Good Evening Everyone,

Soooo I'm on my fourth Jag and this is my first post. Have I been lucky? Maybe. I've never bent a valve, thrown a head gasket, or otherwise, have never had to deal with catastrophic engine failure. 1 tranny rebuild on the '99 XJR V8 SC. In fact, the only time I ever went above boil was due to a sticky thermostat and that was my '99 XJR V8 SC.

Please accept this as my short intro. (couldn't find the intro feed)

__________________________________________________ __________

Now with the issue at hand...

For about 5 days I've been meditating in a quiet corner in my office and under my hood and in the 3000 pages of my service manual. I can't for the life of me find the direct cause of the problem.

The very first thing I noticed was a misfire. Didn't have a scanner with me at this point. I checked the spark plugs and found them to be dirty and changed them to rule them out. Bought premium Denzo plugs $70 and pocket scanner 100$. Changed plugs. Cleared codes. Started engine.

The problem persisted- p0171 bank 1 lean, P0305 cyl 5 misfire, p0316 misfire within first 1000 revs. + RESTRICTED PERFORMANCE @ 4K RPMS WOT

I then decided to clean both MAF sensors as I was also getting a P0171 bank 1 lean code. Before the clean, I was reading .54lbs intake air per minute at idle.

After cleaning the MAF sensors that appeared immaculate I cleared the codes and started the engine.

The problem persisted- p0171 bank 1 lean, P0305 cyl 5 misfire, p0316 misfire within first 1000 revs. + RESTRICTED PERFORMANCE @ 4K RPMS WOT

So I decided to rachet up my approach. (see what I did there?)

I removed the negative battery cable, drained the coolant,
removed the RH Air Cleaner,
removed clean air Y piece,
removed the clean air duct,
removed the throttle body, (was filthy @ air intake elbow with no oil puddle)
cleaned the throttle body (was dirty but not sticking),
removed the RH Secondary Bulkhead panel,
removed the secondary bulkhead panel center,
removed the stabilizer bar,
removed the Air conditioner/heater coolant pipes, ...
and finally arrived at my EGR and of course removed it!

I was hoping to find that my EGR valve was stuck open or completely blocked but it was actually pretty clear. I made it shine inside and out, the solenoid was not stuck or jammed, nor was the valve stuck. Also, I tested that the EGR valve seat made an airtight seal when closed.

Reassembled. Added coolant. Cleared codes. Started engine.

The problem persisted- p0171 bank 1 lean, P0305 cyl 5 misfire, p0316 misfire within first 1000 revs. + RESTRICTED PERFORMANCE @ 4K RPMS WOT

Next, I removed and tested the PCV to intake elbow tube for leaks. It is in perfect condition.

Reassembled. Cleared codes. Started engine.

The problem persisted- p0171 bank 1 lean, P0305 cyl 5 misfire, p0316 misfire within first 1000 revs. + RESTRICTED PERFORMANCE @ 4K RPMS WOT

Please provide any suggestions you may have. This happened from one moment to the next. The engine has never gone over 203- 205 degrees F.

I can provide a freeze frame of my live data if needed. Next on my mind is the fuel filter, or #5 injector, or my accelerator pedal potentiometer going bad.

With KOEO I observe a 12 - 78% ABSTPS% reading. Even if I press the pedal down to the floor it reads 78% max ?!? Is this normal?


SOMEBODY HELP!

 

Well if the 4.2's cylinders are # like the 5.0, or bank 1 = cyl 1357 I'd say you have an injector problem, since both the misfire and lean codes coming from that bank. The mis fire ECM logic see's it on start up (p0305,p0316 #5 cyl) since the O2 sensors are to cold to work. Once heated up the O2 sensors see it (p0171, bank 1 lean).

 

I was so stressed out with the thought something could have been seriously wrong with my engine internally that I overlooked the ignition coil swap.

I was able to induce a p0303 cyl #3 misfire for the first time ever.

This event coincided with the absence of the p0305 cyl #5 misfire.

The p0316 was present both times misfire within first 1000 revs.

Conclusion- IGNITION COIL WAS FRIED!

The silver lining in all of this is that I gained about 20 HP. Gained through cleaning the MAF sensors, I cleaned the throttle body which was filthy, brushed my EGR valve to a sparkling shine, I sprayed an entire can of intake valve cleaner spray. Next is a good motor oil flush/change.

 

Duplicate thread

 

That is where I was headed next but then remembered I hadn't swapped the coils first.

 

Good job, I totally skipped the coil, but had I been turning wrenches... We help each other with experience! I'd skip the oil flush, thins the oil and exposes the bearings, If you've always done regular oil changes, your good.