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