Hot Starting Problem (Long)
11-29-2001, 06:36 PM
#1
Instructor
Thread Starter
Hot Starting Problem (Long)
Any got an idea to this problem.
Now the cold damp weather has started I've started to get a warm starting problem. Cold starting is fine, one turn of the key and it fires up. I think, but not sure, that the cold idle is slightly lower than before. About 1k revs but seems to drop quicker than it used to. Once the engines warm I have to depress the throttle to start it. If I leave off the peddle once started the revs drop to 400 then bounce up and down a couple of times, sometimes stalls. Idle then is steady at 800 (just over) as it always has been. I've checked the engine temp sensor, the idle contact, full load contact and all seems correct. Something I did notice was that when the primary dist. coil was disconnected the engine wasn't as smooth (checking dist belt) as with only the primary connected. Is that normal?
Any other things to check or try?
Thanks
Richard 1990 C2
Now the cold damp weather has started I've started to get a warm starting problem. Cold starting is fine, one turn of the key and it fires up. I think, but not sure, that the cold idle is slightly lower than before. About 1k revs but seems to drop quicker than it used to. Once the engines warm I have to depress the throttle to start it. If I leave off the peddle once started the revs drop to 400 then bounce up and down a couple of times, sometimes stalls. Idle then is steady at 800 (just over) as it always has been. I've checked the engine temp sensor, the idle contact, full load contact and all seems correct. Something I did notice was that when the primary dist. coil was disconnected the engine wasn't as smooth (checking dist belt) as with only the primary connected. Is that normal?
Any other things to check or try?
Thanks
Richard 1990 C2
11-30-2001, 03:07 AM
#2
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Technical Advisor
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Dear Richard,
Based on your post and what you have already checked I would be pulling out the air filter and checking the air flow sensor for contamination. Oil in the airbox will cause this problem. Oil in the airbox is not uncommon especially if the oil has been overfilled. Or people have sprayed various forms of cleaning solutions or lubricants around the engine.
The other component that will mess you around when HOT only is the O2 sensor.
Now to your question about the ignition. Yes if you disconnect the primary ignition and run off the secondary it should run like a pig. The timing angles for the secondary system is different than for the primary.
The fact that it starts when you pump the pedal suggest a potential air flow sensor or air flow problem. However and this is a big however. The most common causes of hot start problems are
1/. The Engine Temp Sensor. It is a NTC sensor which means at low temps the resistance is high and at high temps the resistance is low. You need to apply heat to the sensor and check the resistance falls.
2/. Failed relay R41 the DME/Fuel Pump relay. The contacts heat up because the fuel pump is running all the time, they become pitted over time and when hot and re-energised they do not make sufficient contact to supply the required voltage supply to the fuel pump itself.
It should also be noted that a failed dipstick seal which expands and breaks the seal when hot can also cause similar problems. This is very rare but known about,
Ciao,
Adrian
911C4
Based on your post and what you have already checked I would be pulling out the air filter and checking the air flow sensor for contamination. Oil in the airbox will cause this problem. Oil in the airbox is not uncommon especially if the oil has been overfilled. Or people have sprayed various forms of cleaning solutions or lubricants around the engine.
The other component that will mess you around when HOT only is the O2 sensor.
Now to your question about the ignition. Yes if you disconnect the primary ignition and run off the secondary it should run like a pig. The timing angles for the secondary system is different than for the primary.
The fact that it starts when you pump the pedal suggest a potential air flow sensor or air flow problem. However and this is a big however. The most common causes of hot start problems are
1/. The Engine Temp Sensor. It is a NTC sensor which means at low temps the resistance is high and at high temps the resistance is low. You need to apply heat to the sensor and check the resistance falls.
2/. Failed relay R41 the DME/Fuel Pump relay. The contacts heat up because the fuel pump is running all the time, they become pitted over time and when hot and re-energised they do not make sufficient contact to supply the required voltage supply to the fuel pump itself.
It should also be noted that a failed dipstick seal which expands and breaks the seal when hot can also cause similar problems. This is very rare but known about,
Ciao,
Adrian
911C4