XJ6 Series 3 Cycling on acceleration when cold (amende

(Frank Andersen) #21

If as described, Con - connect the two wires together. That will simulate an open throttle at all times - disabling the fuel cut-off function.

Any trouble with the fuel cut-off microswitch should not interfere with starting. Whether the filters installed plays a part is uncertain, they may have clogged up - which is why clear filters are preferred; easily checked visually.

Have tried starting on the other tank…?

xj6 85 Sov Europe (UK/NZ)

(David Jauch) #22

Keep calm about the filters! If you can overtake on the highway everything’s fine. Well, was. I wonder why it won’t start; have you done some idle adjustments? Did you reconnect the AFM? Any vacuum connections fallen off? Does it turn freely? You’ll get to it. In the meantime you can connect the connectors to each other and be fine.

(Con Saris) #23

Frank, David,
Not sure what has happened, Maybe fiddle factor. The only thing that I have deliberably done is remove the fuel pressure gauge after testing for pressure. Then when it wouldn’t start I put the gauge back on again to make sure I had fuel pressure. I did drop a hose clamp down the side of the AFM but got that out and am pretty sure I didn’t disconnect anything (which would have been mainly ignition related in any case). I have ignition spark so all good there. The gauge is still there. It has tried to fire but just doesn’t catch. My thinking about the breathers is that if they were blocked the fuel being pumped from the tank would eventually cause a vacuum which would mean that the fuel will not flow from the tabk making the pump work harder and struggling to make proper fuel pressure. Plausible? I don’t know? I’ll keep working at it but it’s very frustrating> :slight_smile:

(David Jauch) #24

Is the bullet connector from coil to ECU disconnected by chance? (Runs with the injector wiring, connector is somewhere along the coolant rail)? Is it too cold and the cold start injector important for startup?
You will get to it sooner or later.

(Con Saris) #25

Hi David, I was just outside connecting and disconnecting the bullet connector checking that the injectors were opening. All good there. Not too cold either, we had a max of 35 degrees Celcius today. Plenty warm enough. Thinking of taking the car to my local Jag man to sort it out, nothing that money can’t fix I’m sure! Con

(Frank Andersen) #26

If the gauge is still there, on the CSI hose, Con - there is no fuel to the cold start injector. Which sometimes interferes with starting - so reconnect CSI hose to avoid a complication…

Blocked tank venting is not an issue; the powerful pump will overcome tank vacuum until the tanks collapse. You have verified fuel rail pressure - have you checked that the injectors are actually clicking while cranking…?

One sort of verification that there is a fuelling issue; remove spark plugs after some cranking - check if they are dry or wet. If dry; ‘dram’ the engine with a teaspoon of petrol each - replace spark plugs and crank; the engine should fire up and run for some seconds - if fuel is the issue.

You may have an air leak - introduced during work; reinspect air duct from AFM to throttle body. You may increase fuelling by pushing in the AFM flap while cranking - but a non-start may also result from overfuelling rather than lack of fuel. Hence the check of the plugs…

Basically, a mechanic can only do the same tests as you can do yourself - only reason to use one in this case is a fresh pair of eyes…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

(David Jauch) #27

He checked these and it cranks so it would be a forgotten vacuum hose or something else easily overlooked. Removing the plugs is a good tip, maybe it’s flooded or doesn’t want to run… tanks switched and so on but I would exclude fuel. Leaves spark and air. If you’re still unsure just leave the filler doors open :slightly_smiling_face:

(Con Saris) #28

Hi David and Frank, Yep removed the gauge earlier today thinking the same as you Frank. The injectors are clicking away when I connect and disconnect the bullet connector about every two or three times. Will do the plug removal and dramming next. Maybe a problem with the vacuum hoses. I do have a lot of hoses going no where. The hose from the distributor is connected to a spigot at the back of the intake manifold. The hose from the fuel regulator goes to thin air. Not sure where that is supposed to go but has been like this for some time. There are also other hoses which have been disconnected and plugged so not sure about those either. What is the bare minimum hoses that need to be connected. To be honest I have been trying to find out all the connections and there is plenty of help in the archives but they just confuse the heck out of me. I need a simple diagram showing each hose and where it goes.
Something else I just recalled was when I was testing the pressure, the car was actually running ok except for the cycling that started this thread. I noticed that the idling that was reasonably high at about 1000rpm and seemed to be gradually getting slower and slower over about 10min until it got so slow that it conked out. Hasn’t started since. Have tried both tanks. Not sure if this is relavent or not.
More testing on the way,

(David Jauch) #29

The pressure regulator hose goes through a switch at the fuel rail to the intake plenum. You’ll find a spigot there. You can also connect directly if the switch is broken, it is for hot starts.

