Manning

Well, yet another odd problem. I don't seem to recall this happening last summer or ever before, but whenever I am driving in stop and go traffic, and it gets hot enough for the fans to cut on (and thermostat to open) the car kind of shudders. Not just a little either, but enough to be quite noticeable. I mean really, like all the girls want to ride in my car now <img border="0" title="" alt="[Wink]" src="wink.gif" />

Here are the electrical changes I have made since last summer:

- new high output alternator from Prospeed
- Iceshark lighting harness upgrade, with auxilary ground wire
- Iceshark battery ground wire upgrade

I cannot really imagine the items above have anything to do with this. And I seem to be getting full voltage with only a slight drop when the fans do cut on.

Nothing else mechanical or electical has been changed. Maybe something is wearing out?

Oh, the waterpump and belts are a maybe 18 months old.

emilysgranny

Mike ; recheck your grounds and then the alt belt.Watch your volts when you turn on the lights and see if it drops and comes back.

Manning

Hey Granny,

Where the heck have you been by the way? You only seem to make an appearance every now and again.

I checked the major grounds a little earlier and everything seems kosher. Voltage drops a little when I cut on the lights (Iceshark light cannons) but comes right back up. It doesn't drop at all if I only turn on the parking lights. Voltage comes up right after the fans cut off too.

I'll have to watch more closely and see how much the voltage is dropping when the fans cut on. Could the fan motors be close to cooked and be drawing too much? Would this cause shuddering?

And one more thing, I hate wireless keyboards.

emilysgranny

I suspect a bad connection somewhere.Yes it could .Did you ever drive a car when the alt was bad and it ran down the bat.The car bucks for awhile and then back fires.Try runing the car without the lites and see if it does it when it is hot then.It maybe as simple as a bad bat connection.Hopefully it is not a frayed harness down by the rad support.

IceShark

Michael,

Remember your fond alternator purchase experience with Prospeed?

I don't know exactly what he was doing to up the amperage output to 145 amps or how well it was done. But it sure sounds like the alternator is sucking horsepower like crazy when you load the electrical draw up.

Since your voltage is coming back up after a bit that seems like it may be it. And if the fans' motors are getting worn and binding they are going to draw WAY more current trying to start up. The stuff you got from me should have no effect on this problem, EXCEPT the 90/100 watt bulbs are adding a little over 5 amps, for the pair, extra current draw over OEM (for a total headlight draw of something under 15 amps for the pair) when they are lit. That shouldn't cause any problem for your alternator. But add everything up and the fans may be really taxing the alt when they kick in.

Watch the Tach when this happpens and see if revs dip. And like Granny said look at the belts while it happens. If you have loose mountings for the alternator it will shake when you put a quick big load on it. You should see this show up in the belt action.

emilysgranny

Michael ; listen to Ice as he designed the system for your lights. I would also check the mounting ears on the alternator as they are notorius for breaking or the bolts loosening and hence the loose belt possibility.

IceShark

Granny, I didn't know the alternator mounting ears were notorious for snapping off or bolts loosening. That would certainly raise them up on the possible problem list. I don't know how much alternator shaking would be absorbed by the motor mounts and still give Michael's girlfriends good feelings. <img border="0" title="" alt="[Wink]" src="wink.gif" />

But it would certainly cause shaking when the fan load kicked in. Maybe it is a combo of that and the idle RPMs dropping down.

emilysgranny

Ice; i'm sorry ,I should have said the porsche alts . I am not familiar with prospeed.And I agree ,the lowering idle speed could easily be the reason for the engine shaking.But my concern is the reason for the engine speed to drop.I think you have it nailed as the belt being to loose to supply the draw of the fans kicking in or the fan motors are on their way out.Oh by the way ,keep up your entrepreneurial endeavors.

IceShark

Granny, Prospeed sells, or sold, the Bosch alternator that in stock trim is rated at 115 amps in an uprated form that was rated at 140 or 145 amps. Michael got one of these from Prospeed.

I don't know who was actually doing the rebuild or what exactly they were doing. My guess would be that they were taking old cores and rebuilding them with a different stator, rectifier, voltage regulator, bearings, etc.

Anyway, I think we got Michael on the right track to narrow down the problem. Something on his motor is going fall apart sooner or later with this violent shaking he has.

Manning

Hey,

Well, here is a little more detail.

- The voltage drops by about half a volt when I turn on the headlights, but only as the motor lifts the lights up. It then goes right back to normal once the lift motor stops, which is a little over 14 volts.

