My Lovely but old (1997) XK8 has been with my normal guy who looks after it for 5 weeks now. He normally is very good, cheaper than the dealer of course and I have never before had any complaints about his work.
When I took it to him it had the classic Restricted Performance words on the dashboard. After a couple of days I had a phone call from him to say that it needed two rocker cover gaskets, some spark plug seals, 8 new plugs and 8 coils. Oil had apparently seeped into the plug holes and caused the restricted performance problem. Cost was quoted at $970 including labor. He took for ages to get the parts (wrong ones came, too few came etc) but they arrived two weeks ago. He fitted them, took car for test drive, after 20 miles he told me and it broke down with same problem. He then ordered and fitted a module, this also had no success either. I then suggested to him that most problems like this on this forum appear to be Mass Air flow Sensor related or Throttle body related and although I had already researched and cleaned them myself, he might like to recheck them. He did this and said all was OK with these parts but still changed the MAF!. He was at a loss now and has sent the car to the Jaguar dealership. They have had it for a couple of days and initially diagnosed ECU and did I want it replaced for $5000? Ouch! I told them no and they came back a few hours later and said they now DID NOT think it was the ECU after all and that they needed two more hours at $125 per hour for further diagnosis work.
Can some of you guys on here who I know are really good at diagnosis give me some help before I lose my mind.
Codes given to me by garage are P0101, and A code 2301, D code 2310, F code 2316 and Gcode p2318 if this helps anyone. I cannot find any information on these A D F G codes.

 

I DON'T YET have access to the codes, did you try going to a parts store that has a scan tool ( Napa, Checker, Auto zone, ect) They usually can scan OBDII and OBD I systems AND it gives you a general list of things to look at. You then can match them with your codes, starting with the first one which is usually the hard code. It stopped or slowed after 20 miles with no power? It could be simple like one or both of the catalytic converters are plugged. On a V8 it shouldn't take 20 miles though.If it run ok for a while then after X miles it acts up it could be. Also have them clear the codes then attach a tag- along scan tool to connect to the DADL and when it acts up it will be recorded. You might have done all this but I thought I could throw it out there. Good luck

 

Quick update, codes apparently are now wiped. Garage say that they believe that the problem is that oil in plug hole has spiked the module but not gone as far as the ECU. They think that because of the spike the fault now lies in one of the 5 volt sensor wires, burnt somewhere perhaps, probably to one of the cam sensors.
Can anyone offer wiring schematics to the 5 volt sensors?
Or has anyone got any better suggestions?
Thanks in advance to anyone.

 

Same problem here with restricted performance. MAF sensor and throttle body sensor was changed at the dealer but the message still appears once in awhile. If i restart the engine the message goes away.

 

I had a problem with a 5 Volt reference circuit on my Corvette which caused all sorts of problems with the dash gauge readings. It turned out that current was bleeding off a split spark plug boot routed close to the 5 V reference wire and it was enough to send false signals through the circuit! The moral is that these circuits are sensitive to electrical discharges and ambient electrical charges. They can look fine, and in fact BE fine but still be victims to unrelated problems elsewhere. My circuit was perfectly fine in and of itself, and I changed a lot of sensors needlessly.

Could oil in the hole cause shorting or arcing to the head and set up a similar situation for you? Could current be bleeding off one of the coils? Is everything clean, dry and tidy there?

 

Oil is an insulator. It doesn't conduct electricity.

 

Also new so would not think so but thanks anyway.

 

The P0101 code is for the MAF system. Try cleaning the MAF sensor and checking the harness connections and wiring first as this part is pricey. There are some checks that can be done to determine if the part is good. The other codes might be incorrect as they don't appear in my data base although the second number being a "3" might refer to the ignition system. There is no ignition module in the car, the ECU drivers signal the plugs directly. It sounds to me like you are on the merry go round and if you don't find a way to get off, the money will drain away from your wallet. I would work up the MAF tests first and see where that took me. Also look fo rair leaks in the intake between the MAF abd the throttle body.

 

Many thanks for response. The codes A,D,F,G, I was told were for one set of 4 cylinders. I have already replaced the MAF and had a new pipe that goes between the MAF and the throttle body as the mechanic did not like my one which I had previously modified with rubber pipe when the old one deteriorated.

 

Not sure what you got going on but if you have a restricted performance you need to go in that direction. I am unable to identify the other codes so I will not address them. Can you get the real codes on your restricted performance? RP could be caused by many things and I will cover only a few.
• Bad or low voltage battery
• MAFS and the associated leaks in the vacuum / intake system
• The Throttle Body and in your case if you have the original TB it might be worth looking into
• TB plugs
I am going to list a few links that might help and I hope it does.
http://www.gusglikas.com/AutoRepairTroubleShooting.htm
http://www.gusglikas.com/AutoRepTB.htm
http://www.gusglikas.com/AutoRepairR...erformance.htm and the best for last.
Good Luck and please let us know what you come up with.

 

Gus, many thanks, Is there any merit in what the guy at the garage thinks, in that there is a spike/burnt 5 volt reference wire (caused by the oil in the plug hole) to the cam sensor (or another sensor) or do you think he is barking up the wrong tree?

 

At this point lets try this other stuff and I will look up that info. I am not sure what he is talking about.

 

Gus, I have just taken all of your info to him and he is particularly very interested in the loose connectors at the throttle body. He gets the car back from the Orlando Jaguar dealership tomorrow and this the first thing he is going to try. I will let you know how he gets on. These wires are 5 volt is that correct?

 

Now this http://www.xclusively-jaguar.co.uk/xj04_fandi.html#5 related to the TB replacement (TSB), you need to see if this was done from Jaguar. This may or may not be related and without the codes we will not know. Yes this opportunity has lapsed for the TB replacement by Jag but a reconditioned unit is much less expensive and available.

As for the 5 volt thing give me a little time to look into it.

 

The 5 volt reference voltage is for the O2 sensors, not the coil packs. The sensors take the reference voltage and modify it with resistance to send the signal to the ECM about the mixture. The voltage to the coil packs comes from the ECM drivers and varies in time which is called "pulse width", .eg, at idle, low pulse width, wide open throttle, high pulse width. This time is as low as 3 milliseconds and cannot be measured with standard instruments. To detect it, you will need a noid light, designed for the purpose. I'm afraid your tech may be a little behind the curve.

 

OOps sorry, I was giving information on the injectors, not the coil packs. Senior moment.

 

The primary voltage should be 12 volts. The crank sensor does operate from .3 to 5 volts though.

 

Many thanks Oldmots, do you know if all of the other sensors are all 5 volt as well?

 

Many thanks Gus. The mechanic told me yesterday that the only code was P0101, is this a possibility?

 

I am going to send this link to you http://www.gusglikas.com/images/Auto...%201997-99.pdf in hopes that you and your mechanic can get a better feel of what could be the problem. From what I can remember you changed the MAFS so you need to look at the connection, wire and the existing air filter. Now if you haven’t already you need to check the breather stub http://www.gusglikas.com/AutoRepairPlugReplacement.htm and make sure it is not clogged. As for the air leak you need to check the intake pipe for a leak http://www.gusglikas.com/AutoRepairA...HoseRepair.htm If your mechanic is skilled he could do a smoke test on it to find all the leaks.