Holy Crap MQuinn!! I feel like I got near the end of a great mystery book and someone ripped the last chapter out! Does Lassie ever find Timmy in the well or does the kid drown? ;-P

I am so completely new to Jags, but not so much to car diagnosis/repair. All of this Jag specific information makes it seem like I just found out what car is for the first time!

Even though I read every post, and no time to re-read, did you ever happen upon this section of Bernard Embden's work (man, I wish I had Bernard's garage and tools, not to mention Jag experience-and I thought I was McGuyver) Testing and Replacing the Throttle Switch

I am riveted and can't wait to see how this mystery ends! And I pray my XJS never develops this issue ;-)

BTW, Bernard, one million thanks for your site, expertise and kindness for sharing. You rock!

 

Per, your test is the same as the noid test if I unplug the injector and put the light or are you suggesting tapping into the back of the injector plug with it still plugged into the injector? Still raining here... Need it to stop so I can clean out my garage so I can pull the car in and have better ability to work on it!!!!

 

RealtorMPG, Lassie knows Timmy is stuck in the well because he pusher him down there! ;-P

I think I tested the TPS to be good (using a volt meter found no spikes or drops in the entire range). I know that was done twice now per peoples suggestions (see earlier posts in this stream). It seems to be a standard rheostat which is prone to grounding out or having corrosion that might cause a dead spot that I am experiencing. I used an analog meter so I could watch the needle - (I used a digital one also - but felt it might buffer or I might miss a small change). Had a very steady voltage change from start point to WOT. (Bernard has some great "how tos")

When I get enough non rainy time - I will try Per's recommendation with the light. Only 3 things are needed for the engine to run - fuel (gas/air in the right ratio), fire (spark), timing (having the fuel in at the right time, the piston in the right spot, and the spark to happen at the right time)... Easy..... it is exactly like any other car.

 

"Easy..... it is exactly like any other car" er, sorry but on a Jaguar 5.3 HE it's anything but "easy" or like "any other car" My TR-6.....now that's easy and like any other car.....my XJS has WAY too many sub metering mechanical/electrical management parts to be anything but easy.

 

JTsmks,

Of course I was speaking only of the "how it works" part of the car - not the challenges to get it to do such a thing... It works _just like_ my 66 f100 straight six - but it takes me 2 min. to trace out the whole wiring in the truck or diagnose any problem... and how long has this thread been going on with a "simple" Jaguar? ;-)

I am glad the jaguarforums is here - or I would have gone crazy with some of the "simple" things about this car... Glad there are many that have gone before me on this adventure!!!!

M.

 

Just been reading all this, like a Harry Potter novel.

An '86 possibly still has what is known as a 6CU ECU in the boot. The change to the significantly more reliable 16CU unit was in '86/'87. Dates elude me, but a simple look at the sticker on the ECU casing will confirm what you have.

The 6CU is well documented as having issues with the fuel pump control circuit (not in this case), and the injector control circuit (HELLO). The MAP sensor, mounted on the circuit board inside is also a problem child.

ALL this was addressed with the 16CU, and then the added advantage of this unit processing its data 5 times faster than the 6CU.

This engine runs, OK, only at idle, BUGGA.

The ECU converts vac signal to electronic, and the amount is governed by the vac hose to the ECU. You have established vac in that line, but is it clear?, as in with it disconnected at both ends, can it be blown thru easily. I have had them block/restrict with condensation moisture. In those cases the engine idled, but overfueled, as high vac = less fuel, and low vac = more fuel (simplified wording).

The resistor pack behind the RH headlamp is not a known failure item, BUT, the Lucas plug going into it at the bottom is a PITA, and fills with crud, however odd running at all rev ranges is the "normal" event here, so I doubt it is an issue, but simple to check and clean.

The fact it dies instantly you touch the TPS, tells me it is the ECU fueling circuit, alias the MAF on that board is dead. the "idle" fuel circuit is seperate to the "run" circuit, that is why the TPS idle voltage is CRITICAL.

Also, the fact it is running at all indicates that the shielded wire from the ign amp TO the pin #18 of the ECU is intact. If that is broken that engine is DEAD, no exceptions.

The "green fungus" in the ECU plug/socket is also an issue in damp climates, and should be eliminated as an issue.

The ECU earth, bolt alongside the battery, is also a cause of weird and wonderful issues.

 

Grant,

Great ideas! It is raining like cats and dogs here or I would run out and check the ECU. I found a guy local that does ONLY XJS parts and I just got back from his place with a truck load of parts (for another car) and his willingness to come down and put his eyes on it. He said he even would bring down an ECU as he said that is what it sounded like!

 

Ok, the PO said that the ONLY thing done to this car was maintenence (tires, oil, and such). His dad owned it and then he did. When I removed it the nuts were hand tight and the lower screw (on the wheel well) was only one and it was only half in there. I think the PO was had by the mechanic that was "storing it for free".

