Friday, July 6, 2012

Vehicle Starts,Runs and Loses Power

Starts runs loses power dies won't start wait and same repeats.

2002 Dodge Cargo Van will start fine,then runs for few minutes and it will die.After waiting for few minutes it will again start and run fine but same issue repeats.

FROM WHERE TO START TROUBLESHOOTING IN THIS CASE?

In most of such cases the check engine light will come up on dash and remain steady.If in this case you notice steady check engine light on dash.Then start by getting the error code scanned.The check engine light blinking or steady on dash indicates error stored in vehicles system.Scanning will let you know what error is stored.So you can start troubleshooting by what the error code is retrieved.

THERE IS NO CHECK ENGINE LIGHT BLINKING OR STEADY?

Yes the check engine light comes but only for second while starting the ignition,then goes off.That's it:

In that case there is no error code stored.In that case the most possible cause for this start,run and die issue is 
weak heater on the upstream oxygen sensor.

WHY OXYGEN SENSOR WILL CAUSE THIS PROBLEM?

  • To Know this First Understand the working of System:

The working is as follows:-----

The sensor has a built in heater.Why it has heater, because the exhaust doesn't heat the sensor enough to properly monitor oxygen content, and the heater helps it get into closed loop operation quicker from a cold start. 

The sensor has a 5v pullup voltage on it for circuit diagnostics. This is loop mode.When the key is first turned on the sensor reading will be at 5v which means its in Lop mode.As the heater starts to work it bleeds off this voltage until the voltage is in the normal operating range. And here it enters to closed loop mode.In your case the heater is taking more then required time to get the vehicle out from loop mode to closed loop mode.This is because its weak heater.The Heater built into oxygen sensor and So the vehicle starts,then runs but dies,because vehicle is not getting to closed loop mode on time.

CAN YOU GIVE ME MORE DETAILED EXPLANATION?

Yes sure.This are all technicians details which another garage auto mechanic will easily understand.But i will make you understand in more simpler way.

Vehicle is stand still overnight.You get ready and step out of your house in the morning.
Now in this state ..........
When you enter the car and start your engine it's in open loop mode. 
WHAT is open Lop mode?
This means that the oxygen sensors are ignored and fuel control is managed basically by software alone.
But once the oxygen sensor warms up by in-built heater for a few minutes.Now the engine will go into closed loop.Now in closed  the oxygen sensor readings are then used. 
If you have a weak heater on your upstream oxygen sensor the pullup voltage will be bleeding off too slowly, and when it hits closed loop the sensor is still reading the higher pullup voltage instead of the actual sensor reading. The engine controller sees this and thinks its running rich and leans it out, giving you rough running, hesitation, and often some lean backfiring in the intake. And at last vehicle quits and dies.
As per the symptoms of your vehicles problem it seems that upstream oxygen sensor is faulty.

OK,GOOD and EASY UNDERSTANDING EXPLANATION

BUT WHAT IF I WARM THE ENGINE  FEW MINUTES BEFORE DRIVING?

In any case the Upstream Oxygen sensor has to be replaced.
Also if it's already warm and you park it and let it idle for a few minutes the sensor will cool back off. The longer it sits and idles it may run worse and worse.
In most of such problem cases  you can hear the idle air control motor opening farther and farther to keep the engine running, giving a large sucking sound under the hood. The same goes for if you start it and let it warm up before driving, it will go into closed loop while it's still idling and the sensor hasn't warmed yet.It all works on timing.The Sensor should get warmed up till particular level and in particular time.If its taking more time the engine computer will not get its indication and computer will stop operating the remaining parts.And you notice hesitation,stalling and engine quit and dies problems.

IF OXYGEN SENSOR IS FAULTY THEN WHY CHECK ENGINE LIGHT IS NOT COMING ON?

Its not faulty oxygen sensor.Its weak heater in the oxygen sensor.The sensor is good but heater is weak.The heater alone cannot be replaced.Its an inbuilt heater in the sensor.So your only option  is to replace oxygen sensor this comes with new in built heater.
You would think this problem would set a code, Yes i agree with you if the oxygen sensor is faulty then system will set the code and illuminate warning light on dash.But the software used in these engine controllers let this slip by without setting a code normally, because the voltage is still within normal operating range (not shorted to ground or an open circuit).

OK,GOT IT.BUT WHICH OXYGEN SENSOR TO REPLACE?

Yes there are more then one oxygen sensor on this vehicle.You don't have to replace all of them.
I'd recommend replacing the upstream oxygen sensor, the one in front of the catalytic converter. 
After the sensor is replaced, disconnect the battery to clear the stored fuel control adaptives out that have been falsely learned by the bad sensor.This will not cause same problem with new sensor.
If possible buy branded and original parts.They give accurate performance and last long.
Aftermarket parts are not bad parts,buy they are cheapo material parts with weak materials and they don't give exact performance in many cases.


This details will help.
Thanks.

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