X300 Slight Stumble & Uneven Exhaust
 

My 1995 VDP 4.0L has been almost entirely trouble free, with only a single repair in the many years I've owned it--when the fuel pump hose popped off the fuel pump in the tank. Then there was my investment in the future with all new rotors, calipers, etc. to fully recondition the brakes for many future years of use.

But I have an issue that cropped up yesterday afternoon that I'm not quite sure where to start on identifying. It wouldn't start yesterday & I ended up in the XJ40. It was hesitant to start today early when I went out to begin to try to sort out the no-start issue, but did start & has started every time since, even after cooling for several hours. Ordinarily, it's been the fastest starting car I've ever owned & many people have commented over the years how amazingly fast at firing up it is. The thing I'm noticing that's different, aside from the intermittent slow start today is a slight stumble in the idle. If I throttle up, it sounds smooth. But the strangest thing to me is that ***the left-side exhaust is quite cool, & and fluctuates a bit, while the right-side exhaust is pleasantly warm and rock-solid steady***. I haven't done a search of the forum on that point because I'm not sure how to phrase it to get any relevant information.

Does anyone have any experience with something like this that might lend me a clue about what to start looking at? My inclination is to at the very least put in a fresh set of plugs which would be appropriate even without an apparent issue.. My XJ40 VDP has only ever developed a similar stumble when a bit of corrosion developed on the contacts in its old-fashioned and gloriously simple distributor cap. My XJS convertible has only a couple of times run with a slight stumble for a minute or so, only to clear up on its own. I've spent about 12 hours today reading endless threads on balky, intermittent starting issues.

I figure it's time for a bit of renewal on the car at 120k miles, some whether it needs it or not. Perhaps a new fuel pump, filter & pressure regulator. Plugs. Ordinary things. The car has been by far my favorite for reliability and comfort, so I want to sort this out & enjoy it for many more years. It's a bit cold right now to want to run around with a canvas top on the XJS & while the XJ40 VDP has modest miles, new tires, new brakes & all sorts of things & purrs always, it's way more confining in the cabin than the X300. So I'm itchy to sort this out.

Scratch my back a little, please, if you can. I couldn't get to sleep last night running possibilities through my head so I just got up and began reading here & studying my service manuals. Since it's started several times today even though I'd done nothing at all yet, many things I contemplated seem not likely.

I'm getting a little old & worn out to want to do much mechanical work, but I've done my fair share over the years, rebuilding an XJ12 pretty much completely, and an XJS after a fire. (And lots of everything on the ex's miserable herd of Volvos!) But old & cranky or not, I want my favorite daily driver perfect again.

The difference in the X40 and X300 engine regulation in the start sequence is the replacement in the X40 distributor rotor with a Camshaft position sensor other then the X40 / X300 Crankshaft position sensor on both models .

This is a more refined and accurate position sensor only used in the starting sequence and after starting reverts to the normal Crankshaft position sensor for the duration of your drive

The AJ16 engine will start with the Camshaft sensor disconnected but takes more crank revolutions to get it;s bearings on what is truly the # 1 TDC as the crankshaft makes 2 revolutions in a 4 cycle engine

The Cam sensor is a hall effect sensor that sees a window for each cylinder position TDC vs, only the # 1 cylinder TDC and is a 50 / 50 guess till it tries both options for best ECU results

The hall effect sensor reads as a fundamental meter reading different then the fundamental resistance of the inductor crankshaft sensor on the X300 of 1300 ohms

The actual signal is different then a fundamental meter resistance check

When the Cam position sensor fails it is CEL code P0340

The engine

I'll edit and get with you in the morning

In the mean time see page 77 , 76 , and Z for the sections on the AJ6 , AJ16 , and V12 engine regulation

http://www.jagrepair.com/images/Trai...20-%202000.pdf

Welcome Jaguar06Rick,

With all that Jaguar experience, shouldn't we be asking you for advice? Now that you showed up here, we certainly will be. For a moment I am scratching my own back dreaming of a garage with a sweet XJ40, XJS and teriffic X300VDP. V12s and convertibles.... :icon_steer: Life is good.

Ordinary maintenance will do a lot for our not-so-ordinary cars too. I'd suggest going for a spark plug change. Typically the X300 needs new ones at around 20k miles, give or take. This job will allow you to make some other ordinary X300 checks too: condition of the ignition coils, security of the electrical connections, evidence of arcing, and pooling of oil in the spark plug wells. Worn out spark plugs will eventually cause hard starting and random stalling, with no other evidence of trouble.

Most recommend the original updated Champion RC12YC spark plugs, you can't really go wrong with them. Others report good results with NGK equivalents. Data is unclear as to weather certain types or brands will last longer than others. General consensus is that the higher-end plugs are not needed and might tend to bother the ignition system.

As for the exhaust difference, are you sure nothing has entered the pipe and caused obstruction? As an unlikely scenario, I suppose a converter becoming blocked might have that effect (although I think there is a "crossover" point in the tailpipe).

If you post up in the new members' section, you could show off your fabulous collection for all to see, and be greeted by some of our most generous and active members.

There are numerous potential no start causes and numerous no start threads to review. @aholbro1 made a thread some time ago with links to many of the threads. Here's a link to it

https://www.jaguarforums.com/forum/x...ngines-120221/


Given your specific issue of the uneven exhaust, I think @SleekJag12 suggestion of blocked exhaust is a good idea. A collapsed Cat could do that, and I have also heard of and seen photos of an exhaust that was blocked with ice from frozen condensation. There's another thread that covers this.

https://www.jaguarforums.com/forum/x...orking-108330/

Crankshaft position sensor would be my shout for the intermittent non start

I went out to check for any codes late yesterday evening and found none have been set.

