Splitting Atoms

I was lucky to get my car for a bargain price because it had similar electrical issues. I trailered it home. The first thing I did was charge the almost new battery at two amps overnight and install it in one of my other cars. I drove around for several days while I did further diagnosis and waited on parts. The battery worked flawlessly. In parallel, I took the ground cable located behind the passenger rear tire off the engine and body and made sure both ends were good and clean along with the mounting points on the body and engine. They were. I cleaned both battery terminals and they looked good. I disconnected the battery negative terminal cable at the body and bingo, the connection to the body was bad. I cleaned the cable connector and body mounting connection thoroughly. A bad ground will kill the voltage regulator, and then the rest of the alternator. The prior owner gave me the original alternator and I took it, along with the almost new alternator that I took out of the 996, down to the local Advance Auto Parts. They put both alternators on the tester and they were both dead. Typically when you have a bad ground, like I did, the voltage regulator goes bad and the alternator will put out 17+ volts, when it should be about 14.5v, which will boil the battery and kill it. In my case, the voltage regulator was dead and the new alternator was putting out less than 3 volts. The original alternator was rebuilt by a local shop that rebuilds thousands of alternators each year (United Rebuilders in Seneca SC). They specialize in Bosch and had all the parts on hand. The original 996 alternator has an aluminum clutch-less pulley. Porsche apparently recognized a problem with shredding accessory belts on manual gear box cars during high RPM deceleration early on and they swapped to a clutched pulley. I stuck the rebuilt original in a box as a spare and ordered a correct rebuilt Bosch alternator with the clutched pulley for about $400 from Pelican Parts. The almost new alternator that was installed when I bought the car was a Chinese Bosch replica with the standard pulley so I didn't get it rebuilt. While I was waiting on the Pelican Parts alternator, I installed the battery and measured the voltage drop between the battery and the terminal where the alternator attaches (the end of the "Y" cable that also attaches to the starter) and the engine case. The drop was 0.3v (from about 12.5v at the battery to 12.2v), which is expected. I also inspected the terminals at the back of the starter, which are relatively easy to get to when the alternator is out. They looked good. Note that my car has spent its entire life in upstate SC and has never seen a salty road. The starter sounded good the few times it was jumped, so I did not get it rebuilt at United Rebuilders. I will do that when I pull then engine out. I installed the Pelican Parts alternator and the car has run well ever since, except for the central locking that doesn't work correctly and will drain the battery if I let it sit for three or four days, but that's a separate issue.

One thing I should add is that everything worked on the car when it had the bad ground, but the starter was a little sluggish because there weren't enough amps passing thru the bad connection and the alternator died, of course.

WONGY

The car had new battery alternator engine ground and power cables installed 6 months ago

the garage tested the car - cold start 30 mins drive park up. Then try restart won't - and by that I mean car cranks once then stops like run down battery but it's not . Alternator pushing healthy 13.6v when warm and battery ok

they tried put new starter in same problem

now looking at wiring said something about ecu to ignition missing messages codes? But the ecu was tested refurbished a year ago when first find this problem and immobiliser with keys changed

there can't be much more left in the starter circuit eg cold start runs ok - if ecu problem it wouldn't run properly

strange problem

Ahsai

Really thought you fixed it for good a few months back. It's indeed a strange problem based on what you described. I agree that it can't be an ECU problem. It's more like the engine/starter is somehow hard to turn when heat soaked.

One thing you can try is to jump start it when it doesn't start. If it starts with jump start, there's still issue with the battery or charging system. If it doesn't, can try to manually hotwire the starter. If that still doesnt work, that points more to a mechanical issue of the engine/starter. Try to turn the engine by hand and feel for resistance. If normal, the (new) starter is the only thing left.

