WONGY

Thanks all for the suggestions - will send them onto the dealer

They called me today to say now the car wont start at all - its doing the one crank then stop - which is different from when I left the car for towing = car would start but stop after about 5 mins driving

I'm guessing the computer won't pick up the fault and I do feel its something like wiring or something

Question - ecudoctors said my dme immobiliser were corrupted / damaged. Any clues why that would happen e.g. would Y pipe defect or an earth shorting out make this problem - if so which earth or wire?

Ahsai

Voltage drop test is the only way to confirm a bad cable/connection (unless you have obvious corrosion on the wires). I think the good news is now the issue in persistent and that should make the diagnosis a lot easier.

So currently the car won't crank at all or it cranks but won't start?

WONGY

ok Porsche came back

They said alternator intermittently low voltage output

Not sure this quite adds up eg yes when driving engine stops that could be a cause?

But why would car not start or crank - note previously when this problem before towing they put on battery pack to get car started but still same problem

Surely more likely wire problem eg ground wire?

Ahsai

That is interesting. While you were driving, did you notice your voltmeter in the dash read low sometimes? It should be between 13.5 to 14.5v whenever the engone is running. At cold start, it should read ~14v once the engine started.

WONGY

Good question - I know it was around 13 from memory including when it wouldn't start let me ask

I will go see them Monday - I want to understand how they identified voltage output was intermittently low

If they can prove checking properly not just random guessing - that's definitely showing a problem

Its identify what is the source eg I doubt alternator likely as people said the y pipe / ground strap per part 36 here correct?

http://www.autoatlanta.com/porsche-parts/hardparts.php?dir=996t-99-05&section=902-05

My suggestion then would be change this wire first and rerun the test before try other things

alpine003

Where are you located and how long have you had the car for?

Are you 100% positive your car was never in a flood before? If so, corroded connectors/wiring could have the various intermittent effects that you are describing.

Did you remove the immobilizer yourself? If so, did you notice any dirt or rust in the connectors?

WONGY

Based in Hong kong

Car hasn't suffered flood damage and immobiliser was removed from car by my garage

im going to get Porsche to closely inspect the wiring

Ahsai

Maybe they took it out for a test drive and saw the voltmeter on the dash fluctuating around the low level but I agree you should check with them.

Yes, that's the ground cable. Should be very easy for them to check it both visually and electrically.

WONGY

Yes, that's the ground cable. Should be very easy for them to check it both visually and electrically.[/QUOTE]

Maybe worth let me know how to test in case they're s bit lost . I noticed this link for a 996TT but not sure how accurate - seems to have a number of tests?

http://www.renntech.org/forums/topic/44306-my-last-report/?page=1

or is this post more useful that posted some time ago?

http://www.renntech.org/forums/topic/44471-voltage-regulator-affected-by-heat-hence-low-voltage/

thanks again!

Ahsai

Basically they can perform a voltage drop test on that cable but they should know and if they don't, you don't want to have your car repaired there anyway.

For a complete check for the whole system, check out this link http://www.renntech.org/forums/topic...arging-issues/

WONGY

Yeah tell me about it - I took the car to Porsche hoping their computer and tools, specs, data etc they'd know how to pinpoint

But now they've said alternator doesn't really add up vs symptoms so I'll question them today - see if can show me voltage drop in action, did they carry out these tests - HK are notorious for replacing things on trial and error basis - at owners expense

My other mechanic might be better option eg real mechanic (they rebuild trannies etc)

I can be there do all the testing with him eg test wires and replace as required plus can send the alternator and starter off for testing. He did say could be crankshaft sensor but only thing can do is replace difficult to test

Only worry is will the car stop in between garages!

Ill keep everyone updated

Ahsai

I understand your situation. It's not very different here in the US anyway.
One "good" news is if your engine cranks but not starts consistently (like claimed by the dealer), that would be a lot easier to diagnose.

Regarding the crank position sensor, one quick way to tell is when you crank watch the tach closely and see if the needle bounces 1/8" inch or so when the engine is cranking. The bouncing indicates the DME recognizes the signal from the sensor. If there's no bouncing at all, it's likely you have a sensor/wiring issue. However, if there's bouncing it's not conclusive because the signal could be bad even if it's present. One will need an oscilloscope to check the waveform.

To test the ground cable quickly, you can hook up a fat jumper cable between the car chassis (e.g., the brass metal jump start point in front of the airbox and the engine (i.e., any metal parts that directly connect to the engine such as the exhaust system or the engine brace). If the engine starts w/o problems with this cable in place, then the ground cable is a strong suspect.

One thing to note is diagnostic requires special skill set than pure mechanical one so not just any real mechanic will do, even if they rebuild engines or trannies. I know there are shops specializing in diagnostic in HK but I have no direct experience with them. Can you ask the PCA (or equivalent) in HK who they would recommend?

I would expect the Porsche dealer in HK be better than that. The intermittent engine stop when driving will be quite challenging to troubleshoot but I would expect they could at least diagnose a no start and/or no crank car.

WONGY

Ok great - I met with someone referred to me

he agreed not alternator - also pointed out to him with your diagrams what are chief suspects

he he said will test ground and power wires alternator and starter olus crankshaft sensor - as Porsche do have the specs and tools to test

Not clear if car still not starting but I said that just run at idle for 30 mins until powers off then test

lets see what they come up with!

WONGY

Ok so Porsche cleaned up ground cable on chassis side - said driven car many times over 30 mins - engine didn't stop and car starts no problem - we're hoping that it's not just something else intermittent eg they did resistance check on crankshaft sensor seems ok but ground cable seems a big clue

however voltage still low around 11.5 not 13.5+

So I've said replace ground cable first then retest eg if that doesn't fix voltage problem then can look at alternator and check power cable whilst replacing eg could be do both

will update again next week

Ahsai

If it's truly 11.5v, you have a better chance of a bad alternator/regulator because a bad cable will most likely rob you 0.5-0.7v. It's a problem that needs to be fixed on its own regardless of the starting/no-start issues anyway.