IXLR8

Helping a Porsche 997 friend with some starting issues, as in the starter turns over very slowly, be it from a cold or warm start.

The battery is fine. I performed a 300A load test.
The charging system is fine; 14.1V at the battery.
The starter will be the last item AFTER checking the cables and connections.

As is usually the case, I suspect bad connections and from the two or so hours spent searching the web, I've seen corroded crimps (see last pic that I grabbed from a thread).

I don't know the 997 like I know my 993 so I am looking for help in locating the following electrical connection, I assume both are the same connection in the first two photos.

I will also check the connection (last pic) at the starter.

DC911S

You need to check the voltage at the battery and the starter. I think if you see .5 v or more difference between them you need to replace both cables. There is a DIY thread in the 997 to do it. I had mine done at dealer and it cost 1200 I think mostly due to the labor time. Parts were 300 or so.

IXLR8

I am aware of acceptable voltage drops. No doubt a bad connection is the issue. I do not have the car in front of me, but will take voltage drop measurements when I do.

I need to locate the connection, the one in the red rectangle. Am I looking for it in the engine compartment or under the car?

DC911S

Its under the car. There are a few threads in here by people who did the work themselves with pictures added in.

IXLR8

Thanks. I found some good pics on a "Replacing the clutch in a 997" thread. I now know what to look for when we get his car up on the lift.

Looking forward to solving this simple issue.

Devil Boy

That connection you highlighted is on the passenger side of the transmission.

IXLR8

Thank you!

My friend bought a new rear cable harness (#14) today and we'll be replacing the old one instead of fixing it.

Any idea how the harness feeds down from the engine compartment to the underside? I am sure this will all be obvious when I have the car in front of me on the lift, but just in case.

DC911S

I think lots of things have to come off to get it fished through the chassis

semicycler

Suncoast's website has a good excerpt from a tech bulletin about acceptable voltage drops due to the known issues with a bad cable between the battery/starter/alternator: https://www.suncoastparts.com/produc...97HARNESS.html

Per Porsche's technical bulletin.
Issue: Battery discharged and/or will not charge properly. Voltage drop due to alternator-starter-battery harness damage at starter terminal. This issue is often mis-diagnosed as a bad battery, bad alternator, or bad starter, and these parts are often replaced in multiple repair attempts before the harness is determined to be the cause of the issue.
Before ordering or replacing other parts, have the car professionally inspected. Check the voltage drop between the alternator and battery. Bring the car to normal operating temperature. Turn on as many power consumers as possible (AC, headlights, radio, defroster, etc.). Use the same grounding point for the following voltage measurements:
- Measure the voltage at the "B+" terminal on the alternator.
- Measure the voltage at the battery positive terminal.
If there is a voltage drop of greater than 0.5 volts between the alternator and the battery, and all of the connection points are tight, check the harness terminal at starter. It is possible that the crimps on the starter terminal where the two cables are joined together incorrectly, causing an excessive voltage drop between the alternator and the battery. This voltage drop does not allow the battery to charge properly, and as a result, the battery will continually discharge until it will no longer start the vehicle. There may be no visible damage to the harness, and more measurements may be necessary to determine which cable or part of the cable is responsible for the voltage drop.

Devil Boy

This is the DIY that I used. It is all just nuts and bolts but a definite 10/10 on the PITA scale. The one thing that kicked my *** for some reason was the stupid clips that hold the harness in the tray it sits in on top of the engine. I struggled trying to figure out how to separate them.
https://www.6speedonline.com/forums/...ml#post3427155

BTW while you're in there you will have access to the AOS. Something to consider replacing if your car has some mileage on it. Oh, and you will break something so don't be upset. Just expect it. Those little plastic coolant lines get brittle after a while.

IXLR8

Thanks DB. I am used to working on 911s and have since learned they are an exercise in patience.

For starters, I will load test his battery again. After a 30 mile run to my friend's shop and lift, it will be fully charged knowing that his battery voltage reads 14.1V with the engine running.

That will give me a baseline of the battery. I'll monitor the voltage drop across the battery at the 15 second mark while putting a 300A load on it.

I'll then do the same at the junction at the transmission after I split the connection. I'll measure the voltage drop from the positive battery post to that connection with the load tester at the connection. This is as good if not better than using the starter which is a varying load as the engine turns over.

This test will determine if the two positive cables are fine, the one from the battery to the pin and then from there to the transmission.

IXLR8

A couple of pics showing the location of the cable junction...

IXLR8

Does anyone know where the ground strap (#19) that ties the engine & transmission to the chassis is located?

We could not find one while under the car.

Found it. Attached to the passenger frame rail.

Rampage

Curious, did the voltage check you performed point to where the problem is?

And you're performing this with the vehicle on the hoist, but is this something that can be performed with the car on ramps / jack stands?

Reason I ask is that my recently acquired 997 is also slow to crank, thinking I should check the cables ... debating about whether to attempt the DIY based on the PITA comments above.

IXLR8

Not sure, not knowing what the gauge is of the cable coming from the battery/power distributor (#11) and not knowing what the specification is for the current draw of the starter. If I knew the cable specs (gauge and stranding), I could predict voltage drops at various currents.

From the positive post of the battery to the cable junction at the transmission, I measured 0.34V @ 160A load and 0.79V @ 360A load. That appears high, but not if the starter draws say 100A.

By the way, the much talked about cable to the starter and alternator that the dealer also had in stock, was not the fix.


Yes.

I will be checking the ground strap from the frame rail to the engine.

The ground strap connection from the battery to the chassis has been physically checked (it was clean), but not electrically checked. Simply looking at them is pointless in my opinion; there is nothing like confirming voltage drops to prove their condition.