New member - first post. First Jaguar (2001 XK8 Convertible, 80,000 miles) which I have had nearly a year.
I have been trying to resolve an occasional Restricted Performance/CEL for some weeks. I've been scouring prior posts and have made some progress.......
OBD scans show P0171/P0174 lean fuel on both banks. ST fuel trim is about + 8 to +10 on both banks at idle, and LT trims are both +19.5.
Have done a hard reset (battery disconnect etc) but LT's quickly return to +19.5.


Carefully checked for leaks between MAF and throttle and all seems good after taking apart and reassembly. Pre-MAF, air filter etc is also OK.
Have not smoke tested but cannot find any evidence of vacuum hose leaks. Multiple brake-cleaner bursts do not affect ST trims wherever I squirt. I also replaced the fuel filter.
I'm suspecting I have a faulty MAF sensor, but don't want to spend $100+ if it's not the problem, so am looking for some way to confirm that this is what is wrong. Live OBD data shows MAF pressure at about 3.5 gm/sec at idle, going to about 7gm/sec at about 3000rpm. My suspicion is that it's low., but I cannot find any specs for this. Is this a predictor of a faulty MAF Sensor? What else should I be doing to confirm or where else should I look?

 

welcome to the forum - when you checked between MAF and throttle body, did you check the bellows area on the air intake tube - looking for cracks (especially on the underside). If it is cracked, duct tape it until you can replace it and see if that clears the problem.

As this is your first post, please take a moment to post an introduction in the New Member area: New Member Area - Intro a MUST - Jaguar Forums - Jaguar Enthusiasts Forum

Hope this helps and you get your issue resolved quickly.

 

Thanks for the reply. Yes checked the bellows and it is as good as new. Also cleaned the MAF sensor with CRC (several times!).

 

Have you tried the brake cleaner bursts near the fuel injector bases and also where the intake manifold contacts the head? These are both possible vacuum leak areas.

 

Sounds like you know what you are doing but your first impression that it is a vacuum leak is probably close. Before firing the parts cannon I would do all that again. I do not see any mention of cleaning the throttle body or the part load breather. Might add those to the entertainment list.

 

Thanks WhiteXKR....I haven't checked the inlet manifolds in a structured way. My ST's seem to be evenly balanced so my suspicion is that it is a common (pre-throttle or vacuum) problem. I had 6 months with no Lean problems, so I took a guess that the manifolds would be unlikely to fail identically and simultaneously. I will check more carefully!

 

The plastic intake manifold has occasionally been known to warp (probably from a past overheating event). Also the fuel injectors have a vacuum seal on your particular engine since the engine has a feature called 'air assisted fuel injection'. Definitely worth a check.

 

One if the reasons you do not use starter fluid to start cars with a plastic intake manifold it will cause them to crack.

See if this information helps Link http://www.jagrepair.com/images/Auto...otos/P0171.pdf

 

Check LTFTs at 2500rpm (parked) as well. If they head towards zero you've almost certainy got an air leak (and a swine to find, too).

 

Your maf values seems to be too low. Disconnect the maf sensor contact and see what happens.

There could also be other types of faults:
Fuel pump
Fuel filter
Fuel injector blockage
Exhaust leaks (before catalyst)
etc.

Good luck hunting! / Bo

 

A Jaguar Tech told me one time that any time you want to pull a plug you should disconnect the battery and if you want to get accurate reading you should do a hard reset before reconnecting. This resets the car back to ground “0” and a good 22/30mi run will provide accurate readings. However, keep in mind that you will need to reset your windows, radio stations and you should have the radio security code if it applies.

 

OK, so we are making progress. Thanks to all those who responded with ideas......
I removed the engine covers and, using OBD live data for STFT, and multiple squirts of brake cleaner, I found a very small hole in the Part Load Breather Hose (thanks to TestPoint's post). I removed the hose -those clips are REALLY difficult, and the (now clean!) throttle body has to be half -removed to get access to one of them.
I checked the hose visually but could not see the hole. However by blowing in one end and covering the other two outlets, I managed to find it. $35 later (local Jaguar dealer) I have now fitted the new hose.


