This morning my 2000 XJ8L decided to throw P0305 and P1316 codes...
We don't drive the car a lot -- probably about maybe 25-30 miles on weekends and it mostly sits in the driveway all week. Starting a couple weeks ago, it threw codes for both banks running rich. The car ran fine, although the last time it threw those codes it went into restricted performance mode as well. That was Sunday. Again, other than restricted performance the car ran fine. I reset the codes and the car sat until last evening, when I went out and replaced the air filter (which wasn't really very dirty), made sure the intake was clear into the filter box, cleaned the intake snorkel (out of the car), and cleaned the part-load breather. In the process of removing the left-side engine cover to get at the breather, I managed to break the coolant tank-to-radiator hose right where it goes into the clip at the tank. Ordered a new hose, and in the meantime found a small piece of tubing that fit into both the clip and the end of the hose pretty tightly. I epoxied that in place, buttoned everything else back up, and let it sit overnight for the epoxy to cure. The intake snorkel and full-load breather did have some oil in them, which I cleaned out thoroughly and attributed to the part-load breather being clogged. Which it wasn't really, but I cleaned it anyway
This morning I went out and started the car to let it warm up fully and make sure my patch will hold before driving it. Upon cold start-up (40 degrees outside) it ran a little rough, which it sometimes does, so I just let it do its thing for a while. As the temp gauge came up off the peg, the engine started to "hunt" or have unstable idle. Couldn't decide if it wanted to idle at 650 or 300 rpm. If I nurse the throttle it smooths out. I took it for a drive around the neighborhood, and starting from a stop or accelerating away from a slow corner it falls on its face and stumbles for a few seconds until speed comes up a little. If I floor it, it will stumble up to around 2000 rpm and then light off like a scalded cat right to redline. Partial throttle, falls on its face...
As I pulled back in the driveway, the check engine light came on with the P0305 and P1316. Car continues to stumble at idle.
Some other background info: I got the car running and driving in October of 2018 with 101,000 miles on it after a 6-1/2 year slumber. New timing, coils, plugs, alternator, starter, water pump, fuel pump, filter, relay, ..... Really went through all of it. It has run beautifully since, with 118,000 and change on the odometer now. I plan to do the transmission fluid and Transgo pressure regulator along with some other maintenance items this summer.
The current problem has never come up before. The only thing it's done that could be even remotely related is that it will often run into a bit of a wall at 4000 rpm in first coming hard off a stop. 2nd gear and beyond or partial throttle, no such issue. I have attributed this to potential issues with the VVT solenoids and/or cam position sensors, all 4 of which will be replaced this summer. However, that issue has never resulted in a check engine light, only a little hesitation as though the computer is reluctant to give me that extra boost from the VVTs.
Any thoughts? I'm a little stumped since this came on so suddenly and without any warning other than the recent run-rich situation
Sorry for the long post -- just trying to be as informative as possible to hopefully get past some of the more obvious stuff...
Thanks
-Steve-

 

Do you keep the battery charged with a Battery Tender, CTEK or similar device when the car is not being driven? The battery should show at least 12.4V before starting with a multi meter to avoid getting spurious codes.

 

Battery is a 2-year-old H8 AGM. While I do not keep a tender on it, the car gets driven at least weekly so I'm confident the battery is fine.
Thanks
-Steve-


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Your first post claims you drive 25-30 mi/wk. That may not be enough to keep a Jag battery up, but if you don't want to check the rest voltage, that's up to you.

 

I will check it. Just in my experience batteries below 12 volts won't start an engine so since it started fine (not even slow crank) I figure battery is fine. But I do see where you're coming from -- I know these cars are very voltage-sensitive.
If voltage is an issue, then which causes what problem -- did the rough running cause the check engine light or did the light make the computer think there's a problem and make it run rough? ....
Thanks
-Steve-
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I expect it's a failing coil.

You could check the fuel trims in case they're bad.

