Hello,
Was driving last week about 55 mph and all of a sudden auto became sluggish , as to shut down. will start and run , but not driveable. Code on scanner is P O 300 / light reads restricted performance....any answres ???

 

There is a long list of causes to P0300 Multiple Misfire:

Compression low, camshaft worn, broken valve spring(s) all seem like something that wouldn't happen suddenly.

Fuel pressure low, fuel injectors clogged, fuel contamination, spark plug(s) fouled might have happened. Had you filled up shortly before?

ECM to ignition module circuit fault, ignition module.

Perhaps start with the fuel as most likely. The result of fault is only to limit RPMs to 3000, Restricted Performance, so the underlying problem is causing it not to run.

 

Thanks for the reply and info... since it came on suddenly I am with you that it must be either fuel or electronic related..I am towing it to the dealer today and will be better prepared with the info you have shared.

 

My 99 XJR went out the same way, suddenly with P0300 code. After after a couple months correcting multiple problems, I found a melted spark plug and a dead cylinder. I believe mine was the result of a series of problems that all contributed to lean mixture and overheating. Regardless of each specific cause, they all point to poor maintenance and care before I took ownership. How long have you owned the car and what issues has it had during that time? How about maintenance history? Any past trouble starting? Exhaust smoke on start now or before this happened? How many miles on the car?

In addition to what Test Point had to say, because it is a sudden event, my first guess would be timing. Its possible you have a bad tensioner and a chain has jumped. You could also have developed a vacuum or intake leak which has thrown off the fuel mixture. Having gone through DIY diagnosis and engine replacement, its worth every single penny to take it to a qualified Jag shop for a diagnostic on a computer, so you are on the right track. Make sure you check back here and let us know how it turns out.

 

I have had car for quite a while and so far the only thing I ever had to replace was a light bulb..( Knock on wood) no trouble statrting or smoke or anything. I Have had it towed to Jaguar in Greenville,SC and hope the issue is minor..I will post the progress and keep my fingers crossed.. (comes with owning a jaguar) .

 

Tensioners could be at fault, but there's always the mass air flow sensor. Keep us informed please.

 

The Dealer diagnosed a broken air line to the throttle body, making the car run rich...and fouling all the plugs (WHEW !!!) estimate to replace all parts and labor about $600.00 US..any thoughts ?

 

That's about $75 per plug.

What do you think?

 

Not sure which air line the dealer was referring to, but I can think of only three candidates. The first is the air intake pipe from the air cleaner box/MAFS to the throttle body; the second is from the air assist control valve to the injectors (doing this by memory, so I'm not sure if the supercharged AJ27 has the AAC valve or if it is only on the normally aspirated version); the third is a small hose from the bypass valve to the supercharger. The small hose from the bypass valve to the supercharger is a pretty cheap fix; probably less than $5 for a foot or so of hose from autozone. If AAC valve is present, the hose to the injectors is probably pricey as far as hoses go, but how pricey, I don't know. Assuming it is the air pipe from cleaner/MAFS to the throttle body, your looking at the following cost for parts:

OE NGK double platinum spark plugs @ $13.00 ea. = $104
Air pipe = $40
Air pipe seal = $15
Total parts = $160 + tax

That leaves more than $400 for labor, so 3.5 to 4.5 hours for a spark plug change and a hose replacement. Unless the hose is something I'm not thinking of right now, $600 seems awfully high. Maybe one of the jag techs can set me straight if I'm off on my estimates. I would request a detailed estimate for parts and labor before committing to the work. If you do have them do the repair, make sure you ask for the removed plugs and air line to verify what was replaced and why.

 

That price could be very fair. Jaguar list on the plugs is around $25 each. That's $200 right there. Depending how deep they have to dig for the hose, that could easily explain the rest. If they are doing either the part load breather hose or the full load breather hose, have them do both. They are already in the area so labor should not be much more. And, if there, have them inspect the heater hoses that are in the same area.

 

Not to mention, are they including any diagnosis time in that estimate? Typically there is a fee to diagnose.

 

The Dealer started work and Found they misdiagnosed...Broken Timing Chain.. Looks Like motor swap.

 

Sorry to hear that but it may be the first time I can remember hearing of a chain/tensioner failure other than at start up.

Not every engine is destroyed, some survive, if that is part of your evaluation of repair.

Being a '02 I would be interested in the manufacturer date.

 

Yep, If it is a real '02 that would be new style tensioners and primary chain. Uh-oh.

 

Actually, the metal tensioners were introduced into engine production in August '01. My '02 XK8 was assembled in June '01 and had the spring assisted plastic tensioners.

 

How did they discover the broken timing chain? Was it primary (lower) or secondary (upper)? You might want to explore the extent of the damage before deciding on an engine replacement. If an upper chain broke, it is possible that you have some bent valves that can be replaced. Still not a cheap or easy repair, but may be better than engine swap. Maybe someone with more knowledge than me can advise you on the specific questions to ask or things to look for, as well as the cost analysis of diagnosing the damage and repairing if possible versus engine swap. Just my 2 cents, but I hate to see you replace the engine if you don't have to.

 

Hey Guys,
Thanks for all the great advice... The dealer tells me that he is sure the timing chain is broke and the culprit being the tensioners. I have found a 03 complete engine w/ low miles to drop in, any one see any issues or problems that may come up ? will it bolt right in?

 

I believe 2000-03 XJRs all had the 4.0L AJ27 unit. I'm not aware of any changes from the '02 to '03 engine, so, assuming the replacement is from an XJR, it should bolt right in (I think '03 XKR and S-type R had the 4.2L). There are several posts on this forum about engine swap compatibility, but I think for a direct replacement, you are limited to 00-03 XJR. Other engines will work, but they are not direct replacements and require additional changes or modifications.

 

not trying to hijack the thread, but as I occassionally get a misfire code coming up myself, I'm going to ask a dumb newbie question. How does one get the leads off the spark plugs? I don't want to get in there and just start yanking if there is a specific technique to free the coil/lead from the plug. Advise please and thank-you.

 

The coil pack has a 5" cover on the plug side that slips over the plug. It is not intended to be tight but can adhere to the plug insulator over the years. Just twist a little and pull.

I usually wipe a little dielectric grease on the inside of the cover to prevent that from happening again.