2008 LR2, head gasket replaced, erratic cylinder miss-fire since then
 

First post, please let me know if I can clarify or format anything better.

Bought this car two years ago, it was dealer maintained before then, and I took it to an official land rover tech after I purchased it.

A dying thermostat clogged my radiator that ended up over-pressuring a deteriorating water hose in the middle of standstill traffic. after losing all the water, I got off the road as quickly as possible but the damage was done. It shut itself off right as I was getting off the side of the road, got it towed to the shop, he fixed the water hose and said it was good to drive (despite my being sure the head gasket was gone) drove it another couple weeks, it was constantly sucking water, I took it in to mechanic to get a gasket pressure test, which it passes with, and as I was driving it off the lot white smoke starts pluming from my tail pipe.

turned it back around and asked him to fix my head gasket, which he finally agreed was a problem. 4500 dollars later I drive it off the lot and everything is smooth (they shaved the head and did a valve job), 10 miles to work everything is okay, 8 hours later, drive it 10 miles home and my check engine light flashes (about 8 times I think) and the dash display warns me "Reduced engine performance" and the check engine light stays on, I immediately turn it around and take it back to the mechanic.

a few days later he says its a ghost miss-fire, going between 4 of my 6 cylinders, but there's nothing to be done about it except maybe a new computer which is looking to be another $2500.

I can't really put any more money into it, I want to cap future repairs to my own handy-work and 200$, I looked on ebay and I can get a computer for a few hundred, but I've been warned it probably wouldn't work with a different VIN to what was flashed onto it.

So the check engine light is permanently on, but there are some times I can make it blink, and I think the blinking is when it sends the fault code.

It blinks when the car is under load on the freeway,

and it blinks when I'm driving home (not under much load) and I reach the top of a large bridge and take my foot slightly off the accelerator.

each time the check engine light blinks it's attached to the "reduced engine performance" message.

Please advise how I can make this car last so I can love it again. it has 140k miles on it, I've only gotten to put ~8k of those, and I'd like to drive it into the hundreds of thousands.

Please provide any OBD2 codes & descriptions.

Hi LR2Driver!!

I've got P0300 Random/Multiple Cylnder Misfire Detected
P0301
P0304
P0305
P0306

all Cylinder X misfire detected.

I drove with the OBD hooked up, and wouldn't see any mis-fires while driving under normal loads, I've yet to try reading it live in the two conditions that I described in OP

My dad (retired electrician) has suggested maybe a complete computer restart, take off battery terminals and short them together with the door open to drain capacitors. Once it stops raining here I'm going to try that.

I've had two separate incidents that involved a misfire on one cylinder. The first was resolved by cleaning the Mass Air Flow sensor. The second was resolved by re-sealing the brake vacuum pump which had a leak. But I did not have misfires across four cylinders, so your problem may be different.

Hopefully the additional info you provided on the OBD2 codes will prompt suggestions from others.

Ah yes, I also just changed spark plugs due to possible fouling when the head gasket failed. I'll look at the coil pack and crank shaft sensor next, thanks for the advise!

I will also keep this updated as more symptoms and codes come to light.

Here is a link that talks about Thermostat failure (overheating) leading to coil pack failures

Ignition Coil Failure - 2009 XC70

Please let us know what works

Take care

Paul