sc runs for 30 seconds...and quits

jbiebl · 09-08-2010, 03:53 PM

My 1982 911 sc starts and runs for ~30 seconds and then dies. Jumpstarting doesn't work then either. After a wait of about 1-2 hours, it all happens again. Happened 3x today.

3-4 months ago, I had a hot start problem, and, using this forum, it was fixed by replacing the inline filter at the fuel pump. The fuel filter was changed and the accumulator checked at the same time.

It seems to me like its running out of fuel (maybe using what's in the lines only??).

It has also been sitting outside for a week (a visiting friends RV has my garage blocked off) so has been getting wet, if that could effect anything.

Fuel pump, clogged lines, or ???

Thanks
jb

MotoSook · 09-08-2010, 04:18 PM

I would check fuel condition just because you didn't mention if it's old fuel, or how regular the car is fueled up. I don't think that's your problem though.

Your car cuts out after it warms up (30 secs in the summer may be enough, but you give nontemperature information). Its likely starving for fuel at that point because 1) your AAR is wide open and your WUR can't enrich fast enough 2) your WUR is not working correctly

Best to check fuel pressures.

After it it dies can you lift up on on the air meter to squirt fuel into the engine? Do'the injectors scream?

Does it operate normally for the first 30 seconds? Are you able to increase engine speed with hesitation? Can you drive the car as soon as you start it to apply power to the tranny? Will it die under power?

Obviously, you need to provide more information if you expect good advice, as oppose to 30 Internet suffers guessing at the problem.

JJ 911SC · JJ 911SC's Garage

... Change the fuel filter.

jbiebl · 09-08-2010, 04:32 PM

I have ~100 miles on this tank, and about 1/4 remains. It ran fine until today.

This happens when the car is cold (I can't get far enough to warm it up)

It revs fine and drives away fine...for 30 secs, and then dies.

I don't know how to check fuel press.

I need to go figure out what an AAR and WUR are, and figure out where the air meter is.

Thanks
jb

jbiebl · 09-08-2010, 04:34 PM

The fuel filter was changed ~3 monthes ago (maybe 1000 miles).

Is this normal?

thanks
jb

JJ 911SC · JJ 911SC's Garage

Quote:

Originally Posted by jbiebl

I have ~100 miles on this tank, and about 1/4 remains. It ran fine until today.

This happens when the car is cold (I can't get far enough to warm it up)

It revs fine and drives away fine...for 30 secs, and then dies.

I don't know how to check fuel press.

I need to go figure out what an AAR and WUR are, and figure out where the air meter is.
Thanks
jb

Don't worry somebody will take you there.

Is this the first time you took it down to 1/4 tank but more importantly if you got 100 miles on the tank and 1/4 of the tank left, if it was full when you started that would give you about 133 miles per tank???

Go over everything you did since you last fill up and post it.

jbiebl · 09-08-2010, 05:35 PM

I probably didn't fill it up, being in a hurry maybe. Can't exactly remember. I usually put ~$30 in, and drive until the light comes on.

It has been sitting outside without being started for about 4 days or so. It usually lives inside. And it did rain overnite here, for the first time since it went out.

It's been driven ~5 days a week all summer w/no prob, until this am.

I've only looked in the index of 101 probs... and Haynes, but I didn't find refs to AAR, WUR and air meters. I'll spend more time this pm, when I have time.

Thanks again
jb

Flat6pac · 09-08-2010, 05:53 PM

You really need a set of guages to test the pressures across the injection. You will find the WUR, warm up regulator, is active across the system all the time, not just warming up. The guages will check pressure between the fuel distributor and the WUR
Bruce

MotoSook · 06:32 PM

It is possible for debris to break free at anytime if it is in there. A clogged filter usually does not behave like an on/off switch as you described.

The search feature is your friend. Search "cis fuel pressure" "cis primer" "cis souk"'"cis aar" cis wur". A fuel pressure tester can be purchased from JC Whitney for about $70 and the fuel control pressure-vs- temp curve for your SC can be found with a search.

I would concentrate on poor fuel quantity due to an imbalance caused by a bad AAR or WUR. The AAR reduce air into the engine as the engine warms up. At the same time the WUR reduces fuel by increasing the control pressure. Think of the two as an automatic choke. Because your driveability appears to be fine, do not mess with the AFR just yet. I think your CIS works fine when in warm up mode, but then the imbalance occurs once warm. The two components that influence this are the WUR and AAR.

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by jbiebl

I have ~100 miles on this tank, and about 1/4 remains. It ran fine until today.

This happens when the car is cold (I can't get far enough to warm it up)

It revs fine and drives away fine...for 30 secs, and then dies.

I don't know how to check fuel press.

I need to go figure out what an AAR and WUR are, and figure out where the air meter is.

Thanks
jb

JB,

Unless you are able to check your control and system pressures, understand how the different CIS components work, and know how to jump start the fuel pump, which I doubt you know at this point only gives you a few options to choose. First find someone to do test for you or bring the car to a shop.

But if you are interested and determined to learn the simple tests for diagnosing your problem/s, there are lots of guys in this forum to assist you. All they would need from you are some basic information like fuel pressures, flow rates, ignition or sparks, etc. The ECU and relays are also additional things to investigate.

Since you are able to run the engine for 30 seconds, the ignition system is good for now. Two (2) things come to mind: fuel pressures and vacuum leak. Fuel pressures are easy to check but would need a pressure gauge. In lieu of a pressure gauge, you could use the delivery flow rate. But needs to know how to run the FP manually. Ignore vacuum test for the moment.

Do your homework and read some threads in this forum that discuss WUR, control and system pressures. Borrow a set of fuel injection pressure gauge kit and we'll walk you thru the procedures. Keep us posted.

Tony

jbiebl · 09-09-2010, 11:13 AM

This am, I sat in the driveway until it wanted to die, and 'barely' was able to keep it running this time. It coughed and backfired for about 10 seconds, trying to quit, and then ran smoothly. I waited a bit, revving it gently, and then took it out for a drive...no problems whatsoever. It sat for a coupla hours, and then it started and drove perfectly again.

So...it seems 'fixed', but what could it have been, (or that could pop up again) with symptoms like these?

Thanks again for any help
jb

psalt · 09-09-2010, 02:46 PM

jb,

My experience is that 911 fuel gauges/senders are very inaccurate below 1/4 tank and sometimes the warning light comes on as it stalls. I've had this happen on several cars over 30 years, they were just out of fuel. My advice is to fill the tank with fresh fuel and note how much it takes. Then drive the car more often, it will thank you.