Momentary Loss of Electrical Power While Driving

[jstew039]

Early 2001 986 Boxster (07/2000 production date)

78K miles

Vehicle experiences sporadic electrical failure for only a split second, rarely shuts the car off completely. but the car stumbles...all electrical devices are affected. if the radio is on, it will cut off then back on (displaying "PORSCHE" on the face). headlights will flicker, dashboard lights flicker.

 

Extreme cases will be at idle or off power and applying brakes, if headlights are on they flash off and back on. all dash warning lights will come on momentarily. car will cut off but come right back without having to restart. during this extreme case, when brake lights are activated or window power switch there will be an audible squeak sound coming from the fuse / relay box.

 

this happens 60% -70% of driving time. day or night. with all accessories on or no accessories on.

At idle, under power or off power coasting or braking. the extreme case happens about 50% of drive time.

 

while under power on the freeway and headlight on, you can see the headlights flickering on the road.

 

work i have completed:

i have located and checked all 18 ground points.

there is no evidence of water damage under either seat (convertible top drains are clear)

clean battery terminals

strong battery (i use a trickle charger if the car sits more than a week)

just replaced ignition switch (i thought i had found this to be the problem)

 

i am at wit's end with this one...i am the first to admit that electrical issues are not my strong point.

Help me Obi Wan Kenobi, you are my only hope.

 

thank you

 

 

 

[JFP in PA]

I would load test both the battery and the alternator, and run a voltage drop test on the primary battery cables. 

[jstew039]

thank you, JFP.

 

great suggestions, i will do that this morning.

[JFP in PA]

Whenever you encounter electrical issues, the first step should always be to make sure all the basic electrical systems are functional, otherwise you can end up chasing your tail and endlessly replace parts that are actually all right to begin with. 😉

[jstew039]

5 minutes ago, JFP in PA said:

Wise words:

Whenever you encounter electrical issues, the first step should always be to make sure all the basic electrical systems are functional.

 

I need to make a poster of that quote and place it above my toolbox!

 

[jstew039]

battery was at 12.4 so i charged for 4 hours and retested, battery was at 13.10

load test = headlights on, high beams, radio on, blower fan, lowered the top.

re-test battery 5 minutes after the above load was applied =  12.62 (with all accessories off and key in off position)

started the car...meter reads 11.40 as engine is cranking

while running volts 14.13 at high end and 13.70 at low end (estimates as my meter does not have a max / min mode)

while car was running i raised the top, with accessories on (radio, fan, lights) meter was pretty steady around 13.9x

turned the car off and let sit for 30 minutes.

re-test battery with negative cable removed 12.53

re-test with negative cable attached 12.51

 

i was able to reproduce the issue immediately following the above testing.

i can reproduce the problem with the car running or not.

 

i would say the battery, even though the cranking power is good...has a short and needs to be replaced. the battery was installed 12/20 and i purchased the car in 7/21 so i don't really know the status of that battery. it is an Interstate M 94R

the alternator is working well.

 

i am going to replace the battery, and see what i get.

 

 

[JFP in PA]

Not to be pedantic, but while your “load test” was interesting, that is not how it is done in shop.  We use a carbon pile load tester that can exert upwards of 100 Amp load when required.  We set the device to the appropriate maximum load for the vehicle under test, and then apply the load for 15-30 seconds, awards looking at the battery and alternator voltage outputs to see how they respond.  The load tester can also “tickle” the diodes in the alternator to see how they respond (an alternator with a questionable diode can seem to be putting out the correct voltage and current, but will suddenly drop off when fully loaded, causing both voltage and current swings).

 

Something else that a proper load test spots is sulfated plates in the battery; sulfate builds up over time in a battery, increasing internal electrical resistance.  When a sulfated battery is hit by the high amperage load, the voltage momentarily drops precipitously, often down to as low as 8-9 volts as the battery heats up, and then seems to go back to more reasonable voltage levels as the load comes off.  When the battery does this, it is time to can it, it will not recover.  The trick is to catch this quick voltage move when it happens, which a proper load testing system does.

[jstew039]

i really appreciate the detailed information and i understand my "load test" was inferior to that of a shop...that was kind of my point in explaining the steps i took...the battery didn't pass my simple testing.

 

i have fully charged the battery and i am taking it to a shop this morning for testing and inevitable replacing.

 

again, to reiterate...i really appreciate your time and knowledge. i do not feel your answer was pedantic in any way.

 

 

 

[JFP in PA]

Just as a thought for future consideration, you can have you system tested for free at many auto parts stores, who offer the service in anticipation of selling a battery; or you can purchase a full featured hand held load tester for less than $100 that can be used to test any SLI battery you may have. 😉

[Silver_TT]

Since you are replacing the battery anyway you may want to consider upgrading to an AGM instead of the flooded Interstate M 94R battery.

[jstew039]

i took the battery to an auto parts store to replace it, i had them test first and the battery tested good. so i didnt replace it.

Silver_TT - i am going to research this "AGM" battery you speak of, for i am intrigued.

i had no idea that load testers would be that inexpensive, i am going to invest in that for sure...do you have any recommendations for a load tester / charging (alternator) testing unit?

 

 

 

 

 

[Silver_TT]

I got this for about $40 at advance auto parts ($55 but you can use coupons).