STFTs are now lower - about +7 at idle. I suspect I still have a minor vacuum leak or MAF problem, and I will report back after doing some driving and further OBD scans. We are back on the road! Thanks!

 

Status update. This is still a problem. Since the last post I have:

1. Purchased a vacuum test gauge ($25) and measured the vacuum at about 18in Hg. Measured at 2 locations: The vacuum pipe at the back of the fuel regulator, and at the pipe going into the back of the throttle body. So it looks like I have a decent vacuum and therefore not a serious vacuum leak.

2. Purchased a rather nice fuel pressure gauge set for only $25, and measured the fuel pressure at the Schrader valve on the fuel rail. It's about 43 psi at idle with the vacuum pipe to the fuel regulator removed ( Per TSB 310-04). So this also looks OK.

3. Purchased a replacement MAF Sensor ($45) and fitted it. THis improved/increased the MAF pressure readings and they now look normal. This also reduced the LTFTs to about +14 after a long period of idling...they were previously off the scale at +19.5. So this is better also.

HOWEVER, I still get Restricted Performance and CEL after 10 mins of driving or so. Codes are still P0171/P0174, Lean both banks. Freeze Frame data from the OBD scanner shows that the LTFT's go up to +19.5 which I guess is what causes the RP alarm.

The car worked great for 6 months with no CELs and no RP, then this suddenly started happening for no apparent reason. No other performance problems. Not sure where to turn next. Suggestions welcome.

 

Just to clarify....when the Restricted Performance comes up after ten mins or so of driving, it will stay on for a couple of minutes or so, then go off. Everything will be normal for a while, but RP will continue to go on and off at irregular intervals...typically less than ten mins or so between bouts of a couple of mins duration.

 

There are threads all over this site about those codes. The aim is to find which of several different causes applies. You measure LTFT per bank, engine hot, parked, at idle & about 2500rpm. If they drop a lot then you've an air leak. Post the 4 numbers if you'd rather.

 

Have you checked:

1. EGR

2. Exhaust leak between headers and cats

3. O2 sensors

/ Bo

 

Just as an outside chance check the spark plugs are tight - I chased a similar problem on mine(changed MAF,intake tube etc) - turned out to be a couple of loose plugs - we surmised that these were sucking air on the overrun - would only happen when warm.

 

I have found a "smoke tester" to be a very effective method of locating vacuum leaks. It is a clever gadget.

 

Agreed, mine cost me the price of a pack of cigarettes to build and 30 mins time to assemble, and showed up a TB gasket leak which I would never have been able to find otherwise.

 

OK, thanks for all the helpful suggestions. I will get to all of them in the next few days.
I have already checked around all of the intake manifold ports and injector bases with brake cleaner (at idle while monitoring STFT Live data) and have not found any leaks around any of them.

Just done the Fuel Trim measurements per JagV8 suggestion. I did a hard reset before each test so the LTFTs started out at 0, and then I did measurements at approx 2 minute intervals so I could watch the LTs rise. Here's what I got


At Idle, 650 rpm MAF 3.7gm/s, IGN 4.5deg adv
Time ST1 LT1 ST2 LT2
0 min 18 0 18 0
2min 7 14 7.8 16
4min 0 19.5 1.5 19.5
6min -1 19.5 -1 19.5
8min 0 18.7 0 18.7


at 2500 rpm, MAF 12 gm/s, IGN 28deg adv

Time ST1 LT1 ST2 LT2
0min 23 0 21 0
2min 13 7 12 6
4min 1 18.7 3 16.3
6min 0 19.5 0 18.7
8min 0 19.5 0 19.5

Hope this helps with the diagnosis!