Spectacular experience, here.

Bought the car off eBay. Someone had put seats in it from a 99 XJ8, replaced the carpets, headliner in good shape, most everything about the interior is good except the door locks aren't working.

So I take delivery of it, and on the second day I had it, filled both fuel tanks and the left one starts leaking right over the tailpipe. Crack in the tank about halfway up. I lost 6 gallons in one night and put a hole in my asphalt driveway.

I take the car to my regular mechanic, they replace the tank and tell me the float sending unit for the gas gauge needs replacing, as they've found a crack in the float. The gauge was working when I sent the car in, but I've had floats go bad on XJs in the past so this just seemed like good preventive maintenance.

I get the car back last night for the first time in a month, drive it the 10 miles home from the shop and everything's OK. Go to pick up dinner last night, I get about a quarter-mile away from the house and the car loses power going down the road. I coast it into a parking space and try to re-fire it but it clearly is not getting any fuel at all. On top of that, I switch tanks and the gas needle goes straight to "0" on the tank with the new sending unit.

Either the pump picked a serendipitous time to go kablooey, or there's some kind of electrical power failure back there that is affecting both the pump and the left tank sending unit. The shop swears the sending unit was reading accurately before they sent the car back home to me, and I tend to believe them. Either way, I had to send it back to the shop today via tow truck.

I've had the car two months and have driven it about 20 miles. *Sigh.*

Jess

EDIT: This is the '87 in my signature, not an '86. Typo that I can't edit, for some reason.

 

To edit your signature, go to your control panel and select 'signature'. The float-sender assembly can be accessed by removing the tail lights lens and the bulbs assembly, fairly easy. The connecting wires might be reversed or pinched, the new assembly might be the wrong one, or might be bad. Did the shop show you the cracked float? Always ask for the replaced parts to be returned, it is your right. And never buy any car sight unseen unless you have someone who can verify condition and driveability for you.

 

What was the tank replaced with...a new or used one? IF it was used it was likely almost as bad as yours because the steel allow Jag used is known to rust easily especially with the moisture in today's ethanol fuels. If it was new make sure it's clean and shiny as new should be to verify what you got. These were finicky cars even when new. At 30 year on and for service as a driver car some modifications are necessary. I'd suggest you get two new Spectra tanks, then bridge them and eliminate the fuel switch over system. The one working fuel sender you have will suffice. Then install a hastings GF333 fuel filter on the intake side of the fuel pump in addition to a new OE fuel filter on the output side. This will ensure no debris ever gets in your pump to jam it. If you do that your fuel system will be ok. Of course you lose the "romance" and one of the signature features of the XJ...the dual and switchable tanks. I never saw the point in dual tanks but perhaps there was some rational in the mid 60's when the XJ was being designed. These days dual tanks are pointless and a liability and unless your car is a museum piece, consider this simple and low cost modification.

 

Jaguar went thru a long period of 'dual' mentality and symmetry....duel exhaust duel tanks, symmetrical dashboards, etc. The design rationale, such as it was, for dual tanks was to create different/better luggage space. I don't think it ever really worked that way.




They are pointless but needn't be a liability, even for a non-museum piece.

cheers
DD

 

Never had a problem with my duel tanks. But, you really need to see these cars in person or send a qualified representative to inspect car before purchase. Sure there are certain guarantees on Ebay, but you still need and inspection. Unless your mechanic knows the duel system on these cars, it can turn into a nightmare. Hopefully, with a little diagnostics and line checks it will work out. I always rotate tanks to balance fuel load, but that was me, like it was an airplane.

 

I used to have an 85 XJ VDP and I have a few suggestions. First keep in mind that you bought an old and possibly a very neglected car. The fuel tanks in these Jags have a few areas that tend to need attention.


If I were you, I would do the following just for the reason alone of how old these parts are: drop both fuel tanks and have them replaced with new or reconditioned. Then I would change out all of the switch over valves [I believe there are three of them], then a new fuel pump and floats and finally a new fuel filter. This will pretty much bring up the fuel system to a roadworthy standard and you will have peace of mind that it was all refreshed. I personally love the twin tanks and once you have them both working properly...you will too.


