I cannot say how much this site has already helped me. I believe I've already reviewed just about every thread that has even slightly related to the probem I've been having. So thanks for all your help thus far, it's been invaulable.

The car - 1998 XK8 Coupe. Very well maintained for many years, not so well maintained for about a year prior to my purchase of it.

The first issue - I would be driving along at moderate highway speeds, and the engine would stall. Then started getting a "low Coolant" warning and after the engine was shut off, it would go into Failsafe Engine Mode and would crank but not actually start. The not starting seemed to be linked to the engine temp, as it would not go out of Failsafe and restart until the engine cooled (up to 2 hours of being stranded). And the engine began to have a rough idle, along with the usual problem of a lack of power and acceleration. Occasionally, I would get both a Stability Control Fail, along with the Failsafe Engine Mode and being stranded for around 2 hours before it would restart.

THe first attempt to fix indicated a leaking heater hose. Had all heater hoses, top/bottom radiator hoses replaced and plastic thermostat housing replaced with metal housing. (The water pump had already been replaced to the new gen about 4 months prior to my purchase.) This stopped the "low coolant" warning, but not the other problems.

Had the codes read (by the Jaguar ******* - Ka Ching$$), but to my surprise the only code was P1111, which I understand is just a system check pass.

Replaced the Throttle Body with new OEM. This stopped the engine stall, but not the Failsafe Mode when trying to restart when the engine was hot, or the rough idle. Additionally, the rough idle is only when the engine is at normal operating temp. It idles smooth when cool.

Cleaned the MAF with CRC Maff cleaner, checked all electrical plugs, dried each with MAF cleaner and applied a dab of dielectric grease to ensure no stray cross signals. Particularly the MAF plug, knock sensor plugs and the plugs at the throttle body. I also checked the vacuum tee at the throttle body, and the plastic air intake tube to make sure it has no cracks.

Now the problem is intermitant. It will be fine for a week, then you shut it off at the gas station and it goes into Failsafe mode and won't start for 2 hours until it cools down to the blue portion of the temp guage.

Today, I'm having the knock sensors and crank position sensor replaced - clutching at straws in hopes of fixing the problem.

I really love the car and intend to keep it. So any help any of you might offer in solving this will be very much appreciated.

Thanks,
OldFart

 

Amazingly, your story sounds similar to how my day went. I recently replaced my thermostat tower with an aluminum one and the car could not start after. I had to do a cylinder wash (just search the forum I can't explain it near as well as GUS). The cylinder wash got the car started, however I now have a severe jolting issue at abou 30 mph. Took it to get the restricted performance codes read, was told I am in need of a new knock-sensor. Hopefully tht is the jolting issue also. I will let you know. I also had the pleasure of needing a new battery today, at $158. I am now also loosing coolant from a new spot, there is a basically hidden coolant reservoir on my 99 XJ8 on the driverside, above the bumper. Thats as far as I got today.

I'm not sure why you would need to sit for 2 hours before it starts again.... I think thats pretty strange too. Thankfully I don't have that issue, but I'll put some thought into it and report back if anything jumps out at me. I agree about the forum, the greatest tool an owner could have.

 

if you have Torque and a bluetooth OBDII adapter (or another scantool - general type), I'd ask you to check your fuel pressure at idle, and immediately after you shut it down. I can give It is supposed to bleed down (via the fuel pressure regulator) to a lower value, but not too low that it won't start after a couple seconds. My first thought is too high pressure...but there's plenty of other reasons that this could happen. Try a search on the forums (xj8, stype and xk8/R areas ALL have either the same, or very close to the same engine and components. Some variation, but I think I've read of a similar problem before.

 

If you have a Failsafe mode you should have codes. Knock sensor will provide a Restricted performance along with MAFS and vacuum leaks. Failsafe is caused by TB and you replaced it and the TB plugs, have you checked them? No codes! Fuel Pump or Filter, check the pressure as Matt indicated.

 

Thanks for the tip. One of the first things the mechanic did was check the fuel pressure. I've forgotten what the PSI was, but he deemed it correct. He then had me try to start the car while it was in Failsafe - no start. He then sprayed starting fluid into the intake tube and had me try again - It started. His analysis of this is that the ECM is preventing the injectors from working when in Failsafe.