 

p0305 is misfire cylinder 5. I expect 1316 is just the same misfire (but may reflect multiple misfires, just not enough to set a specific cylinder). Have you pulled the plugs to be sure there is no fouling or tried moving the coil and / or plug to another cylinder to see if the trouble follows? These engines can run minus a cylinder or 2 with no major symptoms showing until load comes on.

One caution is to minimise driving if there is a chance that the cylinder isn't firing at all - as the raw fuel could be getting dumped into the exhaust and will ruin a cat pretty quickly (I learned the hard way on my truck when I reversed 2 plug wires and then tried to clear the resulting miss by going for a short drive - cat ruined in under 10 miles.......)

 

Check the camshaft position sensor for oil saturation; check the wiring leading to number five (left bank front cylinder); is this just a cold starting problem? Maybe temperature sensor in the cross over pipe.

 

I checked resting voltage -- 11.9.....
Plugged it into my CTek 4.3. I'll leave it til tomorrow after work, check it again, and assuming it comes up over 12.4 I'll clear the codes and see what happens.
Stay tuned...
Thanks
-Steve-

 

Overnight on the CTek, charge is at 12.3-12.4 volts. I'm leaving it hooked up til tomorrow, then will check it again and let it sit unattended until Sunday. If it holds at 12.4 or so I'll reset the codes and see where that leads. If the battery fades at all off the CTek overnight, it's under warranty.....
Stay tuned...
-Steve-

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Update time. Battery is holding at 12.7-12.8 volts off the charger, so it came back nicely. This morning I reset the codes and then started it. No issues, smooth idle like it should be. Let it run until it cycled the cooling fans, check engine did not come back. I'll drive it to work Tuesday to give it a shake-down, but at this point it appears all is good.
I've known all along how sensitive these cars are to proper voltage -- I just figured since the car turned over and started fine that the battery must be fine.
Won't make that mistake again.......
Thanks
-Steve-

 

it very well might come back so be prepared, coils do fail intermittently

 

Another update. Went to drive the car to work today. Started OK, but then started into the lumpy idle again. Backed out of the driveway, put it in drive and it fell on its face again as I pushed the gas pedal. Back into the driveway, took the Chevy to work instead...
After work I put the meter on it again -- 12.1V ..... Put it back on the CTek overnight, and am getting the (evidently) defective battery replaced under warranty tomorrow. With any luck the car will run OK to take it to work to do that.
At this point there is no check engine light.
Thanks
-Steve-

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I think your pursuit of a bad battery is taking you down a rabbit hole. 12.1V should be an OK voltage for a charged battery at rest. At the risk of getting other electrical engineers on the forum excited, once the car is running and the alternator is providing current any battery that isn't impaired (bad cell, etc) will be OK - at that point the battery's main purpose is to provide a stable voltage to the power rail.

As your symptoms seem to indicate the car starts and idles fine, with no codes set or other electrical issues apparent (do you see alternator voltage on your scan tool when running?), then I think your issue lies with a bad coil(s), plugged injectors or another issue with the fuel delivery system.

If you want an easy check, as it seems the car won't run with any load, just put the known good battery from your Chevy in the car. For a simple test, you can even use jumper cables as a temp fix if you are only driving around the block.

 

The car starts fine but is not currently idling or driving fine. After sitting overnight on the CTek (the larger 4.3 model) the battery still showed 12.1V this morning. I am putting a new battery in it tonight, and we'll see where that leads. For the record, this particular CTek can take my D34 Optima Yellowtop from totally depleted (running my 55A trolling motor all day on a choppy lake) to fully charged in 9 hours. So if the H8 AGM was going to do anything at all it should have come up at least somewhat overnight.
It may indeed end up being a rabbit hole. I sure hope not though, and being that: A) I work for the company; and B) the battery is covered under warranty, it's a pretty easy box to check off in identifying any further issues.
Wish me luck...
Thanks
-Steve-

 

it’s probably a bad coil

 

New battery fixed it...
Lesson learned -- from now on if the car sits for more than a week or so I treat it like all my motorcycles -- on a battery maintainer...
Thanks
-Steve-
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