i just want to make this perfectly clear.

2 weeks ago the car ran like crap. i drove it 180 miles home.

once i replaced the TPS, it runs unbelievably rich at idle and will foul out plugs within minutes. TPS has power, CTS has power, IAT has power.

the problem is worse than when i started!

 

also the engine has developed a massive vibration such as a missfire on many cylinders.
wont tach above 1900 rpm at WOT.

lots of exhaust smoke, etc.

 

When I was diagnosing mine, I found that as the plugs were beginning to foul I could clean them out by disconnecting the plug to the fuel injectors. The engine would start up and run on the fuel left in the cylinders, and clean itself out some.

 

You have probably stuffed the injector wiring. If it has not been replaced, then replace it. This sounds like you have the injector wires shorting to earth and firing the injectors continuously. The smoke (particularly if it looks like steam) is vapourising fuel coming out of the exhaust.

Basically, when you got the car home and started on the throttle pot, plugs etc, you may well have inadvertently moved some of the injector wires, which being brittle with heat, promptly started to fail. All these symptoms come from the same basic source, stuffed underbonnet looms. Fix them up and I think you will be getting somewhere. It is obvious the engine is mechanically OK, but I believe you will be chasing your tail until you do the loom.

By the by, a replacement genuine vac capsule is not that expensive, ditto throttle pot.

If you have already changed the injector loom, apologies!

Greg

 

Darel wrote:
Greg,
Are you positive about this? I just went through rebuilding my harness last week. If you undo the horsehair on the ECU plug, there is only one YB wire going into the ECU. The wiring diagram in the ROM confirms this.

This accords (so far but see below) with my diagrams which show, for both UK and NA specs, the YB wire comes to pin 19 from the TPS and the CTS.

Then if you trace that YB wire out to the passenger's-side inner fender where the harness comes out, again there is only one YB wire. This wire then goes into the TPS connector where it is mated to a second YB wire under one of the plugs; this wire then continues on to the CTS. Yes, goes from pin 19 on the diagrams I have to the TPS and the CTS?. So far all agrees with my diagrams too.

The ROM confirms this setup, one YB wire "connected" (won't say "feeding" or anything just yet) to one pin of the TPS AND one pin of the CTS together. Check the emissions annex of the ROM. This is why I always maintained this YB wire is the 5v feed and not the "signal" since it is spliced into both sensors.

On the diagram I have, pin 20, for both specs (NA and UK) is a yellow/pink wire and goes to the TPS and the CTS, and provides the 5v.
HOWEVER:
ALSO on the diagrams I have (genuine Jaguar publication) for the NA spec diagram only, pin 7 takes the TPS wiper signal using a YB wire too, BUT on the UK spec diagram the TPS wiper to pin 7 wire is a yellow/white wire. Jaguar diagram misprint? If so, that would clear up the confusion.


Finally, I think it is easy enough to test the whether on your car YB wire is carrying 5v to the CTS. Warm up the car, switch off the engine and switch on the ignition, and put a meter on the wires to the CTS and see what gives.
Greg

 

it does look like steam. its extremely rich and indicative of a fuel injector that wont close and just keeps pouring fuel into the chamber. however, i am getting pulses on each injectors, although with varying degrees of loudness and speed, but theyre all relatively the same. theyre not perfectly in sinc, but i think thats simply because theyre old.

 

I may have overlooked it but I couldn't find any reference in this thread to the vacuum line going to the ECU. If that line is cracked, broken, or disconnected, the ECU will act as though the engine is a wide open throttle (WOT) and will add fuel for that condition.

Go to the ECU and make sure you have full manifold vacuum on that line. Without it, it absolutely will not idle and will run rich just as you describe.

 

I agree with Greg.

I haven't followed *every* posting in this thread, but......

It seems to me that things are getting overly complicated here and have perhaps gone off on some tangents.

I would never presume to know more than others here but I've worked on and owned some old Jags, including XJSs and V12s, and my experience is the same as many, many others; that is, here's whatcha do with an old Jag V12......

"Clean the Vee". Remove everything. Properly repair all damaged wiring. Check/clean/repair all underhood connections and grounds. Buy or build a new FI harness. Replace plugs, plug wires, cap, rotor. Un-seize the distributor's mechanical advance and repair/replace the vac advance. Repair/replace all vacuum hoses. Replace throttle bushings. Clean the throttle bodies and synchronize the throttles. Send the injectors out for professional cleaning. Tighten inlet manifolds and/or replace inlet gaskets. Clean the breather system.

