The subject lights came on in my 2005 XK8 recently. After driving it about 90 miles home with no apparent performance problems, I shut it off in my driveway and attempted to restart it about 20 minutes later to pull it into the garage. At that point it would not idle and stalled out several times until I got it to settle down with much pumping of the gas pedal to rev the engine. Today it started up and ran with no idle problems. I then took it to my mechanic so he could read the ECM codes and he reported the following:

P0171 Fuel Trim System Lean (Bank 1)
P0174 Fuel Trim Too Lean (Bank 2)
P0300 Random/Multiple Cylinder Misfire Detected
P0301 Cylinder 1 Misfire Detected
P0302 Cylinder 2 Misfire Detected
P0303 Cylinder 3 Misfire Detected
P0305 Cylinder 5 Misfire Detected
P0306 Cylinder 6 Misfire Detected
P0308 Cylinder 8 Misfire Detected
P1316 Injector Circuit/IDM Codes Detected
P1582 Electronic Throttle Monitor Data Available (I think he meant to write "unavailable")
P1696 Speed Control Input Switch Fault/Not Cancel

He reset the system and told me to drive it some more and bring it back as soon as the warning lights returned so we could see which codes came back. I suspect a lot of these codes (especially the misfires) were the result of the multiple restarts when the car was refusing to idle. The speed control fault may have occurred when I was playing around with the cruise control on the way home yesterday as I don't really know how to use it yet. It seems to me that the basic problem is probably that the engine is running too lean, possibly due to a manifold leak. The warning lights returned almost immediately after I left my mechanic's shop (naturally--I should have asked HIM to drive it after the reset) so it will be going back there tomorrow or the next day. Before I take it back, I'd like to get some thoughts from anyone out there who has experienced similar problems. Thanks.

Submitted by vineyardman68@… on Fri, 05/09/2014 - 21:50

A smoke test to see that the hose from the MAF and Throttle body had come loose----good Lord, on my 05 XK8 that hose would slap you in the face if it came loose--it's so easy to see.
Good your guy found the bolt issue and bad mounts. Car must have rocked and rolled when driven.
Glad your cars back to "good to go" status.

Enjoy your ride.

Garfield

05 XJ8L & XK8

Submitted by kenkyle4@earth… on Fri, 05/09/2014 - 21:00

OK, here's what I hope is the final word. When my mechanic read the codes again, only two had reappeared--the ones for lean mixture on both banks. He checked the fuel pressure and it was fine. Then he did a smoke test on the intake tract and found that the hose between the mass airflow meter and the throttle body had become disconnected. Unfortunately I didn't get off that easy. My mechanic is a sharp guy and realized that the hose didn't just decide to come off by itself. He then discovered that one engine mount was loose--apparently some moron tried to replace it before I got the car and used a nut with the wrong thread on it--and the other mount was completely sheared, allowing the engine to twist several inches every time the engine was revved. It's amazing there wasn't more damage in the engine compartment. Two new mounts and about 7-1/2 hours of labor later, all seems to be well.

Submitted by kenkyle4@earth… on Tue, 05/06/2014 - 18:42

Steve,

Thanks, now I get it. Regarding the P1696 code, what would constitute a communication fault? Do you think this is connected with the lean mixture/misfiring issue, or could it be a separate problem? What about the P1582 code?

What are your thoughts on the possibilty of a clogged fuel filter being the source of the problem? I'm assuming that there's no sensor and fault code for low fuel pressure, which would be helpful in making a diagnosis. Do you know if bad fuel pumps are common on the '05 XK8? The car has about 46000 miles on it.

Thanks for mentioning what the ASL switch is for. I assumed it was for shutting off the traction/stability control. Guess I should read the manual.

Submitted by stevejag@sbcgl… on Tue, 05/06/2014 - 12:48

Edited on 2014-05-06 12:50:06
What I meant was that information he had for some of the codes was in error. P1316 is not an injector circuit fault in this case, it is a fault code for misfires severe enough to greatly increase emissions. In other words you are a heavy polluter. Codes starting with P1xxx are mfg. specific codes. P0xxx codes are mandated codes, and in general mean the same thing no matter the model year, or manufacturer for that matter. The P1xxx can mean whatever the mfg. wants them to mean, and can change year to year or engine to engine.

Likewise, the P1696 signifies a communication fault on your car, not a speed control switch fault as the information he gave you. That's why the code info has to be for the exact model and model year in question. Some don't pay much attention to that, and that leads to incorrect [sometimes expensive] diagnosis.

Be aware that the console switch you may think is a cruise on/off switch, is really to switch BETWEEN cruise control and Automatic Speed Limiter [ASL]. You have no off switch per se.

Cheers,

Submitted by kenkyle4@earth… on Mon, 05/05/2014 - 23:27

Steve,

Thanks for the reply. I've seen your posts before and they're always very informative so I'd hoped to hear from you.

No, my car is not an XKR, but it does have the adaptive cruise control option. I've never had a car with this feature before so I was playing around with it when I was on the highway Sunday, trying to learn how to use it when it went kind of wacky on me. I finally managed to cancel and re-engage it, after which it seemed to work ok again.

I'm not sure what you meant by "the code information your guy is using also errs with the P1316." Can you elaborate?

Your suggestion about checking fuel pump pressure makes a lot of sense and I will definitely ask my guy to check it out. Do you think a clogged fuel filter could be at fault?

Ken

Submitted by stevejag@sbcgl… on Mon, 05/05/2014 - 19:32

Ken,

While there is some validity to your conclusions, I have a couple other ideas.
First, is this by chance an XKR rather than an XK8?? For 2005, the P1696 is a network communication fault for the Adaptive Cruise Control. That option was very rare on the XK8, and much more common on the XKR supercharged car.

Next, the code information your guy is using also errs with the P1316. For the 4.2L engine that code is indicating the misfires recorded are severe enough to cause very excessive emissions.

I think you should have the tech check the fuel pump pressure. The lean faults, misfires AND your description of how the engine acted for you, makes me think the fuel pump may be giving up at times. That scenario seems to fit the data a little better. A manifold leak would generally favor one bank over the other, your misfires are more global. Still could be wrong, but that is how I would attack it

Good luck!