The distributor should connect to the plenum or throttle body. Subject of debate is how many spigots the throttle body has, I have one and am not sure what for.

The full load enrichment switch (at the throttle cable mount) and AC should see full vacuum just as well. I think at one of the intake runners, 6 or 5, and one can just feel it.

The lowest point of the plenum has a drain that should be capped off. Block every opening you can find.

Fix your vacuum leaks, leave the fillers open for inner peace, and report back: good luck for now.

(David Jauch) #30

I don’t know if these help but the pressure regulator hose is between 5 and 4. Drain is below TB. The display is not exactly correct. All I said is for non-emission versions.

(Con Saris) #31

Thanks for those pics David. I can trace the vacuum line from the fuel regulator to the back of the fuel rail. Is the switch that you mention a brown coloured item that has a slide of cover that the vacuum hose connects too. There is another hose on the side that then goes to the intake manifold? The cover hose is actually cut and plugged and the hose on the side is still connected. I think the cut hose is supposed to connect to the fuel regulator.
There are 2 spigots on the back of the manifold, one is connected to the distributor and the other is plugged.
I found the one on the bottom of the manifold some time ago when I noticed fuel pouring onto the ground. Managed to put a plug on that one as well.

I tried dramming the motor today and it started and ran for about 5 seconds. What surprised me was the state of the plugs. They were very black and sooty. I think this car is running very rich which may also explain why I think the fuel in both tanks is getting very low again despite putting 20 litres in one tank and 10 in the other only a couple of weeks ago. I am going to have to get the senders sorted so I can be more confident in how much fuel there is in there.
Is there anyway to check the richness of the air/fuel mixture without fancy electronics? Is there a default method to get it about right? I know these cars aren’t actually fuel misers but for the fuel to go so quickly must point to an over rich mixture.

(Con Saris) #32

So, I spent a little more time looking for the cause of my problem. Suspecting a drained fuel tank due to a faulty fuel tank sender, I whipped the rear light assembly off and took the sender out. Tested with a multimeter and I am getting a fair range of resistance. Could also see that the tank was about 1/3 full so not out of fuel after all. Maybe the filter is blocked so changed that over as well. At this point I pulled the hose from the intake at the fuel rail and cranked the motor while in reverse. Almost no fuel out. Working back, I pulled the hose from the pipe which is directly after the pump and cranked, no fuel to speak of. So from this either the pump is not pumping, the change over solenoid is blocked even though I cleaned that out on the weekend or there is a blockage in the tank outlets. Maybe the little outlet filters in the tank are blocked up. Looks like I’m going to be draining my tanks again. Does anyone have any thoughts on this?

(Frank Andersen) #33

Well, Con - but do they click while cranking?

The fuel pressure regulator is connected to manifold vacuum - usually using the spigot on the top of the manifold. The dist vacuum hose usually goes to the throttle body - and on ‘European’ versions ; this connection serves other vacuum users, like the AC, by ‘T’ connections. Which explains some loose hose ends…?

In any case; unconnected vacuum hoses/spigots should be plugged/capped until they find a home. While various vacuum diagrams are presented in the Archives - but they vary with equipment level model year and market…so what’s yours…?

The bare minimum is; dist and AC - and brakes, of course. As David imply, if there are two spigots on the throttle body; one has manifold vacuum in idle. The other then has ‘ported’ vacuum used on US ignition - and has no/very little vacuum in idle. However, any spigot on the manifold implicitly has manifold vacuum - but the spigot underneath is a drain as mentioned…

In any case; it’s important to verify what sort of vacuum is delivered. ‘Ported’ vacuum is only used for the US dist - all other users use ‘manifold’ vacuum…

If an engine dies and then won’t start - it is sure relevant, Con…:slight_smile:

While hot engine slow dying may have various causes - there is no obvious ones that prevents restarting a cold engine. Engine rpms is basically related to the amount of air the engine is getting.

Typically, as the AAV closes, idle slows - and with insufficient hot idle the engine slowly and smoothly dies. The AAV then, supposedly, opens as it cools - and the engine restarts.

If fuel pressure drops, lack of fuel will gradually slow the engine, but it will usually misfire before dying. With fuel pressure rebuilt - the engine will restart. Gradually increasing fuelling will again slow the engine - but it will show distress, misfiring, before dying.