Can someone ID these parts and let me know if this would have been original equipment on an 86 XJS? We might have found something here...

(the connections look good though...)

 

Grant - no green fungus on any of the terminals and the ground strap looks good (I removed it touched it with some sandpaper and reassembled all grounding in that area applying a small dab of dielectric grease on assembly - replaced the lock washer stars with new - just to make sure).

 

Looks like this could be a correct ECU - it is a 6U (which could be bad (I am suspect as it was not on the car very well)). Looking at AJ6 site and learning a lot about ECUs... anyone have any other suggestions (of course I am also searching this forum!).

 

OK, STRONG COFFEE, and it's midday.

That is a 6CU ECU, catalyst version.

The first snap, NO idea.

I would be calming down, find another ECU, even if its a 6CU, and swap it out, and note if ANYTHING changes. Preferably a 16CU, but us beggars cannot be choosy.

The number of 6CU failures I have had in my time with teh mighty HE is growing constantly.

The 16CU can be from a S3 sedan, same system. Sadly you will need a catalyst version due to lambda probes that we dont have.

What you are looking for are DAC4118, DAC4585, DAC6335. or DAC6337. these are the catalyst ECU's for 11.5:1 comp engines (your market).

We got 12.5:1 comp ratio, and non-cat ECU's with different part numbers.
\We got the catalyst ECU's in about 1988, but still 12.5:1 ratio, which got very confusing with the rest of the world cars.

 

Local XJS hording guru said he has 3 ECUs and he is willing for me to try whichever one I need! He is a great guy and very generous with his time and knowledge (like a lot of the people on this forum!).

Every time I go out there for one part - I normally end up buying 10 parts... I need to get some wheels up to him sometime this week and will be grabbing a test ECU at that time!

Fingers crossed!

M.

 

Quinn,

How'd you make out?

RMPG

 

Still waiting on the local guy to shed his wisdom on the situation. He has a lot of irons in the coals and now I just started a new contract. It has been way too much frustration on something that should be easy. But I am stubborn and will figure it out. Stay tuned.

 

Still waiting on the local guy to shed his wisdom on the situation. He has a lot of irons in the coals and now I just started a new contract. It has been way too much frustration on something that should be easy. But I am stubborn and will figure it out. Stay tuned.

 

Any new word on what the "guru" thinks?!?! Got an 86 recently and I am running into similar issues. Was curious if the ECM was the problem. Don't want to shell out the cash if it's not the ECM. Does anyone know if the 16CU came in other cars that would be less rare to find? perhaps in a junkyard? Someone mentioned the S3 but that it doesn't have the lamda connections... not sure if I read that right.

Waiting and hoping....

 

I did find that at least one of my rebuilt injectors is stuck open - I would like to share the name of the guy that rebuilt it to have others learn from my mistakes with him (he was a very bad communicator - high on his own talent - and delivered me a solution that required me to flip half the mounting plates (not an easy task) because he did not pay attention to what he was doing!).

Going to pull the rail off (again) and have a local shop look at it and see if they can make it work correctly....

Will also be searching the forum here - someone was saying that this is a VERY unique injector for some reason and is very expensive to replace...

The car has just been a yard ornament for all this time... :-(

 

Can you PM me the details of the local XJS parts guy? I'm about an hour north of Charlotte and it never hurts to have an extra parts supplier, especially a local one

 

I had a few injectors off yesterday just to see the condition of them. They appear to be very robust in their design. From what I could see, it would be far better to have them cleaned than to replace them. Thankfully, mine were pretty clean even though I've run some pretty terrible gas through it recently after it's been sitting. On my 3rd fuel filter with one sitting in standby for after this tank of gas.

Good to see some other NC people in here though!

 

A few comments on the injectors in general. They are not unique to this application. Each car needs 2 long hose and 10 short hose injectors. The short hose is a jag part no only while the long hose is used on numeruous other cars. Obviously the hose can be cut down. The injectors are not really rebuilt imho. You can crimp on a new hose, give it a new plastic nose and even repaint the body. The part that counts, the internals and in particular the pintle can be cleaned in an ultrasound bath and flowtested but otherwise the are sealed for life. The problems that you can encounter is gumming up, rust due to water in the fuel and particles getting past the filter/released from piping and hoses after the filter. As a result the injector can stick open or closed or give a bit too much or too little fuel or finally have skewed spray pattern.

On a separate note if you have one or more injectors stuck open pull the dip stick and smell the oil for fuel. If the slightest whiff change the oil before starting again, it is extremely simple to run a big end by diluting the oil.

Have you finally been able to run an USB scope to check the pulse lenght? Btw, the reason for running the bulb onstead of the scope was that it is simpler if more crude. If you rin a 12V bulb it should glow faintly at idle, getting brighter as you increase rpms. From the symptoms though I would expect it to go dark at once when you touch the throttle.