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Re: engine trouble running when warm Posted by Gary Stottler [Email]  (#1463) [Profile/Gallery]
(more from Gary Stottler) on Sat, 7 Dec 2013 07:08:52
In Reply to: engine trouble running when warm, boot_sequence  [Profile/Gallery]
, Fri, 6 Dec 2013 11:00:11
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I would say that this is not likely an ignition problem (if it starts and runs once you have released the key from "Crank" to "Run"). You were wise to check for vacuum leaks, and you might want to redouble your effort there (make sure that the oil fill cap on the valve cover is on tight and that you don't have any leaks in the brake booster, for example). Also, check that the big rubber "boot" connecting the airflow sensor to the throttle body is correctly positioned and tightly clamped on both ends and that the three bolts holding the throttle body to the intake manifold are tight. Also, pull the rubber boot off the airflow sensor and make sure that there's not excessive oil on the round airflow plate and that it moves up and down freely. Is the fuel in the car reasonably fresh? If it is 2 or more years old you may want to drain it out and get fresh fuel in there.
As far as the fuel system is concerned, I would be interested to know if the problem started suddenly or if it deteriorated over time? If I recall, you do not have a Lambda (Oxygen Sensor/Catalyst) system on your car? Since it starts cold, that implies that the cold start injector is getting something close to the correct pressure, so that suggests that the filter and pump are OK and not restricting flow/pressure.
If all the stuff above is OK, then I would start looking at the Control Pressure. This is regulated by the Warm-up Regulator, more properly called the "Control Pressure Regulator". Control pressure should start out low and slowly rise (over 3-4 minutes) as the engine warms up. Even when fully warm, it should be lower than the line pressure in the main system. Line pressure is regulated in the fuel distributor. Basically, if the engine dies because it's lean (too little fuel), then one cause is the Control Pressure being too high. Do you have a sense for whether it is going out lean or rich? If it were going rich, I would think you would see black smoke from the exhaust and the spark plugs would look black. You would also probably be able to "save" it from stalling by opening the throttle and revving the engine. So, I'm assuming it's lean - and if there are no air/vacuum leaks in the intake system (anything between the airflow sensor and the intake valves), then I'm back to chasing control pressure too high.
High control pressure can be caused by a couple of things. One that's counter-intuitive is if the main return line from the fuel distributor to the tank is restricted, the line pressure and the control pressure will both be too high and the system will go lean. You can check this by removing the return line from the fuel distributor and making sure you can blow back through it to the tank. If it seems restricted, take a look at the rubber hose and check valve that are at the top front of the tank on the right side (behind the right rear wheel). The hose could be kinked or the check valve failed, although that usually causes fuel to leak on the ground. It can be replaced with rubber fuel hose from NAPA or any parts store if this seems to be an issue. Also, look for any kinks in the plastic fuel return line in the engine compartment or near the check valve.
Likewise, if the return line from the Control Pressure Regulator to the fuel distributor is kinked or restricted, this could be a cause of high control pressure. Finally, the Control Pressure Regulator itself can go bad and not vary the pressure any more or do other dirty tricks. The fact that it runs fine for a few seconds and then goes out almost suggests that it's not the regulator, you would have to get the pressure gauges on it to check. One thing you could try is to leave the electrical connector to the Control Pressure Regulator disconnected (it runs a heating element which causes the unit to lean out the mixture more quickly after a start) and see if that improves anything.
Good Luck!
Gary
posted by 50.48.103...
_______________________________________ Gary Stottler
, Fri, 6 Dec 2013 11:00:11, Sat, 7 Dec 2013 07:08:52 <-- Viewing This Message, Sun, 8 Dec 2013 20:43:05, Mon, 9 Dec 2013 16:49:29, Mon, 20 Jan 2014 19:57:44, Mon, 9 Dec 2013 20:05:39
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