Y'all are the knowledgeable ones, so please, help me Jag Forums, you're my only hope. And whatnot.

The drama starts back in November:

Driving home from work one afternoon, and the car gives a loss of power on acceleration. (To me, as someone who was denied entrance to my HS's auto class, I thought "huh, cylinder misfire?")

Nope. I take it down the road to an AutoZone for the codes, and it's P0171 & P0174. Okay. New for me, but whatever. Replace the MAP sensor. Clean the MAF sensor. Have a dude at work check for vacuum leaks with this handy-dandy cool gismo he has. Nada. Decide to go for the fuel filter, as it's the next (cheapest) thing. And guess what? it works!

For a month.

Today, because this week isn't sucking enough already, my car gave the same weird loss of power/stuttering upon acceleration, and the check engine light is back with the same warning.

Cue my freaking out. (Look, the car also needs an AC fan module replacement and my quote was $1300, and I live in Arizona so it's really not an option NOT to, so I'm REALLY not in the mood for this car to be misbehaving again.)

Any ideas on why the fuel filter would die out again? IF that's what it is? What else could it be? I'm terrified this could be indicative of a much larger, more expensive problem.

Thanks for any help in advance.

 

Your in a bit of a minefield here because there are so many things that can cause those codes! First, you may have a contaminated fuel tank so the filter keeps blocking, or there could be some other fuel delivery problem, or you could still have a leak on the air inlet side.

The easiest and cheapest thing to check for yourself is the air leak possibility, regardless of checks done earlier. Very carefully check the air inlet trunking between the MAF and the throttle body for any splits - especially in the bellows section. Then check the pipe that runs from the front cambox cover to the inlet manifold - it's about 1 in diameter - for any splits, particularly along the underside, out of sight. Depending on model year, this might require the plastic engine cover, if fitted, to be removed. Check the small bore pipe from brake servo to inlet manifold and any other pipes that are teed off it.

If nothing out of order with them, it would be helpful to check fuel pressure. Again depending on Model Year you may or may not find a schrader valve on the fuel rail that you could use for a gauge. Better would be a scanner plugged into the diagnostic socket that can read fuel pressure continuously. Then you could see how it behaves when the stuttering engine happens. Pressure should be a steady 55psi.

 

I would check the brake booster hose. That one piece if it fails will cause you to have both those codes. Its easy to take out, but will cost you about 75 dollars to order a new one. Easy install.

 

Agree that a "smoke" test for vacuum leaks could miss the brake booster hose. If the plastic check valve is white, it is likely original. Feel it for crumbling. You can try heat shrinking over the check valve like the updated line comes with.

 

First: I ought to say thank you (here, in a comment, in addition to the thanks button above) to the knowledgeable members who left comments.

Second: I apologize for dredging (hur hur, pun!) up an old post, but I thought it easier than posting everything again - since the problem is back! AAAAAAAARGH.


After my posting in February, the issue went away on its own. No more stuttering, no more check engine lights, etc. Until today, almost a year to the day it happened for the first time.

Why has my car forsaken me?

So, we (and I mean I watched and fretted) did the above things, found nothing, but I will say, when the issue seemingly cleared up, we stopped trying (and fretting).

The fuel filter seemingly was the root last time (tried MAF sensor, hoses, checked for leaks - before and after my last post) so was it just coincidental that changing the fuel filter worked last time? I do drive about ~13,000 miles a year just to and from work, so ...I don't supposed it's just the fuel filter again? *sigh*

Any and all help welcome, please. Thanks, all.

 

Like was said before you should hook up scan tool and check fuel pressure.
I have an iphone and use this scanner.(also works with my ipod touch and ipad)

with the free app "OBDCarDoctor"

Shows me real time fuel pressure.
Also gets and resets all the codes from engine and transmission.
cant go wrong for $14.99

not sure if it works for other phones


Also just out of curiosity how full was your fuel tank? and what grade of fuel was it?
I know your in Arizona but do they switch to a "winter" blend as you had the same problem this time last year........

