'86 XJ engine issues - need help

XJ
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workshop manuals…
store.otpubs.com/brands/Jaguar.html ($90 US dollars) is a great resource for online manuals for the car. From what I’ve been told, and what I’ve dug up or haven’t; there isn’t a multi-volume manual (for example, the XJ-S) for the XJ saloons. I’ve got a couple Jaguar “service Manuals” what I refer to is the green bible - the single volume manual that I purchased from books4cars.com ($119.00). Personally I’ve found it more or less useless as a step by step guide on how to troubleshoot any problems. the OTpubs variant does have some troubleshooting guides - however the service manual is the same as the “green bible”, the only draw back is the trouble shooting includes specialized Jaguar equipment that is more or less non existent. Like the ECU tester.
Where and what is this stuff?

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EFI Diagram

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Welcome to the ownership of Jaguars. Once you get the hang of it, these cars are pretty simple to repair. Easier than my '02 8.2 litre Suburban; and believe it or not, cheaper too.

Cheers!
Mark

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One of the reasons the ‘bibles’ are scant on troubleshooting, Mark, is that there are few people writing manuals that has ever done any troubleshooting…:slight_smile:

Nevertheless, manuals are absolutely essential - and necessary to rectify faults - when they are found. The main difficulty is, however, is that owners only read manuals when a fault appears - and with little knowledge on how things work it is an uphill battle. And the manuals are not meant as pupil primers; some, like factory manuals, are written for experts - and most assumes some prior knowledge, or at least some ability to know symptoms of faults…

Not that I disagree with you - some manuals are better than others…

Frank
xj6 85 Sov Europe (UK/NZ)
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@Frank_Andersen - I should be getting some parts delivered today. I’ll work on the Jag over the weekend and then post the results.

@MLee - thanks for the tip on the manuals. The drawings you posted are very useful. Did they come from the manual you mentioned?

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Adam,
Those drawings look the ones found in my hard copy versions of the Jaguar Series III XJ6 Electrical Guide, Jaguar publication S-57. This is a very helpful technical document to own. It includes drawings of the electrical equipment components, shows where they are located, and includes wiring diagrams system by system with the wire colors shown. I use it regularly and I couldn’t keep my two Series III XJ6s running without it. I purchased my hard copy documents on eBay several years ago. They were in a geen three ring binder that was part of a dealership technician training package. I have heard that they are also provided on the Jaguar CD and available online but I much prefer having the hard copy document to hold and add my own notes on the pages.

Paul

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The drawings I had before I purchased the manual, but in some fashion they are included. If memory serves me.

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Me too. The manual from OTpubs.com has does have a troubleshooting sections, plus training guides, which I found very useful. I’m working on a Series III (a grey one) that would start right up, and run great, then for whatever reason it would start to run really rough, then die, but then would start right up again and run fine. At first I thought it was bad gas because there is something in the tanks preventing the car from taking more than a couple of gallons of gas at a time. I’m not really sure what prompted me to pull the cam covers, but when I did I discovered the intake cam had a considerable amount of slack in the timing chain. The training guide showed me how to take up the slack. Now I’m performing the miserable job of gasket scraping. The last person who had the cam covers off used Permatex gasket adhesive, the stuff that dries hard like cement and is really hard do get off. This will become day two. I have the exhaust side cleaned up, a half of cam cover done so far. UGH!

That’s were I’ve been lately, scraping gaskets.

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While the cam chain slack should certainly be fixed, Mark - I can’t see how cam mistiming can cause the symptom described…?

Permatex has its uses, but not there - and using it in conjunction with gaskets is counterproductive, and dismantling indeed labour intensive…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)
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Hello again Jag experts, it’s been awhile since I posted and I wanted to give an update on the testing and see if I could get some more help.

Firstly, I got my green bible and a Haynes manual. So I’ve been trying to do my homework before just posting to the forum.