- The car runs just fine, smooth as usual, until the fans cut on. When that happens I get vibration, but no drop in engine idle.

- Nothing else seems to cause the vibration, I can have the headlights, blower, wipers and stereo on at the same time and the car runs fine (did that last night). But, if the fans come on, either by themselves or in combo with other electrical accessories, the car shudders.

- Belt is adjusted just fine and the ears look fine. I'll keep my eye on those though.

Also, once the fans cut off, everything seems to go back to normal. And, I haven't experienced this problem at all in cooler weather (since the fans never cut on)

Does that seem to narrow it down a bit? I'm thinking one or both fans. Switches maybe?

Also, from what Mike at Prospeed told me, the folks who he had build the alternators, local to his area since he supposedly could go pick them up, would stuff the guts from an alternator from a big 7 series BMW into the alternator case for a 951.

IceShark

Let's make this clear. Does it just vibrate for a few seconds after the radiator fans kick in or the whole time they are on?

I'm taking an educated guess but I would say each of the fans draw about 20 amps, maybe a bit less. So you should be able to turn on everything, including rear defroster and hit both window switches and draw way more than those fans. If this problem is related to current draw you should get the vibration. If RPMs are not dropping that makes this even stranger.

Turn off all electrical loads and watch the engine and alt for vibration when the fans finally kick in. If it starts shaking, who knows what the deal is because it shouldn't be related to current draw and strain on the alternator. Unless the fans are drawing way more than rated though you should blow the fan fuse if that was the case.

That leaves the fans themselves. Is one missing a blade and therefore out of balance? Are the fans loose, not bolted down tight? I would be sort of surprised they could shake the whole car this bad but maybe they can.

That is my 2 cents.

SidViscous

"I hate wireless keyboards."

Get rid of it. Unless you r enjoy broadcasting everything yo type.

Hey ICE. Similar question. I'm having the headlight not closing issue. I replaced the realy, worked for like two days. Now when I shut off the ehadlights they go down further, but not all the way and there is this continuous clicking under the dash until I get them all the way down.

It's not one of the relays (Touched them all not clicking) in the relay box. It seems to be coming from DME steering shaft area. Is there a hidden relay on the early cars or sumtin?

Manning

Hey Sid, I'm not too worried about broadcasting to the world. Actually it is quite the opposite with the keyboard I have at home. I can't even move the receiver off the desk or I'll lose the signal.

Ice,

I'll watch on the way home, and if power is back on at the house and I can actually get in the garage I'll watch under the hood when this happens. Basically when the fans cut on the idle may drop a bit for a second, but then it seems to stablize back up to normal, yet still the engine shudders.

The only reason I brought up the ground straps is because I have heard of evil ground loops and not knowing much about electrical gremlins I thought there might be something funny happening there.

Oh yeah, did I bother to point out that the voltage drops a little more than 1 volt when the fans cut on?

Oh yeah, Sid, when I was installing my light kit I ran into something not entirely similar but close. I manually wound the lights open while the grounds were disconnected and the motor/relay just went crazy clicking. I don't think the switch was on or not. I know the key was not in the ignition switch. It was a few months ago, but I clearly remember the motor/relay clicking like crazy when the grounds were loose.

IceShark

Sid, I'm not real familiar with the early models but I think they did squirrel away a few as I recall someone saying. My CD unit broke so I can't pull up the wiring diagram off the manual.

Maybe someone else knows. Or you can go to the Porsche Dealer and see if they will let you take a look at and copy the relevant sections of the wiring diagram. I have a real snooty Porsche Dealer but the service guys let me copy away to my heart's content. Be warned, it is a pain to follow a current because they jump from page to page to page.

Michael, naw, there shouldn't be anything going on with the grounding.

However, if you have most everything off when the fans kick in and they drop you a whole volt that means they are *really* sucking current. So take a look-see at the motor and see if it starts to shake. Also take a look at the fuses and see what they are rated at.

SidViscous

Manning:

That's because you have a crap reciever, not everyone does . And the clicking you feel when doing it manually is the position sensors going hey the dash switch says it should be down, but it's partially up (system doesn't like partial) so it tries to do one or the other. Semi-normal. It's the clicking in the dash that's bugging me.

Ice:
I have the diagrams, and they are a pain to follow. Tis why I asked you . I was trying to hunt the relay down last night in the dark. When it stops raining I'll try to do it in the day.