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

Dear Jess,

Put away that hair shirt and sackcloth. Believe it or not, your car should be easier for the shop to diagnose with hard faults. I'm a professional mechanic myself (not cars, but Boeing, Airbus, et al) and the hardest problems to diagnose are the intermittent ones, aka soft faults. It's generally much easier to diagnose active hard faults, and that's what you have now. So don't despair.

UPDATE...

Well, I wish I had good news. Unfortunately, just more problems to report.

As expected, we found a vacuum leak. A large vacuum hose on the 1-3-5 side of the motor had failed. Also the PCV valve and its hose needed replacement. The shop fixed both and only charged me for the parts cost of the new PCV valve, no labor costs, as they were sorry I had to bring it back in (nice of them, I'd say). They test-drove the car over three days, and reported no problems. The car idled smoothly and it was no longer stuck in Restricted Performance.

Then I picked the car up.

About three blocks from the shop, I got the DSC Failure/Parking Brake Fault/Limp Home treatment. Car dropped to 1000 RPM (on a stick-shift 3.0, that translates to about 5 mph). I could cut the car on and off, and occasionally it would let me start it up before throwing the fault again. Sometimes I didn't even have to crank it, I could just rotate the key to "on" and get the Limp Home faults.

After about 5 minutes of this, the car decided it was in the mood to drive again, and I managed to get about 25 miles out of it before we were back to doing the Limp Home Dance. Although not universal, it tends to happen more when I've been traveling at a steady speed and let off the gas to begin coasting. Pushing in the clutch also seems to trigger the problem.

If this were a V8 XJ8, I'd say it was time for a new throttle body. Not sure whether that applies to a 3.0 S-Type or not, but I did find a 10-page thread talking about this issue and I'm inclined to believe that's it.

On the other hand, I'm still throwing a code for "Clutch Position Sensor."

Finally, I'm not crazy when I say this: The hotter it is outside, the worse the problem gets.

Not real sure what to do at this point beyond replacing the throttle body or at least checking the connection to the TPS. I'm still baffled that it keeps sending misfire codes on bank 2-4-6 when the coil packs are brand-new. I guess what I'm saying is I don't know whether to actually trust the codes I'm getting, or not.

p.s.: We're still getting a VVT failure code, even though the VVT solenoid is new. The shop is able to activate the solenoid using its own computer, but the car cannot/will not. My shop tells me this could be a case of not getting enough oil pressure up to that part of the motor; Ford is having a problem with this on its 5.4 V8 trucks, but I've never heard of it on the 3.0.

Jess

Dear Jess, as much as this may surprise you, much progress has been made. A vacuum leak, definitely part of the equation, has been identified and repaired. Furthermore, the car ran perfectly for three days, so it is perfectly capable of behaving itself. The trick now is to figure out the fault(s) based on the current symptoms.

With so many codes and fault messages, I'm still thinking there is a problem with the electrical supply. You mentioned the battery was new. When/why was the battery replaced and did you have the same issues before replacement?

I wish I had a dollar for every time I assumed a part was good just because it was new. Actually, I wish I had a million dollars per instance, because then I'd be rich, instead of just having 50 bucks or so. Maybe a couple of times per year, I've had new parts bad from stock, and it can be tricky to make the mental shift required for troubleshooting based on the actual symptoms, not what you think is at fault. In fact, I've even had cases where I've correctly diagnosed a new part to be at fault, to be followed by a second replacement also bad from stock. Talk about confusing! What I'm trying to emphasize is don't blindly assume a part is good because it's new. Many of the faults you've listed, especially when multiple ones are present, can be caused by a battery.

If the battery is fine, I'd suggest checking the charging system. Make sure you're seeing the specified voltage under load. Also, please run the uber-simple test I referenced earlier for AC ripple voltage. I've fixed many miscreant autopilots and other symptoms by correcting an AC ripple voltage superimposed on a circuit designed to run on essentially pure DC voltage. Humor me on this one and just try it.

The next part of your sleuthing is to consider why the car ran fine for the mechanic but not you. What did they do differently? Was it dry and sunny when they tested it but you drove home in the rain? Did they drive gently, but you tend to emulate Mario Andretti? Did you run some accessory they didn't, like heated seats, defroster, or air conditioning? At work, we once had an MD-11 that kicked our butts repeatedly with intermittent generator problems. We'd test it by running all engines at various power settings and everything was fine and we'd release it for service. On taxi-out, a generator would then kick off and the plane returned to the gate. We'd reset the generator and couldn't duplicate the problem. Off she'd go again, only to have the problem intermittently return. Other times it happened in cruise.

After a few days of tearing out our hair, we finally figured out what we missed while troubleshooting per the book. On shorter flights, meals were served soon after take-off, so the ovens were started during taxi to the runway. On longer flights, the ovens were started later. A controller for galley power was wigging out, feeding an AC ripple back into a DC control circuit, but only with the high load of the ovens in use. Talk about a head-scratcher. So think of it like a puzzle. The answer may be figuring out what was different when you drove the car.

Hope this helps, respectfully submitted.

