nsantolick

Okay;

"Accepted" that I have a ignition problem, it seems, with my car. Let it sit a few days since my last attempt to drive it. Started the car last night...

It ran "rough" from the start. Not firing on all cylinders. I checked the IMU while it was running and saw no lit up LED's at all.

Put it in reverse and applied the brake. The front wheels locked and the rear wheels didn't. THE CAR KEPT MOVING backwards, no matter how hard I pushed the brake pedal... After about 10 feet of sliding backwards, I pulled the hand brake, and the car stopped...

I've noticed this "type of issue" when the car is started. I assume it's a vacuum issue, but, perhaps it has something to do with the as of yet still undiagnosed poor running issues...

The brakes act normally, it seems, after the car runs for a minute or so. This nearly caused an accident the very first night I drove the car actually, albeit going forward after having pulled out of a parking slot. (It was icy, so I thought that I just hit an ice patch...)

Soooooooooooooooooo, how should I proceed? Can this be as simple as a vacuum line leak? I get the feeling that there is a small leak, and perhaps a vacuum reservoir doesn't accumulate enough to properly work the brakes for a few seconds after a cold start???

This, for what it's worth, does seem to go away 100% after its running for a little, and these "lack of brake" type issues have only occurred on gravel or ice. Obviously there's a BIG PROBLEM if full pressure doesn't lock up the rear brakes.

I'm pretty frustrated about the car, but willing to fix it properly, MYSELF this time, although sadly "in my leisure time..." I'm thinking I should start with a compression test, as well as seeing what results that the "software solution that can't be mentioned on RennList" has to say.

RE: "Software Solution..." - I'm just starting to read into which is which, and what they do. The one I found is basically a cable in a fancy box, and with a software license for 3 VIN's, costs about $370.00 or so.

It concerns me that the IMU didn't do anything last night. I am fairly certain that it has "kicked in" over the last few drives. Unfortunately, I didn't know about its existence until just before this last drive attempt. It WAS shutting down a bank of cylinders, it seems, and the problem would "go away" after I turned the car off, and re-started...

This short drive last night was just a few blocks away. I drove to a store, grabbed stuff, and started the car again. The car WOULDN'T START, although after a few minutes and 2-3 attempts, it started roughly, and ran poorly, seeming to miss on some cylinders, just at some times.

As usual, full throttle would seem to "fix" whatever the issue was. I'm not driving it again until this is sorted out, and unless nay-sayers convince me that the "software solution" is not the way to go, will order one of those soon enough.

Do all of these tools, like the hammer & all essentially do the same thing? Is this the sort of thing that I'll plug in once, and never use again? Should I just go to a Porsche factory dealer and pay for theirs, then do the work myself???

This braking issue really scares me. I've read that the brakes on these cars are magnificent. I've not been all that impressed. Panic stops on empty roads didn't do much better than most ordinary cars. The brake pedal, to me, feels a bit spongy.

Before I drove the car, I did have the brake fluid changed, new pads installed and the rotors cut. The mechanic told me that the slightly spongy pedal is "normal" and a few from Rennlist have claimed the same. Hard for me to believe - I mean, should the brake pedal on an '89 S4 be spongier than say a '83 Mercedes diesel??? Even with a vacuum leak, shouldn't one be able to completely lock up the brakes with massive foot pressure??? At one point, I pushed with 2 feet on the pedal and it still kept sliding backwards...

Arrrrrrrrrrrrrrrgh...









Nick - Hazleton, Pennsylvania - 1989 928S4 - Auto - 80K miles

Lizard928

Nick,

I think that it sounds like you just dont have vacuum assist, so if you were to really lean on the pedal you would have stopped. I say this as you can apply more force with your foot than you can by pulling the ebrake which supposedly stopped you.

It sounds to me though that you need to be doing an intake refresh and replacing all your hoses under there.

nsantolick

Sadly, I need to do the intake refresh AGAIN... Shop #1 started it, without my permission. (Rayco Euro - in Kingston, Pennsylvania...)

