I currently have these three codes popping up when using my code reader.

A quick background: I've had these codes for the past couple months, and as a result, I've replaced intake manifold gaskets (upper and lower), spark plugs, IMT o-rings, PCV hose, MAF sensor and brake booster hose. In actuality, they all did need to be replaced on account of cracks or deterioration. Because I believe I've eliminated vacuum leaks as the cause, I've moved to fuel as being the issue. I replaced the fuel filter on a whim, and although it did need to be replaced, I hardly think it changed much. I'm banking that it's either the fuel pump, injectors, or even the MAP sensor.

The engines shakes and shutters from start up, and when using a fuel pressure gauge, I find that when idling the pressure fluctuates rather rapidly between 50 psi and 60psi. When the key is in the on position (not started), psi sits at about 30 psi.

Also, getting past 3000 rpm cause the fuel pressure to drop dramatically and fluctuate between 10 and 30 psi.

Can anyone provide some insight to what may be the cause? I've lurked this site for weeks, and it seems everyone has found their solution in a vacuum leak.

Any and all advice is greatly appreciated!

Thank you,
Stephanie

 

Annnnnd I completely forgot to share my make and model: Jaguar X-Type 2002

 

Stephanie, it sounds like you have been on the right track for where your error codes are leading you. P0171 and P0174 codes are low vacuum codes which have nothing to do with fuel pressure. The reason you are seeing your fuel pressure fluctuate is your vacuum leak is pulsing and the fuel pressure your car outputs is based off of the intake vacuum.

There are a few things I would now check. I would look in the area by the throttlebody and follow some of the lines there. I want to say there is a green hose and a red hose (both are hard plastic). One of those may have cracked and is causing your vacuum leak. The other issue we have seen is the line going to the top of the intake (runs over to the brake booster), where it goes into the intake can leak there (so a new hose will not solve the issue). The last place is to check the accordion tube that attaches to the throttlebody. If that gets a slight rip/tear in it, that can raise hell with the engine.

The last step I would say to do is to find someone that smokes (you or a friend) and what you want to do is to start with the motor cold and the heat off inside the interior (this will garantee that the engine fan will not be running). Start up the car and blow the smoke around the engine bay gently. What you are looking for is the smoke to be floating along and then make a sudden movement towards the engine. This will point out where the vacuum leak is. From there, it is a matter of following the smoke to the bad component.

Another thing I would say to try is to get your hands on a higher end code reader that allows you to look at the engine parameters. You would then want to look at the intake vacuum. Is it at say 0 inches hg or is it floating at same value say around 10 in hg. Based on your fuel pressure, I am guessing it may be up near 0 in hg. If this is the case, you may have a bad pressure sensor for the intake. You can confirm it by attaching your own vacuum gauge to see what the actual vacuum is. The motor is running rough because you are feeding it too much fuel.

Hope this helps you get to a resolution.

 

Thermo,

First of all, thank you for the quick reply. I finally had to the chance to check some of the solutions you offered. While looking for the red and green hoses you mentioned, I found the red one (under black plastic casing, I found it was red) that connects into the back of the intake manifold to be a tad loose. After wigging it around and resetting the codes, I believe that hose to have been my problem; however, I have noticed that sometimes while accelerating after already cruising at a steady speed that I get a hiccup. Although it is a minor hiccup and my CEL has yet to come on, I'm still cautious and weary about it. For now the car is idling perfectly fine and my fuel pressure has returned to normal.

Stephanie

 

Stephanie, keep an eye on things. The hiccup that you talk about can be caused by a lot of things. while I am not advocating this, I have found that if you can find a few highway entrances to use, do a few hard accelerations to go from say 15 mph to highway speeds (70ish). This will sometimes cause a code to lock in and help show a problem. If the car starts to stumble, stay in it within reason (ie, if it sounds like the engine is going to blow, then obviously back out of it). But, hopefully your problem will clear itself. This might be a good time to run a bottle of fuel injector cleaner through the car just as a precautionary thing. This will help clean out any gunk that may be in the car causing random things to act up.

 

I know it's been a bit since I last replied, but between class and work, it's been a hassle trying to get that CEL on so I could finally read some codes. But it finally did go on, and I found that cylinders 4 & 6 were misfiring. I changed the front three spark plugs since I had some stocked up, which has helped the hiccuping a lot, but there are still minor hiccups I notice, mostly when on the highway. I plan on ordering some new coils to see if they may be the culprit. Any and all feedback is appreciated.

Thanks,
Steph

 

Steph, sounds like you are on the right track. A quick check that you can do is to look at the top of the coils in the clear that is there. Do you see white "hairs" in the clear. These are actually cracks in the clear sealant that they use when assembling the coils and this can allow water into the coil, leading to issues. In a lot of cases, these "hairs" will run around the edge of the coils where the clear meets the black plastic. What you will normally see is when it is rainy out or you just ran your car through a puddle/car wash, it will get more picky and stumble more often.

Hope this helps to explain what you are seeing.

Not to ask a silly question, but what did you gap the plugs to? Jaguar changed the recommended gap on the plugs and people have found that if the gap gets too big, it can cause what you are seeing.

 

Thermo,

I'll have to check for the cracks on the coils when I get out of class, but as for the gap size, I was unaware that Jaguar changed the size.

Following what I read in a Chilton's guide, I gapped them at .054 (I believe that's what it is off of the top of my head). I can double check later, but what is the new recommended size?

Steph