Cold start valve 1985 xj6

XJ
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First identify the fault, Mary Pat - then change parts…

Check pump function as per Andy and Paul. If the pump is not running; remove fuel relay and jump between whiteand white green on the relay base. The fuel pump should now run with the ign ‘on’ - indicating a faulty relay…

With pump running, one way or another; open filler lids and listen to fuel returning to the selected tank. Change to the other tank and repeat. (With a possible fuel problem; always try running on the other tank!).

If there is no return fuel to either tank; either the pump is failing, tank empty or lines/filter blocked. Changing fuel filter is relevant - it’s a regular service item.

These are simple preliminary tests - and results gives a clue, possibly saving money and time. Changing working parts will not improve the situation…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)
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Thank you all for this valuable information. This Jag sat unused for about 4 months after my husband passed away. However, it ran fine until right now,. This Sunday, I, my daughter and grand daughter and my son and son in law are going to change the fuel pump, fuel filter, fuel injection relay and the fuel pump relay, and purge the fuel tanks. A tinplate go though the fuel system. Again, thank you very much and please wish us all luck. My late husband loved this ar and it has never until now failed us. We all want to make it work.

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My condolences, Mary, I lost my soul mate in 09. In her mind, it was her Jaguar ! I only the mechanic and driver.
Fine by me, happy wife, happy life !!! Tales of that in the archives…

The family togetherness is impressive.

Oh, if only I could go back ten years and be “only” 80!!

Great and powerful help here by others.

All I can add is to assure a supply a supply of fresh fuel.

Drain both tanks. Not easy, but surely doable .

The valence behind each rear wheel has a ruberoid plug. Pry it out. You may ruin them.

That will reveal the drain plug, Jaguar complicated. Small with in the large. Prep by getting new seals.

And have big catch pans. Open the “large” one and drain each tank of old and possibly dirty fuel.

Peer in. the pickup pipe will have a “sock” , Good, perhaps. If I knew then when I did that, what I have learned, I would have replace them or even just eliminated them. More on that in a bit,

Be prepared, to handle lots of old gas !! I thought I was. Nope, not a by a lot!

Now, the preemptive part. I learned of it too late to install at the time. Credit past lister Bruce Hugo and pal Doug Dwyer, invaluable present lister.

The pipes from the tanks to the fuel pump are not high PSI rated, but only gravity, Cut and insert non Fuel injection filters. Objective : Protect the pump from tank debris… A maintenace item to swap in on replace as needed.

Bonus., Much cheaper than the after pump Jaguar filter. And protects the expensive pump.

Welcome and keep us posted !!!

Carl

g // es/ g!!et \sI ; eh ls se tt

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Mary,
We are all rooting for you and your family to get you car running again and we will do what we can to help.
Carl mentioned two things about the fuel system that I thought I should clarify. First, the fuel tanks can hold up to about 12.5 gallons EACH if full. You can not trust the fuel gauge to give an accurate reading of tank quantity. So you must be prepared to safely handle a lot of fuel (up to 25 gallons) when you drain the fuel tanks. Secondly Carl mentioned the extra aftermarket fuel filters that some of us have added between the fuel tanks and the changeover valve in the trunk area to protect the changeover valve and fuel pump from fuel tank debris. Attached is a picture of the fuel filters that I added to my 1987 XJ6 Vanden Plas years ago after experiencing random fuel pump problems. After adding these fuel filters I have not had another fuel pump failure. These fuel filters are inexpensive and good insurance in my opinion to prevent fuel delivery system problems.

