81 SC died and will turn over & fire but not start

HDBrown · 02-23-2007, 08:05 PM

I was pulling out onto a secondary road with a cold engine and when I gave it a little gas the engine gasped and died. That was 12 hours ago and it still won't start. After sitting for a while, when I try to start it (it will turn over and doesn't make any odd noises) it will fire very briefly then die. I feel like this car is very slow to warm up but am not really familiar enough with the car to have an opinion.

Its my first SC, I've owned it for 2 weeks. 134k miles with an engine that was completely gone through 12k miles ago. The fuel relay has been replaced before. Plugs, wires etc are relatively new. Thanks!

1982 911 Targa · 02-23-2007, 08:16 PM

Sounds like it isnt getting any fuel to keep it running after it briefly starts. See if you can hear the fuel relay clicking when you turn the key. will need someone else in the front compartment to listen. That could be your problem or it could be the fuel pump its self.

Those are my guesses, wait for someone more knowledgeable to add more things that could be wrong. I am new to this too.

HarryD · 02-23-2007, 10:17 PM

Sounds like fuel starvation. Could be clogged fuel filter, partial blockage at discharge from fuel tank, or a kink in one of the fuel lines between the fuel tank and the engine.

VA911 · 02-23-2007, 10:22 PM

could also have backfired in the air box.
Hope you havent blown your airbox

HDBrown · 02-24-2007, 03:24 AM

I have the popoff valve update, but there was a kind of "poof" right when it quit.

When I turn the key to the on position, I hear a relay click once in the fuse box - I assume that is the fuel pump relay.

The fuel filter was replaced july '06 and the car has less than 1000 miles since then.

I'm thinking the problem is something I initiated since it went "poof" when I gave it gas. I think I'd heard it backfire once before when the engine was cold and this did not sound quite as pronounced. I gave the engine a quick lookaround and did not see anything disconnected - it is a squeeky clean engine so connections in plain sight are pretty evident.

This happened to the guys conducting the state inspection on the car, but they let it sit in their shop for a few hours and it started without any corrective action.

jeffrey2 · jeffrey2's Garage

You may have rust in the gas tank; there is a screen that catches all of the rust and can literally choke your engine. I had that problem with my last 911; it would idle, but anything else, it would choke, whease and gasp.

BobTucker · 06:09 AM

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HDBrown · 02-24-2007, 05:10 AM

It Started! I took off the air filter and tried to start it again. It fired but did not start, so to try something different, I put the gas pedal on the floor and cranked it. With a giant cloud of blue smoke it started but would not idle at first so I kept my foot on the gas. It ran very roughly this way for about 30 seconds - the blue smoke continued. Then it seemed like the cold start (warm up regulator?) kicked in and it started running very cleanly at 2000 rpm. I have noticed it takes it a long time to idle down when its cold outside, but it does eventually. Hmmm

BobTucker · 06:10 AM

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HDBrown · 02-24-2007, 06:23 AM

Bob and all - thanks so much for the advice. I'll continue to play with it. I'm happy it is running but since it has done this twice it definitely requires some attention before I get stranded in a tight spot somewhere. I'll keep you informed. Thanks again.

HarryD · 02-24-2007, 07:19 AM

My older CIS had similar symptoms (hard starting) that went away when I discovered that the power connector for my Cold Start Valve was disconnected.

Gunter · Gunter's Garage

Bob:
Read with interest your Tech Article, good stuff:

http://www.ncr-pca.org/tech/tech-cis.htm

The "Idle Speed Controller" you refer to is the Frequency Valve added to the K-Jetronic in 1980-83 with Lambda.

Auxillary Air Regulator (AAR) and Auxillary Air Valve (AAV) are two different components.
The AAR has a heater element that closes the valve as the engine warms up, it's open when cold for extra air during start-up.
The AAV is a vacuum-operated valve working in conjunction with the AAR.
AAR and AAV are often confused with one another.
There is also the non-adjustable Decel. Valve which looks like the AAV for years '80 to '83.
Before that, for '78-'79, the Decel. Valve was adjustable and looks quite different.
Every SC in the US was equipped with a AAR, AAV and Decel. Valve OEM stock.
The CIS is very reliable but it takes some studying to understand it.
That includes the various electrical components and switches.
Cheers.

Paulporsche · 02-24-2007, 09:57 AM

Sounds like your cold control pressures are too high, your mixture is too lean, or your AAR isn't keeping the revs up during warmup. Tell us some more. For example, how did the engine start from cold the day you describe. How did it act prior to the gasping and dying?

Lorenfb · 02:27 PM

"The AAV is a vacuum-operated valve working in conjunction with the AAR."

All three valves (AAR, AAV, DECEL) provide parallel vacuum sources
bypassing the throttle butterfly:

1. The AAR's function controls fast idle during warmup, i.e. a steady-state
idle affected by engine temp and time.
Problems:
a. Low idle at cold start - valve stuck (closed)
b. High idle at warm engine - valve stuck (open), or no 12 volts
2. The AAV's function provides additional air during starting (zero/low vacuum),
i.e. both cold & warm starting, causing a momentary fast idle.
Problems:
a. High idle - valve stuck (open)
b. No momentary fast idle at startup - valve stuck (closed)
3. The DECL's function is to control the rate of change of RPMs to prevent
idle undershoot and to reduce emissions (HCs) during decel.
Problems:
a. High idle - valve stuck (open)
b. Idle undershoot or engine dies on decel - no small vacuum line, stuck valve (closed)

Gunter · Gunter's Garage

Very well put, Loren.

HDBrown · 02-24-2007, 02:10 PM

Paul et al:

Thanks for all of the advice. I'm going to need to study this for a while to get my arms around it. I think I need to buy the Bentley SC manual as well.

Here are the symptoms - but I've only had the car 2 weeks so they could still be an anomoly.

When it is below freezing outside, the car starts immediately, with a belch of blue smoke if it has been sitting for more than a day. It idles for a less than 10 seconds at 900-1000 rpm, the the idle increases to approx. 2100 rpm. It will remain at this idle for as 20+ minutes, and may never idle back down to 900.

Twice it has died when being driven without an extensive warmup. Both times it was difficult to start afterward.

Based on the input I'm receiving, I am thinking it is a sticking valve in the AAR, but that is just a guess based on the education I'm receiving from this forum.

Lorenfb · 02-24-2007, 02:26 PM

"It will remain at this idle for as 20+ minutes, and may never idle back down to 900."

Most likely RELATED AAR valve.

"I am thinking it is a sticking valve in the AAR, but that is just a guess"

Or no +12 volts to valve. This power source also powers the WUR.

HDBrown · 02-24-2007, 05:23 PM

If the AAR was not getting 12 volts, would it still eventually idle down to normal idle, or would it remain stuck at 2100 rpm?

BobTucker · 06:10 AM

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Mysterytrain · 02-24-2007, 07:40 PM

Bob..you need to go back and correct your posts...its the AAR not the AAV!
Maybe, in the heat of summer the AAR would get hot enough without 12 volts to close..but there is no way it will close with 12 volts in the winter. The AAR might be the cause of your high idle..but something else is amuck with the no start.
AAR Revisited

When warm my AAR closes, not sure what the AAV is doing - (look for lots of pics)