Shop #2 "did it" - but left a mess of the vacuum system. 1500 miles later, there's an oil leak... (Arrrrrrrrrrrgh!!!)

I noticed that it's not all that neat in the engine. I'm sure that they haphazardly positioned everything whilst reassembling the top end... I'm going to do it again myself, but was hoping to put it off until Winter. Seems that I may need to do it NOW... : (

Missing power assist makes sense, and the problem does go away, but I've had this happen before. No amount of pressure to the brake pedal stops the car. Can there be any sort of balance issues in the hydraulics that may cause very little force to be applied to the rear calipers???

When it kept backing up last night, I DID have, at one point, both feet on the brake pedal, pushing as hard as I could, and it still kept backing up. It appears that the FRONT calipers locked up but the rears wouldn't, so it just kept dragging the front of the car back with it.

Even when things are functioning normally, the panic stop tests were far from impressive. The brakes would lock up at one point, and ABS seemed to work, but it wasn't as legendary as it's claimed to be, so there is likely to be another problem...

I wonder if the vacuum problems would be related to the engine running so poorly lately? (it is on and off though...)

Speaking of the first two shops that had my car, for 20+ weeks, when I first bought it:

The guy who sold me the car told me the air conditioning works great. When I took delivery, it didn't work, but the light on the pushbutton for AC did light up.

When I finally got the car back, that light no longer lit up. AC definitely doesn't work... Worse still, when you set the controls to cold, you still get hot air coming through...

I checked the AC fuse. It was good. Multiple mechanics were "in the engine" area, so I wonder if something got damaged or not hooked up properly - specifically something that would cause that AC button on the dash to not be lit anymore... Any clues???

I fear that there's still some air in the brake system, despite the last mechanic having flushed the system. I heard that you have to have the ignition on while bleeding because of ABS - true???






Nick - Hazleton, Pa - 89 S4 Auto

blown 87

You must have one hell of a strong motor if it will slide TWO front tires at Idle.

It also sounds like you need to find a mechanic who KNOWS the 928, even if you have to ship it some place.

nsantolick

I'm not making this up - I know it sounds odd. To make things worse, my own car is the ONLY 928 that I've ever been in, and although I've asked ALL mechanics to drive it, beat it, and tell me if ANYTHING seems out of the ordinary, nobody has...

At this point, I'm DONE with taking this car anywhere. The plan was to get a clean car that needs nothing. To say I was in err would be the largest understatement of my life... I, for the time being, have given up on it as a reliable daily driver, to be easily serviced by others. Now it's the headache that I still like, but expect to go over with a fine tooth comb, MYSELF... I can no longer let this cursed Teutonic plaything "get to me" as it has for most of the last year +. I'll do it in my spare time, and not take it too seriously, I hope...

ASSUMING that there are no rear brakes at all, is it that hard to believe that at idle, on gravel or ice, that its larger rear tires could pull the car, even with the fronts totally locked? On a good surface, I wouldn't expect it, but on this gravel crap, it didn't surprise me...

It DOES seem to indicate that I have absolutely no rear brakes until the vacuum assist builds up enough negative pressure to do its job. On the other hand, what the hell could cause "no rear brakes", especially JUST for a few moments, perhaps 30 seconds, say???

My only regret now is that I just didn't start with a basket case. And let this serve as a lesson to those who don't want to pay for PPI's... I "felt" the honest seller out, who admitted that they know little, looked at some eBay pix, and hit the "buy it now" button. The lack of a front spoiler, belly pans, the massive oil leaks, no air-conditioning & more would have been readily apparent.

I don't care how much of a hassle it is. I don't care what it will cost. I don't care what I need buy to do the work. I don't mind.

ON THE OTHER HAND, if this 80K mile 1989 S4 CAN'T be trusted, at some point, for long trips, I think I'm about to ditch it, or worse yet, surrender it to my collection of 8 or so "classics" that don't work...

