NOTE: The title says 85 but it's really an 88.

I've been working to get an 88 XJS back on the road after sitting for several years. The car has new plugs, wires, rebuilt distributor with new cap/rotor/vacuum advance. Fuel injectors were removed and cleaned. Fuel tank was cleaned and renewed with the renue process. The fuel lines were flushed and new filter installed.

I've only started it maybe 10 times and it ran fine every time. Now it is a little hard to start and it dies after about 30 seconds. It runs good for the 30 seconds. It will restart immediately but then die again. Checked the fuel pressure and it's 40 lbs.

Any ideas as to where to start looking?
Marvin

 

Mmmmmm, many hundreds of things come to mind.

My list of "basic diagnosis" would be:

Fuel flow, you can have pressure but flow is just as important. The fact the tank has been treated, I am leaning towards a blocked main filter, and/or the pick up filter in the small tank under the battery.

The tank venting system may not be doing what it should, so remove the filler cap, and see if there is any difference.

Loss of spark, mmmm, maybe, but the fact it restarts instantly is a PLUS, and is taking me away from that issue a tad.

The fuel pump control circuit INSIDE the ECU is hissy. Yours "should" have a 16CU unit, which are way more reliable than the previous 6CU, BUT, then you are saying '85 in the title (6CU), and '88 in the text (16CU), so maybe??. Bridging the relay socket so the pump works whenever the ignition is ON is OK for diagnostics, and eliminates that unit from the list.

I will stop there until some clarity to year is available, and some basic diagnosis is done.

 

It really is an 88. I forgot to mention that I can hear the fuel pump run for a few seconds after it dies. Also I noticed a broken terminal on the transmission kickdown switch but I doubt that would be the problem

 

Sweet, the air is clearer a tad.

Also I did not notice, YOU ARE NEW, so WELCOME TO OUR SIDE, fun will be had, trust me.

The pump whirring is s good thing.

So, run it again, let it die, then CAREFULLY crack the fuel hose connector (double nut thingy) where it attaches to the RH side of the fuel rail.

FUEL SPILLAGE IS EXPECTED SO CAUTION PLEASE.

1) If you get a dribble of fuel, NOT GOOD.

2) If you get a decent squirt GOOD.

The first means you got fuel supply issues causing the cut out.

The second indicates fuel, and pressure, which is good. Meaning another gremlin is at play here.

let us know what you find.

Sometimes these resealed tanks have a flake of stuff blocking the supply pipe TO the sump tank, and once the engine stops the fuel suction stops, the flake falls away, fuel runs again, until the flake gets sucked in there again.

 

i would be willing to bet that your fuel pressure is right on the money, and then dieing off. i agree with the blocked filter from the new tank coating.

when it dies, the fuel pump primes, allowing pressure to build up without being consumed, which might be enough to get it started again.

 

Put a fuel pressure gauge in the feed line and watch as she dies. However if the car just shuts off it is more than likely NOT fuel pressure related.

A bad ignition module perhaps. Try keeping that cool and see if it stays running. Use freeze spray, an ice pack or something to keep it cool. If it stays running you have found your problem.

 

Well it's definitely fuel related as I can keep it sort of running with starting fluid. I'm now thinking it's the filter because it's gotten progressively worse to where it only runs for 3-4 seconds now. I loosened the fuel line and it had pressure even after sitting for about an hour.

Disconnected the line and hooked up my pressure gauge and it's 45 lbs when I turn the key on. I haven't found the right adapters or T fittings to allow me to check the pressure while it's running. Would a pressure gauge at the pump work?

Also, the switch that broke is not the kickdown switch. It's the micro switch that mounts next to the throttle plate. What does it do?

 

The switch is the full load switch.

A fuel pressure gauge at the outlet of the fuel pump will work.

 

Mmm, read this carefully a few times.

I am gathering you have simply plugged the fuel pressure gauge into the hose at the rail, and created a "dead end" connection. I say this due to you mentioning "not having adaptors to "T" it in".

If that is so, 45psi is a tad low. I would have expected 110+psi, on a dead end connection.

The filter being blocked again is REAL.

A tired pump is also on my list.

It sounds like it is developing pressure of sorts, but lacks flow to actually run the engine.

 

I put in a new filter (the old one doesn't seem to be plugged). Tried to start it and after a few tries the fuel pump quit working so I think the pump died a slow death. Going to double check the voltages at the relays and pump just to make sure before I spend the $$$ for a new pump.

Also, where can I get a new full load microswitch (aka enrichment switch, idle switch, etc.)?

Marvin

 

FWIW The fuel pump is the same pump as used in air cooled VWs with EFI. However VW vendors want 1/2 of what jaguar vendors want. It is a Bosch unit. Part number 69414. Busdepot is where I bought mine a few years ago. They have a web presence and an eBay store. You can get either spade or screw terminals. Spade is OE. You want the German made Bosch units not the Chinese counterfeit ones. Also stay away from aftermarket ones.

 

From what I read, I still think it is the fuel filter...
Is it backwards? (arrow)

To check the pump/pressure... turn on the ignition with the key and hear the pump whizzz until it stops. Don't start right away. Do the same procedure of ignition on/pump on/pump off/ignition off like 5 or 6 times. This increases the fuel pressure a bit at a time. Then, start. It should run for a few seconds, until you press the gas, and die. That means not enough gas going to the engine.

 

Changing the filter didn't make any difference. It still starts fine and runs for 15-30 seconds then sputters and dies. Hooked up my timing light and it's getting spark until it quits. I also used my stethoscope and the injectors are firing up to the end.

I'm about ready to assume that it's either the fuel pump or pressure regulator. I don't have a T fitting to check the pressure. However since it's the original pump and it sat for several years with bad fuel in it, it's probably a good idea to change it anyway.