Unable to fix misfires, ready to get rid of car
 

In January shortly after I replace a failed electronic thermostat we started getting random misfire and misfire with fuel shut off codes. Never the same cylinder.

Some times the car would code after driving 2 miles, other times it would be 80 miles before a misfire. I have to pull over shut the engine off and restart to make it run ok.

I have replace: spark plugs, all coils, air flow sensor(MAF), all CCV valves and hoses, Pre cat O2 sensors, inspected and cleaned and replace O-ring on DISA valve, inspected and cleaned throttle and idle valves, replace intake boot, replace fuel filter, removed cleaned and tested injectors, replaced every vacuum hose I can find, engine oil flush and clean. I also washed and waxed the car.
I even took it into a local european import auto repair shop where the guy charged me a lot of money to tell me he couldn't find anything wrong.

I have done everything I can find to do or someone tells me to do. Also checked the compression which is all good.

This is going on for 9 months, we cant take the car anywhere to far from home or on the freeway due to having to pull over and restart.

I have really like the X5 but this is no longer fun.
Im a 30 year licensed aircraft mechanic with quite a lot of mechanical experience and have up till now been able to fix any issue.

Since all this started shortly after I replaced the thermostat, last week I replaced it again using an BMW brand electronic thermostat. Same problem, no change.

Any last suggestions before i start parting the thing out?
Any one interested in a manual transmission X5 with a lot of new engine parts?

Not to be the bad guy, but I'll buy your x5. I'm local :) pm me if your serious

Have you hooked it up to INPA?

What about crank position sensor? Have you checked that.

^I literally came in to post CPS. Has your indy logged it on an Autologic to see if he can get some real time data on the misfire?

Random misfires checklist:

1. Check for leak in vacuum hoses. Some of them are under the I.M., and difficult to see/detect.

2. Cam Sensors (BMW brand only)

3. Crank Sensors (BMW brand only)

4. Coolant Temp Sensor, located near 5th and 6th cylinder area...

You're not a bad guy, if you are willing to buy his broken X. You're only a bad guy if you offer him less then what it's really worth.

Sounds like you been just throwing parts at it hoping it will fix the problem. A misfire is interpreted by the ECU as a cylinder that is not producing the same amount of power as the other cylinders. How can a computer determine this? By noting the rpm of the engine. A lean cylinder could also be interpret by the computer as a misfire. Before throwing more parts at it, you need to perform or have perform a good diagnostic of the engine.

What was the reason for replacing the thermostat? Was it stuck in the open or closed position? You said that you checked the compression? What were the readings? If they are not with in 10% of one another that could be your problem.

You say that this has been going on for 9 month, but it only started after you replaced the thermostat last week. I'm confused????

Do you have a Check engine light on? If you do what was the trouble code?

If you had a rich or misfire condition for the pass 9 months and just ignored it, your cats could be toast. You need to post some more info in order for people to help you.

I may be throwing the hail mary pass, but ive had it once, where the fuel pump /fuel filter, wasnt able to supply enough fuel and thereby caused a misfire, (BMW also adds fuel cut off if it detects too lean (no fuel??) and shuts off the injector(s) in question.
I was able to solve this issue by changing out the fuel filter and reconfirming fuel pressure from the pump. (but not untill most of the ignition system was changed.!)
my big clue was that even with NEW coils and NEW plugs i still had a RANDOM misfire with fuel cut off. meaning there was still not enough fuel randomly dribbling out of an injector somewhere to produce adequet spark!
just my $.02 worth

Upallnight, thanks for the reply. We have chatted about this in the past.

To clarify some things. Original, in January the thermostat stuck open, I replaced it then, a couple weeks after the replacement is when I started getting the misfires. Last week I replaced the thermostat again thinking that since it was an off brand it might be giving bad info to the ECU.

Yes I get a check engine light with these codes; P1351,P0304, P0302, P0306, P0303, P0301, P1345, P1342. P1349,

I understand that the cats could be failing but Im not replacing them until I get the misfires fixed.

Compression test reviled 165 psi cyl 1-4, 160 psi 5 & 6.