Out of ideas need some help, 83 row 911sc running sluggish
 

So when I floor it the car feels sluggish, when it gets over 4000 rpm it starts to feel much better, in fact runs really well up top, previously it was shaky when you reached 90/100 mph but its smooth now, but no power down below. Car also farts when you take your foot off the gas. I checked my Valve job again and it's good, new plugs and brand new wires today, fuel pump is new, cis has always worked properly, brand new vacuum lines today, timing and dwell are spot tested today also. She starts up perfect around 1200 drops idle to about 750 then rises to 900/950. Motor sounds amazing idling but the minute you give her gas she doesn't go like she used to...

Anyone experience this, ive seen lots of threads to do with power loss up top, but not down below.

Is your frequency valve system working? Get it running and pull the plug on the small relay under the passenger seat and see what happens. Should drop the idle speed and run rough, if it was working. The relay getspower from the interior light fuse. If the dome light works, don't bother with that.

My car is an 83 row, there is no lambda system, frequency valve or o2 sensor control.

Maybe post in your signature what you have for future questions. Location too would be good.

Maybe need to drive with an O2 meter to see what it's doing.

Ill do that but do take note that it is in the title of the post ;)

CIS Troubleshooting……….
 

Harv,

There is something wrong with your CIS. Start to investigate the following:

• Fuel Pressures (control & system).
• Vacuum or air leaks.
• Fuel Mixture
• Fuel injectors spray pattern.
• Fuel flow rates.
• Etc.

Your idle speed should never go below the 900/950 RPM setting. It would start HIGH when cold and gradually goes down to idle speed. If the COLD engine RPM goes below your setting, this is already a sign of problem. You need to identify and correct it.

Tony

Thanks Tony. I will recheck the idle at cold start tomorrow and see what thats doing again as I made some adjustments today.

I can pic up a fuel pressure tester, is there a certain size or type that I need? I replaced all the vacuum tube yesterday with new tube, could a bad aav cause leaks or would that only be felt at startup?

I tested both my old aar (not correct for my 930/10) and my new aar (correct for my 930/10) both close in the oven and open in the freezer. I was missing a long hex its coming tomorrow so I can adjust mixture to se if thats the issue. I played with the plate in the air box, if I move it up a bit I get faster idle from 950-1200 and then past that the car chokes then dies. If I tug down on the plate the car chokes then dies. If that tells you anything.

Ill test pressures and leaks once I grab a tester, what tool do I need to test vacuum, the handheld gauge thing correct?

Thanks for the help.

harv

I had a similar problem with a 1980 911SC. It turns out that I had a vacuum leak due to a tear in the rubber intake boot where the hose clamp holds it to the intake. The only way to identify that was buy doing a smoke test.

CIS Troubleshooting………..
 

Harv,

It is mandatory to have a CIS pressure gauge kit to test your fuel pressures (control, system, and residual). Another tool you need is a smoke generator to locate those hard to find air leak sources. And lastly, an inductive timing light. These are the three (3) basic tools a good CIS troubleshooter should have in the tool box.

A vacuum leak in a CIS motor is not easy to locate or identify. But a smoke generator with low pressured air supply is more effective in locating sources of vacuum leak.

Tony

Thanks Tony

Smoke test showed no vacuum leaks, timing is dead on, i have those tools, so it can only be pressure or mixture. I just checked every plug , they look normal nothing wrong they’re all reseated and retorqued. I’ll have a fuel pressure kit in my hands by tomorrow so that’s next. it could be something other than cis though I guess?

Harv

Harv: This kind of problem sounds like the distributor is not advancing correctly. But you said you checked the timing. Did you verify the timing specs with the vacuum disconnected and at various RPM, then connected and at various RPMs? Otherwise, you're back to something related to intake or CIS.

CDI and coil problems usually show up at high load and high RPM, and your symptoms are the opposite, so I would focus on other things first.