Having just replaced my throttle body to resolve the (in)famous: Engine Management Systems fail, DSC Failure, Park brake fail, I thought I would try to clean off some carbon deposits and clean up the top of the engine with something more intensive than a can of fuel injector cleaner. One product I was intrigued by was a Seafoam spray that you inject into the intake with a straw that fogs and coats the intake, valves, upper cylinder etc. This stuff:

• Cures hesitation, stalls, pings, flat spots and rough idle due to carbon buildup
• Use to store and fog 2-cycle and 4-cycle engines
• Helps pass emission tests, epa registered
• Cleans intake valves and pistons
• Oxygen sensor safe

So after replacing the throttle body, I applied this. I didn't spray it through the TB, but instead through a vacuum pick up on the elbow between the TB and the intake, You inject the full can at 2k rpms (helper required) then a 10 min. heat soak, then a round of "spirited driving" as advised in the instructions, lol.

I have seen the dense white smoke that Seafoam is famous (infamous?) for, but when I went WOT on a 4 lane divided highway near my house, well... lets just say %#&*@!!!! -and THEN SOME! I literally blinded dozens of cars in both directions, lol. And I considered my engine clean, with excessive care and short oil change intervals, always with top tier synthetic oils (Mobil 1, Amsoil, Royal Purple) and a fuel injector/fuel system cleaner every 3-5k miles.

The burn off was so heavy that the car threw codes (P0301-P0308; essentially all 8 cylinders misfiring) and went to restricted performance message - at least the warning; the car ran at full power and up to redline in each gear. A restart cleared it the first time, but 3 more smoke outs and it wouldn't clear until I did it myself with a combo OBD2 gauge and diag tool I have plugged in all the time. Used it to clear the 8 DTC's, afterward the smoke levels reduced over perhaps 5 or 6 more WOTs, until fully clear. Another point: Prior to this, I filled the crankcase with the cheapest synthetic oil available. Draining it after the upper engine clean, it was translucent, but jet black. I generally do any type of clean, even adding a bottle of Techron Fuel injector cleaner just before an oil change. These solvents always end up diluting and suspending contaminants in the oil. I have no idea how MUCH this reduces oil properties or shortens the interval to change it, since I usually only do one oil analysis per car/per oil brand. The color of that oil with less than 100 miles on it told me I did a good thing using sacrificial oil during the cleaning. I am considering replacing spark plugs after one of these cleanings next time. For now I am sure the new(ish) NGK Iridium plugs will clean up on their own. Finally, I have a weak dilution of Techron in this take of gas, to finish up the clean and to help get any remaining deposits off. The end result? Engine sounds really good, runs the best I can remember since purchasing this car with 79k miles. I am glad I did it, but it was a bit disturbing getting misfires and blowing so much smoke people were putting fog lights on.

 

yeah i bet it was scary seeing all the white smoke blazing behind you. Glad it worked out in the end. I may have missed it, but how many miles are on your car?

 

I bought a used ‘06 X350 for cash. After driving home all the warning lights came on & gauges quit. (Except gas) This didn’t show at first. Happened on long drive home. (150 miles) Found estimate in glove box advising ECM replacement! (Buyer beware, saw briefly before purchase & assumed service records!)

Only happened on long trips or idling in take out lines. Once happened car was difficult to restart. (Initially saw on test drive but owner said “battery needed charging!” & it started with a jump from his truck. Suggestions HERE offered battery disconnect, inclination reset, pulling relays, jump starting.

I had been doing all those! Then i found THIS:
Jaguar TECHNICAL BULLETIN XJ413-02 (See attachment); even though the VIN did not match EVERYTHING RLSE DID! Now the bad news; the repair “kit” is nada, too long past! I asked a mechanic if interested in repairing based on TSB & he laughed at the suggestion.

So one time out of frustration I simply ‘pressed’ the engine wiring harness (to ‘seat’ firmly at front passenger side connector) & the problem banished! It’s NOT FIXED but manageable. If I could zip tie it snug I would but breaking the exposed wires is probable. Maybe someone handy with a 3D printer could make a cd precise “cover” that seats on the edges & can be ‘tightened’ with zip ties or something better if anyone else thinks of it!

This may not refer to you at all but I only noticed that you mentioned the infamous ECM problem which is what my car was diagnosed with even though I believe that was incorrect.