It ran fine took it hole shut it off then hours later when back to get in and start and Crazy misfiring. off So I’ve a Canadian 16 XJR as some may know. Says cylinders 3&5 are misfiring and I can feel it. I’ve swapped plugs coils and installed brand mew OEM Bosch injectors. (Not fake Chinese ones) No correction nor does the problem travel.

is it possible that I’m on the wrong bank ? My understanding is while standing in front of the car looking down at the engine 3 and 5 are the middle two on my left. Or if you were in the car the passenger side. Am I simply working on the wrong two cylinders ? Any other thoughts other than compression check? Thanks

 

(secret) There is a magic contact restorer that seems to work wonders with the misfire issue...DeoxIT D5 actually improves the connection as well as cleaning the terminals 🤗

 

Bank 1 is on the RH side of the engine when viewed from the driving position, thus cylinders 3 and 5 are on the same side adjacent to each other.

Is there any noticeable smoke or vapour coming from the exhaust during the misfire event(s)?

Do not operate the vehicle under conditions that make the MIL flash as catalyst damage is occurring.

 

contect restorer ? What contacts , like battery terminals ? Plugs and injectors are brand new.

 

so I was correct on my cylinders I worked on. As I’m looking down at the engine from the front of the car it’s the middle 2 on my left. Not that I’ve noticed on smoke or vapor. Well I’ve had it started a couple
times. But no im not driving. So what do you think is going on ? I’m having to use my viper as a daily driver and these streets suck !

 

The contacts on the injector socket are not new, and are oxidized.

 

well the injectors are brand new I just replaced them with new ones so how could they be oxidized ?

 

They're talking about the connectors that you plug the injectors and/or the coils to, which are not new unless you replaced the cable harness.
It's not likely that they're corroded, especially multiple ones. But it is possible, and it's always good to follow their advice and clean connectors that you are not replacing (of the cable harness) when the need to disconnect/connect them comes up - and to apply an electrical dielectric to protect from future moisture intrusion that would eventually result in some amount of corrosion that could interfere with the electrical path.

Another more serious possibility (and unfortunate) could be that the bank 1 head gasket is leaking due to overheating at some point, possibly before you bought it.
A couple of ways to identify this would be using a boroscope or inspection camera to look into the cylinders for signs of wetness in cylinders 3 & 5 after the engine has cooled down. and if the piston domes look cleaner (steam cleaned) than in other cylinders. Also, inspect those spark plugs & see if the color of the carbon looks different from the other cylinders. You could also keep an eye on the coolant and see if it might be slowly getting lower, or building pressure in the coolant overflow tank that remains after the engine has completely cooled - there should be no residual pressure, and coolant should never be lost or consumed.
If any of this is happening you have a head gasket problem on (at least) bank 1.

 

Wow great response thank you. Sorry I wasn’t even thinking of the connectors. Well I’ve unfortunately/fortunately sprayed all those down with some electrical contact cleaner when I did the injector cleaner so I doubt that’s my problem either. But I’ll go check again never know. Thanks what’s more likely is the head gasket I bet. Remember I got the car hot when I blew those pvc pipes in the engine bay and removed my supercharger. But I hadn’t noticed any issues since everything was all back together.

I’ll see what I can find and report back. Thanks

 

Can you post pictures of the injectors you installed? We need the lettering at the top of the injector. Need to make sure they are not counterfeit. Where did you purchase them from?
Do you still have the stock OEM ones you removed?
Generally it's best to replace all 4 injectors on that side of the engine.

If you suspect the head gasket it's simple to test the coolant for combustion gases. The kits run about $40 or so.
How does the oil look? Maybe suck a small sample out and check?
Your symptoms don't point to head gaskets but who knows?
Can you post the codes?
.
.
.

 

so I already feel for the fake injectors and got my money back I got the Bosch ones that I paid up for with the circle H and all the other exact holograms in every spot as the ones I took out. did extensive reading into that so these are 100% authentic this time. So I did replace all 4 of them on bank 1 there. And if they were fake I’d think 1&7 would start having issues also along with 3&5. Unfortunately didn’t take any pics but they are real and I got my money back on the first batch. I’ve not looked at the oil but I guess I can. I doubt it’s a head gasket but who knows.

