When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Keep at it your making progress! It takes some troubleshooting and focus on data and codes. All this noise stuff and phone videos is again useless.
Forget facebook and reddit. The land of morons. No your timing chain has nothing to do with this. Again stop listening to the wrong people. You have a stone cold expert helping you. Please listen to what Karl is saying! Please answer his questions.
Remember we are all just guessing on the internet! You need to help him help you. Step by step.
.
.
.
>> The engine at startup is lubricated exclusively by oil delivered by the oil pump once it begins to turn, as there is no other mechanism to supply pressure to the top end immediately. >> While oil clings well to components due to modern formulations, hydraulic tappets (lifters) often make a noise for a few seconds as they fill with oil after gravity drains it back to the
>> sump...
Ooh, I liked your theory about clatter from the lifters, so I did a little more research. Seems both the V6 and V8 have solid lifters and are adjusted with shims. Nothing hydraulic to them, as found on most other vehicles.
But your line of thinking got me to thinking. Don't worry, it's just social thinking and I can stop anytime I want. Now my idea wouldn't explain everything, but maybe it could. Easy enough to rule out.
The timing chains have hydraulic tensioners to take up any slack. Guess what is used as the hydraulic motive force? Engine oil pressure. Purely conjecture here, but let's say oil pressure is lower at startup than typical, for reasons still undetermined. If this theory makes any sense, there could a little extra slack in the timing chain after a cold start. I doubt it would be enough to affect how the engine runs, but it could make a little noise.
There is another system that also uses oil pressure: Variable Valve Timing. Couldn't find a lot of details about what the default position would be if oil pressure was below normal. Could this affect starting? This is just me thinking out loud, trying to connect the little puzzle pieces. Mostly just wondering if it could all be tied together, both the noise and rough running after a cold start.
But what to do about my latest crackpot theory? OP did mention having changed the oil and filter. My very first thought there was the filter did not have an anti-drainback valve, or if so equipped, it was sticking open. If the oil filter drained back overnight, the engine would have to run for a little bit to refill the filter and then send the oil out to the various destinations. So my latest idea, subject to medication levels and wind direction, would be to replace the oil filter. Do NOT use the same brand presently installed. Be triple sure the new one is listed as having an anti-drainback valve. Maybe a $15 gamble to see if a new filter helps?
Whaddya think?
Remember, we're all just guessing here. I'd certainly try a $15 oil filter before a $2000 fuel pump.
My other thought, of a leaking fuel injector. If an injector didn't fully close, it could dump fuel into a cylinder. This floods the cylinder walls and washes away the oil, decreasing compression. The spark plug may also get fouled and not fire properly.
A basic test is easy enough. Pick a time when you won't need to drive the car for several hours. Set up your scanner to read fuel pressure. With the engine cold, start the engine and watch the fuel pressure. For troubleshooting, it would actually be helpful if the engine runs roughly at first. Watch the fuel pressure and see if it fluctuates. This isn't even the actual test yet. Just establishing a baseline.
Let the engine warm up enough so it stabilizes. Continue keeping an eye on the fuel pressure. Shut off the engine. Quickly turn the key back to Run but not Start. You want the computer powered up so the scanner can read fuel pressure. The value should be stable, with maybe just a slight decrease. I don't have any specs on how much of a drop is too much over X amount of time, so we'll have to use our judgement. Turn off the key now.
Next, open the trunk and lift up the trunk floor. In the rear power distribution box, remove fuse F47. This is the power source for the fuel pump and we don't want it to run for the test. After a couple of hours, turn the key back to Run, but still not Start. We're only doing this so the scanner can read fuel pressure. Normally the pump would operate for a couple of seconds with the key to Run, to pressurize the injector rail before starting. But we pulled the fuse to prevent that. We're only interested in seeing how much the pressure decayed since the last reading.
Won't cost a penny to try this test, just a little time and patience. If the pressure drop seems excessive, we can figure out some means to isolate where the pressure is escaping. Could be an injector leaking. Could be a bad check valve between the pump and injector rail.
@ Karl: Yes, sorry about the hydraulic lifters - did not know, we don't have them in our Jags - I have them in my Ford Fairlanes, and I even swapped them already.
But yes, I agree with the hydraulic tensioners, etc.
Also a good theory about the oil filter - the question. if an oil filter had been used that DOES HAVE the anti-drain-back valve. Thus, which filter did you use, Colin? The internet should give the answer, if that specific filter does have that valve. I have just spend recently several days to find the correct filter for my 3.0L 2004 S-Type (which btw is the same for X-Type), and I certainly came across the issue of the anti-drain-back valve.
@Collin: Yes, obviously you can't be starting the car and at the same time as listing for noises in the engine bay - I thought it to be obvious that someone else needs to start the car, while you are listing up front....
@Collin: Yes, obviously you can't be starting the car and at the same time as listing for noises in the engine bay - I thought it to be obvious that someone else needs to start the car, while you are listing up front....
Another option is to have himself cloned. Then he'd have a helper available at all times.
> Another option is to have himself cloned. Then he'd have a helper available at all times.
