Misfiring Cylinder 5 and multiple misfire on a 96 Jaguar XJ6 Vanden Plas

I used fuel injector cleaner in two different gas tanks; the car started shaking and the check engine light came on. The mechanic changed a sensor but the car was doing the same; I was told that it will take 4 full gas tanks to clean the gas lines. I went to auto zone and they told me that the car had a misfire on cylinder 5 and multiple misfire as well. I do not trust the mechanic any more since I had to take the car back to them several times and still is not fixed. They also did a full tune up and the check engine light still on and flashes when I am going about 55 mph. Is it safe to drive the vehicle to another shop under these conditions?

You need to start laying out details to bring everyone up to speed.

First you need to specify exactly what sensor was changed. This was probably done because of some error code that came along with that check engine light. The error codes look like “P1234” - you need to report the exact code.

The same goes for the codes that were pulled at Autozone - exact codes, like “P1234” (At least one of them will probably be P0305).

“Full tune up” doesn’t mean anything specific on today’s cars. You need to provide a very specific list of what was done - parts, services, labor. Its on your invoice.

You also need to say more about the car. How many miles are on it? Historically, what has your approach to maintenance been - including but going beyond mere “oil changes.”

You also need to say more about the conditions under which the car runs poorly. How does it idle? Hot? Cold? What does it do under 55mph? Hot? Cold? Does it ever seem to run perfectly well? If so, does it seem to have all of its power at those times? Or is it always running poorly at this point? Sounds? Smells? Any other weird things besides shaking?

Do not drive the car with the check engine light flashing. You must get this sorted out or it might turn a simple issue into a car-killing one. If the light is steady & the car is not behaving terribly then you can drive it around to get service. If the light flashes, you’re better off in the long run with a tow truck.

Thanks cigroller for providing me directions!

In February of 2011 (101000 miles) the car was running just fine. I had planned a trip and decided to add a fuel injector cleaner while getting a full gas tank. I added another cleaner in the following full tank; one of the guys from the auto store recommended to do it twice for better results. A few days after I used the second fuel injector cleaner, the car started shaking and the check engine light came on. I took the car to the Jaguar dealership where I used to get the oil changes and regular maintenance; I use synthetic oil. At this dealership, I was told that the car was not communicating with their computer and that I will be charged $200 per hour for them to check it manually (about 3 to 4 hrs).
I decided to park the car for a while. In June, I took it to a closer shop where I used to take my BMW; they only work on imported vehicles including Jaguars. They told me that I had a corrupted transmission sensor. They changed the Transmission ECU (LHE Code), spark plugs, air filter, fuel filter, valve cover gasket, spark plug seal, and ignition coil gasket. All of this because they noticed that oil was leaking on spark plugs soaking the spark plug seal. I got the car back only to drive it 5 minutes from the shop and the check engine light came back on, shaking again, and all needles on the dash going crazy; it shut off twice while driving it. I took it back to the shop and they kept it for 3 weeks and told me that it was fixed. I had to pick up the vehicle after hours due to my schedule; I drove it back home and the light was still on. Called the shop back and I was told to drive it and perhaps the light will go off after a few full tanks of gas because they were not getting more codes for the light. Now (October) the needles are not going crazy nor is shutting off any more but the light still on. When I start the vehicle it feels just fine but when I start going faster (50-55 mph) it will shake for just a moment and the light will start flashing then it will run normal and the light will stop flashing. Then while slowing down to idle for a stop light, it will start shaking again and the whole cycle will start again. The codes at Auto Zone (October 103090 miles) were P1314, P1313, P1316, P0300, and P0305. Although, their system could not relate these codes to a Jaguar just to a BMW, Acura, and Domestic. I went to Advance Auto parts this morning to test the light; they told me that there were multiple misfire and misfire on cylinder 5; at least the computer is communicating. This is what happened and my current situation, any more suggestions??

As near as I can tell what you have is a couple of shops changing out parts rather than diagnosing for all of those reasons that shops do that kind of thing. There’s really good money in it, and its simple.

The “corrupted transmission sensor” thing is a complete enigma. This has absolutely nothing whatsoever to do with a misfiring engine. So you might want to wonder about whether or not you’ve been having the same problem all along. Or you might want to ask that shop what had them changing that sensor.

The rest of the stuff - plugs, wires, filters, etc. are probably reasonable.

But it doesn’t sound like anyone is doing any actual diagnosis - all of those codes come with diagnostic steps. Apparently no one is paying attention.

The P0300 is the random misfire. The P0305 is a cylinder 5 misfire. The P1313, P1314, and P1316 are manufacturer specific - and as near as I can tell on a Jag they about misfires as well (but my search was quick & I have no specifics).

Misfire codes come from 4 kinds of problems: fuel, air, spark, compression (the 4 things needed to make an engine run). The “tune up” type of work got started on the basics. The next things to do are check fuel pressure, check for vacuum leaks and check engine compression.

The key for you is to find a mechanic that will actually take this as an occasion to diagnose the problem rather than just toss parts onto it. Note that computers/scanners/codes CANNOT do diagnosis. They just provide data that an actual thinking human can use to help with diagnosis.

My quick search for the P1XXX codes turned up quite a few mentions on a Jaguar specific forum. You might go do some searching there.