Hello everyone. New to the forum. I have a 1988 Jag. XJS Hess and eisenhart in my shop. 28K on the odometer. The car is in excellent shape but severely low on power. I have replaced the air and fuel filters as a starter. The car is really sluggish at acceleration and will barely maintain 75 mph on the freeway. I am planning on performing a tune up but wanted some input on other things to look at. Any input would be appreciated. Thanks.

 

Well you got the fuel part down make sure too put 93 in these cars 11:1 static compression hates 83 new plugs wires cap n rotor should be done change the transmission filter . There is a specific trans fluid used in these unlike the gm 400. Likelys just needs the basic tune up set the timing check the vacum lines as well i had an issue with mine it didnt want too rev over 3k rpm because of the vacum advance was lacking in vacum!

 

An oil change couldnt hurt either

 

The H&E has a very complicated fuel tank system.Two tanks that are linked by a pump, I think. My money is on not enough fuel getting to the rail. Get a schematic of the fuel system, clean it all out, check fuel rail pressure under load.

Greg

 

Run a can of BG44K and a 3/4 full tank of 93 octane fuel through the fuel system... This really helped my 1990 XJS after a few years of sitting. These fuel systems seem to get gummed/varnished up and BG44K really helped my car. If you are going to change the oil, my XJS runs great on Mobil 1 0W40 and a NAPA gold oil filter. An ATF change would also be a good thing to do. Good luck...

 

Was the fuel filter clogged? Did you empty the contents into a clean jar for examination? What did you see?

Has the car sat unused for long periods of time?


Cheers
DD

 

???

An '88 XJS V12 does use the TH400 transmission. No special fluid required. Ordinary off-the-shelf Dexron will work.


Cheers
DD

 

Mine has two coils. One quit, and thankfully, it was cold. It ran VERY smoothly, I couldn't even tell it was missing on 6 cylinders other than it HAD NO POWER. Pulled one coil wire, no change. Pulled the other one, it died. (use insulated pliers or gloves!)

If this happened when it was hot, the raw gas can and WILL ignite inside the catalytic converter and THE CAR MAY CATCH ON FIRE!
If this happens to ANY DRIVER, please STOP IMMEDIATELY and let the car cool off for an hour or two before you try to crank it again or do any troubleshooting. I just keep an extra coil in the trunk.

 

Good idea to check the coils.

Your car has Marelli ignition. The OP's car almost certainly has Lucas ignition which, if unmodified, also uses two coils.

However, the failure mode is a bit different between the two systems.

On the Lucas system you have a primary and secondary coil. If the primary fails the engine won't run. If the secondary fails, the engine will run normally at low RPM but will struggle to get over 3000 rpm or so.....which certainly could result in a complaint of 'low power'.

Worth checking

Cheers
DD

 

So where is thus second coil? I was under the belief that it only had one coil because of the single distributor. Intersesting haha learn something new every day . Where is the gosh darn fuel filter on a single tank system?

 

On the cars with the Lucas CEI ignition the #2 coil is in front of the radiator. However, over the years many have been changed to single coil operation....with the #2 coil sometimes being removed, and sometimes left in place with the wires disconnected.




Hopefully !




On my 88 V12 coupe the filter was behind the spare tire

Cheers
DD

 

Thanks!!! I do remember looking at that infront of the radiator scratching my head!! It has wires running too it still ill have too check it out. Spare tire? Illlook at that when i get the chance . Are there any threads on the single conversion

 

It's simply a matter of replacing the original #1 coil with a DAC6093 coil, or equivalent, and disconnecting the #2 coil. That's it !

Cheers
DD

 

Sorry for the thread hi jack! Very useful info doug thanks a ton! Going too add you too the list of people too contact when i hit another wall haha.

 

Don't forget seized centrifugal advance. Try flicking rotor counter clockwise and see if it returns quickly. Mine sure was gummed big time.

 

Shop? So dig out your noid light, spark checker and fuel pressure guage. I suspect something will turn up. No easy answers with the V12.

 

I put a vac tester on the vacumn advance. The vac advance is leaking. So far that is all i have found. Awaiting some parts to test it again. Thanks for all your input.

 

Smoke test the vacum system old timer did it for me once works pretty good . Engine off it pressurizes it slightly with smoke hard too miss a leak