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I was driving on the freeway today and my 94 xjs 125k mileage started to buck like it was running out of gas. I pulled over to the right lane ready to get in to the shoulder and and started running ok. It does however feel a bit sluggish.
I installed a new fuel pump a couple years ago so I do not think it is the fuel pump. The fuel filter only has about 5k on it. I also have a new IACV, new TPS, and recent tuneup (these are prob un-related but just for the record).
The fact its "starving" at freeway speeds, and sort of OK lower down has me at the pump/filter first and foremost.
Maybe the tank venting system is AWOL. Not usually an issue with "In tank" pumps. Take tha filler cap off, go for a run, see what changes. Obviously a FULL tank is not recommended.
Last edited by Grant Francis; 07-31-2015 at 09:09 PM.
Grant, I'm not a mechanic, so the obviously part went right over my head. Can you break it down for a noob? Why not? I have visions of fuel gushing out of the filler neck, but I don't know why.
Fuel tank venting, or lack of it, reeks havoc, as the pump simply gets no intake of fuel, the tank gets a vac inside due to no venting preventing air entering the space provided by exiting fuel, so the pump cannot push it up the front.
As I said, not usually an issue with "In tank" pumps, coz the pump is submerged in fuel, and does not rely on a seperate feed logic to be present.
Tank venting is still required however.
Removing the cap will NOT have fuel gushing out the hole, unless the tank is FULL, and the driver takes corners way too savagely/fast, as in Brain Fade, and forgetting he has the cap off for an experiment, and the fuel will "slosh" out. It simply cannot run out with the cap off, gravity keeps that in check.
This is quite a common thing to do with the older cars, Jags included, where the fuel pump requires a gravity feed of fuel from the tank, and if the tank vents fail, that gravity feed ceases, and engine running issues end up on forums.
My X300 had hissy moments, new pump (in tank) etc etc, and when the cap was removed the car performed 100%, so the valve thingy in the tank access lid was playing up, and once removed and cleaned, the car ran sweet, and still does today.
Nothing is rocket science, just a tad special at times, and old school diagnosis and fixes still reign supreme.
Last edited by Grant Francis; 08-01-2015 at 03:38 AM.
I'll start looking into ventiallation. I do have occassinal issues with filling up the tank. It will just not fill without going very slow with the pump and filling it pennies at a time. I usually get what I can in there. Then try again a few days later and it works.
I'll start looking into ventiallation. I do have occassinal issues with filling up the tank. It will just not fill without going very slow with the pump and filling it pennies at a time. I usually get what I can in there. Then try again a few days later and it works.
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Sounds like an air bleeding problem when filling your tank, meaning your putting fluid in but the air that is being replaced has nowhere to go to. What you end up with is blowback through the same passage your trying to fill, this triggers the nozzles "I'm full" mechanism and switches off the fuel flow. My truck does this but if I have it on a slight incline it works fine. Maybe your bleeder hose is blocked.
Rubber hoses are getting old and need replacing. The vent hose might even be filling with dirt ( dust caked over years ) might check for hard or mushy hoses and replace.
Fuel tank venting, or lack of it, reeks havoc, as the pump simply gets no intake of fuel, the tank gets a vac inside due to no venting preventing air entering the space provided by exiting fuel, so the pump cannot push it up the front.
As I said, not usually an issue with "In tank" pumps, coz the pump is submerged in fuel, and does not rely on a seperate feed logic to be present.
Tank venting is still required however.
Removing the cap will NOT have fuel gushing out the hole, unless the tank is FULL, and the driver takes corners way too savagely/fast, as in Brain Fade, and forgetting he has the cap off for an experiment, and the fuel will "slosh" out. It simply cannot run out with the cap off, gravity keeps that in check.
This is quite a common thing to do with the older cars, Jags included, where the fuel pump requires a gravity feed of fuel from the tank, and if the tank vents fail, that gravity feed ceases, and engine running issues end up on forums.
