Hey Everyone!

Bought my dream car 2011 5.0 XJ SC a year ago with 90k. Now it has 125k.

Recently my car has a rough idle when in gear and stopped at a light. The severity of this varies, sometimes not at all. I have had intermittent reduction in power on the highway when accelerating, only once or twice.

No engine light but did get a misfire cylinder 4 code. Changed the ignition coil on cylinder 4, problem persists.

This seems to be an issue on a number of vehicles. Does anyone have any suggestions? Not looking for too much for speculation but actual user accounts.

Thanks in advance!

DS

 

Well then I won't tell you that is most probably an injector that has a bad spray pattern at idle and if it can't be cleaned up they are replaced as an assembly of 4/bank. But I'm just speculating and that is why I only use "Top Tier" rated fuel. You could try injector cleaner in a tank of gas. I always user BG K44 Fuel Injector cleaner and that has worked for me in the past.

 

Thanks again. Id call your input more of a hypothesis than "speculation"



I switched from ultra to 94 octane, which is the highest you'll find in Canada. I ran injector cleaner through but ill try the BG K44, as this is the one always referred.

I think it could be dirty injectors due to the age, mileage and the fact this was never an issue over the last year.

Dan

 

CIts's not the octane so much as the cleanliness and the detergents. that is why "Top Tier" rated fuels is a rating association here in the US and am not sure that is identified on the gas pumps in Canada.Too high an octane is not the answer as it may even impact performance and is no assurance of the cleanliness and detergents in the fuel. check this site out and you will find there are several brands available in Canada.
https://www.toptiergas.com/licensedbrands/

 

Thanks again!

Checked the website and apparently I use a "Top Tier" brand (Petro Canada). Petro Canada has the Ultra 94, which I was told burns at a higher temperature which could help with clogged injectors.

A couple tanks with BG K44 and hopefully ill see a difference.

Dan

 

Octane is a measure of burn rate the higher the octane the longer the combustion time, so using an one much higher than specified is a waste of money and efficiency. The best performance I have gotten is using 1/2 tank of 89 octane Sunoco racing fuel mixed with 1/2 thank Sunoco 93 pump gas. IMHO

 

Do you think increasing combustion time will help with cleaning the injectors?

Especially when run with injector cleaner?

Dan

 

IMHO No as the burn is slower the higher the octane and there are more residual unburnt hydrocarbons that go out the exhaust. What I recommend is using no more than 93 octane and running a full fill-up with the K44 added at the start of your fill. These engines use high pressure direct injection and it's what is going through the injector that needs the cleaner not the cylinder combustion chamber..

 

Thanks!

Is the burn slower because it needs to reach a higher temperature to fully combust with higher octane?

Chemically, it doesn't make sense to have more non-combusted byproducts when combusting at a higher temperature.

DS

 

The burn is slower to allow higher compression without detonation. Ever put the wrong gas in a car and heard it ping, that is detonation and will destroy an engine if used continually. Way back in the 1960s my Father lived in Paris France and had a Pontiac Grad Prix brought over from the States. He could never get high enough octane gas and the engine blew holes in the pistons after 10k. Of course, at that time, it was cheaper to replace the engine. And again 10k and the engine failed.

 

Thanks for all your input!

Rough Idle -->Cylinder 4 misfire code --> changed cylinder 4 ignition coil
Have new plugs
Ran multiple injector cleaners through the system
Cylinder 4 misfire code again

Overall, the problem still persists.

Jag thinks injector needs to be replaced (hopefully, all things considered).

Bringing it to the dealership tomorrow. Hopefully its figured out painlessly.

DS

 

Be aware that any DI engine can suffer from carbon build up on the backs of the intake valves. Since DI puts the fuel directly into the cylinder no cleaner in the fuel can help with this.
There is a Motor-vac service that is suppose to clean this up but I have heard mixed results.

Take a look at this explanation.

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Thanks dude!

This looks like the worst case scenario. Funny this was mentioned to me already by an Audi mechanic!

It will be much more expensive then replacing a injector.

Wish me luck

 

Sure hope you figure it out and post back.
It's a mystery for sure?
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Got my car back today. Have to say, I'm happy with Buds in Oakville.

Cylinder 4 injector changed....now it runs like a charm.

They took out the entire block of injectors on that side and cleaned the other 3 injectors.

It was 8 hours of work though!

With the injector and ignition coil my repair was around 2k total.

DS

 

Glad you got it fixed and also for reporting back what the repair was.

We have so many threads that just die with a problem but no solution!
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