My 1999 XJ8 is running rough and cannot accelerate. When I step on the gas it boggs down when I release the gas it speeds up. I also get an Engine Fail Safe yellow light when I drive the car.
I have changed the plugs but found a lot of oil in the plug boots. I am in the process of changing the valve cover gaskets and spark plug seals to solve that problem but I am not sure this will solve my acceleration problem. I also get a P1647 error code.
What else do I need to do to get the car running right?

 

P1647 is the left lambda sensor; try a search on the forum, your engine is trying to run but it don't know how much fuel to put in.

 

oil on the plug boots causes misfiring, stalling etc. The original seal were too thin. Fix the obvious before looking for more. Troubleshooting with multiple problems does not work.

 

I have changed the plugs and replaced the valve cover gaskets on my 1999 XJ8 and the car still has trouble accelerating. I now get a P1000 and P1647 error codes. What do I do next to get the car running right.

 

Try some simple stuff: clear the codes; clean the MAF sensor; clean the throttle plate and bore; check the tubing from the air cleaner to the throttle bore for air tight; check the vacuum hoses to the throttle bore; check air filter; run a bottle of GUMOUT's Best (or the Lucas equivalent) through a tank to clean the injectors. With care, clean the breather on the left bank (follow the instructions carefully). Let us know what you find.

 

Yes, try clearing the codes and see if it comes back. If it does come back with a P1647, it looks like you need an O2 sensor, upstream, bank B. Might want to verify that, but if it is, I would go ahead and replace both upstream sensors.

 

How do I get to the front left O2 sensor?

 

You will have to remove the plastic covers around the coolant expansion tank and the centre cover. You will need to remove the expansion tank so this needs to be drained first. You can either syringe out the contents or drain the radiator from the bottom hose. Be careful with the hard plastic bleed pipes - use thin wall pliers to free the quick connect fittings. The expansion tank has a bottom hose secured with a spring clip - pliers again to free this.
Then the exhaust heat shield needs to be unbolted and moved out of the way. You will need a special socket to remove the o2 sensor from the exhaust down pipe, available quite cheaply on Ebay etc. It may be siezed so a few days of soaking with penetrant (WD40, PB Blaster, or if you can find it Kroil) may help.
Its a very fiddly job by all accounts but quite do-able.

 

There is a petcock on the bottom of the radiator which is nice to have. I believe it's on the bottom left. The coolant temp sensor probe just snaps into the bottom of the coolant reservoir which is also nice. Getting the hoses off the reservoir can be a pain though.

 

Have spare extra plastic coolant lines handy. They get brittle and crack easily. If you disconnect the battery leads and then touch them together you will clear the driving memory (ECM?). Sometime the computer tries to compensate for other problems and once they are cleared going back to the default setting helps.

 

I have given up trying to replace the left side forward O2 sensor. I have tried from the bottom and I have tried from the top. From the bottom I could get the O2 Socket on the sensor but could not free the sensor. From the top I was unable to remove the heat shield so could not get to the sensor. I am throwing in the towel and will bring my car to a mechanic to see if he can do the job. I hate to quit but I feel I cannot accomplish this task on my own

 

You might be making the right decision to throw in the towel before someone gets hurt or something gets broken. Sometimes you just have to admit defeat (not that I ever do, but). ;^)

 

Before you give up, consider buying a MAPP torch set. I had a bolt that was frozen on my XJ6, and a propane torch would not provide enough localized heat. I bought a Bernzomatic MAPP set from Home Depot for $60, and had the bolt out in about two minutes. It's a much cheaper alternative to oxy-acetylene.

 

Don't try and remove the exhaust manifold shield, it's the manifold gasket also and the manifold would need to be removed.
What type of O2 socket have you got?
You need the long socket with slot for wiring a U.J. a long extension and a long breaker bar to get it to budge, and serious pressure, they're in super tight. Maybe try it when the engine's warm. I've put my whole body-weight into moving these in the past. Protect your wing with a cover, once they let go you can go flying! A normal ratchet doesn't cut it....

 

I suggest a slightly different tack.

There are two grounding studs located behind the headlights. Each secure several ground wires with an acorn nut. Remove the nut, clean each eyelet on each ground wire with electrical contact cleaner and clean the flat surface of the nut as well. Reconnect.

A third ground stud is located on the firewall. Perform the same cleaning process there.

The ECU is very sensitive to voltage changes, including those that are caused by high resistance due to corroded contacts.

Disconnect and clean both the male and female connectors that connects to the left rear side of the throttle body.