928S24 wont start.....
 

Hey Pelicans,

It's been a while since I've been on the forum. Last summer, I finally got the supercharged 928S4 running, and running well. It ran like a bat out of H@!! until about three weeks ago (I was driving it as a daily), and started experiencing issues which puzzle me. I understand that 928's can kill batteries if left sitting for more than a week, but I kept mine charged (for the most part) to avoid that. On my way back from the office a few weeks ago, I noticed that the battery was dead, which required a jump.

I figured that I had left an accessory on or something (i accidentally left the door cracked open in the parking garage all day.) Predictably so, I knew the car wouldnt start, and got a jump. I also noticed after starting the car that it had developed a knock which was quite loud (dont know if this is related). The knock quieted down after it got warm. That night after getting home, I charged the battery to full (using a noko Genius charger), and the next day it started, and I drove it to the office again. At days end, I went to start the car, and found that it would barely turn over, but it did, and after about 15 miles, the car started to sputter as if out of gas (it was low on fuel), and I thought that was the culprit. I never thought that it was electrical, since according to the voltage guage, it was putting out almost 14 volts. I pulled of the freeway to get some gas, and after about a mile the car started violently shrugging, until it just died. I tried to start it, and it behaved as if the batter was dead.

Anyway, I happened to be very close to an auto repair shop, and asked the mechanic for a jump, but the car behaved exactly the same way. it would barely turn over (and the digital display would barely pixelate). Then the tow truck driver tried with his unit, and same thing. I suspected it could be a bad battery, or bad starter, and I checked both after getting the car home. Battery is 8 months old, and checked out with my voltmeter, and also a third party test showed it was fine. Then I removed the starter, and had it tested by alternator/starter specialist -It checked out fine. I verified that the grounds were tight, so I'm out of ideas. Can anyone point me in the right direction.

The motor in this car is a replacement with low miles, and I replaced the oil pump, timing belt, CPS, knock sensors, put in a portensioner, and had the cams reground to factory specs before putting it into the car.

Does anyone have any ideas? That knocking bothered me, but I dont think that is the problem. It seems like an electric issue to me, not a motor seizing. Always something with this car, and I'm at my wit's end with it.

Thanks all for your insight.

I'd try turning it over from beneath using a socket and lengthy breaker bar. That would definitively
tell you if the engine is tight or not.

Ground strap or ground points, ground strap an easy replaced item from Mark or Roger with a quality non Porsche expensive one.

If its an automatic, check the flex plate and release tension on the clamp, measure crank end play.

Thanks for the tips, all. Definitely gives me something to look for. I think the ground strap is most likely the issue, but it looks fine at a glance. Bad grounding is the only thing I can think of that would cause the car to seem like the battery was dead (display pixelates and very hard starting - barely turning over).

The ground strap cannot be tested by "looks". What happens is, the connection inside the crimped end can be bad.

Ground straps often look great, but an inch or two under the insulation its junk. Good replacements are cheap.

Hey guys,

I've finally had the opportunity to test the bad ground cable theory. I ended up swapping the ground cable from another 928 in fine running order, and still same issue. So the battery, ground cable, and the starter check out so far. I've even gone so far as disconnecting the stereo and alarm connections from the positive terminal, to no avail. Where else can I check?

Incidentally, when turning over the car (I tried at dusk), I popped up the headlights, and they were very bright, but then went very dim while attempting to start it (along with the slow rrrr rrrrr rrrrrrr, and pixelated digital readout). Please help.

based on the info provided,
you need a new battery.
Also pull the regulator from the alternator and inspect the brushes,
if they are worn replace the brushes or replace the regulator with another Bosch unit .

do not use aftermarket parts for the regulator

I would agree with that mmerlin, in regards to the battery. After fully charging the battery last nght, I took it to another local auto parts store (the second test) early this morning, and it also passed as being a good unit. The battery is about 8 months old, and believe me I was hoping it was (the battery), as it is still under warranty. They swore that the battery would not pass the test if the tester detected a 'bad cell', but I have my doubts. Also, I will mention that the vehicle behaves the same way when adding power from another source (jumper cables, battery booster, etc).

It seems be a faulty grounding issue; however, you bring up an interesting point - would a faulty regulator cause such an issue? Does the regulator 'amplify the output' when starting?

You still haven't ruled out an issue with the engine internals. I suggested earlier taking a breaker bar and socket to the front of the engine. Before you waste money make sure the engine isn't tight.

And, that's it. I went out and checked it, and it will NOT turn over with my wrench and a 27mm socket. I've turned it by hand before just before re-installing the motor, and it rotated much easier, as I recall. Checked the oil, and it's VERY dirty, almost a dark greyish color, and smells of fuel. The oil only has about 700 miles on it, so it should not be that dirty. I really didn't want to believe it was another motor issue (this is engine #2). I've pulled two plugs (one on each bank) at random, and they seem fine, but I will need to drain the oil, and examine it, then pull the rest of the plugs (then try to manually turn it over again), and do compression test to be sure. Could be fuel lock...

Good luck I hope it's not serious.

Major bummer bro...got my fingers crossed for you...

Frequent advice from Mr Merlin, drip some oil on a dark sheet of paper and look at it in the sun for sparkles.

:eek:...Bummer on the issue...hoping it is not thrust bearing failure!

next step drop the bell housing,
take a picture of the front flex plate coupler,
then release the clamp Bolt.
then try to turn the engine.

This is my best guess you have thrust bearing failure,
though from your description it wasnt pointing to this.
when you installed the engine did you tighten all of the pinch bolts on the drive shaft ,
including the one at the transaxale to 61 ft/lbs

You are right on the money, mmerlin. I did this two nights ago, and just haven't had a chance to update the thread. Based on the observation, it could be a thrust bearing failure. Wow, it just gets better. Not all thrust bearing failures are catastrophic, but the motor will need to be taken apart to see the extent of the damage. Pinch bolt was pretty darn snug when I removed it the other night, so I believe that it was torqued adequately.

well the pinch bolt that matters is the one at the trans axle,
if its loose then the whole shaft will migrate through the bearings and preload the front

Note to self...get under the car soon and check this out.

Brian.