1981 911 SC engine cutting out when warm

haveacamper · 04-10-2010, 11:49 AM

Hi guys,

I'm new to the site and have a problem with my 1981 911 SC 3.0L. in short, whne i start the engine from cold it fires up and idles fine, but after a while it splutters and cuts out. then i cant start it again until its cold.

i've put the original thread in the vw/porsche forum as the engine is part of a conversion i'm doing

http://forums.pelicanparts.com/vw-porsche-conversion-tech-forum/536047-1981-911-sc-engine-cutting-out-when-warm.html

your expertise in solving this problem would be much appreciated

Drisump · Drisump's Garage

Sounds like maybe the ignition timing is out of whack. Could be quite a few other things but thats the simplest.

haveacamper · 04-10-2010, 12:29 PM

the engine was bought off a guy who had it in his camper and i saw it running well. i bought it off him about 14months ago and has been sat not run for about 14months since.

i thought it may have been the warm up air regulation circuit

NaFe

rcaradimos · 04-10-2010, 01:23 PM

rule this out: Head Temperature Sensor Replacement

haveacamper · 04-10-2010, 01:30 PM

the worrying thing is, i cant remember ever seeing this on the engine, and i am pretty sure that i havent wired one up - not intensionally anyway. i'll have to check this

NaFe

vash · vash's Garage

not so sure there is a head temp sensor on an SC.

i'll punt...i bet it is the mixture.

mca · 04-10-2010, 03:58 PM

I'll suggest CDI.

rcaradimos · 04-10-2010, 04:10 PM

Quote:

Originally Posted by vash

not so sure there is a head temp sensor on an SC.

i'll punt...i bet it is the mixture.

your right, my bad

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by haveacamper

Hi guys,

I'm new to the site and have a problem with my 1981 911 SC 3.0L. in short, whne i start the engine from cold it fires up and idles fine, but after a while it splutters and cuts out. then i cant start it again until its cold.

i've put the original thread in the vw/porsche forum as the engine is part of a conversion i'm doing

http://forums.pelicanparts.com/vw-porsche-conversion-tech-forum/536047-1981-911-sc-engine-cutting-out-when-warm.html

your expertise in solving this problem would be much appreciated

Could you tell us more about the 3.0 liter engine? Is it a CIS or carb engine?

Tony

haveacamper · 04-11-2010, 09:22 AM

The engine is a CIS engine that was in a camper. I saw the engine running when it was in the camper and it ran fine. As I've been carrying out a complete resto on my bus its taken me 14months to get to a point of running the engine. I've rewired the whole camper as the porsche wiring wasn't the best. The only bit of porsche wiring I haven't wired up is the cold enrichment start valve because I'm running a vw starter that doesn't have the ballast resistor like the porsche starter has.

The only things that I have changed since buying the engine is altering the idle screw on the throttle body. I can't see how the mixture would be wrong as the engine has been running and I haven't changed itm

Nafe

haveacamper · 04-11-2010, 11:22 PM

any ideas guys?

going to work on engine this evening. NaFe

T77911S · 04-12-2010, 03:04 AM

is there power to the warm up regulator (WUR)?
if if is starting without the cold start valve (CSV) then you may be very rich. why?
also check control pressures, cold and warm
was the O2 sensor used before? is all that wired back up if it was?

haveacamper · 04-12-2010, 04:03 AM

it is starting without the CSV but i think that was because the idle screw was quite far out - 1500-1800rpm. when i put on ignition live (15) i get a voltage across the pins. i wonder if mt WUR is seized? i disconnected the WUR when it was cold and looked down it to see a half moon aperture. i then connected the wires to it and turned the ignition on, but couldnt see the WUR aperture closing up! how slow does this close?

there isnt an 02 sensor with the engine

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by haveacamper

it is starting without the CSV but i think that was because the idle screw was quite far out - 1500-1800rpm. when i put on ignition live (15) i get a voltage across the pins. i wonder if mt WUR is seized? i disconnected the WUR when it was cold and looked down it to see a half moon aperture. i then connected the wires to it and turned the ignition on, but couldnt see the WUR aperture closing up! how slow does this close?

there isnt an 02 sensor with the engine

Nafe,

The CIS component that you have been inspecting is not the WUR (warm-up regulator). It's called AAR (auxiliary air regulator). WUR is located between intake runners #1 & #3. While the AAR is located between intake runners #4 & #6. You need a fuel injection fuel pressure gauge to effectively do a meaningful investigation. Otherwise, a lot of guess work will be involved in trying to find and solve your current problem/s.

You could wire the yellow wire for the CSV (cold start valve) directly to terminal #50 (ignition switch). This terminal gets power only when you crank to start the engine. What pins are you talking about? BTW, 1500 - 1800 RPM (cold) is not really high for 911 engines when they are starting cold. Warm idle is about 950 RPM +/- (50).

Keep us posted.

Tony

haveacamper · 11:02 PM

Thanks for clearing that up Tony,
I was down working on the engine yesterday and I have a little more information for you all.

i took the AAR out of the curcuit and tested the resistance as the porsche book i have indicates - it read 32.4Ohms (approx the 33Ohms detailed in book. before giving the AAR a power supply i looked down to check it was open. It was only partly open - should I be able to see straight through this rather than see a partially closed aperture.

I then connected the AAR directly to the battery to check whether the air regulator closed up. the AAR proceeded to close right up - good news!

i then set about putting jubilee clips on all hoses as this air circuit didnt have any jubilee clips on them from the previous owner.

as i run the engine it fired up and was running at approx 2000rpm (cold). as the engine warmed up the engine rpm started to slowly rise to about 2500rpm before slowly creeping back down to 2000rpm and then further to 1500rpm. However, then the rpm started to drop off at a quicker rate and then die on me.

BUT....since i put the jubilee clips on the, engine would fire back up - which it wouldnt do last time. when i did fire it up the engine would run for a shorter period of time follwing a similar sequence to the one described above.

i tried this several times but i will say that the engine definitely started after priming - it sometimes would just crank and not fire if it didnt get a prime first, even when warm.

Since putting the jubilee clips on the AAR and the AAV(Auxillary Air Valve i think the engine is running for longer and i can start the engine again after it dies which i couldnt do before. I just wondered whether having an air leak in this system would cause the engine to die when warming up?

thanks for all of your help

NaFe

lettera32 · 04-12-2010, 11:01 PM

With my '75 it was the CDI. Coil was way hot, also replaced.

haveacamper · 04-12-2010, 11:18 PM

Quote:

Originally Posted by lettera32

With my '75 it was the CDI. Coil was way hot, also replaced.

I presume you had similar symptoms to what i have been describing?

sorry to sound stupid but do you mean CDI?

my coil was pretty hot after running, but coils generally get warm when running

NaFe

crashmy911 · 04-13-2010, 01:11 AM

Note to self. If see engine in camper leave it there!!!!!!

haveacamper · 04-13-2010, 01:31 AM

Quote:

Originally Posted by crashmy911

Note to self. If see engine in camper leave it there!!!!!!

Thanks for your help!

T77911S · 04-13-2010, 03:54 AM

its not the CD.

you HAVE to verify the control pressures.
you HAVE to verify voltage to WUR.
and you HAVE to fix the air leaks.

you also need to check the mixture, after the steps above. wire in the CSV as tony said.

what about the O2 circuit. was that used before?

starting cold with air leaks and no CSV???