Now for a few other items: If your radiator fan is yellow with a bunch of hairline cracks in it - well get that changed out asap. It is a timebomb waiting to happen. Next: change out your radiator hoses and water pump if it has never been done. And also give your brakes a solid inspection - they tend to be important. The rear brakes in particular need to be looked at. They are inboard brakes and are a bit of work to replace if necessary.


With an older car that is less than perfect you have a couple of choices. You can either drive it around and be in 'reactive' mode, which means every time some part fails, you react, get frustrated and then spend the money to fix it.


Or you can be 'proactive', spend some money now and get it properly overhauled as needed. Then you will be in control of the situation.


When I bought my 1988 Porsche 924S, I paid $4,500 for the car and I immediately sunk another $5000 right into it before I even tried to get it on the road. Now I have a pretty much perfect Porsche without all of the headaches.


Let us know how things work out.

 

Do it all, do it once, do it right....and then enjoy the car. The ala-carte method can be agonizing, yes. Fortunately these old Series IIIs a pretty easy to work on and are not hi-tech, so if a person can provide all the DIY labor you can make one roadworthy and reliable fairly cheaply....as parts prices for most mechanical stuff are not too bad. Of course, you want to realistically assess the car and determine if it's really worth putting any money into at all. If it's rusty and the interior is shot, well, it'll cost a billion dollars to make it nice car again. A blown head gasket is something to look for....and something that might tip the scales against the project.

In my experience of owning a few and working on many, the fuel tank issues and change-over issues are most likely to occur on cars that have been sitting unused. Go thru the system and be done with it. It isn't complex. Look at it again in another 20 years !

Often the changeover and returned valves can be removed and cleaned and are good for many more years. If not, replace 'em and forget about it. Not that big of a deal. Replace hoses, too. The electrical aspect of the system is dead simple....easier than a power window circuit, for example.


Cheers
DD

 

Jess,

Based on your signature, you have some good experience with Jags, so I think you'll be OK. Also, if I recall that particular ebay auction, you bought that pretty right and it looked super rust free, so you're already way ahead of the game. Also, I'm jealous of that upgraded interior. I have a Vanden Plas but miss the seats in my 99 XJ8 for comfort. Just trying to get you looking on the bright side!

I'll bet if you have that mechanic go through the fuel system front to back, it won't be all that major, in that I don't think it's all that complicated (at least in comparison to anything modern).

 

Thanks for all the feedback, I'm going to try to put all this in the same post:

* The car is an 87, not an 86. The typo was in the subject line for this post, which I can't edit.

* The new tank is brand new from either JagBits or SNG Barratt. I'll have to look at the receipt to know, but I gave the shop a list of parts suppliers and let them order from whoever had stuff in stock.

* I did get a look at the old sending unit. Cracked and about half-full of gasoline inside the float (if that matters).

* This is my third SII/SIII car, and I have now replaced 5 of 6 fuel tanks with new. I'm familiar with the drill by now. Was hoping to avoid it on this car due to the lack of rust but, nope.

* thedugger1, it's probably the same car you saw. It was a Southern car all its life, the owner got transferred to Michigan, drove it for one Michigan winter and said "nope." No rust or corrosion on the car, paint's a little faded on the hood and trunk. All the brightwork is in primo condition. Original dash in better-than-average shape. Someone put a custom wood steering wheel in it that looked great in the pictures but is a lot better in theory than in practice. Factory stereo actually works great with only one speaker needing attention, and the antenna actually functions as designed. Sunroof works and doesn't leak. It's an 8/10 car, IMO, and as good an example for the price it sold for that I've found.

* Couple of things I didn't mention: The car has a hard time starting when cold. It's like trying to start it without a choke, if that makes sense. Once it warms up even a little, it will start all day long. Also, for those who are in the market for one, I'm trying to help a guy sell a one-owner 86 in the for-sale section and he wants $1750 for it. Details are over there and I've test driven the car. It's tight as a drumhead.

