There is a problem that I have with my 1990 XJ6 that is beginning to frustrate me. To go back to the beginning, on the day I purchased the car, I had gotten about five miles from the previous owner's house when she started hesitating. I pulled into a gas station and purchased a bottle of Gumout, dumped it in the tank, and filled her up with fresh gas. Almost immediately, she improved and by the time I reached home she was running smoothly. Since then, she will occassionally bog down, or not want to accelerate; mostly after I have been sitting at a traffic light for a few minutes. And the idle isn't staying constant, either. She is set to about 650 rpm now and at times it will drop to 500, or so. If I change to Neutral while sitting at a light, then switch to Drive when the light changes, all is well.
Any thoughts?

 

Many things come to mind, but carefully reading what you did and what happened, I would suggest that the fuel filter is way overdue for a change.

The fuel pump may be suffering from the fuel issues by this time, and I am not sure if the '90 is "in tank", or "external", but others will tell you that one I am sure.

 

Funny you should mention the fuel filter, Grant. I've had this feeling that I should check the fuel filter. And since I've only owned the old girl for a relatively short time and don't know when it was changed last, I'm going to go ahead and replace it.

Thanks for the suggestion, and I'll let you know how it works out.

 

The Haynes manual says that before opening the fuel system - in this case, to replace the fuel filter - you need to depressurize the system. It goes on to say that to do that, you remove the fuel pump relay, then run the car until it dies. Is this really necessary to replace the fuel filter? And if so, where is the fuel pump relay loacated on a 1990 XJ6?

 

YES, depressurizing is prefered. It CAN be done without, BUT it will squirt high pressure fuel in places that could ignite and then BBQ Jag is on the menu, your car, your choice, simple as that.

No idea where the relay is, but look at the fuse chart, pull the fuse, same result. Start the car, it will run BREIFLY and die, now it is deemed depressurized, BUT you will still have fuel spill, and that is also dangerous, BUT it is not under pressure, so just good old gravity.

IF, and I say IF coz I dont know, the fuel pump is "external" there will be fuel hoses in the area, so a clamp arrangement to clamp the hose would limit the fuel that will syphon from the tank, coz the "external" pumps are gravity fed from the tank. The "in tank" pumps do not have that gravity feature so fuel syphon is almost a non event.

Take the required precautions, plenty of towelling type rags to soak up the fuel, and go for it. The first time is always the scariest.

 

Pulling a fuse was the option that came to mind after reading the depresurization procedure in the Haynes manual. However, the fuse chart in the owner's manual doesn't list one for the fuel pump. At least I didn't see one listed when I looked yesterday. But, I will look again. The Haynes manual also stated that the fuel pump relay was mounted near the pedal housing, or something of that sort. But again, I can't find it. So I'll press on and see what happens. It's a nice cool morning here in Tulsa, so it will be a pleasure working on the car. I'll let you know how things turn out.

 

Well, the fuel filter has been replaced. It wasn't a difficult job and I didn't need to depressurize the system. I searched all over that car for the fuel relay, or a fuse for the fuel pump and didn't find one. So I removed the gas cap, loosened the banjo fitting and let the gas run out into a container. There wasn't a great deal of it. Then I swapped out the old filter with a new one and all is well. I did a short test drive and didn't notice the intermittent hesitation. But a longer drive will tell me if I fixed the problem.

 

Glad to hear that the fuel filter as replaced without drama. Report back and let us know if that cured her.

 

As Army Jag said, sounds promising.

Now you got nothing to do, haha, carefully cut open that old filter, and see what you can see, coz that will tell you if you have issues happening inside the tank. I change my fuel filters every 2 years no matter how few/many kms the car has travelled.

For what its worth, whenever I aquire a new to me Jag, I always replace ALL the filters, ALL the fluids, ALL the belts, and ALL the hoses (cooling), no matter what the service history/salesman/dealer tells me, so I know exactly where I am with the beast.

