911 running rich or lean?

LCOX · 11-19-2019, 03:44 PM

When I first crank my 77 911 the idle speed lopes up and down wildly for the first minute or so before gradually becoming steady at around 900 rpms. Is this swinging tach needle a sign of the car running too rich or lean. Car runs good otherwise.

Reiver · 11-19-2019, 04:14 PM

That indicates a rich start but that is what a 'choke' does and if you have CIS that is not uncommon with the initial enrichment that is supposed to take place.

If it is a 'wild' lope rather than a mild one you might back of the AFR to a bit leaner but check it properly.

T77911S · 11-20-2019, 02:50 AM

pull the vacuum line off the WUR and see if it has vacuum on it at idle.

LCOX · 11-20-2019, 07:22 AM

Yes it is pulling vacuum through the vacuum hose plugged on top. There's another smaller vacuum hose plugged into the base of the wur. Do you want me to check that one as well?

r lane · 11-20-2019, 08:04 AM

Even if all the fuel and engine components are within spec, CIS doesn't have the capacity to be very exact on keeping up with the initial warm up curve. I am sure I may have opened up Pandora's box, iliciting contraire rebuttal, but is simply my opinion. Bob

T77911S · 11-20-2019, 09:21 AM

the side one is a vent.

I assume you have the 033 WUR.

if you can you need to start with checking the fuel pressures

LCOX · 11-20-2019, 02:23 PM

Here are the system, control and residual pressure numbers. These tests were done last month when it was still hot here in NC. Air temp was 89 degrees.
- System pressure 5.2 bar
- Cold control pressure 0.7 bar
- Warm control pressure after 4 minutes 2.3 bar. Vacuum hose connected.
Residual pressure after 20-30 minutes 1.6 bar

LCOX · 11-20-2019, 02:27 PM

Forgot to mention. Yes the wur is an 033

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by LCOX

Here are the system, control and residual pressure numbers. These tests were done last month when it was still hot here in NC. Air temp was 89 degrees.
- System pressure 5.2 bar
- Cold control pressure 0.7 bar
- Warm control pressure after 4 minutes 2.3 bar. Vacuum hose connected.
Residual pressure after 20-30 minutes 1.6 bar

LCOX,

The control fuel pressures (CCP & WCP) are both out spec. They are too LOW. Have the WUR-033 re-calibrated and set them to specification. Residual pressure is good and system pressure on the high side. Keep us posted.

Tony

T77911S · 11-21-2019, 02:54 AM

what tony said,

with my 033, cold (with NO vacuum ) on cold mornings was about .8bar. but once the TTV opened and vacuum was applied it was around 1.8
WCP should be about 3.6 with vac and about .8 lower with no vac.

it could be that your diaphragm is bad. you said you did have vacuum on top of the WUR.
I would test the CP with and without vacuum to verify.

LCOX · 11-21-2019, 08:06 AM

I took the wur back off the car and checked both the top and lower side vacuum ports. The lower vacuum port holds strong vacuum when I suck on it. The top port holds vacuum as well but not nearly as strong. The top vacuum HOSE holds vacuum as well with the car running.
. 2 questions: Does the car need to be running when I run these control pressure tests? It wasn't running on the previous tests. Tony do you calibrate it by tapping down on the plunger on top on top of the body while watching the gauge and The readings on it?

T77911S · 11-21-2019, 10:37 AM

i strongly suggest buying a hand vacuum pump for CIS.
its a great tool to have.
you can pull a vacuum on many of the parts to see if they hold vac.

I would verify you are getting the pressure change with and without vacuum first.