My X300 had hissy moments, new pump (in tank) etc etc, and when the cap was removed the car performed 100%, so the valve thingy in the tank access lid was playing up, and once removed and cleaned, the car ran sweet, and still does today.
Nothing is rocket science, just a tad special at times, and old school diagnosis and fixes still reign supreme.
Beat me to it! was going to say the same thing and have seen a few collpased tanks over the years from vacuum in tank which they CANNOT take. And for all I dont know and know about car this very thing burned me for a few weeks last year on my riding mower. After mowing the first couple acres the mower would die and if I let it sit it would restart and run fine. VENTED fuel tank cap became UNVENTED. The fix was leaving it slightly loose. Now goes the whole 5 acres without issue
I tried driving around with the cap unlatched and I still have the same issue.
I am leaning towards it being the coils, the transmission, or bad gas (water in the tank). I say transmission because it almost seems like it is slipping or something. Probably not the case but I do not want to rule it out. At least every time, it seems to want to stall out for about 3 seconds and then it takes off fine again.
As far as the fuel pump, I do not think it would bog at highway speeds. At that point its just relying on suction.
I guess the first would be bad gas, or water in the tank. However I have been through two tanks since it happened and I used an additive. If there is a lot of water in there though it may take a couple more tanks... ?
I tried driving around with the cap unlatched and I still have the same issue. I am leaning towards it being the coils, the transmission, or bad gas (water in the tank). I say transmission because it almost seems like it is slipping or something. Probably not the case but I do not want to rule it out. At least every time, it seems to want to stall out for about 3 seconds and then it takes off fine again. As far as the fuel pump, I do not think it would bog at highway speeds. At that point its just relying on suction. I guess the first would be bad gas, or water in the tank. However I have been through two tanks since it happened and I used an additive. If there is a lot of water in there though it may take a couple more tanks... ?
I guess the first would be bad gas, or water in the tank. However I have been through two tanks since it happened and I used an additive. If there is a lot of water in there though it may take a couple more tanks... ?
Methanol is the only additive that will take out water. I suspect you picked up a load of contaminated fuel. Mileage on the fuel filter makes no difference, it could be brand new and if you pick up bad fuel it will restrict flow because it's doing it's job by removing the particles in the fuel.
I would change the filter before doing anything else. I've had a plugged filter before and the symptoms match. At least a filter is cheap to buy!
Mine did everything yours did, I DID everything you did, including checking for water, pump pressure, surge tank, fuel filter and different ECU and new coil. It was my connection at the CTS. Unplugged it, checked the CTS resistance, checked the signal to the ECU, put it back on, all worked fine, bad or interrupted CTS connection was over riching the injectors, no power, bucking, lopey idle, stalling, pinging all went away. That little CTS when faulty can wreck havoc. Worth the $16 to know the one you have is new.
On your engine the CTS is located on the front, Left thermostat housing. Its a bit buried so you have to look carefully.
Its on top of the engine just behind the air cleaner trumpet. If you follow the wire you will see that is uses the same kind of connector as the fuel injectors.
I have a new CTS sensor. I will check the connections though and hit it with some WD40 to clean it. I am now leaning towards this being a transmission issue. The cars seems like it is running out of gas but in actuality I think it is a slipping tranny, or not switching back to low gear... I notice the issue everytime I come up on the same incline on the freeway... Its highly predictable.... It could be the tank is slanted at that moment.
I know these are two completely different things, fuel and tranny, but it really is hard to tell which one it is. The car bucks and struggles a bit and then it takes off..
I am now leaning towards this being a transmission issue. The cars seems like it is running out of gas but in actuality I think it is a slipping tranny, or not switching back to low gear... I notice the issue everytime I come up on the same incline on the freeway... Its highly predictable.... It could be the tank is slanted at that moment.
I know these are two completely different things, fuel and tranny, but it really is hard to tell which one it is. The car bucks and struggles a bit and then it takes off..
What about try holding it in second on the stick before going up the incline and see if it still bucks?
07-31-2015, 08:40 PM
bucking on freeway like running out of gas