 

Alas, the problem remains although the car does seem to run better. When I removed the old filter, there was some blackness to the gas. Don't know what caused that. I considered cutting open the filter, but didn't want to risk a spark. Tried to open the end of the filter with channel locks and vise grips, but it wouldn't budge.

What's odd is that the hesitation seems to occur after about three minutes of running, whether idling or moving. It lasts for about 5 seconds or so, then everything is fine. And it seems to be when the car is started from cold. Very odd. As for replacing filters, I do want to get that done. The transmission filter is the one I would most like to change, but I'm a little nervous about tackling that one. I've never changed one before.

 

Mmmmm, mainly starting from cold, maybe the coolant temp sensor is not behaving itself, not sure where it is on the AJ6 engine, someone will tell us both I hope.

They are usually located on the thermostat housing, or nearby, on the engine side of the thermostat, and have a plug that looks like a fuel injector plug, with 2 wires in it.

I would be checking the throttle housing for "gunk" build up. the air bleed past the disc is fairly critical.

 

This is frustrating. I thought I had the symptoms for this problem nailed, but this afternoon on the way home from work, I had the usual hesitation after about three minutes of driving, but then it continued. I couldn't get any decent acceleration from a stop. It was as though something was holding me back. But, and here's the kicker, when I shift into neutral and punch the accelerator pedal, the engine revs right up and seems fine. Could this be a transmission problem??? I checked the fluid and it doesn't look burnt, although it is overfilled, I think. Any thoughts?

 

Most engines will "rev OK in neutral", NO laod, not much of anything needed for it to occur. Load the beast up, such as "D", stand on the gas, and that makes all sorts of things come on line.

If it is "loading up" with overfuelling, then black smoke is the usual obvious symptom, and fuel smell.

If it is leening off, then a backfire via the inlet is common (sort of), but no go is the obvious, due to not enough fuel for acceleration.

You say that this started after about 3 minutes from what I will assume is a "cold start", and that is still having me thinking the ECU temp sensor, and/or it wiring. Maybe the MAF is having a moment, I have read lots about these units, but never had issues with them.

I would be checking fuel pressure at the time this actually happens (you dont have to wait too long by the sounds of it), and then of course "fuel flow" must be established, coz you may have pressure but you may not have sufficient flow when needed (acceleration).

A bit of V12 thinking here, are the earth cables from the engine to the chassis actually attached, and if attached, are they in good connection status. The V12 is a real PITA if the earths are not 100%.

There are many other things coming into the mind, but the basics must be established correctly prior to going in too many wrong directions

 

I'll try to check those out tomorrow. Not to confuse the issue, but I found today that it not only happens when starting from cold, but other times, too. For instance, on the way home from the office, I stopped at Wal-Mart to get some carb cleaner, windshield washer fluid, etc. When I got back in the car after about 10 minutes and started driving, the hesitation started up again after about a minute or two of driving.
I'll check out some of those items you mentioned and see what I find.

 

Yesterday, I was checking the wiring and in the process I discovered that one wire, which I believe is for the oxygen sensor, was nearly broken in two. I didn't do anything immediately, but when I left for church this morning there was no hesitation and she pulled strongly and smoothly. Then on the way home, it was fine for the first mile, then the old problem was back. I repaired the wire and will see how things go tomorrow.

 

The hesitation problem is gone! Apparently, the repair to the wire corrected the problem and the old girl seems to be doing just fine. On the drive in to work this morning, she never once hesitated and ran smoothly the entire 15 minute drive.

 

Good to here that!

Got the same problem on my xj40- 4,0 1990. Can you tell me where this senor/wire is located?

 

Well, on my car, it is on the right front fender about 6 inches in front of the battery.

 

The sad part is I was about to recommend checking your o2 sensor.

For Don Hog, the sensor itself is located in the main cat converter on the passenger side easily visable looking down the exhaust. the wiring comes directly out of it and hooks in near the battery on the inner fender. That is what was causing my recent power loss as well.

 

Actually, I was trying to locate the O2 sensor when I found the broken wire. The research I had done pointed to the O2 sensor, and I was resigned to replacing it. Then, I found the broken wire, fixed it, and all is well.