911SC only starts with alternator disconnected
 

I'll try to make this brief and understandable.

First, I've been having an ongoing hard starting issue for a while. In trying to track that down I noticed that the alternator light was glowing faintly so I decided to tackle the alternator. My 1981 SC had the external voltage regular and I found that my alternator was NLA so I bought a newer style alternator with the integrated regulator.

After removing the old alternator, I noticed that the hard starting issue completely went away. I could easily start the car and run it for a few minutes in order to move the car. I never ran it for more than a few minutes so it wouldn't overheat.

I finish installing the new alternator and now I can't start the car. It fires and sounds like it wants to start but doesn't. I get lots of popping. I just had the car running earlier today so I'm pretty certain that if I took everything apart and disconnected the alternator I could start the car again.

Please help - I need a clue!!!!

Did you check and clean the ground strap connection at the altrrnator to the top of the engine?
How is the ground connection between the transmission and the body of the car?

The ground from the alternator to the engine looked solid. I didn't do any investigation of it other than seeing that it was solidly attached. I didn't see any corrosion on any of the wires behind the alternator.

I can check the transmission ground. Would that really keep the car from starting?

BTW, it's not a starter issue. Here is a video of the non-starting:

https://www.youtube.com/watch?v=9BT_B2GpfSc

Starting
 

Hi Anthony,are you sure while removing your alternator you never
touched or did something to your distributor ,the reason the video you showed
reminded me of the exact problem i had years ago ,not with a Porsche
but 65 Buick Riviera GS ,and it was the pertronix electronic ignition had burnt
out module ,caused by the shipping company had left the key on while shipping to Australia
and had, battery dead flat,,etc,etc, plus the pertronix,and that is exactly what the
Buick would do, fire for approx 5 -8 seconds then cut out.

Trans to body cable is the main ground path for the alternator.
Yes it would have an effect.
Also remove, clean and re-seat the 14 pin engine harness to fuse panel connector.
They tend to get corroded.

Wayne, there is no pertronix installed and the car was starting just before I installed the new alternator.

I checked the 14 pin connector and found no corrosion. I still cleaned the alternator related pins with a little emory cloth. No joy. I'll check the transmission ground tomorrow when I get a chance.

Any theories why the car would start with the alternator disconnected?

Double check your alternator wire connections......
 

If the car starts without the alternator connected and won't start with alternator connected, you found the culprit. Either the alternator is defective or the wirings are incorrectly connected. Check if the wires at the back of the alternator are in the right terminals. Keep us posted.

Tony

Well the strange thing was that I was having the starting issue with the old alternator but it was intermittent. I took off the old alternator and had zero problems starting the car to move it around. Now, with a new alternator installed starting problems again.

Usualy, the Alternator' unless its spinning will have no affect on the electrics of the car, as the diodes in the stator of the alternator [if working correctly] will block any current being passed from battery to ground via Alternator, it could be a weak ignition switch i supose, but i suspect there is something going on with the Alternator wiring. Does the car start with the Alternator connected, but with no belt ? Also, is the battery a good one, and fully charged ?
Hope you get it sorted!
A...

Try this suggestion.......
 

Anthony,

Try to start the engine using 'ant7's suggestion (alternator installed less belt) and make sure you have a fully charged battery. Interested to see what happens next. Keep us posted.

Tony

i could not see the video.

did you remove the old regulator. i have not converted one so i dont kneo what is envolved as far as wiring.

if it turns over but will not fire here is what i would do:
check for spark
i would check the CSV for power at the TTS. (or, lift the sensor plate with the key on to put some fuel into the cylinders. then start it)
if it starts you have a CSV circuit problem.
with the alt connected, remove the alt wire from the starter and see if it starts.
remove the rear connector on the AFM and turn the key on to run the FP.

the FP relay gets its ground thru the D- on the alt, that could be something to look at. (also the AFM switch, thus remove the connetor)
the speed relay also gets its ground thru the D-. not sure how it works. looks like it might put a ground on the FP relay to kill the FP at redline. i have heard of this thing causing run/starting issues. dont remember who but he said he had to "reset" to fix the issue he was having.

first i would check spark then the CSV. (lift the plate)

Thanks for all the help. The car is running perfectly right now. The new alternator is putting out voltage. I get 13.5v at the battery terminals and the alternator light is off.