Paul

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Thank you so much! We are going to all of it tomorrow. I have said a rosary for all of you that have helped. Many don[t think this does not help people and that is okay, but it can[t hurt…
Mary Pat

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I do. And thanks

Carl

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Play. We rep[aced the fuel filter, fuel pump, purged the fuel tanks, a wee bit of rust on the right one, but clean otherwise. Put brand new high test gas in the tanks, replaced the fuel puma relay caner filter. and fuel injection relay and checked the cold start valve, cleaned it, lubricated it and iit seems to be right. However, the idle is still very low and bumpy until it gets warm and still is not good, though we adjusted the idle. My son thinks the injectors are dirty. We want to spray in sea foam throttle body and injector cleaner though the intake. However, do you take off the air meter first to do this. A fellow named xj Jesse by passed the air meter when he cleaned the system. Which one is the correct process and is his the way to clean the injectors? Thank you very much for all your help. Mary Pat

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Mary, the injectors won’t get any cleaner if you spray seafoam into the intake. To get them clean you would need to get cleaner inside of them. Some say Techron is a good additive.
However, if it is slow and rough only during the warmup phase, the injectors are of no concern: if it starts well from cold, the cold start injector is working and if it idles reasonably well when it is warm, the injectors are probably fine. Some unevenness is normal.
I wouldn’t use Seafoam into the intake at all.

You seem to have a problem during the warmup phase, so it can only be the air valve you cleaned or the temperature sensor that talks to the ECU.
Good luck,
David

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I assume you set the idle with the engine hot, Mary Pat (verifying that the AAV was indeed closed) - and to somewhere between 800 and 900 rpms…?

And indeed that the AAV is then half open when cold. The slow cold idle is usually lack of air - though fuel starvation cannot be excluded…

Have you checked and cleaned the throttle body (disconnecting the air duct for access) and checked throttle gap to the correct 0,002"…?

A hot engine gets air from the throttle gap and the idle screw. When cold, the AAV adds air to compensate for cold engine drag - which otherwise would slow down idle. In both cases, the amount of air generally decides engine rpm - otherwise controlled by throttle use…

As David says; if the engine idles OK when hot; the injectors are likely OK - they cannot, by themselves, vary fuelling hot or cold. Injectors cannot be cleaned by spraying anything into the air intake; cleansing medium must pass through the injectors…

However, if hot idle is ‘not good’ (xk engine is seldom smooth) - it warrants some attention…

Have you actually checked compression? With uneven compression idle cannot be even - and compression is conclusively testable…

Frank
xj6 85 Sov Europe (UK/NZ)
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I tend to agree with David… Chevron gas is noted for it’s Techron content. A bit more pricey around here than that of other gas stations. It is also sold in the can at parts places. At times, I’ve run one tank down to about 1/4.

Added no more than 5 gallons of Chevron’s high test
More Techron??? .Then to the same tank add the full can intended for trucks!! Objective, lots of Techron. drive… My seat of pants is that it runs better…

There are "kits"to cean injectors. Splice in the fuel supply line. Engine runs on the mix. No experience here by me.

The best is the time tested. Remove them. Send them to a specialist. David Faircloth, fuel injection service.
Somewhere in FLA. Posts here at times. Good guy. good work…

Aye on a wet and dry compression test as per Frank’s recommendation… Tells alot…

Carli . .

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Thank you so much for this advice. The temperature sensor sounds like the most likely culprit. Where is the temperature sensor located? Its this part still available.? Finally, I want to contribute some $ to this forum. Is there an address I can send a check to? Thanks again so much?

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Mary if you scroll to the top of the page there is a donate icon third from the left.

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Mary,
Do you have a copy of the small ivory colored Jaguar “XJ6 SERIES III MAINTENANCE HANDBOOK” that is one of the owners manuals originally supplied with the new car? If you do there is an excellent section on Electronic Fuel Injection on pages 50- 56 with drawings of the component location and descriptions of how they work.
The attached picture shows the Coolant Temperature Sensor (CTS) in my 1984 XJ6 Vanden Plas circled in red. The Jaguar part number is EAC3927 and it is readily available through the suppliers that I provided in an earlier email to as well as on eBay. Often the problem is with broken wires or connectors and not the sensor itself. On page 74 of the same document there is a table showing how you can test the CTS to see if it is working properly.