This brake thing bewilders me... Really.

I'm thinking I'll start with a engine compression check, and assuming that it's good, as the last mechanic indicated, then proceed step by step with everything in the car, making sure that its all been maintained/updated/upgraded/modified/replaced/kept in stock by the case/understood as necessary, very methodically and carefully, until all systems are confirmed...

Is there a way to check brake balance? Nothing to adjust? Nothing that could cause these symptoms???







Nick - 13 months now owner of a "perfect, needs nothing" 1989 S4...

80,000 Miles now on odometer...

In shops for over 25 weeks since purchased...

(~3000 very fun miles since I bought it...)

(~$4.67 per mile in maintenance since I bought it...)

Ben Allison

Maybe a lack of vacuum to the brake booster combined with sticky/partially-seized calipers? Like blown 87 says, in the game of "rock, engine, brake", brake always wins. It doesn't take much brake pressure to stop an engine at idle, so either pressure isn't getting to the calipers or the calipers are frozen shut.

nsantolick

Great. I'll start with a inspection, then flush & bleed the system, properly, this time. There are 3000 miles on the brake pads. They are a "semi-race" pad - the sort that needs some warming up before they grip as hard as they can. They weren't cheap. Should I reuse them or replace them?

I'm expecting to just rebuild the rear calipers too, to be on the safe side. I'll leave the fronts alone, for now, as they seem to be working. If this was you, would you just rebuild all 4?

There IS epoxy on a plastic part that connects to the brake booster. It seems sound, but perhaps it's a stupid repair and related. What am I looking at to rebuild that unit, while I'm at it?

pcar928fan

I agree... NO WAY are the front tires being slid (ie. locked up not turning) and the car at idle and then magically the parking brake stops the car from moving! NO WAY! If you are sitting in the car you can't see what the front tires are doing anyway. A vacuum problem will make you THINK any all brakes MUST be locked up because you are pushing on the pedal with all your might but nothing is getting through to the calipers so brake M/S and the vacuum system that makes it work would be the first places to look FOR SURE.

Think about a "brake stand" in a rear wheel drive car... The front brakes will hold the car no matter how much gas you give it from a stand still and won't even push the front of the car... No way at idle are you sliding the front of the car. If that were the case you would NEVER (in an automatic trans car) be able to stop the thing...

nsantolick

They are. I should clarify. It's not a gravel driveway - it's gravel-like, totally disintegrated asphalt/dirt/crap/gravel. It's also a slight downward driveway.

I feel that the fronts were locking up, despite not being able to see them, because of the noise that the driveway material makes. So, downward sloped driveway, mix of pavement materials, bigger rear tires, high-metallic content semi-race brake pads & a problem related to the rear brakes...

RE: engine problems - assuming I have a major vacuum leak, big enough to mess with the brakes, which isn't yet certain, of course, what sort of problems, if any, could such a leaky system cause to the normal firing of the engine? I doubt anything significant, but wanted to check anyway...

Could air in the rear lines, combined with a bad vacuum leak & semi-race pads make it behave like this, where there's absolutely NO rear brake action, despite pressing very hard on the brake pedal??? I'm expecting a seized caliper here but haven't checked yet. Are the brakes on this car lubricated with that high-temp grease? I had the brakes done by "a professional" so I never read into it...

blown 87

You need to find some who knows the 928 to work on it, or you need to learn it yourself.

Bottom line is, your brakes are not working, it is not safe to drive until it is repaired.

Greg Nettles

Bill Ball

Check that the big hose that runs from the driver side on the intake manifold to the brake booster is seated well at both ends (tight clamp on the manifold fitting, snug fit into tht grommet on the brake booster). Also, check that the hose that "Y's" off this big hose and heads down under the fuel rail is also snugly clamped to the Y fitting and that the "Y" is not broken. That may be contributing, but it sounds like you have other things to check as well.

Lizard928

Nick, please check your PMs.