I have done and he had already, thanks. We're down to the EFI ECU which he tested against another unit and got the car to pass.

Thanks for all the input, everyone!

 

Far out!

ECU failures are a bit rare, but 'a bit rare' isn't the same as 'never', obviously.

Cheers
DD

 

A bit more digging revealed it was a combo-pack of:
•ECU not adjustable from lean to rich-
•Fuel pressure regulator putting out fuel at 38 PSI instead of 29 PSI

and... the big one:
•The wiring harness in the V where the O2 heating elements ground, not grounded so the sensors were never getting up to their operating temperature.

When we first bought the car, I brought it to our regular mechanic who serviced my VW and works on my wife's Suburu. I asked them to have the XJ-S smog checked and it passed with flying colors.

They replaced the steering rack but felt they were out of their depth on most of the other repairs, so they outsourced the car to their local "Jag expert" who replaced the valve cover and cam cover gaskets which were gushing oil, overhauled the distributor because I insisted (per Kirby Palm's book) and overhauled most of the cooling system. Anyway, it would seem he left all of the grounding eyelets for one of the wiring harnesses disconnected and lying at the bottom of the V so my car has been gross polluting since he gave it back to me in December of 2012.

As soon as my current mechanic grounded the wiring harness, the sensors started operating properly and the emissions dropped back down to normal.

Now my ECU can be adjusted from lean to rich, the fuel pressure regulators are working properly and the 02 sensors are working efficiently- for the first time since I've had the car.

 

im pretty sure the specs for the fuel regulator are for it to run between 34-38 psi.


Don't you love not being able to plug in a simple scanner to see what the engine management is doing? wheres the fun in OBD?

 

Right, 29 psi is on the low side. Shop manual calls for 36 psi.
I'm pretty sure 29 psi the approximate spec for the *pre-HE* engines.

Good on finding the ground problems!


Cheers
DD

 

Which shop manual is that? I looked on the JDHT DVD (JHM1146 v1.1) and in the repair section it lists something like 28.x to 30.x as acceptable pressure but that particular section seems to apply to the entire run and does not make a distinction between original or H.E. engines and assumes the presence of a Lucas CEI ignition system.

If I take it up with my mechanic, I'd like to have some solid backup.

Cheers,
Rhett

 

I'm away from my books at the moment. I'll try to get you the specifics books and sections later.

Some of the Jag manuals...DVD or paper...cover both HE and pre-HE V12 and the delineations are not always crystal clear.

Cheers
DD

 

Go to the top of the "XJS" section and open up the sticky thread called "How To"

Select 'downloads', then 'tech guide', then 'XJS Engine Performance'

The fuel pressure info is on page 6

This document is very useful to V12 HE owners

Cheers
DD