Got the '87 XJ6 back from the shop today because the shop can't figure it out and has reached the end of their rope. We're a little hamstrung because we lack the tools to completely diagnose the problem and are in the throwing-parts-at-it stage.

This is what has been thrown at it so far:

* One complete, new set of injectors
* Two sets of spark plugs
* Cap & rotor + 2 sets of plug wires
* 2 coolant temp sensors
* 1 airflow meter from Everyday XJ (used)
* Cleaned/reoiled the K&N air filter

EDIT: Also replaced ...
* Cold start solenoid/injector
* Fuel pressure regulator

The car basically is a brick. It is dumping black smoke out both tailpipes. It builds revs very slowly and is hesitant to rev beyond 3,000 rpm, but will do it. It will not pull a hill of any kind. The in-dash computer, which I've found to be quite accurate on these cars, is reading MPG of between 5-12.

We also believe now that the catalytic converter has been ruined from all the raw gas being dumped into it. At the end of a 10-minute drive this afternoon, it began dying at stop signs, and it had trouble going up a 2-foot incline (no exaggeration) into my garage. When it finally got in the garage, I was greeted with a strong smell of unburned fuel and catalytic converter.

I have no shop around here that has Jaguar diagnostic tools from a S3 car, so we're stuck in that regard. The shop wants me to get another airflow meter, or maybe a new computer. Something is causing the car to dump raw gas, wide open at all times. The car actually runs BETTER if you disconnect three of the fuel injectors.

As simple as these cars are, there doesn't seem to be a lot of components involved in this problem. It would seem to me it's either a computer issue, airflow meter issue or there's compromised wiring somewhere. I'm open to suggestions here but as you can see from the list above, we've already thrown quite a bit at it.

Jess

 

The EFI system is an early analogue one developed by Bosch called L-Jetronic. As such there are no fault codes or anything to give you a clue on what is happening, although I believe it is possible to use an CRT display to show some things like injector pulse width.
You might try reading this: -
Fuel injection and the Jaguar XJ6 4.2 Series 3 / AJ6 Engineering
Look at Para 13 of Troubleshooting on P6

 

the black smoke and hesitation in my 1984 happened when I bought the car. And then the issue stopped by itself. The car had been sitting so that is the probable reason it did it, then it never happened again..

I do not think the catalytic has been ruined, if you have ever opened one, the "honeycomb" material is enclosed in a bag designed to not hold liquid. It is rivetted to one half of the case so any liquid will drain out. Gasoline will not ruin it.

it is obvious you have an over-fueling issue. I have a document in my website about this issue if you want to read it, or you can download it free.

https://jagupgrades.webstarts.com

 

I suggest you meter out all the connections between the ECU and the engine side (AFM, resistor pack, injectors etc)

If you have a wire gone open circuit, that could cause the over fuelling problem.

 

I had a similar issue a few years back, but it was my own doing, after a head gasket replacement , two of the plugins for the engine harness were not clear where they went, laid it out best I could and plugged them into the closest thing they reached, engine fired right away but like you, I had plumes of black smoke, car was undrivable, turned out inhad 12 bolts going to cold start injector all the time, switches the two plugins I was unsure about and it went back to normal! Hopefully this helps.

 

What's the fuel pressure reading at the fuel rail? and what is it when your driving around? What is the CO% from the tail pipe after warm up is achieved? Disconnect the cold start injector plug after start up is achieved if that's in any way suspected.

 

In his article on the EFI system (AJ6Engineering), Roger Bywater mentions the cold start system and says that if this isn't working the engine will eventually start from the fuel supplied via the normal injectors, it just takes longer. So I would disconnect the cold start injector, and see what happens.

 

Have you renewed the injector loom? If not, I would do do, they can short out and hold injectors open.

Also, pull an injector, one by one, and king lead removed, using the starter see what each ones spray duration is, compared to spec.

 

Being lazy.....

Although the regulator has been replaced I'd begin with a pressure test, personally. There might be a problem in the return system....which could increase fuel pressure.

Also check the bundle of ground wires at the rear of the water rail. There will be 5 or 6 of 'em. The entire F.I. system grounds there. Can't hurt to makes sure the grounds are clean.

Cheers
DD

 

Clamp off the hose going to the cold start injector, It could be stuck open.

Thank you.

Larry Louton

 

Doug's point about the cleanliness and security of the EFI earth points is crucial and should be checked and cleaned before doing any tests.

I certainly support what Larry suggests as an urgent (and simple) early exclusion test... clamp the fuel feed line to the cold start injector. The cold start injectors when aged frequently stick in the open state and just removing the electrical connector isn't enough to force them to close; thus allowing fuel to continue to flow - you need to manually clamp the feed hose to be sure no fuel is getting in via the CSInj. If you clamp the line while the engine is warmed up and running (and the CSInj is the problem) you will see an almost immediate improvement as the mixture returns to close to normal (there may still be a rough idle due to fouled plugs... it is worth removing and cleaning them before this test). If you do this test as described and the problem persists, then you can almost certainly rule out the CSInj.

If your O2 sensor has gone haywire, it is going to command overfuelling... that would be where I looked next.

Just a thought... if you know any other Series 3 owners in your area who would let you do a quick swap (only a 5 minute job) with their ECU for yours you could use that to exclude the ECU as the source of the problem. Also, in case you are in an area where you don't have local Jaguar expertise (though of course you always have the collective wisdom and goodwill of this forum) it is worth considering that L-Jetronic was used by BMW and older BMW technicians received extensive training in how this system operates - it is not substantially different in application between Jaguar and BMW cars of the same era.

 

Well, after several months, if not years of trying to find where the issue was, we found it.

Many people had suggested the cold start injector as a potential issue a while back. The old one in the car was leaking. So we replaced it with a brand-new, factory replacement.

Turns out just because parts are new doesn't mean they aren't already broken. We put a clamp on the cold start injector hose and the car immediately started running well. So we unplugged the BRAND NEW cold start injector, disconnected and blocked off its fuel supply line, and everything is fine again. No smoking, no rich condition, no gas smell, and my MPG is back to factory spec.

The car also starts on the first hit every time now. No having to feather the throttle. And given that I live in Alabama, there's only about 3-4 weeks where I have to worry about a true "cold start" condition.

Thanks to everyone over the (many) threads I made here for helping. She's back on the road now.

Jess

 

Delighted to hear you are back on the road Jess! One suggestion... be sure to change your engne oil asap; after such extended rich running it will be sure to be contaminated with fuel that will lower its ability to protect your engine from wear.
Happy motoring!