Altitude change - mile high to sea level

calling911 · 12-12-2007, 03:51 AM

I moved from Denver to Charlotte, NC. I brought my 76 911s. It runs fine but how do I know if its lean? Do I just watch the cyl head temp? What should I watch for?

Is there an auto correction device present in the injection system?

tcar · 12-12-2007, 04:13 AM

The '76 S has CIS fuel injection and will correct for altitude.

calling911 · 12-12-2007, 04:17 AM

Quote:

Originally Posted by tcar

The '76 S has CIS fuel injection and will correct for altitude.

How? I'd like to test whatever corrects..

RoninLB · 12-12-2007, 04:18 AM

If mine

check timing and fuel mix. Note what spark plug heat range is installed and compare to stock install.

My old CIS install ran better with distributor vac canister hose disconnected and plugged. I was only running on mechanical advance and timing set to 35deg max at 6k rpm.

CIS is very altitude forgiving compared to carbs.

calling911 · 12-12-2007, 04:20 AM

Quote:

Originally Posted by RoninLB

If mine

check timing and fuel mix. Note what spark plug heat range is installed and compare to stock install.

My old CIS install ran better with distributor vac canister hose disconnected and plugged. I was only running on mechanical advance and timing set to 35deg max at 6k rpm.

CIS is very altitude forgiving compared to carbs.

Ya know, I noticed the vacum advance line is disconnected.. I just bought this car and need to investigate what has been done.

Grady Clay · 12-12-2007, 05:06 AM

Yes it does compensate for altitude. The sensor plate is a mass-air-flow device.

That said it is probably still too lean. You probably also have one step hotter spark plug and slightly advanced timing compared to normal sea-level settings. This is where a simple plug change, mixture setting and timing check will prevent any problem.

Colorado Pelican Zotman didn’t do this for the PCA Club Race in Texas a couple of years ago with disastrous consequences.

Best,
Grady

calling911 · 12-12-2007, 11:32 AM

Quote:

Originally Posted by Grady Clay

Yes it does compensate for altitude. The sensor plate is a mass-air-flow device.

That said it is probably still too lean. You probably also have one step hotter spark plug and slightly advanced timing compared to normal sea-level settings. This is where a simple plug change, mixture setting and timing check will prevent any problem.

Colorado Pelican Zotman didn’t do this for the PCA Club Race in Texas a couple of years ago with disastrous consequences.

Best,
Grady

I took it out for a 20 minute drive and it stayed at 210 or lower.. I'll watch the head temp.. its running pretty well cept down real low it stumbles and then takes off like a raped ape..

FYI racing is completely different than the street.. you can get away with much much more on the street.. but an advanced ignition matched with improper cooling equals melted parts.. I dont plan on taking this car to the race track this year.. maybe next year though.. in which case it will need a complete tune up and adjustment..

Now if I can just nail down the finese needed to not grind into 3rd.. she needs new syncros I think but with just the right clutch and speed it goes in just fine.. a double clutch always works but I am not good at remembering to double clutch..

SC-targa · 12-12-2007, 12:15 PM

Quote:

Originally Posted by calling911

FYI racing is completely different than the street..

I think Grady probably knows more about racing than you and I could ever learn. He was just giving you a tip about mixtures and ignition that you already understand.

Regards,

Jerry

tcar · 12:25 PM

Quote:

Originally Posted by calling911

Ya know, I noticed the vacum advance line is disconnected.. I just bought this car and need to investigate what has been done.

Make sure the VACUUM line is either hooked up or plugged.

You do NOT want an open vacuum line in the system.

Plug it even if you can't find where it goes (even a golf tee).

Post a pic for help on where it's suposed to hook up.

calling911 · 12:59 PM

Quote:

Originally Posted by tcar

Make sure the VACUUM line is either hooked up or plugged.

You do NOT want an open vacuum line in the system.

Plug it even if you can't find where it goes (even a golf tee).

Post a pic for help on where it's suposed to hook up.

I can't find the vacum hose at all.. perhaps someone could tell me where it originates. I am guessing my low rpm stumble might be due to the line disconnected from the distributor.. or maybe just needs a nice tune up..

Putting in a big order with Pelican right now!

I started racing a 84 VW and I now see this is the exact same injection system which I know inside and out! Sorry, I didn't realize this till I started looking close!

Grady Clay · 12-12-2007, 01:40 PM

“…its running pretty well cept down real low it stumbles and then takes off like a raped ape..”

