I have a 1987 XJS V12 with 98,000 miles on it that I just bought non-running. It was running fine being driven several times a month for the past few years (never really sat for any long periods) and then about two weeks ago it just failed to start and hasn't started since (according to previous owner who I believe). It cranks but will not try to fire at all. He didn't really try to figure it out and just decided to sell it to me instead.

The battery is good and the car will not start with a jump. Checked fuses, cleaned grounds and all the obvious stuff like inertia triggered switch. I have a manual but it is useless.

I tested for spark the other day and the wires do supply spark to the plugs. I tested two of them.

I tested for fuel on the rail and no fuel came out when I cranked the car. Tested both sides of the rail.

I went in the trunk and the relays are working. When key is in on position pump cycles. Pump continues to cycle when cranking. I tested for fuel as far down the line as I could go, which ended up being right after the fuel filter because I don't know where the lines go after that. Fuel comes out where I have the green star in the picture. Fuel does not get to the rail when the key is in the on position nor when the pump is hot-wired using the battery.

What I don't get is HOW CAN THE PUMP BE SENDING FUEL BUT IT'S NOT GETTING TO THE RAIL???? I don't have ANY leaks ANYWHERE. Is there some magical hidden valve somewhere in the lines under the car or in that mini tank thing that I can't find that may be broken???

The fuel routing is a little confusing to me. If I understand right: fuel is gravity fed by line traced in pink into the mini-fuel tank thing outlined in blue. Then from the mini-tank it goes through the line traced in green through the fuel pump and filter and disappears somewhere. Also, what is the line that I traced in white??? Is it some kind of return line??? Am I understanding this right?

Someone has to know the answer to this. Or can maybe point out something I'm doing wrong. Thanks.

 

The hose you point to connects to one of the Fuel Regulators. Sounds like one or both of the Fuel Regulators has gone bad (see photo).

The fuel system in the XJS works as follows;

1. Fuel flows from the fuel tank to the Surge Tank (Mini Tank)
2. Fuel Pump draws fuel from the Surge tank.
3. Fuel is pumped through the Fuel Filter and then up to the Fuel Regulator.
3. Regulator controls the pressure to the Fuel Rail.
4. Unused/Excess fuel is cooled by the air conditioner and returned to the fuel tank.


Mark

 

Undo the pipe leading into the right hand regulator in Safari's photo and see if fuel comes out of it when you turn on the ignition. This is the feed side to the injector rail.


If it does not, you have a blocked pipe between the fuel filter canister outlet and the engine bay. Blow some compressed air through and see if that helps. If not, as the pipe runs under the US passenger side of the car, it might have been crushed by bad jacking or something similar, so you may need to get under and have a look. The fuel pipe is the larger of the two pipes that side under the car, the smaller one is the brakeline.
Greg

 

Update:

So to boost my confidence I sprayed starting fluid in the intakes and the car did catch and fire. Sounded really good for about 2 seconds until all the fluid burned up. So that's good.

I did as you suggested, Greg. Undid the line going to the upper regulator on the passenger side of my North American XJS. Jumped the pump and no fuel came out. So I suspected a clogged or damaged line.

I had about 15 feet of hose lying around in the collection of junk that I keep around so I hooked it up to the fuel system after the fuel filter and jumped the pump again. Fuel did not come out at an impressive rate. I'm thinking the pump might be failing. If it is not supplying enough pressure it's probably not forcing fuel up through the line on the underside of the car into the engine bay to make it to the fuel regulator? That's my thought.

I am not super familiar with how powerful the fuel pumps are on these cars so when I initially tested it in the trunk and fuel came out I thought it was good. Fuel did come out, but it did not gush out like it was under a lot of pressure. I would say it came out at the rate that normal gravity would cause it to.

So now I suspect the pump. I think I am going to order a new one. Does my testing sound thorough enough to go ahead and spend the money on this part? Should I conduct any further tests before replacing the pump? Any input is appreciated.

