911sc Won't Start

vdub117 · 10-21-2010, 10:46 AM

I have an 82 911sc that I just finished putting back together, and now it won't start. Originally one of the rubber sleeves on the intake manifold blew out, so I did a partial drop of the motor, removed the entire cis assembly, and replaced the rubber sleeves. Now that everything is reassembled, and the motor strapped back in, it is cranking but won't turn over.

I removed one of the spark plug wires, and held a screwdriver to it while my wife cranked the car over, and saw no spark, so I would assume my problem is something electrical.

I have replaced the starter, distributor, spark plugs and wires, and alternator over the past two years or so...

Any ideas what my problem might be? Is there something I might have bumped loose, or reconnected the wrong way when taking the intake off and on?

Thanks in advance!

Roby466 · Roby466's Garage

Easy stuff first
Did you double check the plug on the left side of the engine compartment? It may have been pulled partly.
The fuses in there behind the plastic CDI panel could be burnt?
Good luck

vdub117 · 10-21-2010, 11:36 AM

Do you mean the 10-pin plug? I've double checked that one, and it still just cranks...

vdub117 · 10-21-2010, 12:16 PM

Ok, so I was way off before. I checked the spark again, and have no problem there after all. My next step was to disconnect one of the fuel lines, and with the end that connects to the injector dumping into a water bottle, crank again. No fuel. So rather than electrical issue, it looks like I'm not getting any fuel.

1982911SCTarga · 10-21-2010, 12:34 PM

Graham, with the air filter cover and filter off, turn the key to the "on" position and gently lift the air sensor arm inside the airbox. If you don't hear the fuel injectors singing, then your fuel pump isn't running as it should during start-up mode. Don't hold the sensor arm up any longer than you need to confirm whether or not your fuel pump is running, otherwise you may create a hydraulic-lock situation.

Brian

vdub117 · 10-21-2010, 12:46 PM

Thanks Brian, that's definitely the problem.

Now my question is, would the fuel pump not be working because of something I neglected to reconnect?

It was working fine, before I tore into everything, so would it have somehow gone bad, or did I just miss something?

1982911SCTarga · 10-21-2010, 12:53 PM

Graham, yes, carefully check behind and below the rubber boot that connects the air flow sensor plate to the throttle body. There's an electrical connection behind the air sensor plate assembly that goes to ground when the sensor plate is at rest that shuts off the fuel pump.

You can also just jump your fuel pump at the relay panel in the front trunk (the red relay). This procedure should be documented somewhere on here, and it's also documented in the Bentley book and other sources.

Brian

Scott R · Scott R's Garage

When you find the sensor plate plug you best re-trace the others as well. If for instance have the plug for the WUR or the AAR swapped onto the frequency valve you can get a fire. So you need to make sure the freq, valve, cold start and sensor plate are correct. The WUR and the AAR both get the same 12V source.

vdub117 · 10-22-2010, 06:15 AM

Well, I had to give up last night, because I ran out of light, and I'm at work now. The last post confused me a bit....

Quote:

Originally Posted by Scott R

make sure the freq, valve, cold start and sensor plate are correct.

There are three plugs on the back of the airbox. The one in the middle is a 3-prong connector, and the other two are 2-pronged. Now correct me if I'm wrong. The plug on the driver's side is the WUR, center plug is frequency valve, and passenger side is the AAR?

Just trying to get an idea of what might be a simple fix for this so I can try and get it running again when I get off work..

Thanks for all your help.

-Graham

1982911SCTarga · 10-22-2010, 06:51 AM

Graham, just go back and re-trace and check any of the electrical connections that you may have unplugged during your replacement of the intake boots. Do you have the red fuel pump relay in place in the panel in the front trunk?

Also, is your battery in good condition? It is possible to have a low voltage condition in which your starter will turn the engine over, but the fuel pump won't output enough to run the engine.

Brian

bourgeois911 · 10-22-2010, 07:46 AM

Also, check the fuel pump relay. I had to re-seat mine at one time and it's been fine since.

vdub117 · 11-02-2010, 11:21 AM

I've been too busy to work on my car, but today I took another look at it.
I tested the fuel pump and it's working fine, so it must be the wiring somewhere.
After testing continuity in the plugs on the back of the airbox I'm a little closer. Correct me if I'm wrong.

There are three plugs on the back of the 'box. The 2-prong plug on the passenger side runs to the AAR. The 3-prong plug in the center runs to the WUR. Right so far?

The 2-prong on the driver side however, I can't figure out to where it runs...

Any thoughts?

Scott R · Scott R's Garage

You're going to need to post the colors on those plugs. The WUR and AAR are brown/red white I don't know the others off the top of my head.

vdub117 · 11-02-2010, 08:12 PM

The PO must have had to change the switches because I have no brown red or white plugs.... On the back of the airbox the two outside plugs are blue 2-prong connectors, and the center plug is black. The center plug runs to the driver side of the bay to the WUR ( i believe) which has a grey 2-prong connector on it. The blue plug on the passenger side runs out to the AAR connected to the fifth cylinder intake tube, and the plug there is black.

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by vdub117

The PO must have had to change the switches because I have no brown red or white plugs.... On the back of the airbox the two outside plugs are blue 2-prong connectors, and the center plug is black. The center plug runs to the driver side of the bay to the WUR ( i believe) which has a grey 2-prong connector on it. The blue plug on the passenger side runs out to the AAR connected to the fifth cylinder intake tube, and the plug there is black.

vdub117,

What Scott was referring about the 'brown & red/white' color refers to the wires' color not the color of the plugs. At the back side of the engine, you'll find four (4) electrical plugs namely:
1). CSV (yellow & red/black wires).
2). AFS contact switch (brown & brown/black wires).
3). FV (red/black & red/black).
4). Throttle body switch (this one is totally different from the above three (3).

The above three (3) electrical plugs very similar and could be plugged inadvertently at the wrong connection. Physical inspection would show or confirm if the you have the correct plug connection at each individual point.

Tony