Newly Installed parts:
Coolant Temperature Sensor
Spark Plugs
Spark Plug Wires
Distributor Cap and Rotor
Alternator (Not fun to change)

Procedures:
Tested Fuel Pressure / Fuel Pressure relief valve - approx 35 psi when cranking
Cleaned and gapped the throtle body (RPM’s increased by about 300)
Checked the Auxilary Air Valve which I believe it’s working correctly

What’s weird about this problem is when the temperature is cold outside the engine seems to cold start easily. When the engine is hot it’s difficult to start but after some cranking, it will usually fire up. When the temperature is warm (80-90 F) it’s almost impossible to cold start. Often, if I hold my hand over the opening to the Mass Air Flow as to choke the engine I can get it to start. This feels like a fuel or timing issue. Any advice on what to troubleshoot next would be greatly appreciated. Also, I bought another 84 XJ6 off of ebay. I love these cars…

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It very well could be. the injector pulses come off the negative side of the coil. I had the same issue with my '85 Series III Wouldn’t start initially, then spark plugs and grounding clean up. started and ran great until it was warmed up. then it was hard starting. Wait a bit for the engine to cool down, then it would fire right up. I got stuck at Starbucks and ended up running across the street to a Performance Auto Parts store and picked up an MSD Coil; installed it in the parking lot at Starbucks (how embarrassing) and it fired right up, and believe it or not it ran much better and has better acceleration.

One thing to remember, electrics & especially electronics don’t like heat. The coil is located on almost the hottest part of the engine on it’s side. At least with the V12 it’s away from the engine on the other side of the engine compartment. Coils are filled with oil, and technically aren’t supposed to be on their side because it may inhibit the isolation of the primary and secondary coil as well as causing the primary coil to over heat and possibly short against itself. The oil works as an insulator between the primary and secondary windings as well as a coolant.

How a coil works
Coils are constructed of two coils of wire wrapped around a soft iron core. The primary and secondary windings are connected to the positive side of the coil, the negative is just the primary winding, and the center is connected to the iron core. The primary winding contains fewer (a couple hundred) windings of thicker insolated wire wrapped around the secondary windings. The secondary coil contains thousands of fine windings located inside the primary windings and wrapped around the iron core.

When turned on, the primary circuit creates a magnetic field as current passes through its windings. This magnetic field passes through the secondary winding and soft iron core. This induces voltage in the secondary windings. When the primary circuit is suddenly opened, ZAP! voltage passes through and is multiplied to thousands of volts by the secondary’s many fine windings. This high voltage is then passed on to the spark plug through the secondary circuit. The more windings a coil has, the more voltage it will produce.

Oh and one thing I always do, and has proved to resolve many electrical oddities. Check the grounding points.
The first thing I do when I get a new non runner, I start by cleaning up the connection points with some non residue (leaving) electronics cleaner. (CRC electronics cleaner). Then either wire brush or sand off any oxidation at the grounding locations (shiny metal). Then coat with a bit of dielectric grease or preferably OE color paint (I usually have the OE color mixed up in a spray can for this purpose).
I squirt the contact cleaner in both ends of the burrito looking butt connectors and squirt a bit of dielectric grease to keep out moisture too. A good number of oddities with the cars can be traced back to a pour connection but usually a bad ground. There’s also a grounding strap under the car that goes from the engine to the frame. Often these get soaked with oil, which will add resistance in the grounding strap, and has been known to cause electrical weirdness. I hit it with a bit of brakekleen then clean the contact points, sand off any oxidation, Check to ensure the strap is intact. they can get a bit frayed; then bolt it back tight and hit it with paint or dielectric grease. Seriously side tracked.

Check the voltage across the coil should be around 12.68 volts (or if memory serves 1 volt less than the battery. Check the contacts on the coil, and the rectifier (which is connected to the negative side of the coil as well as a lead to the diode pack on the bulkhead - it’s the red plastic covered thingy that looks like a relay. pull the connections off and clean them up too. never hurts. The diode pack is sends the signal (via the coil) to the ECU to let it know it’s time to fire off the injectors.

Hope this helps
Mark
Oh, theirs a couple of posts similar to this mine “Another XJ6 that won’t start” and another about a died on a short trip… check them out.

Cheers!

