Mysterious CIS Problem - Solved and OMG Its a New Day Baby!

94teener · 04-11-2009, 02:31 PM

Hi all - 2.7 CIS - recent tune-up gone bad (see my previous post) -

Found that the distributor advance plate was frozen solid - cleaned it up and got it moving freely.

Re-installed Pertronix ignitor. Re-check all the spark plugs and the valves (what a PIA!).

Hope for the best and start 'er up - nope, same issues, poping and snorting at idle, erratic idle, rough running at speed, etc. Crap! Time for a coffee and a ponder....wife says "Time to take it to Alan (mechanic)..."

But I don't give up that easy - persisitence is half the battle of good wrenching...the other half is knowledge and and the third half is luck...;-)

Just about to call it day....but just for giggles I removed the plug from the vacuum hose (this is the hose that fits into the blocked-off vacuum advance nipple) - hey, whats this then? The engine revs way up but nice and smooth - okay maybe we got something here - turn down the idle to 950 - hey....guess what? Immediate improvement! Wait....really? Rev 'er up a bit - accelerates nicely, and very smooth, yep comes right down to idle speed and stays steady - am I dreaming?

(Now picture a crazy man running around the driveway yelling and leaping in the air!)

This is too good to be true - so, take 'er for a test drive and yep its true - I got my baby back - what a sheer delight to have a smoothly running, non-backfiring, non-pinging 911 that idles smooth at stop signs and accelerates briskly and cleanly, runs cooler and quieter.

I can not remember the car running this fine in the 13 years I've owned it.

What did unplugging this hose do? I believe that hose is attached to either the AAR or the ThermoValve - it is a small black round unit with 2 hoses (1 of those is the hose in question - the other runs into the manifold) and an electric connector on the other side - it is mounted to the left and just ahead of the WUR - above #3 cylinder - this unit must be faulty - because all the manuals always state that the vaucuum hose from the dist. should be plugged. For now, unless I am causing any damage I am going to be enjoying my groovy little Porsche....

James Brown · James Brown's Garage

sweet! that shouldn't hurt anything. and if it runs good, who cares!!!! go for it

jjrowe · 04-11-2009, 03:27 PM

Do you have a picture because I have no idea what you are talking about? Perhaps one of us can help determine how/why the thing you unplugged helped.

Jesse
76 911S

ossiblue · 05:36 PM

Quote:

Originally Posted by jjrowe

Do you have a picture because I have no idea what you are talking about? Perhaps one of us can help determine how/why the thing you unplugged helped.

Jesse
76 911S

Sounds like he may be talking about the ERG valve. It is small, round and has two small hoses--one to the throttle body and the other to the distributor, which he said was plugged. It's the circled part in the diagram, below:

If that's the case, the lousy running could be from a faulty ERG valve, and the improved running may be the result of a vacuum leak now that the hose is unplugged, though that's just a guess.

jjrowe · 04-11-2009, 05:36 PM

I was thinking EGR as well but he said it was on the left of the motor just ahead of the WUR and has an electrical connection. The EGR valve is on the right and has no electrical connector. Maybe the aux air valve, but it is also on the right and does have an electrical connector but has two ~1/2" hoses going in and out. If one of those hose was unplugged and it ran well then there is a very serious vacuum problem. Can't think of anything else that could have the hoses and an elec. connector.

Jesse
76 911S

ossiblue · 05:46 PM

Quote:

Originally Posted by jjrowe

I was thinking EGR as well but he said it was on the left of the motor just ahead of the WUR and has an electrical connection. The EGR valve is on the right and has no electrical connector. Maybe the aux air valve, but it is also on the right and does have an electrical connector but has two ~1/2" hoses going in and out. If one of those hose was unplugged and it ran well then there is a very serious vacuum problem. Can't think of anything else that could have the hoses and an elec. connector.

Jesse
76 911S

Agreed, he describes it in the wrong place for the ERG and the electrical connection too, but what else has such small hoses and is connected to the distributor advance?

Unless...the plugged vacuum line was to the WUR and not the distributor! Then it's most likely the thermovalve. Right location and electrical connection. Unplugging the hose would cause a vacuum leak, I suspect. Hope he can clarify a bit

94teener · 04-11-2009, 08:40 PM

Hi all - this is '77 2.7 CIS - stock, except for Pertronix ignitor.

I tried to take a pic of the suspect but the lighting was not good enough to show it -

The previously plugged hose from the dist. vacuum unit runs to the front and splits into 2 at a tee junction - 1 of those goes to the suspect unit and the other branches off to the manifold, the other hose from the suspect goes into the top of the control pressure reg (WUR). There is an electrical connector on the backside away from the side with the 2 hoses.

The unit is located hanging to a bracket that also mounts the aux. heater blower on my model towards the left front - just above and inboard of cyl #3. It is a small black round flat body - about 1.5 -2" in diameter.

If it isn't an EGR (mine is not a '78 and also I do not believe it was a CA. car) then is it the thermal valve?

Maybe this info will also help - later I went out to start it again to see what it would do when cold - it rev'ed higher than I would like (3000 rpm) for about 30 seconds and then the idle came down in stages every 10 seconds or so until it hit right around 1000 - this was before it ever got up to operating temp. and I didn't leave it running much longer. I assume this means the thermal valve is operating okay?

Just to reiterate - the plugged vacuum line was originally attached to the dist. vacuum unit via a block off plug - this model has no vaccum to the dist. unit. Timing is done with this in place according to the manual.

I very much appreciate all your help.

snbush67 · snbush67's Garage

It's a thermalvalve, must have been a late 77 CIS.

It probably came apart and somebody put it back together wrong.

Check out my thread;

My Thermal Valve came apart and I need help putting it back together