Hi all. Let me give you a brief patient history...

Car is a 2000 XJ8L with a replaced engine (also 2000) due to rod knock in the original engine. When replaced, engine also had timing chain guides and tensioners upgraded and all cooling system hoses redone. Throttle body rebuilt by BBA Reman, I have a total of 16 coils - 8 factory and 8 eBay. Runs perfectly up to 85mph, don't want to go faster due to older tires.

Symptoms:
* Idles rough about half the time.
* At steady speeds, flashes restricted performance

Fault codes shown, with commentary:
P0174 - Only showed up once as a pending code
P0300 - Shows up regularly, usually as a pending code but sometimes flags as a solid CEL code
P0301 - Only showed up once as a pending code
P0304 - Showed up once pending and once as a solid CEL
P1313 - Shows sometimes, never flags as a solid CEL
P1316 - Shows about half the time when P0300 shows

Attempted fixes:
As mentioned, I have swapped coils all over the place. Not just between 1 and 4. Swapped bank to bank and that had no effect on 1313 vs 1316. At this point, I am ready to think faulty ECU. Tried pulling the battery overnight and connecting negative cable to positive terminal. When I reinstalled the battery, my radio presets and memory were still there - made me wonder if the ECU was on the same backup system? Smoke test has been done to check for vacuum leaks. Will check spark plugs soon, but they were new when the issues started happening. Fuel filter is new. Always run Chevron premium.

Throw suggestions at me, folks!

Thanks in advance.

 

The first thing to check with seemingly random codes is the electrical system. Load test the battery, check the charging voltage, and inspect/tighten connections from the battery forward. There is a history of the battery ground strap failing from corrosion.

How's that for a first suggestion?

 

Swapping coils didn't id the misfires, right? Try cleaning up the fuel side: a can of fuel system cleaner through a tank (SeaFoam, Gumout Ultra); clean the throttle plate and bore; clean the MAF sensor.

 

Thanks for the suggestions...

Reminded me - battery is new, ground straps are checked. Sprayed the MAF with cleaner. I haven't sea foamed and I haven't sprayed contact cleaner on the electrical connections for the injectors or the coils. Guess that's the next step, but feel free to keep the suggestions coming. I am also going to check the plugs to see how they are looking. Might replace them just for fun.

 

Faulty/clogged injectors?????

bob gauff

 

Next on the list for sure.

Any credence given to the "angry/faulty ECU" theories?

I would immediately suspect fuel flow if it weren't for the intermittent nature of the fault.

 

Couldn't hurt to remove a battery cable and pull and re seat the ECM. Electrical contact corrosion on 15 year old cars works in mysterious ways.

 

Tried it... No change. Even opened up the ECU to check for any visible damage to the board. All pins present and clean, all looked good. Of course, could have been something not obvious to the naked eye.

 

Check your PCV system for a blockage , especially the small hose on left front of valve cover Poke a 1/8 drill bit into the valve cover grommet to clear any buildup and spray a little carb cleaner into the hole ,, check that Hose Carefully , They crack

 

might have a ECU for you to Try send me your Part #

 

Check the larger PVC hose on the Right side valve cover that goes to the Intake hose as they are bad to crack and give the Air Flow a incorrect reading that would change with engine load due to engine mount Flex and cause a Intermittent lean condition , similar to a Vacuum leak but much harder to detect , need any test parts just let me know

 

What are the Fuel Trims doing both when you have the rough idle and when you do not?

Are you sure it is intermittent and not continuous, but you notice it more some times than others?

 

Dave - thanks for the suggestions and offer. Will play with it some more tomorrow and keep you posted.

Zap - I will check trims and let you know. It is absolutely intermittent. Once the car is warmed up, about half the stop lights have a smooth idle. Half of the remaining stop lights have a rough idle for 5-15 seconds and then a smooth idle The final quarter remain rough for the entirety. No noticeable change when at speed, but it could be mild enough to be chalked up to road roughness.

 

So, the P174 is the "flyer" since it is bank B. Lets dismiss it for a minute, since it was only pending once, then you have bank A problems.

Going "off in the weeds" a bit, the 1313 /1316 "possible causes" include worn cam and valve springs, which I think most everyone would discount, but what about a sticking VVT? The other causes include fuel system components and I assume leaking injectors would give serious negative LTFT on that bank.

 

I assumed the '13 and '16 were simply due to the constant misfires, but we all know what happens when you assume things...

Fuel trims showing at -3.9% longterm on bank 1 and 12.5% longterm on bank 2, but I may be looking at the wrong trims... OBD2 is a mystical beast to me once you get beyond checking codes. Give me some SU carburetors any day...

 

Ok, lets just think about the trims... The trims as you reported them means the bank 1 cylinders are showing low oxygen on bank 1, but only slightly. So the ecu wants the fuel reduced by 3.9 %. The bank 2 trims indicate that bank 2 has excess oxygen and the computer is telling the injectors to add fueling by 12.5%.

Even though a misfire will cause excess fuel in the exhaust, potentially burning the cats, it will be reported in the ecu as excess oxygen, because excess oxygen is there too, since it has not "oxydized" (burned) the fuel. Remember, they are OXYGEN sensors.

So, honestly, I do not know how to resolve your numbers with the bank 1 codes. It seems bass ackwards to me. Maybe a real expert like motorcarman or xjrguy will pipe up to advise you!

In the mean time, have a look at Steve's excellent post here if you want to understand fuel trims.
https://www.jaguarforums.com/forum/g...ed-quiz-49317/

Arguably, in my anything but humble opinion, it is easier to deal with fuel injection rather than those damned SUs!

 

I sort of get it now... Don't like it, but get it

I'm getting ready to just take this cat around back and shoot it, but I will keep plugging away. Keep the suggestions coming!