Cold start issue..............

fred cook · fred cook's Garage

I just finished replacing all the hoses and other rubber components on the top of my '80 SC 3.0 engine. After sitting overnight in an unheated garage (completely cold engine) it starts promptly, goes to a 1500 rpm idle for about 60 seconds and then drops to a steady 1000 rpm idle where remains until completely warmed up when it drops to 950 rpm. Sounds perfect, huh? Well, after starting cold and driving about 1/4 mile, the engine speed will suddenly drop to about 3-400 rpm and usually stall. After a quick restart, it seems to run perfectly the rest of the day, even after sitting in the parking lot at work for 4-5hours. My engine is basically stock SC fare with the exception of having added a 6A MSD unit. The plug wires are fairly new (2-3 years) and while the engine was out of the car, I installed new plugs and filters. The only new hard items on the "top" of the engine or affecting the fuel injection are an alternator and an accumulator. I also installed a new oxygen sensor and connected it to the pin on the wiring harness. Other than the new parts, the only thing different from before the refub is that previously I did not have the O2 sensor connected. The timing is set at 5 degree btdc and the CO is set at 3%. Any thoughts as to why the engine has the one "stumble" in the morning would be appreciated.

Paulporsche · 03-29-2008, 06:00 AM

Just a couple of thoughts here.
Is that drop and stall from the 1500 or the 1000 rpm?
Have you actually checked your control pressures? Since you are in a fairly warm climate maybe the WUR is off just a little.
I think I read in another thread that the sensor plate height is affected by engine compression/vacuum. Have you checked your compression?

fred cook · fred cook's Garage

Paul,

Thanks for the reply. After giving the issue some thought, I came to the same conclusion, check the control pressures. I have not done so yet, but am on vacation next week and will do so. Also, I have a temp sensor that I am going to try as a replacement for the one currently in the engine. I believe that either it or the wur is the culprit. Once I chart the control pressures, I will/should have a better idea of what is going on.

Thanks,

Paulporsche · 03-30-2008, 01:58 PM

Let us know what you come up with.

fred cook · fred cook's Garage

I replaced the thermo time switch over the weekend. On both Monday and Tuesday mornings it started and ran perfectly. Apparently the old thermo switch was dropping power to the cold start valve too soon. Since it has been a couple of years, I will still run a pressure check on the WUR to update my records.