Continuity Test Results, Help to interpret Continuity Test Results Options

[MFejsa]

Need help to interpret results of continuity test results (see attached) and explain what to do next to get my car running right.

Porsche 914 2.0L 1974 (I believe was originally a 1.7L)

My car starts, runs and drives but idles rough and wont rev past 4,000rpm. It hesitates on acceleration. I have changed virtually all components / parts from rebuilt MPS, tested TPS and works, ignition switch, fuel pump, air & cylinder head temp sensor, swapped out ECU to one that was tested to work, and the list goes on.

I am posting my continuity test results with the hope that some may have experienced or had the same results and knows what to look into more deeply or can diagnose.

The test results concluded the following:

1. When testing the ECU power source from main power relay I could not get the 1V voltage difference from the voltage measured at the battery terminal. No difference and remained the same. Voltage at the battery was 12.79 throughout

2. when testing the voltage at start signal from ignition switch the voltage dropped to 9.7V and was not greater than 12V. However, should be greater than 12V.

So, can anyone help, please. I haven't been able to get the car run and drive right since being restored and have run out of options.

Regards

Michael

[emerygt350]

I put a new solid state regulator in mine recently and that fixed low voltage issues I was having. Cheap and easy. Doubt it is the issue though.

What do your spark plugs look like?
What kind of injectors are in it (color if you are not sure)?
Original distributor?
If so, do you have advance and retard? Where are they connected on the throttle body?
Is this a stock 2.0 or a built 1.7?

[ejm]

1. When testing the ECU power source from main power relay I could not get the 1V voltage difference from the voltage measured at the battery terminal. No difference and remained the same. Voltage at the battery was 12.79 throughout

You are looking for a less than 1 volt drop so this is OK

2. when testing the voltage at start signal from ignition switch the voltage dropped to 9.7V and was not greater than 12V. However, should be greater than 12V.

This voltage is only seen while cranking so it cannot be an issue once the engine is running.

Have you checked ignition timing and fuel pressure?

[MFejsa]

Thanks for the response. See below my responses.

I've replaced all serviceable parts and other parts as well.

What do your spark plugs look like?

- New Spark Plugs

What kind of injectors are in it (color if you are not sure)?

- New injectors and were tested running by previous owner who I bought the engine from

Original distributor?

- New 123Ignition electronic distributor

If so, do you have advance and retard?

- Electronic distributor with advance

Where are they connected on the throttle body?

- What do you mean?


Is this a stock 2.0 or a built 1.7?

Rebuilt 2.0 from 75/76 car

[MFejsa]

Appreciate the response. See below my response.

You are looking for a less than 1 volt drop so this is OK.

- As mentioned, there was no difference in voltage drop. The voltage remained the same during the test. So, are you saying that if it remains the same it is good?

Have you checked ignition timing and fuel pressure?

- I have changed the ignition to a 123ignition and spent a lot of setting it up and confirmed at TDC.

- New fuel pump installed and pressure tested to be 28-29 PSI.

[jim-c]

I feel your pain. I'm in the same boat. I have similar issue and can't fix it. Todays project is start from scratch again.

Did you try an injector flow test ? My injectors only flow 2cc's with a fifteen second crank. Supposed to be 7 cc's.

Mine won't rev unless I spray gas into the throttle body .

Sorry I don't have an answer for you. I know the frustration.

[emerygt350]

The throttle body attachments were just to make sure you had the retard and advance going to the right port, but obviously that isn't an issue with the 123.

Sounds like you have everything covered, so this should be doable. I would verify you have the right injectors first, easy and free.

What is your vacuum at idle? Since everything else sounds good and you are having idle and rev issues I might be inclined to look at your valve adjustment.

[emerygt350]

The throttle body attachments were just to make sure you had the retard and advance going to the right port, but obviously that isn't an issue with the 123.

Sounds like you have everything covered, so this should be doable. I would verify you have the right injectors first, easy and free.

What is your vacuum at idle? Since everything else sounds good and you are having idle and rev issues I might be inclined to look at your valve adjustment.

