Ok so about a month ago i aquired my first jag, i knew she needed some work as the last time it was driven was from our barn the 15 miles back into town to my uncle ( the previous owners) new house which was 6 years ago. He has always had jags and knows alot about them.

well anyways onto the problems, fresh battery and gas/seafoam it started and drove onto my trailer took it home, drove it off. Did plugs and wires (PITA) air filters, oil change and new fuel filter, drove OK but hesitated which has since almost gone away since I've put about 200 miles on it. So a couple weeks after that the fuel pump gets really loud and all but gives up with a very slow drive home I replace the pump and filter and it turns out to be just as loud and runs hot like It was starving. so I ripped the tanks out and cleaned them both and the screen. Pump quieted down and it ran better but its always had an intermittent surging problem at cruise like a miss under load but as soon as you get on her she wakes up and goes. The surging at first was VERY slight almost unnoticeable but me being **** and paranoid could feel. And over the last week its been getting worse to the point I was about to call the wife to bring me the ton and a flatbed but it made it home.

In park at idle the left side bank is smooth and sounds like a I-6 on the right though its like there is a miss in one or 2 cylinders. Fuel pump still gets loud after driving for an hour or so.

Does anyone have advise on this before I tear into it next week? I plan on testing o2 sensors, compression, spark, and injector pulse. The only thin I didn't touch was cap and rotor because they looked good but they were Lucas so I'm sure origional. Again it has no problem with acceleration other than a little off the line. Oh I also for got to mention the last couple fill UPS the gas cap was releasing pressure like my semis brakes so the charcoal canister is probably plugged. Could that have something to do with it?
thanks and sorry for the long post!

 

If the tanks releasing pressure then your vent system is not working. Your tank will set up like a vacuum which could be the cause of surging and the loud fuel pump. The vent tube up to the charcoal can on these cars is too small to be effective IMHO and the Rochester valve fails and will not allow purging/venting properly. Turn your cap loose fit and drive the car and see if there's any change. I pulled the line at my charcoal can and put a small fuel filter on it to make it critter proof and drilled a small hole in my cap top And bottom to ensure venting as not to creat a vacuum and to keep the tank from swelling in the heat and collapsing in as it runs. My XJ6 Series III had this system fail and it sucked in both tanks.

 

<p>Yeah. For that size of tank i would think there would be a bigger canister at least</p>
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<p>but here's the weird part is on Tuesday (the last day I drove it) on my way home I kept the fuel cap off. It seemed to perform better off idle but it still had the horrible surge at cruise. Which the running better may have also been a placebo effect sort of thing. But with as much pressure it let out I'm not sure. I'm hoping to get back on it by Sunday to figure it out</p>
edit: I was thinking that either the pickup was plugged again or the pumps on its way out the door from being starved. But I don't think that makes much sense since it accelerates great.

 

If its missing on cylinders, imo start at the ignition specifically the cap. If you went to the trouble of doing the plugs (e.g compressor out) then it was a bit of an oversight not to do the lot while you were down in the V. If you are going back in I would also recommended pulling the EFI harness and strapping it to the top of the rail, also a good time to check for shorts which may be leading to injector's missing.


85 is the same as mine so it will be Lucas ignition, while you are in there check the pick up and vacuum advance - these fail 100% if the fix is not applied. Its normal for the gas cap to have a little whoosh (i.e NOT canning) , but a big one is almost certainly a knackered Rochester valve or plugged canister. Conversely if air cannot get in to replace fuel as it consumes, it generates a vacuum in the tank which would explain all the symptoms you describe almost perfectly. As the vacuum builds it reduces the pump output pressure (increasing load) until the engine stalls.


I can only talk with a bit of knowledge on the topic as I have just done almost exactly the same to mine! Good luck!

 

Yeah well I do plan on the cap and rotor. I actually bought a rotor from AutoZone and cap from pronto (only people that can get it locally) the rotor didn't fit (too tall and tight on the shaft) and the cap was back ordered so I got my money back for both. As for the efi wiring I forgot to mention the work he had put into the car before I got it. It had an engine fire befor he bought it. Toasted everything under the hood. So he replaced the engine. And rebuilt a harness from a donor car so everything is pulled up out of the valley but the wiring still shows its age and needs a little work. I'm sure the fuel tank has something to do with the pump. But I just found another post with similar issues from last year. Can't figure out my phone other wise I'd give a link. Any ways this guy was having similar issues and found a vacuum leak at the ecu for the MAP sensor and corroded wires o the CTS and the IAT sensors, so I may check those tonight and get a cap and rotor coming. any suggestion on brand or part numbers?

 

I found that my misfire was from an injector pigtail that wasn't making connection. The ground pin pulled out of the connector. I'm pretty sure it fixed the surge too but I didn't drive it long enough to know. But now onto other issues!

 

Just had the same problem on my XK8, a surge at 1500rpm with a rattle in the exhaust. The rattle I think was from a misfire, the surge didn't stop the power when required. I held it for a while until it gave me a bank 1 cat error. Anyway I have recently swapped out the downstream O2 sensor and it appears to have done the trick, hope this helps anyone who has the same problem.