Jess

 

I'm sure smarter folks will reply, but my thoughts on a cold start issue would be either the cold start injector acting up or the thermotime switch that sends the signal to the ECU to control it. My second thought would be fuel pressure slowly leaking down.

Here's a good article on our jag's fuel injection system if you aren't already familiar:

Fuel injection and the Jaguar XJ6 4.2 Series 3 / AJ6 Engineering

 

The twin tank business started in the early 1960's and lasted until 1992. I have two twin tank Jaguars and other than a leaking passenger-side tank in the XJ, no problemas with the systems in either car, they both are as they left the factory, stock, unaltered other than defeating the General Motors check valve in the fuel evaporative system near the charcoal canister, and that is a fix that most all Series 3 owners do.

 

Jose:


No need to defeat that valve of whatever origin. Just get one
that works!! So far, so good, in my lump. and, I've a "genuine"
canister and gear in reserve....


All:


The Jaguar is my second "dual tank critter". The first was
bought used. A nice 85 Ford F150 4x4. First year of EFI.
Powered by a 302. I would have preferred the 351, but it was what it was.... Coooold AC, slick. Well "loaded'. Dual tanks!!! I discovered that after I bought it!!


So far, so good, the jaguar's dual tank system works just fine.
One could call refueling a pain ? I don't. the pirouette I do at that ime is kinda fun!!


Carl

 

I'll have to search that later because I'm not familiar with the mod. What's a symptom of a malfunctioning checkvalve?

Jess

 

You can find the check valve towards the right and inside of the passenger front wheel well. It's my understanding that it's not working when there is an excessive "whosh" when opening the fuel tanks. Search around here, you'll find it quick. The "mod" so to speak is either removing or drilling through to disable the check valve. It eliminates that whoshing sound when you open partially full tanks.

Hope that helps. I haven't heard anything negative about the mod and haven't noticed any ill effects on my car after removing.

 

Correction on duel tanks: Jaguar MK VII had duel tanks in 1953, on to MKVIII and IX.

 

the sympton is excessive build-up of gasoline vapor which cause the tanks to expand until you open the filler cap and the pressure is released and you can hear the tank contracting with a sound similar to aluminun foil being crumpled. To fix the pressure build-up, either replace the check valve with a plastic hose connector which accepts two different sized hoses, or push a 1/8th drill bit through one side of the check valte and pull it through the other side. The check valve is supposed to open when pressure reaches a certain psi but it doesn't, causing the tanks to expand to the point where the tank seams start to separate and the tank starts to leak.

 

me too, it is an old remedy-mod being used since the late 1980's when these cars were still new, it was my mechanic who showed me the trick. My '84has been like that since 1990, no side effects, nada, and no leaks.

 

I'm pretty sure I actually learned it from your old posts Jose!! Just sharing your wisdom!!

 

If you get round to reading that article on the EFI system by AJ6 Engineering, then carefully note the little bit about the contacts in the AFM that maintain the volts to the fuel pump, via the fuel pump relay.

When starting these contacts are bypassed by the starter circuit until the engine starts, then the ignition switch is returned to the "Run" position, the AFM flap moves as air passes, and closes the contacts, and the fuel pump can then keep running. The springiness of these contacts can reduce over time so not much pressure is on the contact, so one can be going along and the car stops. It happened a few times to me, most times when I was overtaking; so a bit of a brown trouser moment ! As it was too frequent for comfort, I tested this by arranging a 12v bulb on some long leads, which I connected to the fuel pump terminals, then placed the bulb near me in the car so I could see it whilst driving. The bulb illuminated when the car was running, and when the engine suddenly stopped a glance at the bulb showed it was not illuminated, so that was the answer I needed. I got the black cover off the AFM, cleaned up the contacts, and bent the mounting springs so more pressure was applied. I never had any more trouble. Of course, I had plenty of trouble elsewhere of course, it was a Jaguar XJ6 after all !

 

Picture of the pressure-release check valve used in the Series 3 XJ, and the replacement two-different-diameter-hoses connector I use in my XJ-6: