to protect my equipment)

Suspecting the alternator not giving enough charge and thus the car dying cause too low voltages resulted in me removing the battery charger (i kept it in car due to me having to carnk so many times) and measuring the battery. Suddenly while i was working at the battery end, and a friend cranking the car, the car started.

Looking further I noticed horribly bad corrosion on the two double red wire connectors that go to the main positive terminal, as wel as a bad connection (in the night i saw sparks) and then while jiggling the red wires the car died, but still the LH and other electronics on the car was going.

Resulting in me coming to the conclusion that the EZK is a lot more sensitive to voltage spikes (bad connection while driving) than the rest of the system.

So I just finished replacing the lugs on the two double red wires (soldered them on and not just crimped), cleaned the entire positive terminal, tightened everything with locking nuts, started the car and went for a drive without problems.

So after checking everything (all the ground including the impossible to reach at the back of CE) and checking that the wires at the rear of CE is good (looks brand spanking new) and even swopping out the EZK, it turns out to be the battery positive terminal. (I checked the negative, along with earthstrap a couple of times, but never looked at positive )


In anyway, I thank everyone for their help and will post here if the problem is finally sorted or not

Landseer

Nice find.


Be thankful your CPS came out easily. Though the body of the CPS is stainless steel, it will become immovable if the aluminum oxidizes. I just went through the excercise of slamming one out from below.

Lizard928

I have seen a couple CPS that still showed decent graphs but still caused a no spark issue because the brain was looking for a different range of voltage was all that I could conclude.

I am glad to see that your fix was an easy one though!

Tampa 928s

On your scope I counted 60 cycles "I think", is this 1/2 the tooth count; I heard my 86 has 103 teeth.
This might work for an aftermarket management system but they will not work on the large tooth count on my car.

Volla

Ok, I have been driving the car for the past few days now and so far not one hint of the stalling/dying of the car.

I am going to boldly proclaim "there....I fixed it"!!

Thanks for everyones input and advice

==================================================
19?? VW Baja Bug (Completely custom, Golf 1.8 motor, and many, many mods) - Currently my daily drive
1988 Porsche 928 S4 Euro/ROW (Black with Ivory interior) - Under ECU surgery
1982 Porsche 924 Euro (Silver with cream interior)- Gone
1982 Porsche 928 S (Manual) Euro (Petrol Blue with Blue with black and white chequered interior) - Gone
1983 Porsche 928 S (Auto, NA spec, Red, black interior) - Gone
1994 BMW 530i Manual (Maroon, grey interior) - Gone
Volla is online now Report Post Edit/Delete Message

newworld

87s4 aut.

had a stall today after getting off highway. red light came on and no power. absolute cut off.

i drifted to stop and tried to start up. would not start up cranks no start similar to my hot start issue.

i thought worst case timing belt snapped etc although new so i peeked in inspection hole and it was in tact.

as you may recall i had hot start issue, and it turned out to be ezk relay....

i tried removing it and the cover snapped off. i think these relays are not great quality, as it was very hot to the touch.

i had a spare relay a bosch one, and put it in. started up. ran fine on local roads for next 30 min till parked.

tried to start up again it started right up.

at this point i dont know what this is, electrical purely of some other issue.

oil pressure good and normal. all else normal.

i had another porsche that cut out on me on idle and it was the ecu....the voltage regulator, what happens is that the pins went bad and caused an intermittent stall. dropped voltage quickly down and then fuel pump cut off.

this lh is "reconditioned" and i never touched the ezk.

i am thinking this relay got hot and failed?

it was a meyle made in china.

i replaced with a bosch.

newworld

now i get no start, but cranking.

basically i am getting no spark.

possibilities, ignition coil failure? ignition module failure? lh is known to be good reconditioned but it could also be suspect.

BRB-83-911SC

Symptoms leading up to my failed CPS

1st - momentary cutout of engine while driving
2nd - stalled at stop sign as if key was turned off - restarted immediately
3rd - stalled while pulling into gas station as if key was turned off - restarted immediately
4th - stalled at stop light as if key was turned off - restarted after 5 minutes
5th - wouldn't start at all while in my garage

New CPS cured the issue. You may have other issues, and the hot relay would be of concern. But the CPS is worth checking out.

newworld

thanks for your thoughts. my cps is new.

i was trying to trouble shoot this problem, 928s4 87 aut.

i checked spark, and i got spark during cranking and then i squirted fluid into intake and nothing.

i then got a noid light and put it in the fuel injector harness and then i got a rumblings of a start.

removed noid and put back fuel injector plug and started.

i think just touching the fuel injector harness leads to problems........

i did remove my engine as well recently.


i read somewhere that fuel injector harness is an issue.

my question is this to all experts on this.....i have the plugs etc for each of the 8 and wire leads....if i hack into fuel inecjtor harness and splice and sodder.

how do i know if the issue is not the whole harness i.e from the ezk plug in ce area footwell up to engine, or is the most common problems the boots themselves??

John Speake

The fuel injector harness is connected to the LH ECU.... when you've finished changinging any injector plugs with cracked insulation/bare wires, disconnect the 35 way plug from the LH ECU. Disconnect all the plugs from the injectors. Then plug your multimeter into one of the disconnected injector sockets.

Should measure infinity ohms. Then try moving the injector harnes around and see if you get a low resistance shown on the meter. If Ok, connect up 7 of the plugs to the injectors, you should measure a resistance of about 2 or 3 ohms.

newworld

john-
each time i assess, i have coincidental results leading to misdiagnosis on my part.

this time, the only thing i did was touch the fuel injector harness to put on a noid light and next thing i know i get a start.

i did nothing else.

after i returned the fuel injector plug, it starts and runs no problem.

i think, again i have been wrong many times, but i think the fuel injector harness shorts out

and it can lead to stalls, sudden stalls while driving, and also hard hot starts and sometimes hard cold starts.

so far all leads point to fuel injector harness electrical issue.


this weekend, i am going to remove all boots and rewire the fuel injector plugs, all 8 of them.

then i will test as you suggested.

newworld

clarification....when you mention plug multimeter into socket, you mean black and red probes into the fuel injector plug?

newworld

Update...I took a careful look at fi wires. The boots are in really good shape but there are some sharp angles the wires take from the main trunk to the individual plugs. On one...one of the wires is broken...the insulation is cracked and I can see copper wire.

Since copper not broken I applied insulation sealant and thermal tape so it wouldn't touch other wire.

Tested it and it runs....but since this was an intermittent issue I can't tell for sure now.

Btw....on the fuel injector wiring 2 wires to plug is there any order the wires have to be in for male female plug?

I.e. if I do end up splicing I don't want to mix up wires etc to fuel injector