Engine loses power while driving?

MAUDRIE

MEMBER
1987 JAGUAR XJ6
6 CYL
AUTOMATIC
110,000 MILES

It’s happened many times in the last few weeks and because of this, we don’t drive the car very far, maybe to the market and back home just a few miles.
It usually happens on acceleration from a stop where all of a sudden, the car loses power and if we press on the accelerator there is no power there and then somehow the power comes back on then once again loses power and then again comes back on. Almost like sputtering or just running out of gas. A few times there has been a very small backfire.
The engine, so far, has always caught back on and has not completely shut off.
We have had the car 22 years and have taken very good care. About a year ago, it was having the same problem and had the spark plugs changed a tune up and my thought is the mechanic turned up the idle. Uses a ton of gas. But it ran great, no problem with the stalling.
Then last month we took it in for a large repair; rebuilt rear end, new brakes, and it cost a small fortune but ran really great. Until about a week after we got it back when it started acting up again. Same problem. We have noticed that one of the gas tanks seems to have more “stalling” problems than the other.
That’s the story. We just have one car and it’s beautiful and we love it. Any suggestions would be so greatly appreciated! Thank you in advance.

9 Replies

KEN L

MASTER CERTIFIED MECHANIC
42,861 POSTS

That fact that one tank effects the problem more than the other tank tells us the fuel pump is starting to go out or you have a clogged fuel filter if the filter is new, we can check the fuel pressure to confirm this guide will help with instructions in the images below to show you how to change the pump out.

The Fuel Filter is located in the right, front corner of the luggage compartment next to the spare tire.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

1. Depressurize fuel system.
2. Loosen clip securing cold start injector supply line to fuel rail and remove fuel supply line from rail.
3. Install a suitable pressure gauge onto fuel rail and tighten clip.

CAUTION: The pressure gauge must be checked against an approved standard at regular intervals.

4. Disconnect "-ve" low tension lead from ignition coil, and switch on ignition.
5. Check pressure gauge reading, reading must be 36.25 psi (allow a +/- difference of 0.725 PSI).

NOTE: When the fuel pump stops running, the pressure reading may drop slowly through either the regulator valve seating or the pump non-return valve. A slow, steady drop is permissible; however, a rapid fall must be investigated.

6. Operate fuel change-over switch on center instrument panel and recheck the pressure gauge reading.

Note: If satisfactory results have been obtained, depressurize the fuel system. Disconnect the pressure gauge. If satisfactory results have not been obtained, replace the regulator with a new unit.

Check out the diagrams (below). Please let us know what happens.

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Thursday, August 11th, 2022 AT 11:50 AM

MAUDRIE

MEMBER
5 POSTS

Hi Ken,

Thank you so much for your brilliant and detailed reply! It is greatly appreciated!
Shortly after this morning's email, we took the car to get gas and sleuth around to see which tank was which. We filled the left tank first and when the fuel needle moved, we knew then that was the tank with seemingly less stalling. Then filled the right and took the car for a short test drive. Along the way (a few miles) we switched tanks and no stalling at all on the test drive.
I told my husband he better come with me on all my errands because it never stalls out with him in the car.
We drove all in all about 3-4 miles and no problem until we pulled into the driveway, and I smelled burning oil. We opened the hood, and the engine was smoking and we noticed oil around the back spark plug so that’s where we are now.
Thank you again for your reply. I can never thank you enough!
Maudrie

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Thursday, August 11th, 2022 AT 7:59 PM

KEN L

MASTER CERTIFIED MECHANIC
42,861 POSTS

No problem, which is what we are here for, to help people. Let us know if you need help with the oil leak, please start a new question though. Use 2CarPros anytime, we are here to help. Please tell a friend.

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Friday, August 12th, 2022 AT 10:48 AM

MAUDRIE

MEMBER
5 POSTS

Thanks again, Ken! Will start a new thread, as you suggest, if the oil leak proves to be problematic. We are taking the car into the shop Tues/Wed and will pass on the fuel pump or possible clogged fuel line information you sent. While it’s not exclusively a Jaguar repair shop, they do work on Jags and usually there’s a vintage one in the wings waiting for repair.
A variety of people (some Jag owners) always comment on how gorgeous our Seafoam Green Vanden Plas is. Then they want to know the year and then ask where we get the car serviced. I will certainly pass on a high recommendation of 2carpros! I will let you know how it goes! Thanks again! Maudrie

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Friday, August 12th, 2022 AT 3:39 PM

MAUDRIE

MEMBER
5 POSTS

Hi Ken,

Wanted you to know shop repair time changed so we will be taking the car in for service Monday. Have been doing very limited driving,
probably 25 miles or so total in the last week.
Has not had a loss of power during this time but close. Today 2 small backfires though. We have switched tanks too. I will let you know when we find out.
There have been times in the past where the ignition key got hot, but we have been doing such limited driving for the last year that that has not happened. Thank you again! I’ll let you know. Maudrie/Marianna