Regarding the OBDII reader, I've been thinking of buying one and using it while I'm driving to see if I can get a code besides P1111 which is all that shows up after the car goes into Failsafe.

Can you recommend a code reader?

Thanks again for your help.

 

The lack of a code has been the most confusing thing about this problem. We've hooked up the tech's code reader a half dozen times now after the car goes into Failsafe and the only code returned is P1111.

Yesterday, I had both knock sensors and the crankshaft position sensor replaced - no change whatsoever. It still lacks power and throttle response after reaching operating temp, and it still goes into failsafe upon engine shutdown and will not restart until the temp gauge needle is near the "blue" cold portion of the guage.

The latest recommendation from the tech is to replace the brand new temp sensor located on the thermostat housing. But since this problem existed prior to replacing the housing and sensor, I really don't think that's going to help.

I've read other threads that indicate it may be brake switch. And I sometimes get a Stability Control Fail with the Failsafe Mode. I'm not sure if I'm misreading this thread, but at this point I'm clutching at straws (and going broke) trying to fix this problem.

Any further advice will be very much appreciated.

 

Failsafe related to the brake switch would not prevent the car from starting until it cools down. Is your cruise control on or off? And does it affect the failsafe condition when turned off or on? All indications today lead me to believe it is a TB. Where did you get the TB you recently installed?

 

In the event I haven't made the condition clear:

1. Car runs great when below "normal" operating temp. Good performance and smooth idle.
2. "Normal" for this car is the temp gauge needle pegged dead center of the gauge range, with the needle actually covering the middle white tick mark on the gauge. (Actual temps have been checked at inlet and outlet of radiator and found to be within range.)
3. Upon reaching "normal" temp, there is a loss of power/performance, poor throttle response and a mildly rough idle, sufficient to feel a vibration in the entire car.
4. Failsafe always occurs when the gauge needle gets its own width (about 1/32") above the dead center tick. And the guage never indicates any higher than that.
5. Failsafe never occurs when the car is running. Only after engine shutoff, then it will not restart until the temp gauge drops almost to the "blue" cold portion of the gauge, and the ECM does a system check and Failsafe no longer appears. Then it cranks and runs fine - until it gets to operating temp and has a lack of throttle response and poor power/performance.
6. Even though the codes have been checked multiple times after it goes into failsafe, the only code found is P1111 - system check Pass.

Hope this helps. Because I really need the help.

Thanks,

 

The gauge on this car is nothing but a placebo. When the gauge begins to rise it is when the temperature on the car is near alarming conditions. So you are saying that Failsafe does not come up when the car is running only after it is shut down and then it will not restart until it cools down. But when it is running when the temperature rises it becomes a bit sluggish and unresponsive.
I would be looking at the temperature problem first.

 

I agree with Gus. Sounds like you have a temperature problem; I don't think your car is getting to "normal operating level" I think its getting too hot, and not registering on your gauge. This failsafe may very well be preventing you from blowing a head gasket. The real question is why is the car getting so hot? I had an old minivan a long time ago that had an electrical problem which prevented the radiator fan from operating. My only solution at the time was to put the heat on full blast while sitting in traffic to prevent the car from overheating. While that was less than ideal (especially in south florida!), it saved my engine.

I suspect that your temp gauge is maybe not the most reliable method for deciding the engine is too hot, an engine will run extremely rough right before overheating, I'm telling you this from experience, even if the gauges aren't trying to warn you, thats a sign from the car. I also wonder about the coolant issue. You said that was fixed by repairing a heater hose, but maybe the damage to the heater hose was brought on by the same issue causing the overheating engine. In other words, another heater ose maybe needed in the future (hopefully not, but trying to connect the dots). When you overheat a boat engine the only way to get back to land is to let the engine cool for a couple of hours, this sounds exactly like your problem. If you have full coolant, you will not get a low-coolant message, however if the coolant is not moving you will overheat. I know you said that you recently replaced the water pump, but maybe you should check to make sure that it is in fact working.