Yes, indeed. I just read this out aloud to my wife, and she commented that that would be an idea for me, too.
PS:
I don't think that anyone would contradict, if I were to float the idea that anyone of us ought to have a clone of him- or herself to make life easier...
Just sent your clone to go to work, and when he or she comes home, he or she can lend you a hand for the Jag-repairs, where 2 hands just don't suffice!
Last edited by Peter_of_Australia; Apr 1, 2026 at 08:50 AM.
Reason: Added PS note
Yet another crackpot theory. This came to mind at the gas station today. While watching the total price skyrocket as the tank was filling, I wondered if I could just cry into the tank instead. How would the engine run?
Then it hit me. Are you aware these cars require premium fuel? Perhaps the seller didn’t mention it and you didn’t notice the tiny sticker inside the fuel door.
I'm not sure exactly how the engine would respond with peasant-level fuel, but it probably wouldn’t be good. Just a hunch, but any trouble might be worse on a cold start. That’s when the engine runs on default values in open loop, for a short time before the O2 sensors kick in.
For giggles, see if your scanner’s live data has a display of open vs. closed loop. If so, see if the rough running ceases when control switches to closed loop.
Wondering if the knock sensors are also inhibited in open loop, and the computer is unknowingly advancing the timing based on default values with premium fuel. The noise you’re hearing could be ignition knock.
If your scanner also shows ignition timing, see if it backs off when the rough running stops.
see if your scanner’s live data has a display of open vs. closed loop...
Played a little with my '02 V6 today. After a cold start, approximately 20 seconds elapsed before switching from open to closed loop. With the engine warm, the changeover was much quicker, maybe 3 seconds.
I realize the control system had some big changes 2003+, but my observations may still be helpful.
There’s a lot to respond to so I’ll start with what I remember, my scanner doesn’t show open and closed loop, I know for a fact the previous owner put 87 in it (😭😭😭 but I have only ever put 93 in it. Also about the injector test, I maybe will be able to try it tommorow but I’ll let you guys know. Also the fuel pressure doesn’t drop below 45 when driving at 70 mph. (Around 1900 rpm) so it might be getting too much fuel? It does also smell like fuel from outside the car but I’m not sure what that means. It is also burning oil whenever I “really drive it.” Not sure if that helps on figuring out the root cause but thought I would throw that out there.
If the car is getting too much fuel it will set a code for that? Have you checked?
Thanks for the fuel pressure numbers as any data you can post is helpful!
.
.
.
I don’t think my obd tool shows ol or cl, atleast not any live data that says that, but I sent a picture of the fuel trims earlier. I also thought it would be worth noting that this thing in the engine bay was making a pretty loud clicking noise? First time I have noticed it but it was pretty distinctive enough to were I could feel the whole thing vibrating. (Look at picture, no idea what this is, ChatGPT says Evap purge valve)
Okay, 55-60 might be high at idle. Look at the chart in post #2 above. It says you should have about 43.5 at idle. I'd have to do a little research tomorrow to confirm this. Anybody else with a N/A V8 that can verify this value on the scanner? IIRC, the value reported to the computer is not raw data, but is compensated for engine vacuum.
alright, I was wrong about when the ignition was in “ON” position. It said 58 psi, which I understand is probably a significant amount more than it should be? Also the key had been in on position for about a minute because the scanner takes a hot minute to connect and then identify vehicle and then load live data…
Me too. Did a little more digging. The expected value isn't always going to be crystal clear. That chart in post #2 above? I believe that is the value you should see with a mechanical pressure gauge. The value reported back to the computer? That doesn't always match the actual pressure, as it is offset by manifold pressure. However, if I understand the control logic, the computer always sees around 55PSI with the engine running. At idle, with high manifold vacuum, you'll actually have around 40PSI at the injectors but this is reported as 55 to the computer. More long-winded details in this thread:
Normally I'd suggest hooking up a mechanical test gauge to verify the accuracy of the sensor, but IIRC the test port has been deleted on 2003+ models.
So from what I gather, under low power settings, the actual pressure at the injectors will be less than what is reported to the computer. This is all fine and dandy, by design. The computer is happily regulating the pump output to the 55PSI feedback, even if that isn't entirely accurate. Now if you had a tired pump or a clogged filter, you might actually see feedback LESS than that, as the pump would be commanded to run full bore to keep up pressure but can't do it.
However, for the life of me, I can't picture a scenario where the feedback is substantially MORE than 55PSI. If the feedback is too high, the computer will command the pump to slow down to get back in range. Yet you had 66PSI in one screenshot, which is 20% too high. No idea how you got that, unless it was a brief excursion that you just happened to catch. Call me confused.
The only thing I can think of for this situation is a faulty fuel pressure sensor. Maybe it has a bad spot a little bit above or below 55PSI. Most of the time it can happily report 55PSI, but when it hits that bad spot it sends 66PSI. Heck if I know, just thinking out loud.
So you are thinking the fuel pressure probably is normal just reading too high for some reason? Anyway the car started pretty rough this morning, this is the first time this has happened while the scanner was in, the ecm threw 4 codes. All seemingly unrelated which makes me wonder if it could be the battery..