 

Oil appears normal and fine to me

 

I hope not; I wouldn't wish that on anyone that isn't looking for an opportunity to tear their engine apart.

 

Oil doesn't tell the whole story unfortunately, you can have an internal headgasket leak in the water jacket that doesn't affect any of the oil galleries. Coolant test for hydrocarbons as mentioned above would confirm that.

Have you tested compression in cylinders 3 and 5? Have you tested your coils for proper resistance values? If you pull out the spark plugs are they wet with fuel or completely dry e.g. is an injector stuck closed? Are your spark plugs gapped correctly? Are your engine to body grounds properly connected? You didn't smear dielectric grease on the head of the spark plug before reinstalling the coils did you? There is a common misconception that dielectric grease promotes conduction, but it is quite the opposite. It is an insulator.

 

I agree that an oil test might not help, although when I had a "blown" head gasket with the AJ133 engine (but in my 2012 Range Rover) when I sent oil samples to Blackstone Labs they did identify what they expected were higher than expected traces of coolant elements in the oil.
I do have a coolant test tool & although I tried that several times to find hydrocarbons in the coolant, it only changed the color of the (fresh) detection fluid barely if at all - so that didn't help either.
The slight head gasket leak that happens when these overheat is tough to detect.
I posted in this forum about the experience with my Range Rover AJ133 head gasket because it is the same engine. The biggest indicator I had was that after a good highway trip of a 5 or ten miles or more, my cooling system would be pressurized higher than from coolant expansion alone. And after the engine had time to fully cool afterwards (a few hours or overnight) residual pressure would remain in the system - if I opened the coolant tank after it cooled completely I would hear the pressure escape..
And I also used my boroscope to look into the cylinders and saw the middle 2 cylinders on each head looked cleaner than the outer cylinders, and the look of the spark plugs.
And of course occasional misfires on start-up that I wouldn't have noticed other than from OBD data.

All that said, I drove my RR for four or five years (and 30k - 40k miles) with the "blown" head gasket while I tried myriad head leak chemicals and products - none of them worked. But as long as I did monitor the coolant, usually cracking the coolant tank cap after getting out after longer drives and adding small amounts of coolant as needed, it was fine until I got around to finding the time to pull the heads to replace the gaskets while also replacing the timing chain tensioners/rails.
But again, that was after years of just managing/mitigating the problem.

 

Depending on how long you’ve been misfiring and not knowing it, recheck your spark plug gaps, especially on those cylinders. If the gap has grown - your cats are likely destroyed - at least on the passenger side of the engine.

Just went thru the same thing. Failed injectors (unknown how long they were failing) to Fake Chinese injectors, to factory Bosch genuine. Ran fine until I started getting cylinder 3 misfires. Pulled the plug to find a massive gap change. Changed all 4 plugs on that side again. About a week later I started getting cylinder 3 misfires at anything over 1/2 throttle. Pulled cylinder 3 plug and the 3rd plug is gone.

Pulled my hair out trying to figure out how.

Clogged cat. How am I solving it? No more cats.

 

Exhaust should be really loud now...

 

LOL. It was loud before that considering it’s got a muffler delete.

 

Joining to the thread.
I’m having similar issues with 2015 Land Rover Range Rover 5.0 Supercharged Engine. Misfire on cold strat (cylinder 5, sometimes 6 as well). No signs of blown head gasket. Leak down test shows 5-6% on every cylinder. New spark plugs, swapped coils, new injectors. One thing to notice about injectors: 2 came 2023, 2 - 2025. These 2025 didn’t have the plastic cups. After installing them the misfire didn’t change, so I doubt they are fake.
After couple of minutes obd shows no misfire, but I still can feel it slightly.
Will do the head gasket test shortly.

 

I don't think you're chasing an actual mechanical problem. Sounds like you've got the wonderful task of chasing vacuum leaks. Since JLR engine bays are full of plastic hoses that get brittle with heat, there's likely a small crack somewhere that's causing your issues. Probably at the back of the engine around the stupid symposer. I've slowly replaced all my plastic hoses with silicone. Just cut the factory connector off and building custom lines is super easy. It's how I solved all of my miss-fires after injectors, plugs, coils, valve cover with integrated PCV that cracked, etc... Good times.