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“…the AAV which I belief is working correctly”; ‘belief’ is not enough, Adam…:slight_smile:

The xk is a strictly ‘feet off’ starter - touching the gas pedal; the engine is prone to baulk. To obtain this, the AAV, throttle gap and idle screw setting is working together. They give the engine just the right amount of air for prompt starting, 2 - 3 sec or less, at any temp…

The only temp variant is the AAV; gradually closing as coolant temp rise - a heating coil makes it close faster. The point being that once starting to warm up the engine needs less idle to run satisfactorily. And while driving, the AAV effect is insignificant compared to the open throttle…

While engine cools down; the AAV gradually opens, and ideally takes the correct position for the necessary amount of air. If incorrect, the engine may baulk when warm/hot - an indication of AAV function is the idle when started…

Depending on ambient air; ‘cold’ idle should be some 200 - 400 rpms higher than hot set idle - caused by the AAV opening. Which, while ‘cold’, slide is about 1/2 open - and fully closed with engine warmed up. You can check slide opening in-car at various temps - like at ‘cold’ start, say 80 - 90F when your engine baulks. It is not conclusive, of course, but may offer clues…

The AAV can be tested out of the engine by heating and cooling - observing slide movement. Due to the build-up of gunk in the slide tracks, the slide may be erratic - ‘massaging’ it with a small screwdriver, the slide is moved by a bimetallic spring, may ease the slide movement…

As a crude test; you may ‘strangle’ the AAV by clamping the air hose to it - engine may get too much air for effective starting…

While engine will start OK at various idle settings; it is important that idle is set with engine fully warmed up. And the AAV slide must be fully closed when hot idle is set - otherwise cold/warm starting may be affected. As a curio, when doing shopping, the short cooling may throw the system off kilter - the AAV and engine doesn’t quite agree. This shows up as delayed starting - and the idle, when started is lower than hot set…

Some components, like ign amp and coil, may become heat sensitive - impairing ignition. Usually this shows up with the engine hot, whether starting or driving. Ignitions should then be tested; connect a spare plug, triple gapped, to any plug lead - and observe spark quality. Which should be strong and blue - but it should be counterchecked with engine cold, to see any noticeable differences. A weak yellow spark may still run the engine effectively - though indicating impeded ignition…

With temp related problems, the resistance/temp gradient of the CTS should routinely be measured - including wire/connector integrity. Just changing the CTS may be insufficient. Indeed, changing components without some verification of their status is not really ‘best practice’ - components working to spec cause no problems…

As for ‘choking’ the engine by blocking the AFM inlet; this effectively stops air flow through the AFM. This means less deflection of the AFM flap - and the flap position tells the ECU how much fuel should be delivered. Ie, ‘choking’ the engine this way prevents both air and fuel to the engine. Which may have some diagnostic value - engine response may tell something. Or the engine may have started anyway - one method if the ECU is confused, is to crank WOT…

Frank
xj6 85 Sov Europe (UK/NZ)
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@MLee - thanks for the feedback on the coil. I wouldn’t have thought to look at that since the car runs so well when it’s driving down the road.

@Frank_Andersen - Frank, you’re a wealth of knowledge which is very much appreciated. I didn’t realise the AAV could be tested off of the car as I thought it needed electricity to activate the valve. I’ll pull it off tonight and put it in the freezer to see if it opens up. I’ll also test the spark as you mentioned.

You also mentioned that the only temp variant is the AAV. Doesn’t the thermo time switch activate the cold start injector? I did pull the lead off to check for voltage at the CSI, but I’m not sure what temperature it kicks in. Thanks again for the feedback

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I’m not sure that it was the cause, One thing taking up the slack did quiet things down a bit.
Oh, By the way. The Acronyms are losing me on this thread.
AAV - figured that one out Aux. Air Valve. only because I was reading up on air fuel training material so I could figure out why the fuel pump isn’t firing when there (wasn’t) something stuck in the Air Flow Meter.
CTS - Coolant Temperature Switch, Right? I gleaned this by reading through the thread.
ECU - we all should know that is.
WOT - Haven’t got a clue.

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Mark,

CTS is Coolant Temperature Sensor and WOT is Wide Open Throttle.

Paul

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Thank you Paul. I appreciate it.