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Paul

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It is easily tested with a multimeter, Mary Pat - to tests are required…

Ohm the sensor, the resistance vary with coolant temp, and a precise temp/resistance chart is given. However, as a rough test; at 10C (50F) - resistance 3,7 Kohm. at 80C (176F) around normal operating temp, - resistance 325 ohms.

If the resistance is very high when cold, and low when hot, the sensor, CTS, is an unlikely culprit. It simply varies mixture from ‘fat’ (cold) to ‘normal’ (hot) - and a rough test is just to unplug it with the engine running. CTS working properly; unplugged cold, around freezing point, it has little effect - engine is already running fat. Unplugged hot, engine will overfuel and likely stop…

‘No change’ when unplugged; disconnect connector and measure resistance between the two wires. It should be around 2Kohm - and importantly; should not vary when bending the connector or wiring.

If sensor or wiring is shorted, 0 ohms, the engine will run lean at all times - and idle will improve as the engine warms up. This is easily verified…

Changing easily testable items without testing them is waste of time and money - items working to specs cause no problems…:slight_smile:

That said; items making no change provides spares - which might be useful later…:slight_smile:

Incidentally, with the engine running; clamping the AAV hose is a valid test. Clamped cold with a working AAV the idle slows down (or stops) - with the engine hot; there is no idle change…

Frank
xj6 85 Sov Europe (UK/NZ)
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From my experience with two XJ6’s, a 1986 & 1987, over time, two things occur: 1) coolant temperature sensor goes bad or 2) the ‘pigtail’ connector or the wiring connected to it goes bad from years of heat exposure and wear. On the 1986 car, I was able to get a new pigtail connector and solder the wires together. Since the car has never been entered in champion class in the concours, it didn’t bother me. On the 1987 car, I experienced the same problem but purchased the connector from a different supplier. In this case I did not solder but used crimp connectors and electrical tape. It’s been more than five years since these developments, and I’m pleased to say both cars start up cold with no problems. Since the post began, I had a feeling the CTS or its connectors was the problem. That’s not to say it couldn’t have been the AAV. That item I had to replace in the 1986 car five years ago as well. With these cars, information is king.

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Thank you very much for this info. And yes, knowledge is everything if you want to keep these cars running. This Sunday, all my children and grand children and son and daughter in laws are coming over for my friend chicken which is really really good sand then we are all going to work on the Jaguar with the booklet that I do have and get to work on this car. Then we are all going for a ride. Thank you all again.

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Well, we’ve done everything instructed so far, including changing the spark plugs, distributor cap and rotor. All looked good when changed. At this point, we think it may be the fuel cold start injector–no change when we pulled it out and in, the distributor itself, or the mass air flow meter. Idle still in up and down al little better when hot but not by much. Again idle hunts and almost dies but runs well at high RPM.

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Bear in mind that the cold start injector can operate only with the key turned to the ‘start’ position. At all other times it is inactive.

Now, if the cold start injector was leaking, that could cause running problems.

Did you check (or replace?) the Coolant Temperature Sensor, by the way?

Cheers
DD

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I bet it is not the cold start injector, Mary. The only check you might want to do on that is to clamp the fuel hose to that injector. It really is a separate circuit and only active as per Doug.

If it is not the fuel pressure and not the injectors, go back to step one and check for air leaks and of course the temperature sensor.

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My son-in-law has double checked everything and he thinks it might be a distributor. Does that sound possible. After everything we did nothing got better When my husband got the car it has a very very slight miss at idle. This problem got worse. Also, could it be the air flow meter. My son told me that my late husband took the air clear assembly off and used throttle body and duel injection clearer, I think it was called B-12 and spayed it into the air meter and into the engine. Actually, that made iit idle better for a while. However, I’m afraid perhaps this may have hurt the air flow meter as it is suppose to be very delicate. Anyway, we do not want to take it to a repair shop because the two here are not nice people. One of my husband’s friend took his Jaguar to a shop here and they charged him $246.00 to tighten a battery cable. We are really on our own here in Colorado Springs In summary, thank you gentlemen for your help. We will persevere. Thzanks again and God bless