hello all, just wanted to post this update hoping I could get some help again. I finally got my XJ8 back from the shop, and the car was given to me as is, in what I was thinking, was safe mode as the mechanic had told me, but when I arrived there, he told me that the car was functioning just fine, oddly. I drove the car off the shop, and it was working perfectly, and I mean perfectly. Perfect shifting, no smoking or weird smells, nothing. I took it to the car wash, and when I drove off the car wash onto the gas station that was right, besides the car wash, the car started to stutter, and shake, and the RPMs went down to around 400. Then the car turned off, and I had to push it to the pump. I genuinely thought that it had run out of fuel because it has done this before, since I can't tell when it's empty (my fuel gauge doesn't work). After $80 worth of fuel, I tried to start it back up, but it would crank, start, stay on for literally about one second, and turn off. it stayed like this for 40 minutes, while I let the car rest(?). I thought it was a bad fuel pump, so I went to the back to see if I could hear anything at all, and the pump sounded just fine. I tried doing a hard reset as well, to see if that would solve the issue, and that did nothing. eventually, after about 40 minutes of me just waiting in the car, not really doing anything, I tried again, this time, putting my foot on the accelerator and tapping it repeatedly. I heard the car turnover, and so I kept stepping on the gas over and over, until the RPMs went up, and it finally started. After this, I drove it home as quickly as possible without letting the car idle, because I knew it was gonna shut off. I Finally got home, and let the car with the ignition on to see if it would turn off, but it didn't. It stayed on at around 500 RPMs, perfectly stable and quiet. I'm so confused right now, this is clearly not a transmission or throttlebody issue anymore, or maybe it is, but it doesn't make sense that it only happens sometimes. It makes even less sense that the accelerator pedal tapping worked. I think the car hates me, because every time that I fix an issue, quite literally within that same day another issue pops up. Maybe the universe just doesn't want me to have a jaguar lol. Any ideas would be appreciated, thank you

 

The next time you have the engine running, at idle with no loads on using a voltmeter take a voltage reading under the hood at the bulkhead, rearward of the passenger side shock tower. My car reads 14.5 volts. Then take a reading at the battery terminals (my car is 14.2 volts), then put the negative meter probe on the body itself, there should be no change. If you were to let the engine idle for about 10 minutes, *carefully* touch each terminal of the battery. If one them is HOT to the touch, it is likely the battery cable is defective and needs replaced. The older these cars get, I’m running into more bad battery cables. The braided battery cables develop excessive resistance that’s likely where the braids meet the ends.

If you put $80 worth of fuel in it, it must’ve been really low??? Is it possible that the fuel pump got hot and is causing the issues? Multiple times we’ve had cars towed in and they had just filled up from near empty and when they went to restart, the engine just died. The fuel pump let go. Maybe yours isn’t happy either?? I know you said you heard the pump though but I’m wondering about the volume as well.

 

How about stuck open gas tank vent valve ? When you fill the tank fully gas vapors does not go to the charcoal canister but to the engine. Thus filling intake up with gas fumes. It takes some time to clear up from that.

 

Thanks for the suggestions gentlemen, I will try to find what I can. I should mention the car has another issue, it loses throttle information at random. I mean it works just fine when cold, shifts and accelerates perfectly, up until it just loses throttle info and goes into limp mode.
And I realized the air intake tube to the throttle body was badly positioned and not tight enough

 

Drove the car this morning and it worked amazingly good. Not sure what's wrong with this thing, but I drove it around the block several times, accelerated it a little hard, turned it off and back on, on and off, on and off, nothing. No shaking no shutting off, perfect shifts too.

 

Just realized the car is also making a whiny clicking noise on deceleration. I'll upload a video so you guys can hear it.

 

Get the codes or we have nothing to work with?
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that's the thing, there are no codes at all. previously, I had C 1156, P 1632, and P 1121 I believe. But they're all gone now.

 

The car seems to turn off when hot.

 

When it shut off, I'm going to assume that you still have lights on your dashboard? Were you able to restart the engine right away or did you have to wait a few minutes?

If you still don’t have any codes, does your scanner have a live data list?

 

Yes everything else still works, the whole car has power, I even had the A/C on. There are no error messages on the dash however, and no codes on the scanner. Yes, I have live data but I haven't been able to replicate the fault. I'm kind of worried of driving the car anywhere as the last time I had a car break down less than a mile from home I was charged $275 by AAA. I did however, drive it up and down the street where I live for about 15 minutes yesterday, shut it off right after and turned it back on, nothing. No issues. Even turned it and off and on several times.

The first time this happened I had to wait 35-40 minutes for the car to finally turn on. I tried several times to start it and finally the last time it worked. But like I mentioned before, I had to tap the gas several times until the car "woke up" and slowly increased in RPMs. It's like it's not getting enough fuel pressure or something, and pressing on the gas repeatedly built that up enough for it to start.

 

When it's not starting and you are cranking the engine, do any rpms register on the tach? If not, could be a bad crank position sensor

 

They register just fine, when the car died they went down and down until it shut off. Then when it finally turned on, the RPMs started to slowly go up. MAF maybe? I checked this morning and fuel pressure is just fine.

 

If it shuts off when hot, (I’m sure you mean it’s been running awhile) the engine isn’t overheating is it? Monitor coolant temps.

If you suspect a maf, either clean the sensor out or you could disconnect it with the key off then restart.

 

Just to be clear, when the car isn't starting and you are cranking...the tach flickers?

Mafs generally don't cause stalling as even disconnected, the car will run mostly ok

 

Yes, RPMs register. This is how I noticed the car was starting to turn on, because the more I pressed the gas, the higher RPMs went. I think it started around 1,000 rpms and then went up with every tap.