 

Perfect; I'll order this today (I have an iPhone too, so at least I know that'll work). Thank you much!


(As an aside: it's likely correlation but not causation: it's finally cold here in Phoenix, and it rained all three times it happened. )

 

another useful free app is "Elm327 wifi terminal"

gives you instructions on how to set up your phone and test connection

 

App installed, scan tool connected, drove it at lunch, and this is what it gave me:


P0171: System Too Lean (Bank 1) (Powertrain, Generic)
-Fuel system status: Fuel system 1: Closed loop (1)
-Fuel system status: Fuel system 2: Closed loop (1)
-Calculated engine load: 34.9 %
-Engine Coolant Temperature: 113 °F
-Short Term Fuel Trim - Bank 1: 12.5 %
-Long Term Fuel Trim - Bank 1: 16.4 %
-Short Term Fuel Trim - Bank 2: 13.3 %
-Long Term Fuel Trim - Bank 2: 15.6 %
-Fuel Pressure (gauge): 56.1 PSI
-Intake Manifold Absolute Pressure: 17.7 inHg
-Engine RPM: 1261 RPM
-Vehicle Speed Sensor: 3 mph
-Intake Air Temperature: 84 °F
-Air Flow Rate from Mass Flow Sensor: 1.5 lb/min
-Absolute Throttle Position: 9.8 %

 

Thia: Chances are there's a vacuum leak in or around the intake manifold. ~16% long term fuel trim on both banks means the ECU is adding extra fuel to compensate for extra air leaking into the intake manifold thru a vacuum leak.

To confirm, run the engine with the transmission in Park, the scan tool connected, and press the gas pedal to hold the RPM steady at ~2,500 for ~30 seconds or so. If the long term fuel trim declines from ~16% to ~5-10% on both banks, you have an intake vacuum leak.

This post describes the 3 most common vacuum leaks and how to fix them: https://www.jaguarforums.com/forum/x...1/#post1309725

Two more common vacuum leaks are:

4) The ~3" black ribbed rubber hose between the air filter and throttle body, which can split on the bottom, or a metal band clamp may be missing: https://www.jaguarforums.com/forum/x...28/#post379092

5) An old PCV valve may be staying open too long, and need to be replaced for less than $15 and in less than 15 minutes.

Why would a vacuum leak be more noticeable / more disruptive when the weather turns cold? Two reasons:

a) Cold air is more dense than hot air, so when air is cold, more can squeeze thru the vacuum leak and into the intake manifold, disrupting the fuel / air balance.

b) Rubber becomes stiff when cold. So the rubber IMT O-rings and the rubber PCV hose do not seal well when cold and are more prone to leak air into the intake.

If you don't find the vacuum leak in the 5 spots listed above, let me know and we can talk thru how to pinpoint the vacuum leak using a can of carb cleaner and your scanner.

 

+1 what he said

If LTFTs drop you've an air (to vacuum) leak. If they don't then it's something else (post and say).

 

Confirmed; both long term fuel trims went between 3.1 and 5.5%

One of the guys at work brought his vacuum leak...sniffer tool, and it did seem to go crazy near the lower IMT valve area, so we've ordered new o-rings for it. The hose between the air filter and throttle body did have both clamps, but will look for a crack on the bottom as well.

Thank you SO much for your fantastic post/helpful info, I really appreciate it! I'll report back when repairs are done.

 

Thia: Great that you confirmed and found the vacuum leak. When the new IMT O-rings arrive and you remove the IMT valves to install them, you'll discover that you can't fully remove the lower IMT valve because the engine valve cover blocks the path. No worries. The old O-ring, probably factory original yellow, will be stiff and likely break as you remove it. The new green O-ring will be elastic enough that you can carefully stretch it over electrical connector-side of the IMT valve and into position.

