Starting System Issue

[kidrock]

I've been attempting to diagnose an intermittent "no-start" issue with a friend who is an independent certified mechanic. What we found has us a bit baffled. I have tried to attach a .pdf file with a picture of the starting system from my Bentley, but this site will only allow .gif and .jpg attachments....so I will do my best to describe the issue without the benefit of a schematic.

We used a VOM at the 14-pin connector to test for 12 volts from the ignition switch (yellow wire, pin #1 at the 14-pin connector). At the first "click" of the switch (from "off" position to "acc" position ), shows no voltage being sent at the yellow (solenoid) wire, which is normal.

However, when we turned to key to the 2nd "click" ("acc" position to "run" position), the yellow wire showed the ignition switch was sending 12 volts to the 14-pin connector.

This does not appear to be normal? My understanding is that the yellow solenoid wire shouldn't see any voltage until the key is turned from the 2nd "click" ("run" position) to the third "click" ("start" position).

Be advised that I have cleaned every single ground, fuse, connection and cable that is associated with the starting system. I've also replaced the electrical portion of the ignition switch recently with a brand-new original Porsche part, and have made no changes whatsoever.

Soliciting all advice, suggestions and questions. Thanks in advance for your help.

[steely]

Kid,

No comment on this situation, but if you want to, you can select/copy the pdf figure you want by using the icon below in adobe to put it in the paste buffer. (it looks like a camera.) clicking the icon allows you to select the portion of the figure/schematic you want to turn into a jpg

Then paste it in word, then right click on the pasted figure and save it as it's own .jpg. (you can close/don't save the word doc) - not sure how to do it with fewer steps.

[timmy2]

You are correct, this does not appear to be normal.
I would suggest to re-check the connections on the back of the ignition switch. Sounds like you may have landed a wire on the wrong terminal on the switch.

[boyt911sc]

Kidrock,

You could easily diagnose this problem by starting to investigate the FP relay socket and the relay. Check the connections with and without the relay installed. I suggest to use a test light instead of a VoM. Keep us posted.

Tony

[86 ssinit]

Has anyone resolved the Key not activating the Starter 83 and Below 911? hey kid this is an earlier thread with the same problem it may help you.

[kidrock]

Originally Posted by 86 ssinit

Has anyone resolved the Key not activating the Starter 83 and Below 911? hey kid this is an earlier thread with the same problem it may help you.

86 ssinit, I've gone over the 14-pin connector with a fine-toothed comb. Clean as a whistle, receiving 12 volts and plenty of continuity to starter.

Originally Posted by boyt911sc

Kidrock,

You could easily diagnose this problem by starting to investigate the FP relay socket and the relay. Check the connections with and without the relay installed. I suggest to use a test light instead of a VoM. Keep us posted.

Tony

Tony, I'm unaware of my '88 having any other fuel pump relay aside from the DME relay itself. Please correct me if I'm wrong?

Originally Posted by timmy2

You are correct, this does not appear to be normal.
I would suggest to re-check the connections on the back of the ignition switch. Sounds like you may have landed a wire on the wrong terminal on the switch.

Timmy, I'm afraid you might be on to something. Although I recently replaced the switch, I generally disregarded the condition of the wires from the back of the switch to the 6-pin connector at the bulkhead. My buddy and I pulled the wires out which revealed a bit of an abortion, which is tied into an aftermarket alarm system.

Here is a schematic of the system, with lots of help from Steely (thanks bro):

[boyt911sc]

Kid,

I misread your post and thought your car was an '83 instead of '88. Sorry for the wrong advise. My bad.

Tony

[T77911S]

porsche did something really odd and i dont understand why they did it. they ran power for the AC relay coil to pin 50 of the starter. you are probably measuring this voltage with you MM. if you use a test light, you will not see the voltage and thus not have the confusion of why you have 12v there.
also, if you have 12v at pin1 in the ON, why isnt the starter running? or is it?

use a test light, not a MM.

could be a bad solenoid. search starter rebuild and read my thread on the solenoid.
make sure all your grounds and pos cable connections are clean.

[kidrock]

Originally Posted by T77911S

porsche did something really odd and i dont understand why they did it. they ran power for the AC relay coil to pin 50 of the starter. you are probably measuring this voltage with you MM. if you use a test light, you will not see the voltage and thus not have the confusion of why you have 12v there.
also, if you have 12v at pin1 in the ON, why isnt the starter running? or is it?

use a test light, not a MM.

could be a bad solenoid. search starter rebuild and read my thread on the solenoid.
make sure all your grounds and pos cable connections are clean.

That is very interesting, we noticed the AC relay coil being fed when reviewing the schematic. I don't have a clue about it, and my buddy was scratching his head and mumbled something about "those crazy Germans".

We'll go back in there with a test light and look at it again.

I guess I should explain: Yes, the starter is working, but intermittently. We discovered the 12v issue while attempting to nail down the cause of the intermittent starter issue. I'm sure that the 12v issue is not the cause of the "no start", but I had to find out about the 12v issue first. I was concerned that I would be un-doing more crap that the PO has done.

I had a reputable shop replace the starter when I first purchased the car about 5 years ago. He replaced it with a "high torque" starter and gave me a great deal on the starter and install labor, less than the cost of the IMI unit sold here. It worked great for about 6 months, then began displaying the hard solenoid click "no start" issues that the original stock Bosch was displaying. It is definitely not an IMI, and I have no idea if the unit is a cheap remanufactured unit.

