My 2005 LR3 displayed a Reduced Engine Performance signal and began hesitating and idling rough. My mechanic diagnosed it and the codes showed a misfire on 6 and 7. He put all new plugs and ignition coils in the 2 cylinders with the misfire. It didn't fix it so a more advanced diagnosis said it was the PCM. I bought one off ebay that had matching numbers but then found out it couldn't be reflashed except by a Land Rover dealer. I bought this vehicle to sell so obviously I don't want to spend $1,800 for a new PCM and whatever other charges they may tack on. I now wonder if maybe the original PCM just needed reflashing. Any suggestions would be greatly appreciated.

 

What was this more advanced diagnosis? Anyway, are you sure its not the PCV valve or such? Rough idle, hesitating can be lots of things but a new PCM would be the last thing on my list. In all the years I have owned and worked on cars, I have never experience a bad PCM. It can happen, but its not likely.

 

Thanks for the response. I buy and sell a few cars as a side business but if you put what I know about engines in a thimble it would rattle like a BB in a boxcar. My mechanic first used a portable code scanner but when the new plugs, etc. didn't fix it he used his friends computer. It said the problem was the PCM. I would love nothing better than that to be wrong but that's what it read. Everything else works fine.

 

The Rovers like very specific software for accurate diagnosis. Unless it was Rover software it could be a misinterpretation by whatever it was. Misfires can happen but there are things that can cause them. I suspect if you have a rough idle, you have multiple misfires but the only codes stored were for those two cylinders. The PCV test, lets just do that for the heck of it so we can rule it out. Remove the beauty cover, it has captive bolts so they wont come out all the way. Very small heads, like 6 or 7mm, four total. Once removed note the flat disc shaped item on the passenger side of the engine towards the front. Almost under the intake tube. There is a black plastic hose. Unplug it at either end and block each opening. Or have someone start the vehicle while someone plugs both sides with a couple fingers. See how it runs. Its a common failure item and causes rough operating. It fails wide open and is basically a large vacuum leak. Same goes for the oil dipstick tube or oil cap. They all need to be tight or they can cause issues, but the PCV is the worst offender.

If there is no charge, we can move onto a few other things before we assume the PCM is toast. Ideally proper Rover code reader may help to really dig into things.

 

I'll try it. Thank you very much. Hopefully you save me lots of money and headaches. I owe you a steak and a beer if that's it.

 

Definitely not a PCM. Also, even the dealer cannot program a used PCM, its new or nothing at all.

I would suspect clogged or faulty injectors as he already changed coil and spark plug.

Also, Fire your mechanic. He should have moved the plugs and coils to other cylinders to see if the misfire followed.

 

Thanks. My mechanic usually just handles simple things. He has changed out an engine for me but it was on a Ford Focus. I realize a Land Rover is a horse of a different color. There is another garage nearby that specializes in imports and has been there for years. He's as good as there is. He's expensive but still cheaper than the dealership. He will figure it out.

 

Cool. It’s always tempting to just change a new part, but to diagnose you should always swap around components when you have multiples to help diagnose.

 

He has taken out the injectors and has them soaking. PCV valve checked out fine. It's idling fine now but still skipping and hesitating on grades when the engine is in a strain.

 

He should do a fuel rail cleaning. But maybe his soak method will work. There is also some you tube video on making a home testing/cleaning set up for injectors with a 9 volt battery.