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You’re absolutely right, Adam - the thermotime vary the duration of the CSI spray with coolant temp…

Extracts of specs durations; 8 seconds at -20C, 3,5 sec at +10C, and 0 seconds at +35C. The TT picks up heat from the coolant, a bimetallic spring ‘makes’ (cold) and ‘breaks’ (warm) the ground connection to the CSI. In ‘crank’; power is applied to a heater coil - which heats the spring, breaking ground…

While the time/temp relation can be precisely checked with a stopwatch; a crude function check is simply to disconnect the TT plug and measure resistance between the two TT pins. Cold, below +35C you will read the resistance in the heater coil - above, you will read ‘break’…

Since the engine starts OK when cold the TT/CSI probably functions then. But if the CSI sprays with the engine warm/hot; overfuelling may cause the engine to baulk. However; the only way to positively eliminate the CSI as a hot start impediment is to clamp the fuel hose to it.

When testing the AAV you will notice that the opening is but a little different between fridge and freezer temps. No spec opening is given, about half open with engine ‘cold’ is usual - but it may vary with individual AAVs. But it is important that the slide moves smoothly as temp changes.

Easiest to check while heating the AAV engine operating temp - the AAV should end up fully closed. Then let it cool down, watching slide moves smoothly to its open position. Be aware that the AAV reaction to temp changes is rather sluggish - it has to absorb heat before it reacts…

The AAV may work perfectly, as may the CSI/TT. But verifying that things work is just as important as finding faulty ones in the diagnostic process…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)
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@Frank_Andersen I pulled the hose off of the AAV and was able to see that the valve is closed @ 85-90F. I also pulled the hose off of my second Jag and it’s also closed. Before I pull off the AAV, I wanted to see if you knew at what temperature the valve starts to open and at what temperature the valve should be closed. I’m starting to think that the AAV is bad but I thought I would get your thoughts before pulling it off completely.

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There are no specs to answer your question, Adam…:slight_smile:

However, while the intermediate slide positions, with ‘semi warm’ start, may cause starting issues; the general test, ‘fully open’ with engine ‘cold’ and fully closed when 'hot - is adequate.

Backed up by verifying that the slide opens and closes smoothly. If so; starting difficulties only when ‘cold’ or only when fully ‘hot’ is unlikely to be due to the AAV itself…

When the engine is running, the AAV is less important, but it ensures that the engine doesn’t stall during initial warm-up when you have to stop the car in traffic. It’s basically a starting item - at speed it is redundant…

To elaborate; the AAV and CTS/ECU function together to give same choke function as a manual choke on carbs. The AAV functions as a fast idle cam varying with temp - the CTS indicates coolant temps to the ECU to enrich mixture. If not entirely ageing; the result is the same as miss-setting a manual choke - engine may baulk when starting…

Frank
xj6 85 Sov Europe (UK/NZ)
**

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I was looking through my manual, and I can’t tell if the AAV will require a gasket to pull off and replace. Can someone tell me if I need to pre-order a gasket to pull the valve? Does it go inside the coolant rail?

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Adam,
Heat is transferred from the coolant rail to the Auxiliary Air Valve (AAV) by conduction. Two Torx screws (T30?) hold the AAV in place against a flat plate surface on the coolant rail. There are no gaskets or seals between the AAV and the coolant rail to worry about or order.

However, there are two rubber hoses connected to the AAV and they can get hard and brittle with age. I have had one or two crack and break on me when I removed them. The hose that you can see between the AAV and the Air Distribution Block is EAC1596 and the hose that you can not see that goes from the rear of the AAV to a nipple at the rear of the Intake Manifold is EAC1471. If in doubt, you might want to get these two hoses to replace the ones you have just in case they break on removal.

Note that Jaguar has also referred to this device, EAC3883, as the Extra Air Valve (EAV). I have no idea why they called it the AAV and EAV. Just another reason for me to sit back and think “my, isn’t that odd?” or something similar. :wink:

Paul

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Just plain metal to metal contact as Paul says, Adam - you may find either torx or ordinary hex, neither easily accessible…:slight_smile:

When unbolted; initially lift the AAV just enough to see the ‘lower’ hose - it is very little slack. If it looks OK it likely is functional. Ensure that hose does not slip off and disappear - it complicates matters unless you plan to change the hose…

Frank
xj6 85 Sov Europe (UK/NZ)
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