Misfires galore...
 

To those that were reading my catalytic sensor thread, the problem has changed.

I took the car to a muffler shop and had them snake-camera the cats. In the tech's opinion, one cat was borderline and the other OK. Then he pulled the codes from the computer.

Some background: The car has all-new coil packs and plugs, plus a new VVT solenoid already. This is a 2003 S-Type, 3.0 V6, with MANUAL transmission.

P1314 (Misfire Rate Catalyst Damage Fault Bank 2)
p1316 (Misfire Rate exceeds emissions)
P1396 (VVT Solenoid B Circuit High Input)

Also, codes for the following:

* Random cylinder misfire
* Misfire cylinder bank 2,4,6
* System Lean Bank 1
* System Lean Bank 2
* Clutch Pedal Sensor Switch

Obviously, there's a whole lotta misfirin' goin' on. Yet we've already replaced a lot of the parts that could cause it (VVT, coil packs).

Kind of overwhelmed right now, to be honest.

Jess

What were the actual codes for the ones you didn't specify? Clutch? haha

What are the fuel trims at idle & 2500rpm (hot engine, parked)?

Might be worth checking that all disturbed wiring and connectors are OK. Wouldn't take much to cause misfires.

I didn't write the other codes down, I'll have to get them again the next time I visit the shop. The only reason I wrote down those three were they were "manufacturer-specific codes" that non-dealers can't read on their systems, so I had to research them. And yeah, that's a clutch pedal position sensor that is throwing a code, which is odd because it functions normally otherwise, the cruise control works fine, etc.

We didn't do fuel trims. I'll make a note to get them if I can.

I'm worried about the wiring, honestly. This car was wrecked before I got it and the level of professionalism that went into putting it back together was pretty poor.

A couple of other things I left out: Brand-new battery, and we just had a dealer re-flash the ECM in accordance with a TSB.

We're also starting to get a bit of a rough idle, like a mass airflow sensor is going bad, but that's not throwing a code anywhere.

Also, and this may be the biggest thing yet, the problems seem to get worse the warmer the ambient air gets. Is there an ambient air sensor that could be contributing to these issues?

Jess

I'm thinking that if it's been wrecked then you need to be good at DIY or this is liable to cost more than anyone would want to pay - and you'll need someone who can troubleshoot multiple faults on a complex car i.e. a jag specialist (not at most dealers).

+1
Also, you should invest in a code reader if you're gonna DIY. They're not that expensive and will provide lots of diagnostic insight.

Talked today to the guy who does most of the work on this car ... his latest advice is to "shoot it." I'm not altogether sure he was joking.

He believes the PCM may be the culprit. Unfortunately, he mentioned something else that I'd thought of -- potential damage in the main wiring harness resulting from the wreck. I don't even want to think about that one.

If I were to switch out the PCM on this car, it would have to go back to a dealer for a reset before it could run again, yes?

Jess

It's behaving like a working PCM. You could remove it and look for signs of water damage to it but beyond that they more or less never fail so you're almost for sure going up a blind alley with yet more cost.

Dear Jess,

If I may, allow me to get on my MisfireSoapBox(tm). The term misfire, in OBD-II land, simply means one (or more) cylinders is producing low power in comparison with the others. It could be an ignition fault. It could be a bad fuel injector. It could be low compression, and so on. So don't get tunnel vision that an indicated misfire only means an ignition problem. I don't care to discuss how I learned this...

With the random misfires (and other codes) you've experienced, my first thought was excessive AC ripple from the alternator. If you have a digital voltmeter, it's quick and easy to rule this out. The first link is for Mercedes, but the prinicples are the same on all modern brands:

http://www.pvv.org/~syljua/merc/TooSeptST07.pdf

http://assets.fluke.com/appnotes/aut...e/beatbook.pdf


Excessive AC ripple can cause all sorts of strange symptoms, but with no corresponding warning light or fault message. By any chance is the alternator non-stock? I would suggest spending 5 minutes to quickly rule out this potential headscratcher of a problem.

My other thought is what brand of fuel are you using? Many off-brands and non-premium brands can cause weird symptoms. ARCO, for example, is notorious for causing problems. When friends tell me about car trouble, one of the first things I suggest is to switch fuel to a premium brand like Chevron, Texaco, etc. In many cases, the problems then go away.

There you have the sum of what I can offer. At least neither will cost you anything, so it's worth a shot before tearing further into things.

Keep us posted.

No harm checking if cheap & easy but don't expect it to be ripple.

Agreed, but I forgot to mention something in the original post that caught my eye: The problem seems worse at higher ambient temperatures. That's what made me think of a marginal diode pack in the alternator.

