A fuel pressure test is a good idea. Pull the cold start injector hose of the fuel rail and attach your gauge there. You want 36psi while cranking.

The fel pump circuit is a little tricky. First let's see if the pump itself even operates. Locate the fuel pump relay---it's on the firewal up there by the starter realy. It is recognizable by having white/gteen wires. Take the realy out of the plug-in conenctor.

Now, using a jumper wire, apply 12volts (from the battery "+" post is fine) to the terminals on the inside of the conenctor that are associated with the white/green wires. You should hear the fuel pump run. If you do hear it run try starting the engine.

If you don't hear it run you've either got a A) dead pump or B) a bad ground at the pump or C) a wiring fualt to the pump. Choice "A" is most likely.

If you hear it run but the engine doesn't start, post back

Cheers
DD

 

Ok, here is what Ive done today. I tested the fuel pump as directed and heard nothing, I disconnected it and plugged it directly to the battery and still nothing. I went to the local auto parts store and purchased a new pump and installed it and I now have a humming pump sound. so that's fixed. I also drained the gas from both tanks because it smelled like varnish. I used the plugs on the bottom of the tank. One tank was empty and the other had some in it. I added about 1.5 gallons of gas to the empty one last week and now it's gone. Not sure why. I wonder if those drain plugs don't actually drain out all the gas. The reason I believe that is because the passenger side tank started overflowing when I was adding the 2.5 gallons to it even though I thought I just drained it. I added about 2.5 gallons into each tank and tried to start it and its still not firing up. Also, the number one 1 wire on the green relay in the trunk was disconnected and taped up for some reason, I connected it and no difference. Can I disconnect one of the lines that is going to the front and see if gas is being pumped. What else can I check?

 

The green relay is for the antenna.

Pull the fuel filter and shke out the contents into a clean container. What you see will help decide your next steps. I suspect your tanks are loaded with rust.

Don't run the fuel pump any more.....a new pump can be ruined by rust/contaminants.

I also suspect a fuel changeover problem where fuel is being drawn from one tank but being return to the opposite tank. But let's get it running first....

Cheers
DD

 

I'll do that tonight if I can bare the cold. I can tell you that the car was hardly driven the last 3-4 years so the gas was old. The new pump has a small pre filter so hopefully it will be ok. If the filter looks good, what is the next step. I will post back on the filter results In a little while. Thanks

 

Doug, you are truly godsend when it comes to repairing automobiles. You were correct again about the rust. When I drained the old fuel out, it was darker than usual. I did remove the fuel filter and the gas that came out was filthy. I pored it into a clear container and there was some fine rust like layer on the bottom. I assume that is rust and I need to deal with that first. I found a product called metal rescue that should do an excellent job in removing the rust from the tank. It's not supposed to mess with any rubber or sensors in the tank to I should be able to keep in mostly intact. In your opinion, what should I do now? I really want to get this car running.

 

There are several options on cleaning the tanks, including removing them for professional cleaning.

I haven't heard of the product you've mentioned but that doesn't mean much. Go ahead an try it. However, install two additional in-line filters---one in each line from the tank to the pump. This way your pump is protected. Check the filter regularly.

NAPA (and probably many others) has in-line filters for the 1/2" fuel lines.

Cheers
DD

 

Thanks doug, this is what I found today. The drivers side tank looks to be ok but the passenger side tank needs cleaning. I was wondering for now, is there a way to bypass the aux tank temporarily until I can get it cleaned. I assume I can bypass the tank switch by removing the switching unit and couple the fuel line from the tank to the pump with a 1/2 " coupler or inline filter so it will always draw from the drivers sIDE tank only. The only question is how to bypass the return pipe? You think that's a good temporary work around? The filter i removed was probably completely stopped up so i assume i just need to replace it. Also, the reason no fuel came out of the drivers tank was I had to push something in the drain hole to open it up to drain so the gas wasn't disappearing. Thanks

 

Ok, I replaced the fuel filter and with a little effort got it cranked. It took about 2-3 minutes before it started running half way decent. But it keeps cutting out on me. It's like it's loosing power then it stops. Also, I still feel the fuel in being sent to the opposite tank. When I add a little more fuel to the tank, it eventually starts again. ) I disconnected the metal tube at the bottom front of the passenger side tank and when I started the car, it would poor the fuel like it is sending Fuel back into fhe tank but the opposite side.

 

IF the changeover system is working correctly you can just leave that tank (whichever side it is) turned off. But since we're not certain the changeover system is working right, yes, you can just bypass the tank in question.

Don't mess with the switch. Just remove and plug the supply line from the tank to the changeover valve in the trunk and remove and plug the return line hose to the return valve in the wheelwell. The return valve will be behind a little tin plate...probably hidden by road dirt.