Numerous is right. I think I spent about 12 hours yesterday reading them. :-p

I'm thinking a collapsed converter, too. That happened on my '76 XJ12 once & gave a similar result.

Also, I wondered about ice. We'd been in single digits over night & it'd been very damp. I wondered, too, if there might even have been a bit of water in the bottom of the fuel tank that might have frozen to block the strainer with ice.

It certainly seems like that. I'd forgotten that bit. It was my only other repair besides the fuel pump hose. I put one on 3 months ago. It was a 10 minute job & I totally forgot about that, until this happened. It *does* seem the same. When it didn't start, my first thing was to unplug and replug the CPS connector, to no effect. Given that I bought an expensive new microwave that failed in 2 days, it's warranty replacement arrived DOA, & the third died in 3 weeks, it wouldn't surprise me if the CPS I mail-ordered is bad. It's such an easy job, I'll likely buy another just for the heck of it.

Hey! Thanks for that! That's a useful reference.

(Spent 2 hours yesterday looking for my X300 factory service manual. Found the ones for the Series III XJ12s, the XJ40s, The XJSs. All together, where they should be. But not the X300. Of course.)

I think I'll watch patiently for a bit. We've several warm days coming up (up to 70!). It *has* been extraordinarily damp, with lots of fog, then followed by super-cold temps. Ice may be an issue. That left exhaust is not totally blocked. There is *some* flow, just nothing like the right, which seems totally normal. And I noticed there is an occasional spitting of outright drops of water in that side of the exhaust, and there *is* a rather distinct "gurgling" sound that correlates with the erratic volume of exhaust there as it increases or decreases. I think before I assume "collapsed converter", I'll wait & watch. When the old XJ12 converter collapsed, it began spitting out large chunks of that honeycombed material from it's guts. (I should have saved some of the better bits for my brick-a-brack cabinet.) When the car's running, I detect no fault with performance, other than that slight stumble at idle. At any road speed, it seems super smooth & there's no sluggishness nor loss of power.

If I'd found that thread with that collection yesterday, it'd have saved me some time. Good job. I'll likely go through those links today. (Probably read many of them in my own searching. There's certainly plenty of no-start threads!

Thanks to everyone who has replied. I truly value places like this where we can share our experience. It's way more efficient than making the trip to a favorite Jaguar/Rolls mechanic to pick his brain as I used to do in the days before the internet. (But you guys don't give me a Rolls as a loaner like he did.)

Hi Jaguar06Rick,

Welcome to the Jaguar Forums! It's great to have you with us!

You could do a simple check of the exhaust with an inexpensive no-contact infrared thermometer (Harbor Freight sells a decent one and Lowes and Home Depot carry them too). By measuring temperatures at various locations you could see where the left exhaust temps diverge from those on the right. You can also check the temps at the weld rings (not the heat shields) at the input and output of each cat. The output temps should be significantly higher with a healthy cat, typically by 100-150 degrees. Here's one of many online references available that I grabbed with a quick google search:

Testing Catalytic Converters with Infrared Thermometer

Cheers,

Don

I think it's a good idea, Don. I've been intending to pick up an infrared anyway, for other uses. I saw that suggestion in that other uneven-exhaust thread and think it's a good idea as it'd certainly indicate a point of blockage.

Finally I can report back on this one. It's been 7 weeks since I originated the thread, but I only today had time, weather, & health to put in the time to sort out my issue. A day or so after the original post, the car began requiring excessive cranking to start. If I turned the key 3-5 times to cause the pump to run, it'd eventually start with a very long crank. Then a day or so later it would not start at all. Then we had Big Snow. Then Big Flu. Then Big Winds (80 mph CONSTANT for TWO days). Then Big Rain. (Oh, and several days of Big Lazy.)

Anyway, the problems were all related--the uneven exhaust, slight stumble on starting, long cranking, etc. It's "deja vu all over again", sort of. I mentioned how my most significant problem with the car had been the fuel line coming off the top of the fuel pump. This time, it had not come off, but the hose had delaminated. The outer layer had peeled away from the inner layer, exposing that webbing in between. Doubtless the pump was in the end just circulating gas right back to itself & sending none to the engine. And prior to that, sending not enough. Of course, since I had it open, I put in a new Denso pump.

So my favorite daily driver of my herd is back to whisper quiet, ultra smooth idle & truly great pickup I like the car well enough I intend to keep it my daily driver till I drop dead. So while I was in the ordering parts mood, I bought a few things for the garage shelf, for when & if. Including a new starter (not rebuilt) fuel pressure regulator, 3 filters, an extra pump, and top of the line Bilstein shocks (those aren't going to the shelf. Next nice day, they're getting installed.

I can't tell you how miserable it's been having to drive the XJS V-12 convertible all these many weeks. :-p (Actually, there's an element of truth in that. Getting in & out of that thing isn't as easy as it used to be. The VDP sits higher, particularly the seats. This old ass needs all the help it can get. It's the *dimensions* Jaguar finally got right in the X300 sedans. I took out the XJ40 VDP a couple of days, & it's nearly as confining as the XJS once inside, & little easier for old bones to enter. But the X300 is *just right*. Count me happy tonight. Eating a dozen donuts & having coffee to celebrate.

Thank you for all the suggestions

This is a new find, in between poor-start and no-start series.