2002 4.0 110k miles.

When cold (sitting over night) the engine stumbles, pops, hesitates and will die.
Once it's close to operating temperature, it runs perfectly normal.

The Discovery was sitting for a few years when I purchased it as a non runner.

Recent work I did includes (but not limited to) a new timing chain and oil pump gears.

I swapped MAF, coil pack, wires with no change. Checked for vacuum leaks but nothing obvious.
New copper plugs.

My thought is I don't have the cam sensor plugged in all the way.

I have yet to read the codes or get a fuel pressure reading.

Once it's warm it runs normal.

Anyone experience anything similar?

 

If the cylinder block is cracked or the cylinder sleeve comes loose in the bore, coolant will flood that cylinder over the period of time that the engine isn't running. When you start it for the first time the coolant is being burned out of that cylinder in the beginning (your problem) and engine usually runs OK afterward until it sits dormant again and the process repeats itself.

 

A wonky O2 sensor can cause this type of behavior at start-up even if the system is not throwing codes. In my experience it's usually one of the sensors downstream of the cat. Also, copper plugs may be problematic -- i would swap in some platinums.

 

any decent OBD reader with live data function and other various hardware will show the data on the sensors so you can watch the values at startup. As the engine progressively warms-up see if any of the values change correspondingly to confirm or deny that logic. i don't know about the sensor. Are you not able to check it? I would have checked that long before making this post if that is keeping you awake at night. I mean what are the odds some guy says "oh yeah I half-*** left a camshaft sensor unplugged and my truck was doing the same thing yours is."

 

During cold starts 02 sensor data is ignored, the ECU runs a "cold start" tune until a specified temperature is met (closed loop). Further, downstream 02 sensors (post cat) only monitor catalyst efficiency, not rich lean conditions.

 

Interesting. Could be a number of things (huge help, I know...)

The ECU would throw a P0340 if the cam sensor was disconnected.

I would look at Evap system (vacuum lines included) and ICV.

 

Just pissing in the wind without plugging into the OBD port....My 2 cents.

 

Then the Disco's ECU is substantially different (read: less sophisticated) than some others I have encountered in past vehicles owned where I'm certain O2 sensors play a significant part in the cold start program. I may be mistaken, however, in my assertion of downstream vs. upstream sensor involvement/role.

 

I may be misinformed but, as I understand it the computer supplies a bias voltage signal to the O2 sensor any time the key is on.

This is done so the computer can monitor if the O2 sensor is warm enough to start operating. A cold O2 sensor outputs NO voltage signal. And as the sensor warms up, it starts producing enough voltage to either pull up or pull down the computer-supplied bias voltage. Once the computer has determined the O2 sensor is warm enough (ready) to start operating (as detected by it seeing the O2 sensor pull up or down the bias voltage), and other qualifications are met (water temp sensor data) it will go into Closed Loop mode and start using the O2 sensor to make adjustments to the AFR.

If the O2 sensor is not ready to start operating after a set amount of time once the engine has warmed up, the computer may set a Code.

 

I think this is sound logic. I can tell you unequivocally that I have changed O2 sensors in the past to resolve cold start issues, and you can find evidence of same if you search outside this forum. My experience was with a '98 Dodge RAM Van with a 3.9L V6. All I can think of is O2 sensor providing voltage at startup when it's NOT supposed to and fouling up the fuel mapping. Somehow, in certain circumstances the vehicle's ECU (SMEC for Mopar) does not pick up the anomaly and illuminate the CEL.