But I have a feeling that I will be back soon to still figure out the non-starting issue. I think the non-starting issue is not related at all to the alternator. It just looked like cause/effect because I disconnected the old alternator and magically the car started every time without an alternator while I worked on the car and moved it around the driveway. Then, as soon as everything was back together it decided to not start again. ;-( It appeared as if the alternator was the culprit.

Today, thinking about what you guys have written, I've jiggled the fuel pump relay, looked at the connections and fuses and boom the car starts right up and is purring right now as I type. I've even shut it off and restarted it several times just to be sure. I'm going to go ahead and check the ground strap on the transmission and a few other things mentioned.

Still, I think I'll be back. :-( I'm hesitant to even drive the car in case the issue happens out on the road.

Sure enough, the starting problem happened again. Are you supposed to hear the fuel pump buzz every time you turn the key? I noticed that I'm not hearing it now but was hearing it before.

More jiggling of the FP relay didn't see to make any difference.

Could be a faulty fuel pump relay, or a wire broke, to be honest, it could be a lot of things! You need to go through the connections properly, and examine each and every one, including the cabling, if the car seemed to start ok after fiddling with the relays, and cabling, then its probably around that area, also, dont forget to check the fuses, they may look intact, but can break down with age, the fusebox connections are also an issue, my advice would be to go through every fuse and contact, clean them, and check each one for continuity, and if you suspect that they have seen better days, just change them, they are not expensive!
A...

hearing the FP with the key on depends on if you have the connector on the back of the AFM connected or not. with it connected and everything working as it should you will NOT hear the FP with the key on.
while cranking the FP should run.

does the not happen when its hot, cold or anytime.

when it wont crank, pull the connector off the AFM and try it see if the pump runs with the key on.
also check for spark when it wont run. (dont remeber if did that or not)

I'm not sure why you couldn't see the video. It's a standard youtube video with permission to anyone who has the link. The car turns over. It just doesn't start. It sounds like it's popping, sometimes. It's not just turning over.

https://youtu.be/9BT_B2GpfSc

I don't have someone to help me check for spark. Is there a way to do that solo?

I turned the key to on and then lifted the plate (under the air filter right?). The car didn't start after that. Should I hear the fuel pump running putting fuel in? Do I have to hold it for a certain period of time.

I also cleaned the connections at the fuel pump fuse. They look very clean and not corroded in general but I sanded them anyway. No luck there. I've swapped relays around and that doesn't make any difference.

I've been cleaning various connections with no success. After trying to start it I smell a little fuel at the tail pipe. I think it's spark related. I'm going to work from that angle for the time being.

I found my ohm meter and tested the coil. I get .5 to .7 ohms between the terminals. (It usually settles on .7 after moving the leads around a bit.) And I get 698 ohms testing from the center of the coil to one of the terminals. Either terminal actually gives the same reading.

Are these good readings? I've searched a lot and find conflicting values.

Is there a list of the ignition troubleshooting steps I can run through?

Sounds like fuel. The engine revs then shuts off. It appears to me getting spark.

Test: get a spark plug. Take off a plug wire and plug into the spark plug. Ground the plug. Have some one turn the key. If you see a nice intermittent spark then you need to check for fuel.
Remove filter. Turn on key lift the air flow plate you should hear the injectors and pump working. Do not over do it you do not want cylinders full of raw fuel.
If you don't hear the injectors you have a fuel delivery problem.

I'm definitely not hearing anything when I lift the plate.

spark
 

Hi Anthony , me again from link 4 , thats why i ask you re about your Distributor
even though you dont have pertronix ignition, the modul or inside points what ever you have is critical ,hope you get her right soon regards,.

CIS troubleshooting........
 

Anthony,

Avoid doing guess-work and you will find the problem with your car. You need a fuel pressure gauge to begin with. Without one, you will be wasting a lot of your valuable time. The FP maybe running but you don't know if the FP delivers the correct pressure or volume. At this point, you don't know the status of your FP (?).

Second, you have to verify and test the presence of ignition sparks. An inductive timing light does a good job of demonstrating the presence of ignition signals. Doing it in a dark work area or at night gives a good visual effect.

Spraying starting fluid or carb cleaner liquid to locate vacuum leak/s work only with a running motor. I prefer to use a continuous supply of low pressure air into the system and spray bubbled water into suspected areas. If the air box is cracked underneath it, it is almost impossible to detect the leak with the engine installed.

