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Re: What happens if you unplug warmup regulator/cold start Posted by Gary Stottler [Email]  (#1463) [Profile/Gallery]
(more from Gary Stottler) on Thu, 12 Dec 2013 06:18:37
In Reply to: What happens if you unplug warmup regulator/cold start, Dan Burkert, Wed, 11 Dec 2013 17:32:55 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Dan,
The warmup regulator (Control Pressure Regulator) and the Cold Start Injector are basically completely unrelated to each other, so I'll address your question as two separate ones:
1) The Cold Start Injector performs two functions: First, when the engine is cold (as defined by one set of contacts in the Thermo-Time Switch being closed), it will turn on and inject fuel while the starter is actively cranking only. No cranking, no activation. Second, it acts as a "pump shot", delivering a quick (<0.5 sec) pulse of fuel when the Vacuum Impulse Contact senses a drop in vacuum related to the throttle being quickly opened. This function is controlled by the second set of contacts in the TTS - once the engine warms and the contact open, this stops. All that said, if you unplug the Cold Start Injector on an otherwise healthy engine, it will be hard to start the engine when it is cold and the engine will stumble when you step on the gas until it warms up after a cold start.
2) The Control Pressure Regulator (also called the warmup regulator) manages the control pressure of the fuel distributor which, in turn, controls how rich or lean the overall fuel mixture is. Internally, it contains a pressure regulator with the spring mounted on a big bi-metal strip - as the strip gets warmer, the regulator spring effectively gets stiffer and the control pressure gets higher. The important point to remember is "cold engine = low control pressure = rich air/fuel ratio (low lambda), warm engine = high control pressure = lean air fuel ration (high lambda)". The bi-metal strip is warmed both by the heat of the coolant in the cylinder head (as the metal of the CPR housing warms up)and by an electric heating element wrapped around the bi-metal strip. The purpose of the heater is to lean out the mixture more quickly than would otherwise happen, this is generally done to control HC and CO emissions, and if everything else in the engine is healthy, it does not need the extra fuel anyway - the metal of the cylinder walls and intake port warms up much more quickly than the bi-metal strip after you start the cold engine. However, in some later CPRs, the lean-out was agressive (CIS was pretty bad in terms of emissions) and you could get some lean stumbling problems during the warm-up. All of this is effectively the same function as the choke in a carburetor. So, if you unplug the electrical connector, the bi-metal strip will warm up more slowly and the control pressure will not rise as quickly - it's like keeping the choke on longer after a cold start.
Historically a lot of CPRs got "messed with" to try to fix fueling problems that really originated elsewhere in the system. They also tend to eventually "stick" output only a constant pressure no matter what the temperature. They can be taken apart and rebuilt, but resetting them to the correct pressure calibration is tricky.
As a general statement, both of these actions are helpful in troubleshooting system problems, but should not be needed to make the engine run well if everything else is working properly. In diagnosing the K-Jetronic CIS fuel system, I always suggest starting with pressure checks if possible, and then digging into the vacuum, electrical, and mechanical items that make the fuel system work.
Hope that helps!
Good Luck,
Gary
posted by 198.208.25...
_______________________________________ Gary Stottler
, Thu, 12 Dec 2013 06:18:37 <-- Viewing This Message
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