Cheers
DD

 

Ok I'm not quite following you on redirecting the fuel lines. I do know for a fact that it is sending the fuel to the opposite tank. So basically, a gallon of gas will last a couple of minutes idoling and then the car runs out of gas. As you know, there are 3 fuel switch valves on the system, one between the two tanks going to the fuel pump and one fuel return valve by each tank. It looks like the passenger side fuel tank valve is stuck open and probably the drivers side is closed. There is a black and white wire connection going to the return valve but the black is connected to the white and white is connected to the black wire. I did switch them ( white/white and black/black ) and made no difference. Is there a way to check the return valve using a 12 battery. If I can use it to open one side and close the other using the battery, I would just disconnect the return valve wires so it can't open back up. I hope I'm explaining it good enough. In not, elaborate a little more on how the switch the fuel line around to bypass the secondary tank altogether. Thanks

 

This might be of interest to you on general principles:

http://www.jag-lovers.org/xjlovers/x...changeover.htm

Hoses: what I am suggesting isn't re-routing hoses per se but rather to isolate the tank so fuel can neither leave nor enter. If it's the right tank you want to isolate then remove and plug the right tank hose from the changeover valve so that no fuel can be drawn from the tank (if there is fuel in the tank it'll gush out of the hose so be ready to plug it quick). Then remove and plug the hose going from the engine to the right return valve. Now no fuel can possibly be returned to that tank. Of course, the other return vale must be operational as the fuel needs to go somewhere. And the changeover valve must be open for the left tank.

If it's the left tank you want to isolate then everything is just the opposite, of course.

If the right side is stuck open....I presume you mean the return valve when you say that...then A) voltage is being applied to the solenoids or B) the valve is mechanically stuck. Disconnecting the switch would solve scenario "A", as doing so would open the left return valve and close the right valve.

Voltage is applied or not applied to all 3 valves at once. Zero voltage opens the left valve and close the right. Voltage applied does the opposite. The return valves are the same except they are oriented reverse of each other.

The valves are just simple solenoids. Default state is "no voltage" so as soon as voltage is removed they'll move to "left tank" status so you can't power them up in hopes of them staying in that position when the voltage is removed

Cheers
DD

 

OK, I finally got the Jag running pretty good. It turned out the dash fuel switch button is bad. Its always sending power the the fuel solenoids but when I press and hold the dash switch, the power turns off. As soon as i stop holding it, it turns back on. To utilize the left tank only, I simply unplugged the power to all 3 fuel switch solenoids and now i'm drawing and returning fuel to the left tank only. BUT, there is always a but , I found out there is a fairly significant fuel leak at the left tank after i filled it up at the gas station. Its coming from the top of the tank somewhere and I'm almost certain it has something to do with the return line around the tank somewhere because it mainly leaks then the car is started and stops after the car is turned off. Gas coats the tank when its on so its leaking pretty badly. There is no leak in the trunk so i'm OK there. This is my last issue I need to solve and its road ready. It didn't leak until I unplugged the solenoid switch (basically switching to the left tank which i wasn't able to do before). As i said, I'm pretty sure its has something to do with the return fuel line at the top part of tank. What is the best way to get in there to check exactly where its leaking from without pulling the fuel tank. I assume its somewhere in the wheel well. Thank you all so much for all your help, especially you Doug.

 

I guess disregard the last post. It looks like both tanks are leaking at the seams when pressure is applied. I can get it re-sealed with a tank epoxy coat but will it seal a leak at the seams. Also, how do i disconnect the filler neck on those tanks. I know there are 4 screws on top at the filler but i cant seem to pull it out?

 

Hi OTGT

I have worked on a 1980 Series 3 and I know how frustrating it can be; I had it 14 years !

The fuel tank filler caps are quite a substantial assembly made of Mazak, and to remove them you first take off the 4 screws as you have done, (two of these are very awkward as the pivoting cap gets in the way. You then have to "persuade" the assembly to come out. This is done by pulling upwards and at the same time rotating the assembly slightly back and forth to loosen it off. Apart from the gasket, there is an 'O' ring seal on the cylinder part that fits down the filler tube on the tank.

 

OK, got the tanks pulled and they were filthy from sitting. Both fuel sender unit were bad and about an inch of rust sitting on bottom of tank. I used the KBS tank cleaner and sealer kit and it cleaned those tanks like new. I did have to use a pressure washer to break up some of the chunks of crap in the tank. I plan on using the sealer tomorrow and have the tanks back in by the weekend. I will keep you posted on the results. Thanks again everyone