You could perform all the above suggested tests under 15 mins. and in your case I will give you another 15 mins. I have a remote starter but I seldom use it and could perform these test procedures conveniently by myself with no assistance. Do what ever you could do and keep us posted.

BTW, what is the resistance reading (Ohms) of the WUR when cold?

Tony

I wish I could do all that in 15! It takes me 20 minutes of research just to figure out how to test at each step. I'm ready to test spark as soon as I can get a friend to turn the key. Getting fuel pressure gauges would be a half day project for me. (Researching what to get and then figuring out each test, etc.)

It seems that my number one symptom right now is that when I lift the plate on the air flow meter (key is on), I get zilch. I hear no injectors or fuel pump working. So what is the next logical step following that test?

The problem seem binary. The car either starts and runs great or doesn't start at all. It makes me think that one connection or component is going on/off.

Overcome your anxiety.......
 

Anthony,

There are several ways to skin a cat. Other people have a different ways or methods of approaching the problem/s particularly about fuel injection (CIS). There is nothing difficult about CIS troubleshooting and I have not encountered a CIS problem that a typical DIYer like you or me could not diagnose correctly. The key to a successful troubleshooting is to eliminate or reduce the variables for a given problem. How do you do it? Test and confirm. Refrain from relying on luck on your problem solving.

Examples:

Fuel pressures...........use a pressure gauge.
Ignition......................use an inductive timing light, spark plug, etc.
Vacuum leak..............for a non-running motor, starter fluid or carb cleaner won't work. Perform a pressure test similar to finding a pin hole leak on your tires.
Electrical....................loose connection or open circuit could be tested.

Use a known good working part as a substitute for ECU, relay, and other electronic or electrical components unless you know how to evaluate them. Hands on experience has no substitute. You could read all the manuals and literature about the subject and you won't gain any experience or know-how until you put it into practice.

Tony

I've done a lot of DIY wrenching but I've been so lucky with this 911 that I really haven't had to learn much about CIS, fuel, spark, etc.

I think I'm getting closer. Things are leading towards the fuel pump or the power to it. I tested voltages at fuel pump relay socket and get:

30 - zero
85 - 12.35v
87a - .05
87 - 12.35
85 - zero

Next I tried to jumper the fuel pump relay (key on). I jumpered 87a and 30 and the fuel pump is silent.

Next step is to get at the fuel pump, check connections, test directly with 12v, etc.

Ok, I don't think it's the fuel pump. I jumpered incorrectly before. Direct 12v on the fuel pump makes it run and also jumpering 87a to 30 makes the pump run.

I'm sort of back to where I was above. (Key on, and lift air flow meter plate and fuel pump does not run.

So, with the fuel pump jumpered and running, nothing happens when you raise the plate?

What you should get is some sound, which is indicative of fuel running out of the injectors.
You can confirm this by pulling an injector out and sticking it into a bottle (plastic water or the like works well, as transparent) and seeing if you get a flow. You don't want to do this too long, because you don't want the other five to squirt too much fuel into the system.

As you have figured out, there is an interlock connector on the back of the base part of the fuel distributor side of things. Normally, if you pull this connector with the ignition key turned to run, the fuel pump will run without any air flowing to raise the plate. Similarly, in this configuration the FP will run (you can usually hear it) as soon as you turn the key on.

When the plate is in its rest position, as long as the system is set up right, a running fuel pump will not send any fuel through the injectors. This is because at the rest position the internal plunger is situated so that no fuel can come from the center barrel out into the any of the six fuel lines. So you won't get any of the buzzing sound which appears when air flow (even just from cranking the starter) doesn't lift the plate, and thus the plunger in the FD.

If this doesn't happen, chances are good that fuel under adequate pressure isn't reaching your FD. And that you need to check the fuel pressure to confirm this before messing with anything else. A CIS system and warm up regulator (better called control pressure regulator) is indicated. You can get them for less than $100 from JCWhitney or Harbor Freight. My JCW one from years ago came with enough adapters to allow its use on metric CIS fittings, and I suspect the HF one does too.

So where is the electrical connection to the air flow meter? I don't see anything obvious. I push the plate and my fuel pump doesn't go. I'd like to trace that electrical connection or at least check the connections.

I also found this connector unconnected:
http://forums.pelicanparts.com/uploa...1435783171.jpg

Thanks Walt and Tony and everybody else for your patience.

