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06 A8L 4.2L BVJ D3 engine starts hard in cold weather

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06 A8L 4.2L BVJ D3 engine starts hard in cold weather

  #1  
Old 12-31-2016, 12:41 PM
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Join Date: Aug 2012
Location: Vermont
Posts: 13
Default 06 A8L 4.2L BVJ D3 engine starts hard in cold weather

I have been having starting issues when the temps have been below 30 degrees and as the temp gets colder the harder the engine starts to the point of will not start without applying the throttle manually for a few minutes which depends on the temp.

I have no check engine light on.

I have one code which has to do with the left motor mount open circuit to do believe

I did try to search the forum with any like issues came back none found so I am sure didn't do something right. I cant believe I am the only one lol

Any ideas out there?
 
  #2  
Old 12-31-2016, 12:45 PM
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also add after the engine warms up it runs fine.
 
  #3  
Old 12-31-2016, 05:37 PM
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It's the coolant temperature sensor. $20 part, easy switch out. Be sure to get a new retainer clip for it as you'll probably break the one holding it in now. They get brittle over time. Yours will be similar to the one in the video. I'm pretty sure it is located in the same place as the earlier A8's like mine. At the rear of the engine there will be some metal coolant lines. On will have a sensor mounted into it. This is the one you're looking for.

Here's my recommended removal/install sequence to prevent loosing coolant (actually it's not likely any will come out except for a few drops anyway).

1. Once you've located the sensor and have one replace it, prep the new sensor for installation by putting a little grease on the o-ring. Petroleum jelly will work here too. Just a thin coat to allow it to slip into the hole easier.
2. Remove the retaining clip. (Do not worry about disconnecting the electrical connection just yet)
3. Remove the sensor by pulling it out of the hole, quickly insert the new sensor to prevent coolant loss. Insert new retainer clip.
4. Pull the old sensor up to where you can get the electrical connector off. It's a hell of lot easier when you can SEE and hold the connector to get it loose.
5.Reconnect the electrical connector on the new sensor.

What is happening is the coolant temp sensor is not correctly reporting the true coolant temp to the ECU so it's probably not going in to "Cold Start Mode". This means a richer air/fuel mix to get it going.

Here's the video. While not identical, the sensors are the same, as is the connector and retaining clip.
 

Last edited by dave944; 12-31-2016 at 05:40 PM.
  #4  
Old 01-01-2017, 09:24 PM
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Location: Vermont
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I changed the Coolant Temp sensor didn't seem to change the way it started. Temp was around 30 degrees attempted to start the engine it started ran for 5 seconds engine stalled. attempted to start the engine again which it started and continued to run. but it slowly lost engine RPM's and engine stalled once again. I attempted to start the engine for the third time. which the engine stayed running.

One other thing I am loosing coolant and it seems to only loose coolant when it sits around didn't seem to loose any while driving it. since it has been parked I have put 2.5 liters of coolant. with no evidence of coolant leaking on the ground which is really weird.

any ideas with this issue?
 
  #5  
Old 01-02-2017, 12:17 PM
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Gotta find that coolant leak.. That's lot of coolant to loose just sitting. If the coolant gets down so far and is not touching the sensor, the sensor cannot report the correct temperature to the ECU. My radiator started leaking around the area where the plastic reservoirs are meet the aluminum cooling cores. G12 leaves a powdery orange/white residue where it evaporates. If you see any of this anywhere, you're close to the leak.
 
  #6  
Old 01-10-2017, 05:44 PM
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Location: Vermont
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Well just tried last night to start the car in 10 degree weather. It wouldn't start on first try but would on the second or so try it would run for 1-3 seconds then die. might crank and not even run at all. I even try giving it some throttle and still it wouldn't stay running would stall out after many times doing this it finally stayed running while helping with manually applying throttle.

I need to figure out what the problem is. I will ruin the battery or starter or even worse the engine.

I do have a Ross Tech program was checking water temps and air temp which seemed to be correct.

Is there something that I could be checking with the Ross Tech any air or temp readings or fuel pressures etc.?

I didn't realize but until know but my car is 2007 not 2006
 
  #7  
Old 01-10-2017, 09:23 PM
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Here's a crazy hunch. Disconnect the MAF sensor. It's in the air filter box or located along the ducting from the air filter box to the throttle body. Start it up and see if it runs. If it does, the MAF is bad or may need to be cleaned. I know it's crazy but give it a shot

If the engine is getting erroneous readings from the MAF, it will cause issues. If the engine cannot see the MAF sensor, it will use the O2 sensors to adjust the air/fuel mix appropriately. The MAF just allows for more accurate, air fuel mixes since it is getting air measurements before combustion, not afterwards. It won't hurt anything to try it.
 
  #8  
Old 01-14-2017, 02:44 PM
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Well I did try disconnecting the map sensor and the engine cranked over but did not run at all or no ignition etc.
 
  #9  
Old 01-15-2017, 12:08 PM
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That doesn't make sense. Just about every car I've ever worked on with a MAF sensor will run with it unplugged. It trips the Check Engine light but it'll run. Most of the time much better indicating a bad MAF sensor. Interesting.

Did you crack the accelerator open to see if it would run while the MAF was disconnected. Perhaps the Throttle Position Sensor isn't working correctly. It tells the ECU 3 things. Idle, anything between above idle to just below the last item. Wide Open Throttle (to the floor). If the thing is not consistently reporting the throttle position at idle (on start up with no accelerator pedal input from you). it may fail to start because the ECU isn't being told that it is in idle position. Once you press the accelerator the ECU is able to then make the engine run like it should...
 

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