Houston928

PORSCHE 928S 32v 1985.
Just fitted a new set of fuel injectors and changed all the rubber hoses around the inlet manifold and have a no start. Car was running before.
Fuel pump is not turning on when i turn ignition, if i jump fuel pump relay pump runs.
If i jump relay xv1, EZF, the fuel pump cycles when i turn on ignition as normal.
There is 12v at pin 30 on both fuel pump & EZF relay sockets.
Any ideas on what else i can check ?.
Thanks.

dr bob

If the tach isn't moving when you crank the car on the starter, I'd be looking carefully at the CPS and it's connector. The Crank Position Sensor is a magnetic pickup that is fitted at the rear of block, under the air cleaner housing, points straight down through a hole the block to determine that the engine is turning and where it is in its rotation. The connector (on mine...) is in a bracket on the top rear of the right (passenger side on US cars) fuel rail next to the intake on my later S4+ car. With your organ-pipe intake it may be in a slightly different position. The CPS itself and the wiring/connector get crispy with age, and suffer even more quickly if you've used solvents (read: Brake Cleaner) to clean the valley under the intake. Replacing the oil breather, idle air control and vacuum hoses under the intake undoubtedly disturbed the wiring and connectors. If they were crispy, that disturbance can easily cause failure.

The tach signal is derived by the ignition module from the pulses it receives from the CPS, so no tach bounce on cranking would point you to the CPS. The tach signal is used by the injection controller to signal the fuel pump relay to run the pump. So easy to point to the CPS and wiring as a probable fault.

Houston928

Thanks bob. Just cranked the motor a few times and tach is not moving/bouncing. The connector and wiring for the CPS looks poor, should have done it when I had everything off.
Would a bad CPS stop the fuel pump from cycling as soon as the key is turned on ?. That's the 1st thing I noticed, before I could always hear the pump run briefly when the key was turned to position 1.

Houston928

Quote:
Originally Posted by Houston928
Thanks for the reply to my thread regarding no start, it seems the CPS is the problem. I get no tach movement when cranking. New one on way
Was wondering if you could take a minute to look at a couple of questions.

The CPS has a 3 wire connector to the harness, one white , one brown and one black which appears to turn into a shield. Can I check for continuity of the white & brown wires by checking at EZF plug ?.
What is the reason for the black wire turning into a shield ?.
Thanks.

You should be able to test at the EZF plug. In fact that's the recommended method, as it includes the connector in the test.

I'd have to sleuth the wiring diagrams to get the colors right. In the car itself (not necessarily in the actual sensor wiring...), BROWN is chassis ground. I would expect the shield to connect to BROWN, but would need the diagrams to confirm.

The CPS uses a magnet in the center, with a coil of wire wrapped around it, to detect the presence/absence of the teeth on the moving flywheel gear. Each tooth distorts/disturbs the magnetic field as it pases, enough to induce a small current in the coil. The best real test uses an oscilloscope to see the waveform from the coil. As you can imagine, the signal amplitude isn't huge so it's not something you'd be able to see on a common digital multimeter except as a milliVolt AC signal present when the engine is cranking.

The shield protects the signals from the coil from induced current/voltages from nearby wiring like the injectors or secondary ignition wiring.

dr bob

OP PM'd his questions to me. I responded and recommended that he share the question and my reply with the group. I'll parse his post so that it will make a little more sense to readers:

His questions:
My reply:
You should be able to test at the EZF plug. In fact that's the recommended method, as it includes the connector in the test.

I'd have to sleuth the wiring diagrams to get the colors right. In the car itself (not necessarily in the actual sensor wiring...), BROWN is chassis ground. I would expect the shield to connect to BROWN, but would need the diagrams to confirm.

The CPS uses a magnet in the center, with a coil of wire wrapped around it, to detect the presence/absence of the teeth on the moving flywheel gear. Each tooth distorts/disturbs the magnetic field as it passes, enough to induce a small current in the coil. The best real test uses an oscilloscope to see the waveform from the coil. As you can imagine, the signal amplitude isn't huge so it's not something you'd be able to see on a common digital multimeter except as a milliVolt AC signal present when the engine is cranking.

The shield protects the signals from the coil from induced current/voltages from nearby wiring like the injectors or secondary ignition wiring.

Houston928

Fitted a new CPS yesterday and car is exactly the same, no start and no tach movement when cranking. Checked continuity on the three wires for CPS connector to EZF and all check good. Checked all the engine bay grounds, will check other grounds tonight.

I am also in the middle of replacing drivers side door handle/hinge and am wondering if the alarm is stopping the car from starting. I deliberately set off the alarm last night then stopped it by unlocking passenger door. Does this re-set the alarm or could it still be active ?.
Thanks.

John Speake

Does the car have spark ? BTW the fuel pump does not run until the engine turns, as long as the CPS and EZK ECU are working correctly.

Please check for spark first.

Houston928

Thanks John, I will check for spark tonight. Doesn't the fuel pump normally briefly energize/cycle when the key is turned to the position before cranking ?.

John Speake

That is true for the L-Jetronic fitted to pre 1985 US cars (16v engines).

But not true for 85 and onwards with LH Jetronic.

Don Carter

What part of Houston are you in? Are you aware of the gathering and drive this Saturday? PM me if you're not part of the Houston Google Group and I'll send you details.

Sounds like you are on the right track on the no start, but happy to help if I can.

Houston928

Don, I am in Southwest Houston and am already a member of the Google group.
Hopefully soon I will be able to come on one of the outings. ( Hopefully ).

Houston928

I have spark when cranking, does this mean I can rule out the alarm from causing the no start ?.

When fitting the new fuel injectors I noticed some of the insulation on the wires cracked, though the wires below looked ok. Would 1 bad/broken injector wire cause all 8 not to fire ?.

Mrmerlin

yes a shorted injector will take them all off line if you found a crispy injector plug I would suggest to swap out all 8 plus the temp 2 connector they are all the same connector Roger sells them with new rubber boots

Houston928

Thanks. Think a broken/shorted wire is the most likely cause of the no start.

The car ran before I worked on intake & injectors, and i know i have spark and fuel at the rails.

All the cranking has drained the battery, which was old, so will get a new battery tomorrow and start again. Thanks for the help.

Houston928

Removed all fuel injector connectors and am only showing 4 volts between 1 side and ground. Think it's supposed to be around 12v.
Looks like I have a bad wire or ground somewhere.