 

https://shop.advanceautoparts.com/p/schumacher-battery-load-tester-and-voltmeter-100-amp-bt-100/9200014-P?searchTerm=Schumacher+load+tester

 

AGM batteries use a superior technology over a traditional flooded lead acid in many regards.  They are definitely the way to go, I will never buy a flooded battery again for sure.  Many of the newer Porsche models come with AGM batteries standard.  Even my 2014 Audi Q5 came with one (probably because of increased power demands--heated seats, liftgate, navigation systems, etc).

Edited February 21, 2022 by Silver_TT

[jstew039]

i have ordered the Schumacher tester.

 

thank you, i appreciate your time and help.

 

now that i have ensured my battery is good and at full charge...i will continue on my electrical anomaly search.

 

thank you

[jstew039]

new information on my electrical issue...

after acquiring the proper testing equipment and ensuring that the battery was at full charge. i have gone weeks of driving (it is great convertible weather here right now) without anymore issues.

 

THEN last night we went to dinner and for the first time i locked the car because i parked on a street several blocks from the restaurant. The buttons on my key fob are worn out and the only way to lock and unlock is using the key in the door. however when i do this the alarm always goes off when i enter the car and i have to put the key in the ignition to disable the alarm. driving home the electrical issues were back.

 

this kind of makes sense because the vehicle behaves as though the entire electrical system is shutting down...something i would expect the alarm or immobilizer to do.

 

as you drive the car down the road the electrical is just on the verge of shutting down, headlights...dash lights...engine power...all flickering.

 

any thoughts?

 

thank you.

[Silver_TT]

So you tested it with the Schumacher?  Assuming your battery is good ......

 

Sounds like my exact experience on my 2002 996 -- stuff flickering, etc.  There were two issues:

 

First of all there is a thick gauge wiring harness that is known to corrode (believe there is a TSB on this). Replacing this solved a ton of my voltage drop.  There are threads here that you can use to use a multimeter to trace the drop from hop to hop.

 

Second the alternator was marginal but this was very tricky.  It passed a bench test at a place like Auto Zone but after my issue persisted I was confused and suspected it must have something to do with it so had it tested further and they found the alternator was doing funny things -- not working to spec at specific RPM ranges, etc.  Anyway, after replacing that all was golden again.  I recall the key fob and alarm going off, total PITA

[jstew039]

i will get the alternator tested at my Porsche shop, good suggestion.

 

another oddity...the just barely audible mouse like squeak that accompanies the power drops, coming from the fuse / relay area...or possibly from under the driver seat.

 

thank you

[JFP in PA]

The only thing under the driver's seat, besides the floor, is the electronic controller for the locking system, alarm, and immobilizer. 

[ARModen]

I would definitely be suspicious of the alternator diodes.  That squeak is quite possibly the belt.

[JFP in PA]

Alternator diodes can be tested in the car, but you need the correct hardware to do this.

[Silver_TT]

Ya you need a Snap On or similar machine that can test it in the car (much easier, the flange on the back of the alternator was a PITA) .... the problem I ran into was the initial test that said my alternator "PASSED" was done with a very cheap/crap machine at Auto Zone.  I would avoid a place like this in general.......

[jstew039]

new wrinkle that has me very suspicious of the alarm / vehicle immobilizer:

 

when the car is acting up (lights, radio, etc) going on and off very quickly. definitely loss of electrical power...when i turn the car off, there is total loss of electrical power. no interior lights, no dash lights, no horn, nothing at all. turning the ignition switch on / off repeatedly does nothing.

 

moments later...literally moments later, 1 - 2 minutes. there is power again AND the radio has not reset (i don't need to enter the code) the digital clock is not reset. at this point the car starts right up.

 

more odd noises...when the car is sitting dead, there is a very light thud about every 10 seconds. sounds like it is coming from the passenger side.

 

this got worse just from the other night. the key fob is not locking / unlocking the doors any longer so i locked the doors with the key. when we came back to the car i had to insert the key into the door to unlock. it worked, but the alarm went off and i had to insert the key into the ignition. that stopped the alarm, however the red light on the door lock rocker switch didn't go out right away and it wouldnt operate the passenger door lock...i had to reach across that open the door.

 

since that time (tuesday night) i am now having these more extreme cases of power loss.

[jstew039]

7 hours ago, JFP in PA said:

The only thing under the driver's seat, besides the floor, is the electronic controller for the locking system, alarm, and immobilizer. 

precisely!!

 

[JFP in PA]

You should check that control unit, looking for signs of moisture or corrosion. 

[jstew039]

6 minutes ago, JFP in PA said:

You should check that control unit, looking for signs of moisture or corrosion. 

been there...there was no sign of moisture, corrosion. it wasn't even dirty. that was all part of my initial searching out and cleaning of all the 18 ground points on the car.

 

i will definitely check again!! as this must be the culprit.

[jstew039]

the car will die while idling - when i say die i mean complete electrical shutdown, no horn, no dash lights, nothing...after a few seconds, it is back. i don't have to reset the radio or clock.

 

i have had the electrical shutdown also happen when i turn the ignition off and then as i pull the key out of the ignition (this is the clicking sound) the power cuts off.

 

totally baffled.