Hello,
My vehicle is a 2008 Land Rover LR2 with 144K miles. I’ve had it for two years now. It's been an excellent vehicle. I try to stay on top of general maintenance. My only major expense was replacing both rear wheelbearings. Anyway, I had my spark plugs replaced recently but was unaware that I needed 6 rather than 4. So, a friend replaced 4 of the 6 about 2 weeks ago, and I ordered 2 more, which have yet to arrive. Up until a few days ago, everything was fine. My truck was parked sitting in idle when my temperature gauge increased and the engine light illuminated. I turned off the engine and checked the coolant level, which was normal. So I plugged in my OBD scanner and received several misfire codes: +Random misfire & +Cyl 6, 5, 4, 3, 1 misfire.

My questions are whether this is because the 4 new spark plugs are overcompensating for the 2 bad ones, and whether I was using unleaded gas instead of premium gas the week before this occurred (because gas prices are out of control)? I understand that using unleaded may cause damage to my engine, but I have only done so a few times. Any suggestions on where the problem is coming from would be greatly appreciated. Thank you.

P.s. Only spark plugs were replaced, not the wire harness. Not sure if that is a problem or not.

 

Guessing that this problem is a result of the work recently performed, and optimistically hoping for a simple fix:

> Check if the cable for the MAF sensor is tightly connected. It goes to the air intake above the air cleaner box. Your friend might have knocked it loose while replacing the plugs.

> Listen for vacuum leaks (hissing). He might have knocked a vacuum hose loose.

After you eliminate those two possibilities, the remaining scenarios are a bit more involved.

 

And you used 85 octane as opposed to the called for 91 octane... you may have a pre-ignition situation. Either get some octane booster in there or fill it up with the spec's fuel.
What's interesting is that I run high octane even in the lawn mower... as the engine does run better.

 

It's possible the car is adjusting stuff based on the o2 sensor, which will be an average of all cylinders... obviously you have two which probably are sparking differently than the rest. Best get those other two plugs in soon.

But that should have nothing to do with the coolant temp.

Definitely run 91 octane (or your premium if you're at a high elevation).

 

One problem at a time.

Start with the Temperature gauge increased.

The Thermostat on the 3.2 inline 6 cylinder is a known failure point and there is some evidence that a broken Thermostat may cause the ignition coils to run hot and for the coils to fail prematurely. Replace the Thermostat they only last about 10 years.

The second item to consider when the Temperature gauge rises is the cooling fan for the radiator. These also are know to fail. Does your Fan turn on? If the Temperature is above the middle the Fan should be on and at it highest setting.

It is possible that the Thermostat broke the coil packs and you may need 6 new coil packs.

Summary

1. Don't use low octane gas (see the responses from the other posters)

2. Verify the Radiator Fan is working and replace it if it isn't

3. Replace the Thermostat

4. Get a scan tool that can check for misfire counts and use it to verify your fix (the MIL is only illuminated if you have so many misfires that the emission may not meet specification of the Catalytic Converter may be damaged.)

I use this one

Autel AL539B OBD2

Good luck

Paul

 

And low or medium elevation. The car has a high compression engine. Not running premium gasoline risks knocking and mechanical damage.

 

For clarity, gas stations at high elevation (above 3000?) will sell a lower octane fuel as their "premium". That's OK when driving in the less dense air.

I've seen 91 (and maybe 89?) sold as premium in mountain country.

So don't fixate on the octane, just buy premium from a Top Tier brand: https://www.consumerreports.org/fuel...e-a7682471234/

Nuance... if you fill up in the mountains and then drive down to sea level, that's OK occasionally, that's what your anti-knock sensor for. But if you happen to say commute between Tahoe and the Bay Area on a regular basis, try to buy most of your gas down at sea level (probably cheaper anyway, than in mountain towns).

 

This is correct. At altitude the lower air density will result in a richer mixture, so if you regularly drive at higher altitudes using lower octane gas is OK, but if you alternate regularly between higher and lower altitudes you should stick to at least 91 octane with these engines.

 

Just to be clear, it’s not a richer mixture. Our cars have high altitude compensation systems. At high altitude, the compression in a normally aspirated engine is lower because there is less atmospheric pressure, which increases the margins for preignition, hence lower octane fuel provides the same margin as high octane fuel does at lower elevation.

 

The gas engine does not have such a system. The diesel engine has one to prevent overboost at high altitudes. Look in the service manual -- there is no mention of what you speak of.