Thanks for the suggestions. We'll check the alternator but I just wonder why we're seeing this only on the 2-4-6 bank and not also the 1-3-5 bank, if it's an alternator.

As for gasoline, I tend to use only name-brand stuff, and around here that means BP, Chevron, Exxon, Shell or Marathon. I have not noticed the problem being any better/worse with one above the others but I'll start logging it and see.

By the way, it's started doing something else it never did before is having a rough cold idle with Restricted Performance light immediately upon startup, then the Restricted Performance light going out as I get onto the interstate. Honestly, the problem seems to be changing in nature ever couple of weeks, which makes it hard for us all to diagnose.

Jess

I'll keep logging the problems here, just so people can see the evolution (devolution?) of the car's behavior. If you want to chime in, please do, but this is more of a diary at this point.

We have not yet taken the car to the shop for follow-up diagnostics. We're doing so in the next couple of days. We had to take the car out of town this week on a four-day trip.

The car now idles roughly when cold. When first cranked, it will die unless you hold the throttle at about 1200 rpm. It's acting like my father's old military jeep, to be honest. Once it warms up, it will idle extremely roughly around the 600 rpm mark. There seems to be a slight oscillation in the idle, as if it had a bad MAF sensor, but it is not throwing the code for that.

The car is now hard-locked to 3000 rpm. The moment the engine turns more than 3000 rpm, it goes into limp-home mode, which on this car (stick-shift 3.0) means a total loss of power until one of two things happens: I get off the gas completely for a few seconds, or I keep my foot in the gas and the motor reaches 1000 rpm again (I can interrupt the process by manually getting off the gas and letting the process reset).

The Restricted Performance and Check Engine lights are now illuminated 100 percent of the time, with no flashing.

The car accelerates somewhat roughly, but as long as it is kept under 3000 rpm with no to-the-floor spikes in acceleration, it will drive normally. At a steady pace, the engine smooths out. But come to a stop light, and the roughness comes back.

If this were a much older car, I would say it sounded like a problem on the fuel side, not the ignition side. All the codes are pointing to ignition, but the only way this is possible is if one or more of the brand-new coil packs on bank 2-4-6 are bad. If that's true, then I have to wonder whether the pack(s) went bad on its own, or something caused it to go bad, and I don't know what that would be (i.e., voltage spike from somewhere). Honestly, I suspect more of a fuel injector/pump/filter issue due to the rough idle and the codes indicating a lean condition, but I could be wrong.

More updates as I get them.

Jess

Have you checked fuel trims yet and are you aware of the loom problem behind front bumper? Chaffed / broken wires there are a known problem causing all manor of electrical related problems.

Checking fuel trims this week, probably Tuesday or Wednesday. A cursory visual inspection of all the wires I can see produced no obvious failure points, but I'm going to have a shop do a more intensive inspection when it goes back in for the fuel trim check.

What's bugging me is that I'm seeing a steady degradation in performance. Each day is a smidge worse than the day before. The car did the same thing a couple of years ago, we parked it for several months, then replaced all the coil packs and spark plugs, plus a VVT solenoid, and it ran great for about 3 weeks, then started slowly dying again. It's like the car has a tumor somewhere and is slowly succumbing to its illness.

Jess

It's like it has a fault you've not diagnosed thus haven't fixed so keeps occurring. Well, what else would it do....

5-speed '03 must be a rare manual. Air leak is what it sounds like so get on and check trims.

Took it to the shop today and made the appointment to get the fuel trims looked at. The shop agreed with you it sounds like an air leak, and the shop owner's guess was that we're going to end up finding a cracked intake manifold.

It's not a gasket, unless we have a defective gasket -- all manifold gaskets were replaced with new ones when we replaced the coil packs back in Feb/March.

I'll know something next week; we're waiting on the arrival of new testing equipment at the shop to check the trims.

p.s.: On the subject of rare manuals, I think Jag made around 500 of these cars, only in 2003, and they're all base models. No V8s. I don't even have a sunroof, heated seats or memory seats in the car, which is pretty standard on most newer Jags that I've seen.

Jess

There was no option to have a manual V8.

i'm putting my money on the lower "elbow" being perished

I don't think that applies to an '03

Exactly, that's what I meant by "all base models, no V8s."

Although, I have seen someone do an aftermarket conversion on a Lincoln LS with the 4.0, and they used the shifter and pedal set from a Jag V6. I'd love to know how much that cost him. Actually, scratch that, I probably don't want to know how much that cost...

Jess