cold start problem

Alan L · Alan L's Garage

My friend has a 2.7, 1977 S.
It is a pig on first start up - too lean. Once you actually get it firing, the warm up is fine. But lots of backfire, misfire at the cranking stage.
We have done all the obvious stuff, I think. The CSV is working, as is the thermo switch (but I still suspect something wrong here). The only thing we have not done is pull the CSV out and actually watch fuel go thru it - but I dont think they have a screen, and you can hear and feel it click on/off.
The WUR cold pressure is 16 psi - which must be about as low as they go for cold WUR numbers. And the warm up phase is fine. The thermo switch which controls vac enrich/lean to the WUR is working and cuts in after about 30 sec.
The dizzy vac adv is working.
As far as we can find, no airleaks, and the car runs fine at all phases other than cold crank.
The accumulator is holding pressure as per the book.
Apparently? the 911S around this era had a cold start issue?
Not sure where else to look now. One possibility would be to try and extend the thermoswitch duration to full crank time?
If you prime the injectors at dead cold, it starts and idles first off.
Alan

Flat6pac · 08-05-2009, 03:18 AM

Make sure you can Ohm across from the valve to the left rear chain cover. Its possible you have the 2 wires on the front of the engine crossed. This will show up as the fuel pump running when the key is on. If you lift he air flow sensor and the pump starts everything is correct.
I dont have a graph readily available but the cold pressure is or seems to be low. 30# would seem like a better number with a warm up to 45 to 50 #

Bruce

T77911S · 08-05-2009, 03:51 AM

hey alan,
with about 1 bar CCP, it should be fine once started. i was getting .8bar cold on mine, but that was maybe in the 50's or 60's outside temp. once the thermo valve (TTV) opens, my CCP was 1.8 bar.

CCP is fine.

if it is hard to get started, look at the CSV stuff.

Alan L · Alan L's Garage

Thanks guys. Flatpac - you may be on to something - but I dont quite understand you. But I did notice the pump running with key on. I thought it odd, but figured maybe the '77 is different to my SC. Can you explain which wires you mean.
Thx
Alan

Flat6pac · 08-05-2009, 01:54 PM

There is 2 connectors on the front of the engine that you cant see without a mirror. One is the cold start valve and the other is the shutoff for the pump when the engine is not running.
The connectors are both blue green so they get mixed up..more than occasionally.
The wire on the left rear chain cover will OHm with the coldstart valve.
I would just switch the 2 and there should be some success without metering anything
but that is how the coldstart checks out.
Bruce

Alan L · Alan L's Garage

Ah yes - the airplate switch and CSV valve. Pretty sure they are right - but will check - green for air plate and blue for CSV from memory.
Thanks
Alan

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by Alan L

Thanks guys. Flatpac - you may be on to something - but I dont quite understand you. But I did notice the pump running with key on. I thought it odd, but figured maybe the '77 is different to my SC. Can you explain which wires you mean.
Thx
Alan

Allan,

Your FP should not be running when the ignition is @ ON position for your '77 CIS (911) car. If it does, there is something basically wrong in your wiring set-up or connection. Troubleshoot and correct this anomaly first before doing any further work. You seem to know and understand CIS, and setting it correctly should not be a problem for you. Keep us posted.

Tony