I've had this car for a few years now but it's just been sitting and this is the first chance I've had to play with it. I understand the difficulty and frustration that will most likely accompany ownership of an old Jag. I'm just hoping to find some technical advice here.

The car is 1982 XJS HE with 79,350 miles. The starter runs fine and it turns over just will never start. I've checked fuel delivery and pulled the whole fuel rail out with the injectors to make sure they were all working. I check the ignition and it's fine.
It starts fine when I spray starting fluid into the throttle bodies but dies after a few seconds when that runs out. I don't have a compression tester but I'm inclined to believe that it's fine since it does run on the starting fluid.
Is there something I'm missing or does anyone have any tips for me to try? Any help would be appreciated.

Elazar

 

I just drained the fuel tank and pulled the lines off the tank to flush them and thought I'd try dropping them into a can of fresh gas and the car ran out of the can. I pulled the fuel gauge sender off and looked into the tank and it looks pretty clean. So I put it all back together and will kind of start and idle but very rough (barely able to stay running) and if I open the throttle any tiny little bit it dies like it's not getting enough fuel. I'm doing all this with the fuel gauge sender unit removed so I know that fuel tank venting is not the problem (it never runs long enough to create a vacuum in the tank anyway). I can't find any blockage anywhere in the system.

 

moved to the correct area of the forum

 

So many possibilities but we gotta start somewhere, so here are some random-order thought starters...

The primary mixture control devices are the baro sensor in the ECU and the throttle sensor under the throttle turntable. Make sure the long vacuum supply hose from the engine all the way to the trunk (where the ECU is) is connected at both ends.

If you have a volt-ohm meter you can check the throttle position sensor

Do you have a fuel pressure gauge? Mere presence of fuel at the rail isn't enought. Has to be at the right pressure. And....do you have pressure actually cranking the engine?

Any large vacuum leaks?

Are the backs air filter housings still bolted the the throttle bodies? If not you'll have a huge vacuum leak via the missing bolts.

Remove the connector at the (fuel injection) coolant temp sensor and jump the terminals with a paper clip. This bypasses the CTS and takes it out of the picture. Post back if anything changes from doing this.

Check wiring at the coil and ignition amplifier....injector trigger voltage to the ECU comes from the ignition amplifier.

Post back for more details on any of the above, if needed.


Cheers
DD

 

Look under the battery, there is a small fuel tank (sump tank), and that has a very fine filter on the end of the pick up pipe, and is known to clog up, so supply (primarily gravity) to the fuel pump is a non event, as is engine running/performance. The large hose that goes from the bottom centre of the main tank to the sump tank also can clog at the main tank inlet, usually rust and gunk from sitting with fuel in the main tank.

The fuel filter is also clogged, which will limit fuel as well.

A tired/lazy fuel pump also reaks havoc on a V12.

As Doug said, fuel pressure readings are a must for any sort of proper diagnosis. Fuel flow is also a requirement.

The fact it appears to run "out of the can" is heading me to the fuel supply TO the pump from the factory system.

 

Thank you. I wasn't getting any response.

 

Well I have the fuel tank out right now to clean it, it's not very bad at all. The sump tank does have some debris in it but I cleaned that fine pickup filter (it was pretty bad) and it runs much better, just running out of the sump tank since the main tank is still out right now.

It runs but still seems way too rough so to your questions, Doug:
I don't see any vacuum leaks anywhere but I can't find any vacuum hose to the ECU. There are two lines that go through the firewall on passenger side, one is not used (capped with a screw in the engine bay). I can't find where they go but not to the ECU.
I think the TPS is bad. I don't know what the values should be but it is not a smooth curve. It shows open most of the time and at WOT the resistance intermittently drops to anywhere between 400 and 1500 ohms.
I just jumped the CTS and it seemed to run better. But now my fuel pump just quit so I'll post back when I get a new one on.

 

The hose TO the ECU begins life at the centre of the engine balance pipe, that 1" pipe across the back of the engine, between the 2 inlet manifolds. Have a feel around and there will be a hose connected from the centre on the underside, and about 10mm diam. Found it, good.

Now go to the boot/trunk, and alongside the battery is the ECU, and hanging out of the lower edge, just forward of the big electric plug, is the other end of that hose. It is known to split at that point and the engine overfuels.

I reckon you are onto it, the fuel pump is dead, so a new unit will restore correct pressure (failing something else being buggered), and good flow.

The TPS is definately flaky, and that will reek havoc with the ECU fueling maps, so a repalcement there is almost mandatory, and set correctly also helps. I run the XJ40 TPS on both ours, and they were s/h units, coz Jaguar wanted mega$$ for the V12 unit 12 years ago, so whatever was around went on, and since it is still working why change it (Aussie thinking here).

I have a fairly detailed write up on what and how I did it if anyone is interested, let me know.

 

Since I am still waiting for a fuel pump I started pulling the intakes off so I can polish them and clean everything under them (it's pretty bad). I found the vacuum hose to the ECU .

I'm just wondering what the piece is in the picture. The 'stems' pass through the intake flanges and into the head. When I removed the intake manifolds, those 'stems' were completely clogged with carbon and the holes into the head are as well. I cleaned the stems out but how can I clean out the holes in the heads without all that junk falling into the heads? And what are those for anyway? I don't see them in any manual or parts catalog.

 

Those are the air injection tubes.

Cheers
DD

 

Possible your ECU. I had a similar problem with mine and upon replacing the ECU the car ran fine.

 

Since I got the new fuel pump and I'm still waiting for the money to get a new TPS I cleaned up the intake manifolds and air filter boxes, painted everything. I got bored and started playing with it again today, cleaned the fuel tank and sump tank out, fresh fuel. It started fine but idled up at 2500 rpm and died if I opened the throttle at all, probably because of no TPS. Was able to check transmission operation and brakes though! After about 10 minutes of that it died and the fuel pump wouldn't run anymore. The screen on the pickup had fallen off, I was curious so I took the pump apart and there was alot of specks of dirt in it. I cleaned it and put it back together and the pump motor runs fine but it doesn't push any fuel. Why? I checked my reassembly several times and it appears correct.

 

You can remove those air injection tubes and the rest of their piping. They most likely so plugged with carbon that no air flows through them.

Tap the holes in the intake manifold a plug them with small bolts or screws.

 

After some more research, I've decided that I'll just take all that out along with the air pump.