 

1 more thing while I'm thinking about it, this may be a stupid question so no disrespect is meant at all, but when you replaced the thermostat housing, did you install a new thermostat or was the old one reused? I imagine that a new one was installed, but its a relevant question.

 

After discovering the local dealer wanted $2,300 plus tax and shipping (from Honolulu to Maui), I chased around on the web and purchased from Terry's Jaguar Parts/Engle Imports in Michigan. They were the only ones that acknoledged the Service Bulletin on the throttle body (that got you free replacement till 2009 when they stopped). They at least gave me a discounted price. It was a brand spanking new OEM part and had the little sticker on it that was noted in the related Service Bulletin.

What are the chances I've got a partially malfunctioning MAF?

 

Good advice. Tomorrow I'll have the inlet & outlet temps checked again and this time I'll record the temps and post them.

 

When I first took the car to this mechanic (original work of hose & thermostate houseing was done in Honolulu, prior to my move to Maui) he performed about 5 hours of troublshooting. He noted that I had only water in the system (of course the first shop had charged me for coolent but hadn't put it in). So he flushed and drained the system and refilled with the correct coolant. Checked inlet/outlet temps and checked flow, which he says is good.

At this point I kind of wish it would be a water pump issue just so I could fix it and be done with it.

We've also checked compression in all cylinders to make sure it's not a head gasket allowing cylinder pressure into the water passages. Nope, good compression on a leak-down compression test.

But what you're saying makes a lot of sense, and others have warned me the temp gauge is about as good as an idiot light, maybe not as good. So running it and checking the actual temps and flow again is on the agenda for tomorrow.

I'll post the findings.

 

Actually, I'm on the third thermostat. When I got the first "low coolent" message, I went to the Honolulu Jag dealer and bought a thermostat as recommended by the mechanic I was taking it to at the time. (Prior to housing and hose replacement.)

I ended up taking it to another shop for the housing and hose replacement, and they put in a new thermostat, at least they charged me for one, but this would be the same guys that charged me for coolant and didn't put it in.

Then after I moved to Maui, the new shop recommended yet another new thermostat, as they suspected the "new" one was bad. This was 2 weeks ago. So in the last two months I've had 3 new thermostats. (or at least two, but I've paid for three).

I've also considered just removing the stat, as the chances of it ever freezing here are pretty slim, and if it does - I've got much bigger problems that a poor running Jag.

 

Since I'm on a small island, I have only used the cruise twice since I purchased the car about 4 months ago. Once when I was test driving it, and once about a month ago when I happened to be on one of the two 4 lane roads on the island, at 5:00 am. Basically, there arn't many places or driving conditions where you can use cruise here.

I've read the threads related to the cruise, brake wheel sensors, brake light switch and Failsafe and taken them to heart. I haven't sprayed the brake switch with CRC yet, but I'm thinking of doing that out of desperation. The wheel sensors have been checked by the tech and he advises they are fine. I don't know how he arrived at that conclusion though.

 

You can do that but I would focus on the temperature problem.

 

My advice is to take the radiator to a professional and make sure it has no restrictions. Make sure the fans both work and then a new thermostat. Do a compression check on your car. make sure you dont have a head problem before going any further. If the cylinders all check out then you need to go with the radiator to the professional and have it checked completely.

 

Hi,just to chip in.......... is the ECM getting sufficient cooling, ie fan working?
Bob

 

For the very first time - I got a check engine light and "Restricted Performance" readout today.

So I dashed over to the mechanic's and he read the codes:

P0171 - Fuel Trim too Lean (Bank 1)
P0174 - Fuel Trim too Lean (Bank 2)

So beyond telling me the fuel/air is too lean, can anyone tell me what this is pointing to and whether it has any bearing on the overall "Failsafe Engine Mode" issue I've been experiencing?

And I'd like to thank everyone for their help thus far. And I'm going to follow some of the advice I've already received. Today I borrowed a lazer temperature meter (one of the expensive ones from our service department), I also purchased some good engine flush that's good to use with aluminum, and some fresh orange coolant. It was my intent to flush the cooling system and refil. Taking temp readings both before and after. I'm still going to do that since I'm not confident it's ever actually been done properly.

But any additional help on this too lean condition will be very much appreciated.

Thanks,