Just became the owner of a '11 XJL with a 5.0L, non SC., 145k on the dash. she idles fine, but hit the gas and it coughs and sputters, but revs fine out of gear. my first thought was fuel filter, but where is it? any ideas on what else it could be? all i know about it's history is that it sat for months, fouled injectors?

 

Check the air intake filters first. They are cheap and easy.

 

Fuel filter or fuel pump. Had this problem on x308 XJR, ended up driving with a fuel pressure gauge hooked up so I could see it when driving. If I accelerated, fuel pressure started dropping. It’s supposed to actually rise (vacuum operated fuel pressure regulator).

 

Well you can't change the fuel filter believe it or not!
Unless you replace the low pressure pump in the tank as the filter is part of that assembly.
Also the XJ has 3 fuel pumps. 1 low pressure one in the tank pretty much like any car. Then 2 HP gear driven fuel pumps mounted on the engine.
The HP fuel pumps are chain driven off the engine.

With DI the fuel pressure is so high (Like 12,000-18,000 psi) I would NOT hook anything up. In fact I have never seen a fuel pressure gauge for DI but I bet they are out there.
You can monitor the fuel pressure with most hand held scanners.

First do you have any codes?
Have you monitored fuel pressure?

What I would do is run some BG product or sea foam in the gas to see if anything changes.
Remember with these DI engines and your high miles 145K there is a possibility of carbon build up on the back side of the intake valves.
It's tough to check for this and without pulling the intake I don't know of any other way to do it.

Please post back with your repair.
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Many of us use BG44k.

I have also used CRC intake/ valve cleaner for turbos. Very important to get the one that is compatible with turbos. I feed it through the vacuum line that attaches to the bypass valve.

All the best.

 

Thanks for the inputs, I'll order some filters,air and oil, I did get an OBD app that lets me see sensor values, at high idle i'm getting around 600psi, is that normal? seems low to me, but then I'm more of a common-rail diesel guy. digging through the archived DTC,s ?, i see several for the MAF, so i.m thinking i'll also do seafoam in the tank with some sprayed through the intake. What values should I see on the O2 sensors? When i graph the O2 sensor voltage, they are quite often totaly opposite. still working on the learning curve here so bear with me guys and gals!

Value of a Jag in the driveway
Pi****g off the Inlaws and neighbors?

PRICELESS

 

MAF sensor codes suggest air intake filters or MAF sensors. You can clean the MAF sensors easily with MAF sensor cleaner. There are two MAF sensors, one next to each air box. Very easy to access them.

I don’t think you can use Seafoam in the throttle body if you have the supercharged XJ. You need to use stuff that is compatible with supercharged/ turbocharged engines.

All the best.

EDIT: Quick look around suggest people run Seafoam through supercharged cars without incident.

 

Maybe a little low?
On my XJR I get about 800 psi at idle.
So your probably in range.

But floor it and see what it's reading?

Please post the error code as that helps. Be sure and clear all codes every time you read them.
You want to work with new repeatable codes.
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