This is a sign of lean running.
... or a high voltage ignition issue.

Best,
Grady

calling911 · 12-12-2007, 01:55 PM

Quote:

Originally Posted by Grady Clay

“…its running pretty well cept down real low it stumbles and then takes off like a raped ape..”

This is a sign of lean running.
... or a high voltage ignition issue.

Best,
Grady

I'll check the plugs. It happens cold so I doubt its a lean condition unless the cold start circuitry is messed up. At this age I would not doubt it if the fuel pressure regulator is no longer functioning correctly. I used to modify mine for racing (very tedious but the payoff is big!).

I'll try a high rpm engine shutdown and read the plugs. I noticed the left bank is gonna be a PIA to get to.. lots in the way.

As for the ignition.. dreaded perma tune.. I have heard really bad things about this little box.. should I ditch it and go back to a stock box?

Paulporsche · 12-13-2007, 06:29 AM

I'm w/ Grady on this one. Provided other items, like plugs, points, wires, timing, dizzy, injectors and WUR are fine, the first thing I would do if I had a low end stumble followed by a rapid rpm buildup would be to slightly richen the mix.

Do you know the procedure for that? Try doing so in about 1/16 or 1/8 turn increments. Just 2 or 3 should do it. If you get a hunting idle back it off a little.

calling911 · 12-14-2007, 05:58 AM

Quote:

Originally Posted by Paulporsche

I'm w/ Grady on this one. Provided other items, like plugs, points, wires, timing, dizzy, injectors and WUR are fine, the first thing I would do if I had a low end stumble followed by a rapid rpm buildup would be to slightly richen the mix.

Do you know the procedure for that? Try doing so in about 1/16 or 1/8 turn increments. Just 2 or 3 should do it. If you get a hunting idle back it off a little.

Ya know, first off, don't get technical with me buddy!

Seriously.. I don't know what the following is even though I know Bosch CIS inside and out.. "dizzy", "WUR".. please educate..

Now, way back in the early 90's I raced a 84' vw GTI.. I knew that car inside and out and the CIS included.. if I remember right it was a huge NO NO to mess with the adjustment screw.. Apparently you would screw up what was effectively a mechanical map for the fuel injection.. the way to increase richness was to carefully file on the fuel pressure regulator.. actually, it was called a warm up regulator.. but once the temp sensitive bar was warm it was effectively THE fuel pressure regulator.. now, the VW did not if memory serves have any sort of altitude compentator.. but I could be wrong.. its been a long long time.. I will do some reading after this and all of this will start to come back to me I am sure..

Perhaps someone could point me to a good article on this particular CIS.. but not some hacker please.. My Bosch injection manual is very deep inside a moving truck at the moment and I dont have access.. I wish I did because it has all I need to make this adjustment...

I drove the car for several hours yesterday... I hope my fuel pressure gauge is messed up or I may have a problem.. about to search for normal at idle pressure...

RoninLB · 12-14-2007, 06:46 AM

calling911 · 12-14-2007, 06:51 AM

I'm not seeing my problem on that chart???

Grady Clay · 12-14-2007, 06:54 AM

Thanks Ron. That is still a very useful chart.

JP,

Even I get caught up using jargon.
I try and write in complete sentences and use proper words and syntax.
People read this Forum world-wide and not all are English speaking.
We should all run our posts through a couple of language translations and back to English and see the result.

WUR = Warm-Up Regulator.
Dizzy = ignition distributor.

My post above was a little curt.

A ‘stumble’ on take-off can be a too-lean mixture issue OR arcing in the high voltage parts of the ignition system. With a CO tester (or a simple twist of the adjustment screw) the mixture is easy to diagnose.

The ignition is usually less easy. This can be from either a crack or carbon track in the cap, on the rotor or a plug connector. There can be a wire failure under the shielding. It can be as simple as the plug connector not ‘snapped’ onto the sparkplug end. It can also be a symptom of the ignition distributor ‘hanging up’ and not returning to its idle advance.

For racing, I have a spare complete ignition system; CDI box, wiring harness, ignition transformer (coil), distributor (tested and run-in), rotor, cap, ignition wires, support grommets, plug connectors and set-up sparkplugs. Sometimes replacing everything in the ignition system is the only way to diagnose if the fault lies with the fuel system or the ignition system. Occasionally the running symptoms are the same.

Best,
Grady

calling911 · 07:06 AM

Quote:

Originally Posted by Grady Clay

Thanks Ron. That is still a very useful chart.

