Help!! What have I done to my SC??

Kirk911SC · 04-13-2005, 03:45 AM

Last night I installed new Bilstein rear shocks in my SC.

It went realtively smoothly - the only problem being the top nut on the passenger side.

Also, while I was in there I removed the cruise control servo, as it's been non-operational for years. One thing I noticed was that there was only one large hose attached (large one, which I believe is a vent line). I couldn't find the small hose.

After installing them I took the car out for a drive to check out the feel of the new shocks (feel great, much better than my old Boge shocks).

During the drive the car bucked a couple of times with the odd backfire. This was only during acceleration, not cruising. Acceleration felt a little choppy too. Otherwise the car started normally, and idled fine. The car has never done this before.

This morning I started my drive to work in the 911 and about 3 minutes in (and still close to my house) the car practically died. Car will idle, but barely responds to throttle. I was able to limp it home with it backfiring constantly and the rpms never going above 2000.

What have I done??? Have I knocked a vacuum line off somewhere? I couldn't see anything obvious.

Car is a daily driver, had an oil change 3 days ago, and new air filter, fuel filter, fan belt, spark plugs, cap and rotor about 2000 km ago.

Ideas?

Kirk

johnsjmc · 04-13-2005, 04:24 AM

Make sure any hose removed with the cruise control servo is plugged at it,s source.Check for other obvious faults. I had something similar and I found I had knocked one of the distributer cap holddowns off allowing the cap to wobble.

Kirk911SC · 04-13-2005, 04:34 AM

I plugged the large hose that was attached to the servo, but after searching on these forums I believe that line is just a vent to atmosphere. I couldn't find the second smaller vacuum hose that is supposed to be attached to the servo, and I don't remember ever seeing it in there in the past. Where does it go from the servo?

Could I have knocked another hose off of the back of the throttle body when I was wrenching on the shock mounting bolt? Would that cause these symptoms? The car was running great prior to this.

Kirk

Kirk911SC · 04-13-2005, 05:17 AM

Any other ideas?

spydr32000 · 04-13-2005, 05:21 AM

Kirk, have you checked that you have not bumped any wiring around the CDI unit, coil or distributor as your problem sounds like an electrical one. Carefully look around the wiring plugs for breaks in the wires!
Regards Mike

Rot 911 · 04-13-2005, 05:21 AM

Sure sounds like a vacuum leak and considering there is a vacuum hose to the servo, you need to find and plug it.

Kirk911SC · 04-13-2005, 05:29 AM

Nothing looked out of place around the distributor or CDI unit. The coil is a relatively new (8 months) MSD Blaster (high-vibration) coil. I had three "made in Brazil" Bosch coils go bad on me in the last 2 years. All three leaked oil out the top. The MSD is epoxy internally.

I do have a spare brand new Bosch coil I could swap to check the coil condition.

Cap and rotor and plugs (W5DC) are very new (~2000 km). Wires are 1 year old Magnecores.

Kirk

Kirk911SC · 04-13-2005, 05:32 AM

Would a vacuum leak cause these symptoms? Almost like there is no timing advance, or the A/F is leaning out.

ruf-porsche · ruf-porsche's Garage

Advance timing work on vacuum. Vacuum leak means no advance timing.

Kirk911SC · 04-13-2005, 05:53 AM

That's what I thought, but what about centrifugal advance? Would a vacuum leak not also change the idle (increase)?

Kirk911SC · 04-13-2005, 06:44 AM

Would a cracked airbox or an unseated pop-off valve show these symptoms? I haven't check the airbox yet.

bigchillcar · bigchillcar's Garage

have you tried the 'ol method of spraying car cleaner around your airbox, wires, hoses, etc. to look for the leak? listen for the idle to increase when the spray finds the leak..
ryan

Kirk911SC · 04-13-2005, 07:02 AM

I'll be trying that tonight, and checking the pop-off, and airbox for leaks/cracks.

Funny how this all happened after changing shocks of all things!

osidak · 04-13-2005, 07:31 AM

Sounds like a cracked airbox. Since you have a blow off I would look to make sure the back fire did not break the seal on it.

sammyg2 · 04-13-2005, 11:29 AM

Get it running at idle (warm if possible) and gently lift the air flow sensor plate. if the idle improves, you are idling lean. If it doesn't, pull the oil filler cap off. The idle should stumble. If the engine dies, you are too lean. If it idles better, you are too rich.
That won't solve your problem but it will give you an idea of what to look for.
My bet is you have a hose either cracked or lose.
I would also check the connectors for the cold start injector and throttle position sensor, both are on the back (front of car) of the throttle body.

Kirk911SC · 04-13-2005, 11:47 AM

I did disconnect the two oil breather hoses and move them around to access the shock top nut. Maybe I pushed something loose on the throttle body.

I'm itching to take a look at it............still at the office.

Kirk911SC · 04-13-2005, 03:32 PM

Okay, here's a bit of an update.

I've started checking my car to see if I can find any problems.

- Airbox looks good, no cracks or backed out screws.
- Pop-off valve still in place and moves freely.
- Checked electrical connections - no visible problems.
- Car starts right up and into a fast idle - like normal
- Checked vacuum to distributor - blue hose on right has vacuum and idle speed increases if pinched. Black hose on left has no vacuum and no apparent effect with removal
- Don't see any evidence of the small vacuum line to the now removed cruise servo
- Car will rev freely to redline after starting, but I haven't tried driving it yet
- Moved sensor plate and idle got rough.
- Removed oil cap and idle dipped very slightly.

Ideas??? Please??

Kirk

Kirk911SC · 04-15-2005, 03:45 AM

Well the verdict is in.

WUR was bad - showed cold control pressure of 65 psi, system pressure 75 psi, and rest pressure 22 psi

Replaced the WUR with a new one last night and the car runs MUCH better. Mixture was still very lean (backfiring with heavy throttle)......richened it up but it still seems a bit off. There is hesitation on acceleration, especially with a lot of throttle (no backfiring though).

Still needs to be richer?

Car starts fine, and idles at about 1000 rpm. Drove it to work today without any real issues other than having to ease up to speed.

Kirk

Kirk911SC · 04-15-2005, 06:20 AM

Anyone?

Hladun · 04-15-2005, 07:07 AM

What value was wrong with the WUR readings? Changing WUR's is adjusting richness the hard (and expensive) way.