I have a 2004 XJ8. Very random, can go 10 times with no issue then it'll be very tough to start, then the next several starts will be trouble free. It does it when it's cold (as cold as it gets in Los Angeles), does it when it's hot, when the engine is cold or hot or warm, there's no codes, runs fine otherwise. I replaced the throttle body a couple months ago thinking that was the issue but it still does it. It's got about 70k on the clock.

It seems like if I try it and it doesn't start then turn the key off and wait about 10 seconds and try it again it will start easily but I've only done that a couple times so I'm not sure. My thoughts are:

Low fuel pressure at start
funky computer
An issue with the key chip or sensor

Most of the issues I would normally consider would probably make it hard start more often or run less than perfect but it seems fine.

Anyone else have this issue?

 

I would discount the key diagnosis. Before start I would put the key in and turn it, but not all the way as to turn it on. Just so the fuel pump primes. Give it a few seconds, even 10. Then crank it all the way to the start position. If your issues persists even with this step I think you can discount the fuel pressure issue. Unless I'm missing something. Either than that, I'm afraid i can't be of much more assistance. Good luck bro. Hope u figure it out.

 

I may try that; of course I'll have to remember to do it everytime and see if it'll go 20 or 30 times without issue

 

Hi pianohero,

VanJaggerstien's suggestion is a good one.

Another thought is battery condition. A battery may measure fine statically, but if its voltage falls much below 11V while cranking, the ECM will not trigger the ignition to fire. It would be worth measuring the voltage while cranking with a meter that can respond quickly enough to voltage changes to give you an fairly accurate reading (some digital meters react too slowly to be useful for this test - an old analog meter may be better).

Are you using a standard OBDII scanner to check for codes, or a system that can read the proprietary Jaguar codes? It is possible that network codes (U codes) or proprietary powertrain (P codes) have been tripped but a generic OBDII scanner cannot read them.

How long has it been since you did a tune-up (air, fuel and oil filters, plugs) and cleaned the MAF sensor and its electrical connector, and cleaned the relevant ground studs?

Lots of other possibilities (failing sensors, corrosion on connectors, lazy relays, etc.), but without codes you're going to have to do a lot more guessing, and the cost of guessing adds up quickly.

Cheers,

Don

 

Those are some good leads, I'll run down a few tomorrow and report back.
The only codes I can pull are OBDII. A tune up was done about 20k miles ago.

 

It would be worth having the proprietary Jaguar codes scanned by a good independent specialist or dealer, at the very least to rule out any stored fault codes that your OBDII scanner can't read.

 

Are you saying it cranks over for longer than normal, then starts, maybe, 10 seconds of cranking or so? First thing I would check is fuel pressure. The fuel system on the 4.2 is a returnless system, and the fuel pump has a check valve that prevents fuel from draining back. It will maintain some pressure at the rail when the car sits not running. More importantly, it keeps fuel at the fuel rail, and allows for some pressure bleed off when the car is shut off and fuel heats up and expands. If the check valve is not working properly, allowing fuel to drain back to the tank, this is the classic symptom. Typically, a restart within a minute or 2 is normal, quick start, all ok. Wait 5-15 minutes or longer, and the issue appears. Sometimes the symptoms are intermittent at first, other times it just happens one day and always does it until fixed. The check valve is part of the fuel pump assy, and not available separately. It requires fuel pump replacement. There is some speculation that ethanol in the fuel contributes to premature failure of the check valve, but there is no definite smoking gun. If the car sits, or sat for a long time without being run, it could exacerbate the issue, as ethanol will separate, and any moisture can result in further complications with gumming up things. Nothing I have found or heard of regarding fuel additives will "fix" this once it happens, the only solution I am aware of is fuel pump replacement. The pump is quite expensive. I had a bad fuel pump replaced on my 2004 XK8 due to a different failure. After that initial pump replacement, I had this check valve problem, and Jaguar replaced the fuel pump 4 more times because each one had the same issue with the check valve. The dealer told me that Jaguar admitted to them they had a rash of bad fuel pump assemblies. Other XK8/R owners have had similar check valve issues with their original and replacement pumps.

 

@Don, I did the MAF cleaning, checked the battery voltage and cleaned the studs (cheapest and easiest first I always say!) We'll see how it goes, pulling the codes will be next if it still does it, I may get the British diagnostics kit.

@Steve, my gut told me that, it's so damn intermittent though, sometimes it won't start after a minute or two of being off, it normally starts after sitting for days but sometimes not. Do you happen to know if it triggers a code?

BTW, thanks to everyone for your help.

 

I never had codes, and no one I heard of has either, I think it is because when the engine is actually running, the fuel,pressure is normal.