I do have a tank pump and inline pump from a Volvo 760 turbo that I might hook up and try to run as a test just for the hell of it. Not tonight though. It is dark in Columbus, Ohio and the car is parked on the street right now.

Thanks, all.

 

I don't know the actual volume spec for these pumps but a good one is pretty darn powerful....enough to produce 75psi or so 'deadhead' pressure.

I does sound to me like your pump is weak

Let's wait for others to chime in.

One thing, though.....and maybe I just missed it....but have you pulled the filter off and tried blowing through it? It might be clogged.

Cheers
DD

 

I agree with Doug. The fuel pump should put out a lot of pressure and tons of fuel. If yours is just a trickle then it is bad.

However, before you install the new pump I highly recommend that you drain the fuel tank and then open up the Surge Tank. The Surge Tank is well known to collect sludge. It also contains a filter that can get clogged.

You need to thoroughly clean the Surge Tank and filter. Then you can install the new pump. I would recommend that you also install a new fuel filter and any rubber hoses that look suspect.

Now you will have clean, full pressure fuel. If all goes well your regulators are ok and the engine will run.

Mark

 

What Mark says is 100% true and needs to be done. But having now looked more carefully at your original photo, I actually think your fuel system in the boot is completely wrongly plumbed. Look at this diagram:


Pipe 14 is the main feed from the exit at the bottom of the main tank where you have the long white highlighted hose. It joins the surge tank at the welded spigot at the side. In your photo it is connected to the filter.
Pipe 13 (pink highlight on your photo) is an air bleed back to the main tank from the welded spigot on the top of the surge tank.
The feed to the pump should be from pipe 15/16/17 via a short wide hose.
The high pressure feed to the engine FROM the filter should be via the long hose highlighted white by you and it exits at the front right lower corner of the boot where it joins a brass fitting.
I am pretty sure if you sort this out properly you will get fuel to the engine. I think that somehow, and goodness knows how, your pump is reversing fuel and effectively pressurising the non pressurised feed and miraculously a dribble gets through somehow! This is what it should look like:

The feed coming from the pump TO the filter is on the RHS of the (in my case Red) filter. The feed from the filter TO the engine is exiting the LHS of the filter
greg

 

Hmmmm. That is interesting. I know the PO did remove the tank and had it cleaned and repaired at one point and perhaps he re-plumbed it wrong? I never considered this as a possibility.

Okay so I will reverse the lines and see what happens.

Question: how do you remove the battery tray from above the surge tank? I know there are two bolts which you can see I removed in my photo, but I still can't get the tray out. Are there hidden bolts somewhere and how are they removed?

 

The PO certainly did plumb it wrongly, no question about it; but do not just "reverse the lines". Follow the diagram exactly or you will not solve the problem.


From memory there are two hard to see bolts at the side towards the back of the battery tray, you have to get your head down under the tray to see them.
Greg

 

IT RUNS!!!

Greg, you were totally right about the plumbing. Thanks so much for pointing that out. I just arranged the fuel hoses according to the diagram/picture/explanation you provided and it fired up and ran. Plumbing seemed to be the only problem. I don't know how exactly it was running up to this point like that though.

Safari, Doug: thanks to both of you as well.

The PO apparently did not disclose a few things to me though because after driving it around the block I've noticed several things that need fixing. I will plan to tackle those this weekend. It's super awesome to know that there is an active forum like this with guys like you to help us ignorant folk along the way. It would have taken me a long time and much more troubleshooting to figure this thing out by myself.

I'll post pictures and whatnot in the new member forum at some point. Thanks again.

 

We're gonna call you "Old Eagle Eye" from now on, Greg


Cheers
DD

 

Well named Doug.

Another simple fix for a very simple car, awesome.

GOOD ON YA GREG.

 

Doug and Grant


Old eagle Eyes blushes to receive such accolades from the true Maestros.


JW, I am glad the car is running, congratulations. Many XJS V12s would still be going well if it were not for their previous owners!
Greg

 

Hit any hard bumps or pot holes? Passenger side door fuel cut off switch re-set?