Just a word of caution about the MAF sensor. I bought a can of cleaner today from one of the auto parts stores, asked for MAF sensor cleaner. They sold me CRC Throttle Body and Air Intake Cleaner. Read the can and it says DO NOT USE TO CLEAN THE MAF SENSOR! Glad I read the label.

I did take off the air filter housing and pipe back to the throttle body today. Checked the MAF sensor, it looked clean, but dark color. Ordered a new air filter.

I did find that the throttle body was very dirty around the valve inside. I blocked it open with a piece of wood and cleaned it with a clean rag dipped in WD40. Nasty black crap came out, I suspect this may have been the cause of a my delay at full throttle acceleration.

But......I still have the code P0174 and an occasional restricted performance notice on the dash.

Bought a can of Sea Foam fuel injection cleaner. Looks like to work it wants a small amount of gas in the tank before you toss it in. Not sure if this is a good move or not.

I hate to sound ignorant but I have no clue as to where these VVT things are located and/or if my 2001 has them. I know that stands for Variable Valve Timing, but thats the extent of my knowledge.

I had the fuel pump replaced back a few years ago, I think 5 years, and I think the fuel filter was replaced then too, not sure about that and may go ahead and replace it now.

What equipment do you use to test the fuel pressure at the rail port? I assume that will tip you off as to a fuel filter or pump problem.

Thanks for your comments and assistance.

 

If there is dirt coating the throttle valve, chances are some of the same stuff is coating the MAF sensor. How bad was the air filter? You should probably get the CRC MAF sensor cleaner from the same parts store and try it. Chances are it is toast, though, and should be replaced. You need to locate the proper DENSO part#, and shop around. These can be found insanely cheap. I spent $22 on eBay for my '03. I generally avoid throwing money at problems, but if it is cheap enough, starting with known good parts works, too. Also, check the o-ring seal at the base of the sensor.

Double check the instructions on the bottle. It is typically a can for a FULL tank. The problem is that these products swell rubber seals. If the concentration is too high, you will do more harm than good.

They are on top of each of the valve covers, towards the front of the engine. The VVT actuators have a plug coming off of it, at a 90 deg angle. The base of the actuator has a seal with the valve cover. Chances are, it is leaking a bit of oil already...

Best of luck, keep us posted.

 

I just did a fuel pump pressure test and came up with some interesting numbers:

Key on, not running - 21 psi

At idle - 32 psi

2,500 rpm - 32-33 psi

There's concurrent thread on fuel pump pressure which states that it should be at least 35 psi with the key on, and anywhere from 45 to 55 psi idling and revving respectively. If that's the case, than the fuel pump is likely the problem. Can anyone suggest a another source where I can confirm the proper fuel pump pressure before I commit to dropping the fuel tank?

Thanks.

 

I bought a can of CRC MAF Sensor cleaner and sprayed it down several times. Added that can of seafoam to the gas tank.

Now when I punch the gas hard it stumbles and backfires. The backfire is a first. Hummmmmmmmmmmmmm............................anothe r mystery.

I have not been able to find a connector to connect to the fuel rail to test fuel pressure. Have the old style vacuum/fuel pressure tester with the hose and no connector for the type of fuel rail connector. Will see if AutoZone sells an adapter on Saturday.

I do have a fuel filter but hate to mess with it unless I know for sure its a pressure problem. The filter and fuel pump were replaced back about 5 years ago at 40K or so on the clock. Car only has 50K now.

Grrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr............ .............frustrating.

Put in a new air filter, cleaned out the throttle body, cleaned the MAF sensor. More to do I guess.

 

Normally, the fuel pressure is regulated by the manifold pressure. The idea is that there is a constant pressure for the injectors to work with, and so fuel metering by mass can be done by controlling the time the injectors are open. So the absolute fuel pressure is going to change with different throttle positions.

I have not done this on this car, but normally, there is a fuel pressure regulator on the fuel rail. It is typically attached to a vacuum line. For a test, you could disconnect that line (and plug it I suppose to avoid a vacuum leak) and check the max pressure the pump can deliver.

In my (limited) experience, fuel pump work and then they quit. I have not heard of them gradually not able to provide the requested pressure. If that is the case, it sort of points to the filter instead. There is also the possibility the air flow is just measured wrong to begin with...

Best of luck, keep us posted.

 

I just commented on the other thread that my local foreign car expert set mine at 40# and claims that is the correct level.

 

I would look at the fuel filter first, its a $16 item or less at autozone. Many members have suggested that previously. Try replacing that before digging in that nasty fuel pump replacement, thats an expensive and time consuming project.

But of course, as members suggested, you need to put a fuel pressure tester on the rail to find out of that is the problem first.

