I recently changed plugs in my XJ8 and also two Ignition coils (one at number 3 cylinder and one at number 2 cylinder). The car purrs like it should until it comes up to running temperature, and then starts missing and goes into a " restricted performance" mode. OBD reading states a "lean left bank". If I let it cool down, it runs fine again until it gets to running temp. I should state that I replaced the thermostat about 1300 miles ago (smog requirement) and it took about 1100 miles to clear the code from the computer. The car ran fine until now. Could that have caused the current problem? I don't want to have to try and solve this one problem at a time. Any help would be appreciated.

 

So you've changed coil for cylinder 3 ( Bank 1 ) and coil for cylinder 2 ( Bank 2 ). Now once it warms up, you get lean code for bank left bank ( Bank 2 ), should be P0174.


Did you replace with Genuine plugs and coils? Sometimes aftermarket coils can cause issues....


1 common issue is the air intake pipe from air box to throttle body - they become loose on throttle body end, make sure this is fitted correctly and tight.


If you're able to read codes - what other codes do you have logged, if any?

 

Thanks for the quick response. I only received the P0174 code using the OCB reader. The plugs are the required ones per the owners manual, and the coils are aftermarket models. I would imagine them to be equal to dealer coils (but at a greatly reduced price).
I will look at the intake hose tomorrow and hope that tightening all clamps will eliminate the problem. IF NOT, could clogged injectors be the problem?

Thanks again to all "Cat fanatics" that are on this forum and help the rest of us newbe owners. It's been over ten years since I owned my first JAG (1984 XJ6)
That one was easy to work on compared to this one. No computer modules to deal with on that one.

Oh for the good old days!!!

 

I remember when the S-type came out, and when the coils needed to be changed, we were seeing issues when customers wanted to get aftermarket ones, sometimes they wouldn't last very long. Just keep in mind that with these newer ones, sometimes its better to stay with genuine.
Was it doing the same thing before you changed the plugs and 2 coils, once reaching operating temp, then goes into restricted performance?


A fuel injector could cause issues, but I haven't seen a fuel injector cause a P0174. Seen them cause misfires, or will log an actual code for injector itself. I have seen on occasion MAF cause P0171 & P0174 to be logged. You could try taking it out and cleaning it, see if that makes any difference.

 

Why don't you simply troubleshoot by swapping oem ignition coils, placing all oem coils to left bank and two of the aftermarket coils to the right bank and see if you have the same code. If code now lean right bank, then you know aftermarket coils are bad. If you have same code of lean left bank, then it must be other issue.

 

Thanks again for all the quick responses to this problem. It seems that the original problem code PO174 is gone only to be replaced by a new one PO202 (injector circuit/open cylinder 2). I changed plugs, including #2 and replaced the ignition coil for #2 after the last bout of code battles. After checking the plugs again, I find that even though they are the same manufacturer and the same part number, the almost invisible last three digits are different, 658 for the old and 558 for the new. In holding one against the other for comparison, the new (558) is about 1/8" longer than the old. If my memory hasn't turned to dust in my old age, I remember that would mean a hotter burning plug, am I wrong? and wouldn't that affect the entire scenario. Oh for the days of spark plugs and distributors and four barrel carbs, or in the case of my old 58 Corvette, 4 Stromberg 98"s

 

I meant Stromberg 97's. I guess the memory is getting dusty.

 

I can't answer your question specifically without knowing exactly what plugs you installed but I have had personal experience with the wrong heat range plug cause a problem once the engine reached operating temperature. Actually the problem would start regardless of engine temp since once the plugs got hot enough they'd start breaking down and misfiring.

It's certainly worth checking the specs for the plugs you actually installed.

 

Thanks again to RDMinor, annamiata, and JBzXJ40 for your help in diagnosing this gremlin.
I took the car to a mechanic I have used for years, expensive but honest. He told me that the brown injector wire into the fitting had a signal, but the black wire was dead, he also said that the area around the injectors had animal feces. The car was sold to the dealer from an auction site hear in SoCal. It may have been sitting for a while near an open field to get critters in the engine bay. He is going to check continuity from the computer thru the wire to the injector later today. Hopefully that cures the problem, a computer is $2000.00 where the replacement wire will cost $305.00 including labor.
Fingers crossed all will come out OK.

 

Just got the word --- it's the computer. Anybody want to buy a slightly used jag??

 

There are plenty of modules on the Jag so which is it? Specify and get the part # off of whatever one it is.

A used but generally tested ECM for example is available on eBay for anywhere from $138 and up. Other modules are also available so don't pull the trigger on unloading it so quickly.

https://www.ebay.com/itm/2004-XJ8-En...taUwS8&vxp=mtr


Search eBay automotive under parts and use the query 2004 XJ8 ECM and you'll get a listing of all kinds of Jag electronic modules. Match the model, year, and part # and you may find a winner.

 

Thanks for the Ebay tip, got one for $138.00 with a warrantee. Right after looking at the wiring harness, and then deciding to take a break for a couple of days, the Jag magically healed itself. No more misfires, even when punching it. Guess the mechanic did something mystical with his tester. I'll hang on to the ECU though, sure as I send it back, the trouble codes will reappear. Thanks again for all your help through this code unscrambling mess. Go Pat's (Superbowl Fan).

 

REAL electrical problems and bad modules don't fix themselves so I'd be a bit concerned about your tech's call on this one. I certainly hope your problems are behind you though.

 

Thanks for the input: I don't know what happened, but I'm going to drive it and keep the computer and a tool set in the trunk, for that whatever moment. speaking of past and present cars:
Present: 2004 Jaguar XJ8, 1998 Dodge Ram 2500 V10, 1988 Jeep Cherokee Limited (273,000 mile strong), 1971 MG Midget, 2010 Mustang Cobra
Past cars: 1949 Ford Convertible (my first car), 1953 Oldsmobile 98 Convertible (Huge car), 1955 Buick Century (My first engine mod- went from 322 cubic inches to 411), 1958 Corvette with both tops (military called and the car went), 1961 Ford Station Wagon (2 kids now), 1965 Lincoln Convertible (talk about a huge car), 1967 Lincoln 4 door sedan, 1972 Ford Thunderbird, 1984 Jag XJ6, 1996 Volvo Sedan. Also Had a few Motorcycles in the mix, mostly Yamaha's. Getting too old for anything other than maybe a trike.

 

An Update: Seems the tech didn't release the injector pigtail lock, on both numbers 2 & 8.
found out when I went to replace the injector on #2. Then when I plugged it all back in, a series of code came up on #8 that made me think I would destroy the engine if I let it run a minute longer. That's when I discovered that the injector connector was halfway off the top of the unit. I pushed it back on and all codes disappeared. Car is running great now but has the "Parking Brake Fault / Apply Parking Brake" notice. I had the battery disconnected while working on the injectors, could that have caused this reading? Thanks again to all who have helped me on this forum.

 

has the "Parking Brake Fault / Apply Parking Brake" notice. I had the battery disconnected while working on the injectors, could that have caused this reading?

Just turn your ignition position 2 and press the footbrake while pulling the electronic brake lever upwards and letting go.

 

Yes. Just reset it.

 

Did the steps you outlined, and it went away, Now the car runs great, and I haven't had to replace the computer. Fingers crossed !! Thanks again to all the members that have helped me through this seemingly endless progression of codes.