The CTS plays a vital part in fuelling, it gradually leans out the mixture as engine warms up. If it does not; mixture stays rich - and the engine will gradually overfuel, and may die. Again; a cold engine will restart. If the CTS fails ‘lean’; it has no effect on a hot engine, but cold start may be an issue…

Failed ignition will lead to misfiring, which will slow rpms - but not slowly. There is one combination. The AB14 module is sometimes heat sensitive - and in some cases; as the idle gradually drop during warm-up, AAV action - the ign amp may reach a cut-off point, and the engine suddenly quits.

However, cooled down, the ign amp may recover and the engine starts cold - unless the ign amp decides to call it quits. In which case there is no ignition and no start. ‘Dramming’ the engine will clarify if the ign is working satisfactorily…

There are probably more possible, or impossible permutation - but getting the engine running is first priority…

For the record; you start an xk strictly ‘feet off’ - engine will baulk if gas pedal is used.

xj6 85 Sov Europe (UK/NZ)

(Aristides Balanos) #34

What do you mean crank the motor while in reverse?
The engine will not crank if not in P or N.
Can you hear the pump working?
Better connect the pump with a permanent +12v for testing.
If fuel is not coming out there lies your problem.

(Con Saris) #35

Sorry Aristedes I meant I turned the ignition key to start so I could get fuel from the intake hose.Like priming. Sadly there wasn’t a lot coming out. I went back to the hose from the changeover solenoid to the tank with virtually no fuel flow when disconnected. There should be a reasonable amount of fuel coming out under gravity but there is almost nothing. Even when I disconnect the line to the main filter and run the pump it pumps but with little out flow. I think I’ve got blocked filters on the outlets to the tanks. Will be better prepared this time to empty the tanks.

(David Jauch) #36

If it’s still the same with the AFM flap pushed open it’s time to go over the fuel system. But you have to fix the vacuum system. Also see if there is liquid in the manifold after your many attempts.

(Frank Andersen) #37

Which indeed is very wrong, Con - even with moderated tank fill it should gush…

Did you do that on both tanks? It is most unusual for both tank filters to clog. And indeed the filters then usually clog as the pump sucks - and debris is sucked onto the filter screen. When switching to the other tank with a clear filter, the debris falls away, while the engine keeps running on the other tank. And after some time the other filter clears and when used; the cycle repeats…:slight_smile:

But didn’t you place additional filters between the tank and the changeover valve. And did you check them…?

xj6 85 Sov Europe (UK/NZ)

(Con Saris) #38

HI Frank,
I don’t know how much fuel is actually in the other tank. The sender needs attention. I decided when I ran the tank down unknowingly that I would just keep fuel in the right tank where the gauge is borderline ok… There is some fuel in the left tank but not a lot. Yes I did install extra filters in-between the tanks and the change over solenoid and there were some finer rust bits in both of them but I am thinking that the in tank filters may be very clogged up. I did empty both tanks a couple of months ago and tried to flush them out but at that stage I didn’t know about those in tank filters so did not remove and clean them. I think I am going to empty the tanks again and just remove them. The new filters should do just as good a job with the added advantage that I will not have to drain the tanks to clean them. Just need the time again, we are currently in the silly season for our industry so free time is in short supply.

(Aristides Balanos) #39

I think you should start from scratch…
Drain your tanks and clean your pick up screens.
Check your fuel senders and that the floaters aren’t full with fuel so you know how much fuel is in your tanks.
Discconnect all hoses, filters and change - over valve, claen and make sure everything works as it should.
There must be a blockage somewhere.
Then check your pump and continue downstream.

(Frank Andersen) #40

It would be extremely unlikely for tank filters to clog to that extent, Con…

Whenever there is no fuel flow from a tank, my immediate thought is an empty tank - relying on fuel gauges is ‘not on’. Which is why I asked about flow checks at the changeover from both tanks - and splashing in a couple of gallons, and retesting is pertinent…

That you have fuel pressure but ‘no start’, signifies a fault unrelated to fuel delivery. Admittedly, I have never checked whether the fuel pump can deliver 36 psi of air at the rail without fuel. It is not an efficient air pump - and I have never heard of 36 psi at an empty fuel rail…:slight_smile:

In short; feeding the pump from an external canister is worth while. Together with the ‘dramming’ test it will be a pertinent overall test of ignition and fuel…

I very much doubt that your problem is in the tanks - but considering the work involved; you should seek conclusive evidence that they are the cause of the non-start before removal. And indeed; the in-tank filters can be ‘easily’ accessed and changed by removing the drain plugs - or removed as you suggest…:slight_smile:

xj6 85 Sov Europe (UK/NZ)