It used to give me a non-start about once in every 20-25 starting attempts. Now it is more like 50% or more, and I'm super pissed. Even worse, I found that I can replicate the "no start" condition by manually turning the motor over until the compression stroke. When I release the compression, the starter turns over fine.

At one point when we were scratching our heads, I suggested that we attempt to tap the solenoid with a BFH while in a "no start" condition. I was able to do so, leading me to believe that I will be replacing this relatively new "hi torque" starter. Hmmpph.

[T77911S]

thanks for more details.

do you have a car alarm?

if the solenoid is pulling in but not turning under compression i would look at the current path for the starter MOTOR. that is, your large cables. make sure all connections are CLEAN, as in remove them and clean them. youhave a body ground at the battery, you have the cable from the body to the tranny. dont forget to clean the battery cable on the starter.

your next big thing is the solenoid. the contacts inside the solenoid get burned and pitted. your starter is not that old and should not have this problem. but what you can do is pull the solenoid apart and clean and rotate the contacts as per my thread. this gives new life to the starter.

if you want to play with your metter, put it on the battery cable at the starter while starting.
do the same with the yellow wire at the starter. then try it with the test light.

i assume you have done battery tests and charging of the batt so i wont go there.

one other thing you can do is when it wont start, connect a push button switch between the battery connection at the starter and the yellow wire and start it that way. it takes a lot of current to pull in the solenoid.
if you pull the solenoid apart, put some grease on the solenoid so it slides easier.

[kidrock]

yes, I have an aftermarket car alarm...and apparently, it was installed rather poorly.

All cables, connections and major ground points are spotless.

2 questions:

1) Where do the ignition switch plug and the 6-pin bulkhead connector go?
2) How is the yellow wire routed from the 14-pin connector to the solenoid?

[T77911S]

usually they hack into the start wire and put in a relay to disable starting of the car.
find that relay and remove it and iwould solder the yellow wire back together. get some heat shrink and slide over it first. much better than tape.

same thing happened with my brothers car. int starting. he replaced the ignition sw and starter. then he said it had a car alarm. i found a crappy crimp on connector at the relay.
this is why i solder adn crimp connectors.

[ZOA NOM]

DME relay under the driver's seat, most likely has a cold solder joint. Replace it and buy an additional spare to keep in the glove box.

[T77911S]

the engine wont turn over. DME is for wont start/run

[scarceller]

The feed loop from the starter to the AC system is so that the AC comp can NOT run while cranking, even if the AC is on.

The reason this works is because they are obtaining the ground for the AC relay from the '+' side of the starter but since the starter coil has extremely low resistance (down in the 1ohm range) and the AC pick coil resistance is much higher (most likely above 10ohms) this means that most of the 12vdc voltage drop is across the AC pick coil.

But during key in 'START' you always have 12vdc on the starter '+' line and this disables the AC relay during 'START'. The engineers were very clever here and used this approach to insure that while 'START' all available power goes to the starter.

Try this: pull the AC relay and see if the power on the 'Yellow' wire changes at the Ign Switch.

[kidrock]

Thanks guys. I'm working on this issue as time allows, so if I don't respond immediately, it's only because I've got my hands full with some other cats that I'm currently trying to herd.

T77911S, you are right about the alarm and the yellow wire / kill switch. It's been tapped into very poorly. I plan on taking your advice and Sal's advice on the AC relay and see where that leads me.

I'll be back with some answers soon.

[scarceller]

Here's the 88 factory schematic for the AC system, look closely how the AC relay is tied to the starter coil. I marked up in RED the reason you see 12v at pin 50 of the ign switch. It's because it feeds back via the AC relay pick coil! Unplug the AC relay and the feedback loop should go away.

Here's the schematic:

[scarceller]

The Alarm system does indeed control the DME relay. The 12vdc power to pin 86 on the DME relay comes from the Alarm module. If the alarm is triggered you won't have 12v on pin 86 of the DME relay. So you can do a very simple test to rule out the alarm system. If you have 12v on pin 86 of DME relay with key in 'RUN' then your good.

Another very simple test to test that the DME relay is active and the DME is alive: turn key to 'RUN' and the IdleControlValve will be vibrating and humming. If the ICV is humming then the DME and the DME relay are working. But keep in mind the DME relay has 2 internal relays and this test has tested the main relay but not the Fuel Pump relay yet. To further test the FP relay after you verify the first ICV test you simply turn the key to 'START' and the FP will get power. Test the FP power right at the FP fuse in the front trunk with a test light while engine is cranking.

[scarceller]

Just read all the posts here: the DME and the DME relay have nothing to do with the starter. The starter circuit is not hindered in any way by the DME. If the starter is intermittent then it's the starter, the ignition switch, a bad ground or a after market alarm.

Even the factory alarm system does NOT hinder the starter, it simply disables the DME relay but the starter will still crank.

[T77911S]

funny how one off the wall post can make the topic take a left turn. dont get me wrong, i have followed the left turn myself.

he has an aftermarket alarm. some teenager at a hack shop put it in. they usually splice into
the start circuit because..... i will be nice.


i would like to know if he sees the 12v with a test light.....it would just confirm my reasons to not use a MM for this type of work. it would not add to the confusion factor by giving you some erroneous readings.

i was thinking an 83. read tonys post and i had 83 on the brain. anyway, still pretty much the same