JP,

Even I get caught up using jargon.
I try and write in complete sentences and use proper words and syntax.
People read this Forum world-wide and not all are English speaking.
We should all run our posts through a couple of language translations and back to English and see the result.

WUR = Warm-Up Regulator.
Dizzy = ignition distributor.

My post above was a little curt.

A ‘stumble’ on take-off can be a too-lean mixture issue OR arcing in the high voltage parts of the ignition system. With a CO tester (or a simple twist of the adjustment screw) the mixture is easy to diagnose.

The ignition is usually less easy. This can be from either a crack or carbon track in the cap, on the rotor or a plug connector. There can be a wire failure under the shielding. It can be as simple as the plug connector not ‘snapped’ onto the sparkplug end. It can also be a symptom of the ignition distributor ‘hanging up’ and not returning to its idle advance.

For racing, I have a spare complete ignition system; CDI box, wiring harness, ignition transformer (coil), distributor (tested and run-in), rotor, cap, ignition wires, support grommets, plug connectors and set-up sparkplugs. Sometimes replacing everything in the ignition system is the only way to diagnose if the fault lies with the fuel system or the ignition system. Occasionally the running symptoms are the same.

Best,
Grady

I'm not sure what the first part of your repsonse was directed at but.. hope it wasnt me.

Well; I did find two things a few minutes ago.. first off the vacum advance line has been located! It has a screw in the end

. Shall I plug it back where fritz designed it to be? (fritz is my slang for german engineers.. no disrespect to the german culture intended its meant as a term of indearment actually)..

I also found a chip on the bottom off the cap.. it might just barely allow air in and out of the cap area.. Not sure but I suppose it could be an issue.

That being said.. I'll try and figure out which screw you want me to tweek on the CIS to richen it up.. I am sure its on the fuel distributor somewhere or right near the "mechanical map device".

EDIT: is it the CO you want me to adjust..? I believe that is the only setting that might change richness other than the cold start fuel pressure regulator.

RoninLB · 12-14-2007, 07:08 AM

i assume you went through a basic tune up before going for below info?

Unfortunitly my old CIS ran perfectly and all i did was collect info.. just in case.

CIS psi testing
CIS Fuel Test Pressure Question '77 2.7
cis test questions

CIS MIX TEST----- Charlie Kstylianos says,
http://forums.pelicanparts.com/showthread.php?threadid=170802

Manual fuel mix adjustment,
Cis
Adjust Mixture now that I have the tool?

WUR.....
http://forums.pelicanparts.com/porsche-911-technical-forum/89694-another-try-adjustable-wur-sketch-post936218.html

and JW says, system pressure should be 4.8-5.2 bar. control pressure
3.4-3.8 bar. control pressure starts low, like 1-1.2 bar and goes up
to the top range in just a few minutes. if the w/up reg had power to
it for very long, it would have started to warm up. if you had
excessive control pressure on cold starts, the engine would be very
cranky for a few minutes, until it warmed up a bit. CIS gauges won't
allow the engine to run very well if the lever is in the system
pressure mode. the system pressure check is done quickly, and then
the lever is turned to the control pressure mode. system pressure
stays the same, control pressure rises. a "fix" can be attempted.
notice the 1/4" wide, round, depressed spot on the top surface of
the WUR. it's actually the top of a pin in a hole. if you can
depress it a tad more, the cold mixture will be richened. with the
gauge attached, engine cold, and WUR plug pulled off, so it doesn't
warm up, use a hammer and punch to move it just a few thousandths
deeper. watch the gauge as you try tapping it down kind of gently,
because if you go too far, and make it too rich, where it surges.
shoot for 1-1.2 bar. (search for "adjustable warm up regulator").
before you do that, follow the top vacuum hose to the thermo-valve,
just above the left valve cover, over cylinders 2 and 3. the valve
needs to be closed when cold, so the WUR can run richer cold. when
it opens, vacuum reaches the WUR, and it goes leaner. the hose
should not have vacuum when cold, until the t/valve warms up. check
for power and ground at the plug on the valve.

calling911 · 12-14-2007, 07:12 AM

Guy's first off thanks to ALL of you for your help.. I should point something out.. I just moved cross country and all of my test equipment is deeply buried in the back of a moving truck.. I am trying to work on this car with 2 adjustable wrenches and a really nice Leatherman Wave knife tool. I should probably just wait until I buy a house and get into a garage... but I am being impatient and am just really curious about how this car works.. I have a set of CIS pressure gauges waiting for me in a box somewhere!