WONGY

Thanks Ahsai - yes I thought all sorted too as its been good for last six months , though the alternator was clearly broken given low voltage output

it's defo something been triggered due to heat soak - after towed to garage they started it no problem 1.5 days later. They drove for 30 mins, switch off then on and wouldn't crank - note that's the key point it not that car cranks not start it cranks once then stops

we tried jump start with power pack same problem. Sometimes it would crank once, then next time just not crank at all when turn the key

they said starter motor initially - I think they changed to new one tried it didn't work

This is what he said

"We found there are some errors from and missing the main ecu which leading to mis-communication with battery control. Our techs are now measuring the wirings one by one see where goes wrong."

when first had this fault we sent ecu immobiliser for testing, got new immobiliser keys and cleaned up ecu - has 5 year warranty so I doubt that's the fault

Could it be wiring as they say? I'll ask them check the battery ground wire though it looked ok not dirty, also ignition switch though changed that before

otherwise difficult fault to find

Ahsai

If it is the DME, the starter should not spin at all. Wiring is possible but it's unlikely given the heat related symptom. The usual suspects including the starter and the starter cable have already been replaced and jump start has no effects so that's why I suspect the engine itself or anything it's driving on the belt.

WONGY

Latest from my dealer. Not sure it adds up eg because when I first had this problem the ecu immobiliser and keys were sent for testing and refresh to ecudoctors who gave me a new immobiliser and ecu was cleaned up and tested. The car surely wouldn't run even if bypass if ecu broken?

that and ecu is obviously very expensive - but I've told the dealer prove it works first. Seems it's their strategy remove replace parts see if it works

thoughts?

"After all the tests done these days, we found the starter and ignition run after bypassing the main control unit but we would like to make it certain, a new main control unit is ordered and delivering to us by courier. Hopefully it will be arriving early next week and i could provide an answer to you. Sorry for keep you waiting and thank you for your patience."

ECU Doctors

Wongy,

I was just reading this thread and noticed that this is a job that we did for you at one point.

In your message above you said that they are "bypassing" the "main unit". Do you mean the ECU?

If you have the invoice # of your job I can look at more details from my side to help you.

WONGY

I already sent a note to lee pennant ecu doctors directly 8/6/17 at 10.33am EST - maybe you'd like to review there and reply as appropriate given the part is supposed to have a 5 year warranty

tompdx

Resurrecting this thread. First, thanks for all of the great clues thus far!
1999 Boxster. Problem started when ignition switch failed. Car was running great, then the ignition switch broke internally. The accessories stopped working in "on" and I couldn't completely turn to the "off" position. Could not remove key, and went part way back to "on." had to disconnect battery with key in ignition.
I replaced the switch the next morning with a standby (leftover from replacing a good switch before I diagnosed a bad starter). Car started right up with the new ignition switch. I turned it off, and removed key. Next morning all lights on dash, but no 12v power to starter.
Here's what I've done so far: checked fuses C 1-4 and F1, installed another (new) ignition switch, bypassed clutch switch, jumped 30 to 87 on the starter relay and starter and solenoid tuned the engine over just fine, but won't fire up. I replaced the starter relay and no change.
If the key is turning the engine with the jumper wire in place, isn't my key being recognized by the immobilizer? What should I try next?

Ahsai

I assume you meant fuse E1 (there's no fuse F1). With the jumper wire between start lock relay 30 and 87, the DME is bypassed. Power flows from the battery to the ignition switch, jumper and then the starter solenoid directly. So that only means your ignition switch is good. You can try the following:
- another key
- retrace your ignition switch work and make sure all the connections are tight
- use Durametric to scan for code

tompdx

Thanks for your reply.
Yes, sorry, E-1. Sadly I only have one key. I am confident in the switch work, so I ordered a Durametric tool from EBay. If jumping the start lock bypasses the DME I'm thinking it must have something to do with the immobilizer. I have tried to reset it in the two ways suggested: lock and unlock the door 3 times with everything shut (my mechanic), and lock and unlock the car with the key in the ignition. Neither worked.

Ahsai

Right, jumping the relay will bypass the DME, as shown in this wiring diagram here.

tompdx

Received the Durametric. Plugged it in, but it can't find any fault codes. The only information I can get from it is when I check the A/C, is says it isn't communicating with the DME. Getting ready to give up and tow it in. I think it must be the key not being recognized, but I don't understand why that would not throw a code.

DBJoe996

Generally speaking, the starting circuit(s) will not throw codes, and are difficult to diagnose. Remember, codes (P-codes) are related to running parameters, such as O2 sensors, misfires and MAF sensor faults - emissions related stuff. The immobiliizer, key RFID read in the start sequence is not something that will throw a code.

tompdx

That makes sense. Thanks for your response.