Although I guess you could still have the vacuum line going to the wrong port if you are running advance on your 123 and it is a 74. Some 74s have both vacuum and advance ports on the Throttle body. Make sure yours is hooked to the port closest to the distributor if you are doing advance. Is this a bluetooth 123 or the pot one?

[JeffBowlsby]

Sounds like an ignition timing/advance issue.

[emerygt350]

I agree with Jeff. And now I notice that you think it is a 75/76 2.0 Those did not have an advance port. That could be your problem. Either unplug (and plug the port on the throttle body) the vacuum line to your distributor or switch it to A rather than 1 if you have the POT version of the 123.

You never know if they swapped out the throttle body or modified it so the port facing the distributor (if it is there) is the advance vacuum port. The port facing the direction of the rear passenger wheel is the retard port.

[Van B]

Wait, are we gonna talk about that 9.7v?
What was your voltage at the battery? If you’re getting 12v at the battery and only 9.7v between that pin and a ground, I recommend looking into that first. If you’re only getting 9.7v at the battery too, then you need to make sure you’re meeting required voltage. All kinds of weird gremlins can appear when insufficient voltage is in the circuit.

[MFejsa]

Mine is not a bluetooth version so must be a POT one. The throttle body on the engine only has the one port and ive connected the vacuum line to that port which is located at the rear of the throttle body (towards the rear of the car). Is it possible that I've hooked up the 123iginition to the retard? (there is no port closest to the distributor).

[MFejsa]

Im getting more that 12v at the battery but 9.7V at the pin and ground

[rjames]

Mine is not a bluetooth version so must be a POT one. The throttle body on the engine only has the one port and ive connected the vacuum line to that port which is located at the rear of the throttle body (towards the rear of the car). Is it possible that I've hooked up the 123iginition to the retard? (there is no port closest to the distributor).

Yes- the port on your TB is retard, not advance.

[MFejsa]

Thanks. Will take another look at the hoses.

[Van B]

Im getting more that 12v at the battery but 9.7V at the pin and ground

Search around and make sure you got a good ground when you measured at the pin. But that’s a huge voltage drop and needs to be looked into.

Let me elaborate further. On the Porsche 996, the hot cable to the starter is known to corrode inside the sheath. The behavior exhibited is exactly the same, won’t rev past 4K. Looks and feels like voltage regulator, and it can be. But generally on the 996 it’s either a regulator, crank position sensor, or the corroded cable. The cable is the one most often overlooked.

[914Mels]

Im getting more that 12v at the battery but 9.7V at the pin and ground

Looks like you have a voltage drop at the relay plate in the engine compartment. You said you replaced the ignition switch already. Pin 18 gets its power from the ignition switch thru the relay plate. I'd pull the plate and clean all the contacts and the wire ends. I'd also get a vacuum gauge and check what your engine vacuum is. This can tell you a lot about engine condition. read up on the different types of readings and this will point you in a direction to follow. Is your rough idle traceable to one cylinder dropping out or do all seem about the same? Pull plug wires one at a time to see if one cylinder is weaker than the others. Valve adjustment is critical so don't overlook this even though it is a pain in the butt to do. Good luck.

[MFejsa]

Thanks for the advice.

I pulled the relay board from the engine compartment today and split all the pins with a blade and cleaned them up too. Ive also redone my vacuum hoses as I believe based on todays advice that I connect the retard to the new 123iginition distributor. It seems idle a bit smoother but need to take it for a run tomorrow to see if any improvement. Also, need to do some more research on engine vacuum as havent look at that as yet.

And not when I pulled the plug wires one at a time didnt not much change at all.

Thanks again

Michael

[MFejsa]

Hi, thanks for the message.

Check all grounds many times and made sure that they were all firmly crimped.

Also, swapped out to nee voltage regulator early today and still get the same reading at 18 pin.

Cable to the starter has also been replaced with a new one. When you say hot cable I assume you are referring to the cable from starter to battery?


Regards

Michael

[emerygt350]

Just out of curiosity, did you just disconnect the vacuum from the distributor or did you switch to the A setting? I didn't really like the A setting on mine but mine is a 73 so I could switch to the advance setting on the 123. Haven't tried it on the advance setting without the vacuum attached. I suspect it would be little different.