Ricardo Vega II

Hey guys, was wondering if anyone knew why my 1987 928 S4 might be dying when I come to a stop in Neutral or Drive? It's maybe happened like 4-5 times in the last 6 weeks.
One thing I have noticed is that when I restart it (after it dies) the RPM's start a little high, like 1000 and then sink to about 500 for a few seconds then come back up to 750 which is the normal idle reading I've always seen.
It's been recent so I'm wondering of maybe fuel pump might be going bad? Fuel filter might start getting clogged? Any suggestions would be awesome! Thanks
Ricardo Vega II
1987 Porsche 928 S4
Black/Red

NickT

A few things come to mind.
ISV : Idle Stabilization Vale. Might be sticking. There are a few threads around here on how to use WD40 to clean it. It's under the intake so not easy to get to.

TPS: Throttle position Sensor, drivers side of the intake. Tells the LH when to engage the Idle map amongst other things. Might not be working right or just needs adjustment.

False Air: Maybe you have a vacuum line loose or some other type of air leakage.

Fuel : Not sure I would lean (no pun) towards them yet, a failing pump or clogged filter you show up worse when the engine is under load that when in an idle condition.

That's just off the top of my head . .

Mrmerlin

check the battery terminals,
and the ground strap connection,
and the fuses ,
and the relays ,
and the 14 pin connector,
fit a hot post cover if you dont have one.

did the car get wet?
are the coil wires running clear of touching anything on their run?
have you checked the ends of the coil wires?

NascarRacn

When mine did the same thing, it was the fuel pump relay...

fraggle

might also be the kickdown relay. I can see something going wrong and it shorting the tach signal to ground when you don't want it to.

James Bailey

And then there is Thrust Bearing Failure where the crank shaft is eating it's way out of the block which as it progresses makes the engine not crank on the starter motor until every thing cools down. More than one auto 928 has been sold because it will not crank/ restart when hot....sadly it destroys the engine block. You might want to check crankshaft end play.....

mickster

Was wondering when an expert would chime in with this...I wasn't going to post as I am no expert...

Mrmerlin

as JB said have you ever checked the preload on the flex plate?
This should also be done as well as checking the crank end play.
Pull the dipstick and drip the oil onto a black piece of cardboard look at the oil in the sun with a magnifying glass if you see lots of letallic particles then you have a thrust bearing being worn.

MainePorsche

Hopefully it will be the things NickT has referred to above. Read the NEW VISITOR thread in the Admin threads at the top of the home page for general information, but have a look at the links regarding Thrust Bearing Failure. You can check to see if this is occurring, and if not, you can take measures to KEEP IT FROM OCCURRING.

Best Wishes

Ricardo Vega II

So thanks for everyone that chimed in with their knowledge and the first step I took was checking the oil and sure enough, there was a good amount of metallic debris in the oil! But just how much is too much is another question. I don't know if I maybe should pursue this avenue first since it looks like it can be a project and a half. Or knock the other suggestions, any suggestions? Where the F$&@ is the thrust bearing anyways???????????
I'm about to pass out just thinking how screwed this might turn out to be...............
Ricardo Vega II
1987 928 S4 Black/Red

MainePorsche

Ricardo,
Sorry to hear this. Was hoping it was another more innocuous reason causing your symptoms. The crankshaft rides/sits in this bearing. From what I know the engine/drivetrain had by design an anomaly that causes the crankshaft to want to migrate. The flexplate was supposed to 'absorb' some of this force and movement, but the engineering/design was not enough to keep damage from occurring. we release the tension on this flexplate and some have developed clamps to keep this migration from occurring.
Some of the Texas crew will chime in and offer their advice to you.
Keep your chin up !

Ricardo Vega II

Hey guys thanks for your input! I'm looking forward to this weekend and going all the checking on it. One thing I want to ask you guys was why, if it is the TB for the driveshaft that is the issue (which at this point I can say 99.9% that it is cuz of the amount of metal in the oil) would the car die? I don't see the connection at all. If anyone has the time to explain that would be awesome! Thanks!
Ricardo Vega II
1987 928 S4
Black/Red

MainePorsche

'...an anomaly that causes the crankshaft to want to migrate.' isn't enough ?

Here's a link.

http://jenniskens.livedsl.nl/Technic...ingFailure.htm

Ricardo Vega II

At MainePorsche or anyone else that might know, since I do have metallic debris in oil is that a for sure that I need a new block? Or is there a chance once I adjust it and keep doing so that I can maybe save it? Like I said its died about 4-6 times. And never had issue with restarting it. Thanks
Ricardo Vega II

69gaugeman

If you caught it before it ate into the block you should be able to replace the thrust bearing.

This also assumes no issue with the crank.

You can pull the pan and you will be able to determine what the situation is. Get the pan off and post pictures. We will better be able to figure out how bad it is.