Pboden

After a intake refresh, I can not get my -87 startet. After several hours and many tries and errors, I see that there are no voltage from the injector connectors when cranking the engine.

How much voltage should I expect ?

Checked the relays but the fault must be somewhere else.

Suggestions ?

Thanks

Adamant1971

Check that you did not swap the CPS connector and the the TPS connector. The plugs are the same and can easily be switched by accident. If the CPS is not sending a signal to the LH the injectors will not fire.

Auto or 5 spd? Have you moved any relays? If manual the auto kick down spot should be empty.

Confirm that you have spark and listen to see if the fuel pump is running. You can bypass the fuel pump relay to confirm.

It would also help if you list everything that was done or not done during the intake re-fresh.

Pboden

It's a Auto.

In November I actually removed the engine and did som internal service like new gasket an so on. Nothing electrical. I remember I did open the CPS screw just to check, but it went back on.
How do I know if the CPS is working or not ? The Tachometer is jumping when cranking.
I have bypassed the fuel pump relay and made sure it got fuel and pressure.
I have lots of relay "53" and tried them all, just to check whether any is faulty.

Adamant1971

If your tach is bouncing it's sending a signal.

Also check that the plugs for the Temp II sensor and tank evap solenoid did not get swapped. Triple check all connections on the injector harness and check for shorts with an ohmmeter. Another easy item to cross off this list is to test your LH in a running car, is there anyone near with an S4?

Ground wires at the V on injector harness are also crucial. Not likely your cause of the no start unless they are both disconnected, but worth double checking.

Pboden

Been checking further and there is no spark going to the plugs. There is 12V coming to the coil but no pulsing sparks trough to the sparksplugs. Can this maybe been caused by a faulty EZK ?

Another question: The ground wire that goes to the coil GND - has no continuity to other ground spots. Is that correct ?

(BTW I found 12 volt on the injector connectors.)

Adamant1971

- Have you pulled spark plugs to see if they are wet or dry?
- How did you test for spark?
- Are the spark plug cables all routed correctly?
- Have you checked your 14 pin connection at the jump post?

The grounds on the coils should have continuity to the chassis, if not you will get radio interference.

Michael Benno

Here is the Porsche Guide to testing no start and a variety of other Fuel Injection and Electrical Ignition issues. It's supper important to follow the sequence of tests because a failed component upstream will cause false failures in other components.

Test Plan for EZK-Ignition and LH-Jetronic
https://drive.google.com/file/d/1mbG...ew?usp=sharing

Here is a snippet from the document showing the troubleshooting quick reference

Pboden

The plugs looks ok, either too dry, wet or oily.

Sat the plug in the spark cable and put it against ground - cranked the engine. No spark.
Cables are all in their specific length, so it's hard to rout it wrong I say. They have not been removed from the distributors, since it ran previously,

14 pin on the jump post - is that on the front right side ?

I will check further regarding the ground on the coil.

"Dumb" question: The EZK - is it not suppose to send signal to the coil to deliver sparks ?









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Pboden

Thanks Mr. Benno for the test plan. It will be helpful.

Michael Benno

You have no spark at the plug and you have no signal at the injectors. you need to work backward to the source.

The injector pulse comes from the LH which is driven by the engine speed signal that comes from the EZK, which is sourced from the Crank Position sensor.

The ignition pulse comes from the EZK via the Crank Position sensor. Here is the complete ignition signal path.
--> CPS Engine speed signal --> EZK --> Ignition Pulse Signal --> Ignition Modules --> Coil --> Distributor --> Plugs

A failed CPS sensor will show no signal in either system.

I am dealing with this exact same issue on my car post intake. I believe my newly replaced CPS sensor has failed. Maybe you and I have some of the same bad batch. I will post a reply later today with my test procedure for the CPS using a multimeter rather than the WSM recommended Oscilloscope.

Michael Benno

Here is the test proceedure I did for the CPS sensor without a scope:
- https://rennlist.com/forums/928-foru...l#post15639047

I'd be curious what your test numbers are for you CPS sensor.

SwayBar

In my experience, the first thing to check is for a short in the injector harness.
​​​​​​
Pull an injector-connector off an injector, and measure the ohms between the two connectors inside that plug and report what you find.

There are two injector banks, so you may have to pull an adjacent plug and measure it too.

What happens is that when the harness is moved during the intake refresh, etc, the hardened insulation for the wires can crack-open and short against one another.

It's a very easy test to perform.

Mrmerlin

when was the last time the engine was running

justaguy

Your in good hands here lots of good advice given already.

Buy a noid light if you don't have one , it's the easiest way to tell if the injectors are firing as well as a spark plug indicating light. Those two simple tools will help you track and diagnose your issues very quickly.
If you have spark and the injectors are firing the thing will run as log as you have fuel pressure.
If the noid light doesn't flash and the spark indicator light doesn't flash when cranking you can start looking for shorts in the wiring.

MrMerlin is the expert in this field he has helped many people many times including me, so like I said you are in good hands.