I must be confused about the raise plate test. I thought I've read that you turn the key to on, go to the back and raise the plate and that should energize the fuel pump.

Do I have to jumper it in addition to that?

Ok, I'm getting somewhere. These last few posts were inspiring. I jumpered the relay, and with the fuel pump going, moved the plate and yet I hear the injectors working.

There came my inspiration. I jumpered the fuel pump and then started the car. The car fired up and ran perfectly.

So I know the problem is fuel pump relay / socket / wiring. (I did try every relay I have and none worked.)

Let's start from square one...........
 

Anthony,

Search for DKlever48's post about FP relay. Read it again and again until it makes sense to you. If you have any question, don't hesitate to ask. Post here or sent PM to anyone that could help you.

Once you get a feel of how the fuel pump relay operates, the rest would be easy to digest. Right now you are following instructions blindly and have no concept why and what you were doing specially with AFM (air flow meter) switch which is actually terminal #85 in the FP relay socket.

Do you have a reference shop manual like Bentley or the factory wiring diagram? It would help a lot if you start visualizing by making sketches and diagrams of the FP circuit.

Everything you need to know about FP relay testing are more or less discussed in that particular thread by DKLever48. Let us know your next question/s.

Tony

Believe me, I'm not trying to fly blind. I've been reading, and reading, and reading. I will search for DKlever48's post. Thanks.

I do have a Bentley manual.

Wow, DKLever48 has exactly the same symptoms.....reading that topic now!

The connector you picture is not part of the CIS fuel system.

If you look at a picture of the front of the engine (the side closest to the front of the car), or a CIS system diagram, you will see that there is one of those funny Bosch rectangular colored plastic connectors for the frequency valve (on the left looking toward the front of the car), and another similar one on the right. There is also one on the right side of the intake manifolds by the auxiliary air slide - and easy to see there. The one in question is reachable by sticking your hand around the front of the motor from the left side. This is easiest to do with the hot air blower removed, though I recall it can be done with that in place.

It should be plugged in because it is a safety feature which shuts off the fuel pump if the engine stops. It works backward - when it is plugged in, it works, and you need air flow for it to allow the fuel pump (controlled by the hard to understand fuel pump relay circuitry) to run. Except for when the key is in the start position, which bypasses all this. When it is unplugged, turning the key to run will make the fuel pump run - assuming the relay and so on are all in order.

That two wire plug is for the cruise control, I think, and I bet your car doesn't have CC. Porsche made the same wire loom whether you had CC or not. I've got one of those on my SC as well.

So good to know the engine starts and runs fine with some jumpering of the relay. You might try one of the other relays, and see if that works without the jumper. The red fuel pump relay differs from the horn relay, for instance, only by the addition of a diode, which is intended to prevent reverse voltage spikes. Just how important that is is unclear to me. But this could be diagnostic on whether your red relay is working right or not.

I went through DKlever48's thread and did a bunch of the tests. The results Tony's first round of tests jumps out (testing at the FP relay socket):

test #1
Key off
all voltages zero

Test #2
Relay removed
Key turned to on position
86 --- 12v
87 --- .05v (should be zero)
87a --- 12v
85 --- zero
30 --- zero

Test #3
Relay installed
key turned to on position
86 --- 12v
87 --- .03v (should be zero)
87a --- 12v
85 --- .14v
30 --- .02v

On this last test I wasn't sure how to perform it. I pulled out the relay a little bit and touched the probe on the exposed relay terminal.

For test #2, I see .05 volts for terminal 87 when it should be zero. .05 is not a lot but I'm guessing that it should be a point of concern. Any comments?

I also tested the ground path from 85 to AFS per Tony's procedure. When I lift the plunger the ground breaks.

The connector in your photo is unused after 1979 in the US/CAN engine harness. Still included up to '83 harness for Euro CIS version.
It runs the thermo vacuum switch in '78/79 CIS.

I don't have a CIS car but doesn't the brown wire (ground that energizes the fuel pump relay coil) go to the D- terminal on the alternator? It looks like it runs from the air flow sensor directly to the alternator where it picks up ground.

EDIT: It also looks like the fuel pump is directly powered (yellow wire, normally closed relay contact) when the key is in start.

Suggestions........
 

Anthony,

Use a simple test light for the tests in analyzing the FP relay and socket. It is good to have a multi-tester but for this kind of work, a TL works well. Please repeat your tests using a TL and post the results. Thanks.

Tony