The new green O-rings will be thicker than the factory original yellow one - Jaguar's solution to vacuum leaks. Sometimes it helps to put a little engine oil on the new O-ring to help it ease back into the manifold.

In your original post, you also said you need to spend $1,300 replacing the AC fan module. Is this the module for the radiator fan under the hood, or the module for the passenger compartment ventilation fan under the dashboard? I ask because the good folks in this forum can probably help you with a much lower cost solution.

 

Hi dwclapp, thanks for your post and info; it was helpful for us in replacing the o-rings, which was done almost two weekends ago. With the holidays, I've barely driven at all, and the MIL WAS off - until Monday, same code @ banks too lean. Didn't drive yesterday, went out to start it today, and holy rough idle - then followed by a flashing check engine light. (Since, I've gone to check the codes, and the light is no longer flashing, just on, but the idle is horrible.)

Codes:
P0171
P0174
P0300
P0302
P0303
P0304
P0306
P1313
P1314


Sigh. If anyone needs me, I'll be over here wondering how early is too early to start drinking.


(I will say, we noticed those codes right after the o-ring replacement, but thought it had to do with the battery being off/back on? I cleared the codes, and it was fine for over a week and a half.)


Thankfully, my awesome coworker, who is also the person who is helping me fix this damn car, is coming to pick me up so I don't have to panic attack drive it.


(Should I be looking at the fuel filter, etc., again? It ...seemed? to clear up the issues. Sort of. For a year last time. Sigh.)

 

Sounds like you need to change your intake manifold gaskets because of all the codes related to multiple cylinders. I bet if you check the plugs you'll find oil in there. If the gaskets and plugs have never been changed that would be a good place to start.

Chances are before when you changed the fuel filter it was an intermittent problem and it was just a coincidence it went away. although it was certainly not a bad thing to do anyway . Would still also be a good idea to check the PVC hose and if it is smooth and not ribbed, after 13 years chances are that needs to be replaced anyway. Also would still be a good idea to change the brake booster hose. That has a tendency to fail as well.

 

The misfires will cause the ECM to think the engine is running lean (excess O2 in the exhaust gases). Check the spark plugs for oil. You don't say how many miles on the car but if it's near 100k it would be time for plugs. While the manifold is off the intake manifold gaskets could be changed easily. Oil in the plug wells would indicate valve cover gaskets leaking.

 

Thank you both for the info, I really appreciate it.

There's just over 100k on it and plugs were next on my list (target date of two weeks, ffs, car) so we'll be doing those, as well as the manifold gaskets.

Forgive my ignorance, but: are these issues related? I see what you said, clyons, about the misfires causing the "ECM to think the engine is running lean;" does that mean that whatever is causing the misfiring (oil in the plugs...?) is to blame for everything, that perhaps it's not an actual vacuum leak? (Although it is certainly behaving as one?)

I can't fix my car myself, so understanding what is going on is as close as I can get (and helps me feel much better).

 

Yes. That's what I'm thinking. The lean readings will cause the ECM to add more fuel - the misfires pass that fuel and the O2 to the catalytic converters and they over heat. There may or may not be oil in the plug wells. You'll have to look and see. Cylinders 2,4 & 6 are on the radiator side of the engine and can be checked easily by removing the air filter assembly. Cylinder 2 can be checked without removing anything.

The plugs are due for a change and could in themselves cause the misfires, but I don't like guessing. Throwing money at parts can get expensive even if you replace them yourself.

Let us know what you find.

 

+1 that misfires do that -- all the car can see is the unburned O2 so it thinks it's not adding enough fuel

Then the fuel+O2 burns in the cat, which is not good news

There's a good tutorial in (I think) General Tech... by xrjguy I think

 

Again, thank you both so much for the information. Apparently, he did see oil in the front 3 plugs, and that's what I know so far. (He's probably very wise to keep me away while working on the car, so I'm not asking five million questions as he is elbow deep in Jaguar.)

I'll update again when I know more. For now, wine.

Thanks again so much!