SC Warm Up Problem

chuckr · 10-06-2003, 06:49 AM

MY 1983SC has developed a interesting problem. In cold weather my car idles very low, about 400rpm and backfires when I push on the gas, after she warms up she's fine, rock solid tach at 800 rpm and runs fine. I had this problem at the end of last winter and
replaced the aux air regulator and about the same time the weather warmed up and the problem went away.She ran great
all summer and now that the weather has gotten cooler, my idle
has gone back to bunk. While the car is trying to warm up I can unplug the Warm up regulator and nothing happens so I suspect this is the problem. My WUR is only three years old. Before I replaced it before, my idle was wandering during warm up, like going between 400-1200rpm back and forth, I replaced the WUR and all was good. Now I am just not sure what is going on.
Any thoughts ????
Thanks
Chuck

MotoSook · 10-06-2003, 07:26 AM

If you suspect the WUR, test the fuel pressure from a dead cold crank and see what numbers you get.

If you don't have a CIS Fuel pressure tester, get one from JC Whitney..about 60 bucks.

Unplugging the WUR while the car is warming up won't tell you much. The power to the WUR is for heating of the WUR, unplugging a good WUR will only prolong the warming of the WUR, which will then only be done by the heat from the engine.

Get a pressure tester and you should see the control pressure rise as the engine warms up.

Also, when you replaced the WUR, did you check you mixture setting?

I have noticed that with a change in weather, the supposive altitude and temperature compensation on our cars are not perfect. That is, it won't lean out or richen enough without a little adjustment by human hands.

Is your O2 sensor connected or not connected?

bigchillcar · bigchillcar's Garage

Definitely check your mixture...a faulty WUR shouldn't cause backfire to occur, often that's associated with points closing (on my '74) or a too lean mixture. Cold weather can give you this condition...the air density is much greater with cold air, thus the mixture tends to lean more.

The function of the WUR, however, is in fact to lean the mixture after initial start. At start, the cold start valve (if engine block temp. is < 95 degrees according to thermotime switch) enriches the mixture for start, then shortly thereafter, the job of the WUR is to begin to lean the mixture out for normal operating temps.

You don't have to have a CO gas analyzer to check your CO if you have a dwell meter. Set the dwell meter on the 4-cylinder scale, connect the dwell meter to the pulsed side of the frequency valve or the duty cycle test terminal of your car. Start the engine and allow it to warm up. With your lambda sensor still connected, use the 3 mm allen wrench for mixture adjustment and adjust mixture until dwell meter reads 45 degrees.

I'd also spray some carb cleaner around your hoses, intake, airbox, etc. and check for vacuum leaks. This will cause a lean (backfire producing) mixture.

You can check your AAV by removing and putting it in the freezer for fifteen minutes, the valve should be open. Put it back on the car, run it for five minutes, the valve should close.
Ryan

chuckr · 10-06-2003, 08:26 AM

I have no O2 and I had a 4gas analizer to set up my mix.

MotoSook · 10-06-2003, 08:34 AM

OK. So what are you telling us? If you want help, you got to give up all the information. What have you done or not done.

I hate this...guys come on this BBS and fish for answers, but don't tell us all that they can about their problem..

Make a list and then post...it would be much more helpful for everyone.

Sorry..having a rough day, but the messege is the same...just excuse the tone.

JonT · 10-06-2003, 10:04 AM

I had starting problems in my 3.0 too. Rough idle when cold and such. I put a 3.6 in---PROBLEM SOLVED! No more idle problems and 100 hp more to boot

chuckr · 10-06-2003, 12:06 PM

I am explaining the best I can, New Aux air reg is all I have done.
In hot weather car runs great
In cold... idle starts about1200rpm then drops after a minute or two
to about 300 rpm and the engine stumbles to maintain running, if I gicve it gas it backfires and the rpm stays the same, After about 5 minutes of this I can get the rpm's up to about 1000 by giving it gas and holding it there.At this point I can drive away by keeping the gas up and feathering the gas pedal, after two or three miles everything smoothes out and after about 20 miles all is OK, she runs fine and idles smoothe at 800rpm, no backfire, everything good. If I go out after she warms up, say, stop in and get a beer or three, she starts right up, runs fine.
This pretty much happened this week, Two weeks ago I went out and everything was perfect, I was out of town the next weekend so I did not use the car, she was in the garage, covered.Last Saturday I got in and started the car and the problem happened, it did the exact thing last winter, I put up with it till I tried replacing the Aux Air Reg, but at that time the weather changed and it got hot and the problem went away.I did adjust my fuel/air mix to get it to idle up enough to start,
I turned it up a couple of turns so instead of trying to keep a 400 rpm at start up, it now struggles with a 600 rpm idle till warm up is done, then she keeps a steady 800 rpm idle.

stealthn · 10-06-2003, 07:57 PM

Chuck,

I vote for mixture/timing....

I had my car in for some work and she just didn't "feel" right afterward. Some similar symptoms to what you mentioned, but it would backfire once, going underload up a hill.
Took her back to the shop, the wrench hooked up a laptop connected to a O2 sensor and plugged it into my exhaust. He said it was setup for an 83SC, and modified the mixture and timing for a 79 volia I could tell just by sound it was purrrfect.

Been running awhile now on it and it pulls great, idles right, and never backfires.

Good luck

tt_targa · 10-09-2003, 09:47 AM

I have recently replaced my 15 deg. temp. switch to correct a warm up problem. This sensor controls the change from open loop to closed loop operation.

My 83 ran to rich at idle. I measured a sensor resistance of 180 ohms.

The sensor is easy to test. Try grounding the input wire. I grounded the wire at the computer under the pasenger seat.

pomaro · 10-09-2003, 02:04 PM

hi,

got another hint:

check all ignition cables, connectors and spark plugs....
in cold and wet weather an amount of small faults can make the big effect (i.e. failure of engine).... when engine warms up and dries up all the stuff, everything seems to be ok.

greets
pomaro