Ok, first let me say, I've searched the forums until my eyes are blurry. I can't find anything that specifically points to my issues.

Here's the history:
1994 Jaguar XJ6
While driving home on a road trip my father started experiencing a loss of power/engine miss situation. The way he explained it made it seem that it was a constant problem. He parked it and said, "It needs a fuel filter" and left it at that. My dad HATES working on vehicles in general at this point in his life, and I hate working on this vehicle in particular. So, the car has sat in the same spot since mid-July. Finally I decide that if it's going to get fixed it's up to me so I replaced the fuel filter yesterday. (Here is where I went wrong, I didn't drive the car myself to see what it was doing) After letting the battery charge all night and having to coax it to start because the fuel pressure had bled off I started it. It still had a rough idle/intermittent miss. After fogging the neighborhood for mosquitos for about 5 minutes I shut it off and let it sit for a minute or two and restarted it. Hallelujah! No miss! ...........Wrong. I was called away from the mechanic duties to perform some mom duties. I came back and started the car with the intention of driving it to see how it ran. The miss/rough idle was back. I took it around the block a couple times to see if it might just still be some air in the fuel lines. It doesn't seem to run badly, and the power seems the same as always to me (I've always thought this car was slow as Christmas). But a couple of times when coming to a complete stop the car died! (But not every time) And when I pulled back up at home and let it idle the rough idle/miss was still there. I thought that the exhaust smell was especially strong as well so I opened the hood and there is smoke coming from the most rearward exhaust manifold.

I'm about to go clean the TPS, because that was the only thing I could come up with from my search, but I don't hold out much hope that this will fix the problem.

Any ideas?

 

How about trying some of the simpler things like checking the plugs, distributor and rotor.

Make sure to check for good spark, bluish in color. If it's yellow, there's not enough spark. That could be the battery or ignition coil.

Other potential suspects are the catalytic converter, or even stale fuel for that matter.

Let us know on how you let on.

 

You might have a clogged cat (the one thats in the rear ex manifold).

 

Check fuel pressure as well as the ignition. The pressure regulators sometimes stick, fuel pressure rises and the engine will run rich (chug black smoke) and then it will operate normally the next time it is started. Black spark plugs will indicate a rich mixture. Where in Texas are you?? There are a bunch of us in the DFW area and alot of people Houston as well that might have a fuel pressure gauge to diagnose the fault. The fittings are different from most cars.

bob gauff

bob gauff

 

Thanks for the replies guys.
I didn't get to check the TPS last night because I had to do the mom thing again. I forget that when I join a new forum people don't have any clue who I am or what I know. I left out the obvious stuff like checking the plugs and wires because that's the first thing you always do when your engine develops a miss.
I had to run to the store after dinner and decided to take the car and see how it did. The miss is still there at idle, but very faint. The car seemed to run better than it did in the afternoon but that could also be wishful thinking on my part.
I've decided that instead of pulling parts off I'm going to run a fuel system cleaner first because when one of the injector in my truck got clogged it created a faint, intermittent miss. So, my next question is, is there any particular brand of fuel system cleaner that is preferred for these cars?

motorcarman, I live in Aledo, near Fort Worth. I have several fuel pressure gauge fittings, however, the gauge itself died (although the dial said it would go higher, 35 psi from a holley blue pump with some modifications was more than it could take). I've got a new, better (not so cheap) gauge on my wish list because with a diesel truck the problems are almost always fuel related.

 

Crew,

Since you're in the US, I recommend STP Complete Fuel System Cleaner. The key word is "Complete". The other STP types are fuel injector cleaners only.

For regular maintenance, I use marvels Mystery Oil for both the oil and gas. Great item to have for our cars.

Best of luck in troubleshooting the problem. BTW, I think you are correct in adding a fuel injection cleaner first. It's the simplest solution for the initial troubleshooting process.

 

Thanks for the reply! I like STP products so I'll go get some of the stuff you recommended tomorrow. Thanks again for the help.

 

Does it seem temp related? These do like to have new FI temp sensors periodically. Any vacuum leaks? It's at the age for that as well. Check down in the cracks of the accordion hose.

 

If the basics are covered (cap rotor plugs and wires) and I assume that your getting no check engine codes on the vcm. Then I would let it run for a bit and check the cats to make sure neither of them are glowing cherry red and emitting a rotten egg scent from the tail pipes. I would also take a moment to check the exhaust pipes to see if they are coated in black soot.

If the cats are fine, no smell noticed and no soot on the tail pipes. I would look at fuel pressure, and filter as possible culprits.

If the cats glowing and stinking replace the offender, there are 2 cats, one off the manifold and one underneath back towards the rear axle.

If the pipes are all black and sooted, take a look at the coolant temp sensor, for the injection, or the o2 sensor. Those can both cause the care to loose power and run like butt.

For fuel system cleaner, I lean toward lucas products. That is personnel preference in the end.

 

ArmyJag,

Are you sure that the coolant temperature sensor can cause the car to feel sluggish?

I've done a considerable amount of work on my car this summer and for some reason, it doesn't have the power it used to. In fact, the engine pings more than usual with hard acceleration. The tail pipes are a little sooty and gas mileage is down considerably.

 

When mine went out about 2 years back it was running rich and was a bit sluggish. I didn't have a bad sensor in there long enough to find out how much it was effecting mileage as I changed it out that night after work.

Basically it's not letting the car know its warmed up and continues to over fuel a bit.

 

Had the same problem you have described, it turned out to be the oxygen sensor which is located on the exhaust manifold just where the the two exhaust pipes converge you can see it if you look downwards from the firewall, it is visible just where the pipe bens to the horizontal