 

I put the Harbor Freight Fuel Injection fuel pressure tester on the rail and got 35 PSI when the key was turned on. 40+ while running. So maybe the pump and fuel filter are ok.

Or maybe that seafoam in the gas tank is cleaning out the big chunks in the fuel filter.

Cleared the codes again but car still has that hesitation when the throttle it quickly depressed. I am beginning to wonder if I just need to run out that tank of gas, change that fuel filter and see what happens.

Running out of things to check.

 

You need to figure out what is going on then. I have done fuel pressure tests like this before by taping the fuel gauge to the windshield so you can kind of keep your eyes on the road, but see the needle on the gauge at the same time. When under load, if there is a fuel problem, you would see the pressure drop.

The other possibility is a defective air flow meter. If it "slow" to react, you would have a temporarily lean condition. Here, the fuel trims would tell you what the back side of it is measuring.

 

The fuel filter was just replaced, which eliminates that possibility.

When you hooked up the gauge did you remove the vacuum line from the fuel pressure regulator, or are those the readings with the vacuum line connected? I'm considering re-checking my readings (never above 32 psi) with the vacuum line removed and plugged to get a better idea on the condition of the fuel pump.

Took the car out for a short drive on local streets, and it ran great! Smooth idle, no hesitation starting from stop, and excellent throttle response. And no codes. Of course I didn't really get my foot into it which will likely be a different story. Waiting on the VVT seals to see if they're a factor.

 

Wondering where you got the VVT seals? And cost?

My fuel pressure figures were with the vacuum line connected to the pressure regulator.

 

does the xj8 2002 have a EGR

 

The VVT seal part number is AJ82856. You can find them at SNG Barratt, Rock Auto, Partsgeek as well as several ebay vendors. Prices seem to range from around $ 7.00 to $ 14.00 each. I got them from a place on ebay called Parts Container for $ 28.75 for the pair.

 

On Saturday my son and I installed the new fuel filter. Car started immediately which I thought was a good indicator the pump was in good shape. We still had that stumble so i put in a new Walker MAF solenoid. That seemed to smooth things out.

Erased the Codes and we will see how it goes.

Filled up the gas tank with the best high test I could find to dilute that can of Seafoam I had added to the tank some time ago.

Car seems to be running great, but did not put my foot into it big time. I will let you all know if the code comes back or if the problem is sorted out.

 

Glad to hear that you're getting it sorted out. The last time I drove mine it seemed to be fine also, but I'm going to change the VVT seals today and do (hopefully) a final confirmation drive.

 

Next on my list too. Replacement of the VVT rubber seals. I have seen a little oil weeping out around the edges.

 

Well, I replaced the VVT seals, a surprisingly simple job (for a Jaguar), and took it out for another test drive. Got my foot into it a few times and noticed that after it hit around 4,500 rpm it bucked and upshifted to the next gear. At idle, the STFT's vacillated around -3.9 to +2.1; about where they've always been. Checking for codes on my Torque app, I got a pending P0174, Lean Condition on Bank 2. Still wondering if my comparatively low fuel pressure reading (32-33 psi tops) is indicative of a failing fuel pump (already changed the fuel filter) which isn't providing enough fuel volume at high rpm's. One left thing to replace before I bite the bullet on the fuel pump; the dipstick o-ring seal (the fit feels sloppy). Anyone have a part number or source for this o-ring? Seems like it shouldn't cost more than $ 1.00, but we all have experience with Jaguar parts prices.

 

Just a thought, have you had the top end smoke checked for vacuum leaks? I had a mustang that had a plastic intake that had a crack, but you couldn't see it until upper rpm when the plastic flexed slightly, opening the vacuum leak making it bigger, it was pure luck I saw it when I did, and I wouldn't have been able to see it without the smoke machine.

 

Yup. It's obviously, a $20 O-ring.


Take a look at what they want for the vibration isolators ("Instrumounts") we use on the air filter box, oil cooler and heater pump & valve tray. About 50 bucks a pop. I guess they just don't want to sell any, so after another decade, the Bean-Counters will abandon them altogether.

 

I actually bought one of those isolators brand-new a few years ago from someone on the forum for the cost of shipping ($ 3.49). I still have it, don't need it (Mina intake system) and will gladly give it away to the first person that can help me find this problem! (Just joking, if someone needs it, PM me).

As far as a possible intake air leak goes, I'll re-check all of the connections (metal intake tube), why would I go from having lean conditions on both banks to a lean condition on only Bank 2? And what does "Pending" mean? Is the car waiting to make up its mind?

Haven't tracked down the dipstick O-ring yet either.