Quick timeline for this car ... purchased it in the summer of 2009 (if I remember correctly) out of Texas. The car had not been cared for by the previous owner. It's been wrecked front and rear and wasn't put back together well. The first oil change I did on the car, which came at around 40k miles, may very well have been its first ever. I changed oil every 1k miles for the first 5k miles I had it, and the first couple of changes came out looking like tar even though it was new oil. Nevertheless, the only problem of note I had from the car the first couple of years after purchase was the standard DCCV failure.

Two years ago, around this same time of the year, the car started doing the same thing it does now. I live in Alabama, it gets hot here around late March. I kept having Limp Home failures that grew in frequency until the middle of the summer, when a two-hour trip one night ended up taking six hours and eventually ended on the back of a tow truck.

Even though the battery had tested fine late that spring, I went ahead and put a new one in the car. It didn't help. Having exhausted my talents as a shadetree mechanic, as well as those of a couple of professional shops, I parked the car late 2012 and it sat unused for all of 2013 while I tried to sell it.

Then, in summer 2013, my wife and I found out we were expecting our first child. Our other cars are a 1998 XK8 and a 1989 XJS. Can't get two people and a baby seat in an XK and it's a tight fit in the XJS. The two older XJs we have are pretty much done (they were project cars to begin with), certainly not fit for family transportation. So I decided to try to sell them off (still am, in fact) and rehabilitate the S-Type.

We began in February. I put in a brand-new battery then, since the other one had discharged to nothingness. I knew from the last time we had problems with the car that I was getting coil pack failure codes. So I had my favorite shop replace any belts and hoses that needed replacing, and we replaced all 6 coil packs, the two VVT solenoids and any other wear items.

From around March 1 until late April, we had no issues. Then the car slowly started going back to old habits. Now it is doing exactly the same thing it was doing two years ago.

I'll have the shop do this next.

It was dry and sunny the last couple of days. Both their driving and mine was done in similar conditions, but when I started getting failures today, it was later in the day after things had warmed up and the humidity was higher. No rain, though. As for driving style, since it previously had been going into Restricted Performance at 3k+ RPM and/or when under aggressive acceleration, I had them test it on the interstate and around town. I pretty much always have the HVAC system running and it was on when I picked up the car (95 degrees F here today for a high), so I'm assuming they ran it as well. Neither of us ran the heated seats or defroster.

Thanks for the help/suggestions!

Jess

Jess,

Is the car consistently acting up, or just sporadically? What if you were to fabricate some extra long test leads so you could temporarily set up a voltmeter on the dash or center console? Then when the car acts up again, compare the voltage reading present to when it was running okay. This might provide a big clue, as the existing warning system has nothing to show low voltage. (Not sure on the details, but I think there's a message that comes on at a VERY low voltage, too late to be of any use.)

The other thought is the condition of the wiring harness. You mentioned this was a rebuilt wreck. Perhaps the harness(es) was repaired in a substandard way, and now is starting to fail. That could explain an intermittent nature. I've seen some details on this forum about a harness behind the front bumper that is prone to damage due to its routing. Supposedly a problem with this harness can cause all sorts of weird engine problems. Due to its location, it's likely this harness was damaged in a collision. Maybe somebody more in the know could help refresh my memory on that one.

Karl,

Yesterday, the car was consistently having faults and stranding us. Today, we've been driving it all over town doing local errands and we have had no problems. This is not unlike some of our experiences two years ago -- fine one day, undriveable the next.

The wiring harness for the throttle body/TPS is right behind the radiator grille. I inspected it last night for looseness or water intrusion and found evidence of neither, but that doesn't mean there's a problem. The flexloom around the wires themselves between the TPS connector and where that group of wires rolls back into the main harness, though, was cracked -- evidence of repeated heat exposure, although given where it sits, that's not really unexpected.

I found a used throttle body and TPS off a low mileage car for $40 and will install it next, and I'll have the TPS harness inspected/rebuilt at the same time. I figure for that amount of money it's worth a shot.

One question I do have at the moment: Last night, while looking at the TPS harness, I turned the key to "on" but didn't start the car, and I heard the usual solenoids opening/closing, electric motor noises from under the hood that modern cars make. However, I continued to hear a whine coming from somewhere around the throttle body that never went off. It seemed to have an uneven tone quality to it, like whatever electric motor was involved wasn't completely healthy. Any ideas what that might be?

Jess

Update...

Replaced throttle body and TPS with known good parts temporarily to see if that made a difference. It didn't. Wiring harness at the front of the engine looks good; we de-loomed it all the way back to the back of the motor to look for crimps or cuts and could find none.

The car actually went into fault while we had the "new" TB/TPS on it, which was actually a good thing as we'd never been able to get it to fault while we had diagnostic tools already hooked up and running. So we checked codes, and ..... zilch. Not just no NEW codes, but no codes whatsoever. Yet the car was locked to a hard limp-home status.

One wiring harness on a VVT solenoid looked sketchy, so we fixed it just in case. We put the old TB/TPS back on the car, performed a hard reset and everything is normal again.

As unlikely as it might be, I have to consider a main computer fault at this point.

Jess