This is all very well documented procedure when resurrecting an old V12. Do it all at once, do it right, be very systematic and thorough....and it's *very* likely that your V12 will be running and responding as it should. I wouldn't think about replacing any more parts, aftermarket "upgrades", switching to carburettors, etc etc until all the above has been done.

Unless all the wiring and connectors have been carefully and systematically inspected and repaired, all test results will be suspect....and very possibly take you down the garden path.

To be honest, and I absoultely mean no offense in saying any of this, I sense lots of frustration which invariably brings trouble. Personally, I'd fall back, regroup, and have a fresh go at the project following the above procedure.

Maybe all these things have already been done and I've missed the posting. I dunno. But I really sense that things have gone off the rails a bit. .

Just my 2-cents and, again, I'm not trying to disparage anyone. I just think it's time to step back and take a deep breath.

Cheers
DD

 

i get no difference in the way the jag runs if i unplug the vacuum line to the ECU or if i leave it plugged in.

that being said, when i first drove it home, it DID make a difference as to whether or not it was plugged in. also i am getting some vacuum to the hose. although it doesnt seem like as much when i first got it, i am getting some vacuum. i think ill double check this line just to be sure, but it was functioning properly when i brought it home.

 

Greg,
I think you may be on to something about the error in the diagram. It makes no sense to me to change that aspect for different emissions markets.

However, I really can't confirm. I have already rewrapped my harness in electrical tape and I'm not really thrilled about the prospect of undoing / redoing it.

I will say that the chassis-side plug end of the TPS is a HORRIBLE jumble of "yellow-with-some-kind-of-color-stripe" that all look pretty much exactly the same after they've been baked for 30 years. So, I ended up undoing the entire harness and tracing out the pin 19 YB wire by hand.

Literally, I think there are 6 wires on the TPS and they are all yellow with some color stripe that all looks beige after a while.

 

theres 5 wires on the TPS. yellow, yellow/black, yellow/white, and yellow/pink.

 

Thanks M90, and wouldn't you agree that a black stripe, white stripe and pink stripe all look remarkably similar after 30 years?

 

Absolutely agree!

M 90 said "theres 5 wires on the TPS. yellow, yellow/black, yellow/white, and yellow/pink. "

There are only 3 wires coming out of the TPS on a Lucas ignition V12. Now their colours, that IS a question!

But generally, I think Doug's advice is very sound. Worth taking the trouble too, because once sorted, the car will be reliable for a long time, and a joy to drive.

 

Greg,
The TPS itself only has 3 wires but the plug they plug into (attached to main harness) has the 5 yellow wires.
D

 

then you wonder why i went to a standalone system!!

it came with all engine harnesses NEW,modern wires, sensors and plugs!

 

ok everybody. heres an update. i unplugged the ECU vacuum hose, manually put vacuum on the hose and then capped it off. the idle settled down quite a bit, leaned the engine out, and overall ran much better than the last few days. when i uncapped the hose and let the vacuum out it died instantly. the idle vacuum at the hose in the engine bay is too weak to even have an effect on the richness. maybe 5-10in/hg.

right now the car still has a serious backfire issue above 3k rpm and appears to have a missfire with a rough idle. so i seem to be back to square one.

so im gonna replace that hose, find a better TPS that runs a little less idle voltage, and fix the vacuum advance. hopefully thatll solve the majority of my issues.

 

nevermind. the ECU hose is fine. the amount of vacuum it take to get the ECU to map fuel correctly is WAY more than this engine will ever produce at idle (or any blonde for that matter)

 

Oh the drama, I missed it so much!

Start with fuel injection harness, BTW, I found one perfect harness from BMW i6 motor for you, it has tons of excellent wire and plugs on it, almost enough to build the whole new harness. Come visit and it is yours!

 

ill be sure to come visit sometime and check out your project. think ill wait till its finished first. i did order a couple of harnesses. ill be rebuilding the harness tomorrow. i noticed that the pulses were violently loud at idle. sounds like the fuel injectors are really pouring on the fuel, obviously since its running so rich. so whats causing that?

hopefully its the harness. if not, im really looking into a 3800 series II swap out of an F-body. 4 speed w/overdrive & W-body heads/intake/Supercharger anyone?

 

Got it, Darel. The other two wires at the harness side plug are the splices to the ATS (5v feed from pin 20, yellow/pink) and to the return from the CTS which uses the same wire as the non-wiper return from the TPS (to pin 19, YB).

Greg