I’m comparing two XJ6’s ('84 and '86) The '86 usually fired up, hot or cold, immediately on the first touch of the starter. However it is becoming intermittently more like the '84 which always requires either the “put it in gear and “operate” the starter several seconds trick” to effect the fuel pump to build up fuel pressure or alternately just run the stater for several seconds, and maybe twice, before it will start.
How long should the non-return valve hold fuel pressure? Is this the first place I should look for a solution to the above situation?
I’ve looked thru the posts and found some discussion recently about the non-return valve and the fuel temp. switch and the clear advice was to install NAPA 3299 filters just aft of the fuel lines coming from the tanks.
The FPR should hold pressure for a few days I would have thought, if not longer.
Unless the filters you are looking at have a non return function then I don’t see them alleviating the problem.
I had that problem on my ‘92 ‘40 and placed a non return valve in the fuel line in the engine bay.
There are two non return valves, one at the air/fuel separator and one at the pump. Both could have failed.
I added an extra non return valve after the fuel filter but also a small circuit that keeps the pump running for about 8 sec when the ignition switch is turned on.
The later made a noticeable difference when the engine sat for a long period of time and at hot starts when there are some vapour lock issues, albeit this is more of a problem on the V12.
The pump will repressurize the fuel rail within 2 seconds, with or without actual cranking - and the engine ‘should’ start within 2 - 4 seconds of that. If the non-return valve has failed; pre-charging the rail prior to starting has no effect beyond 2 seconds. And if pump is stopped prior to actual cranking, pressure will immediately leak down with a failed non-return. So in your long delayed starting the non-return is not a factor - look elsewhere…
However, to check the non-return; connect a pressure gauge to the fuel rail inlet hose and run the pump. Then watch pressure; if it drops quickly/instantly, the non-return valve is the culprit.
As Robin says; a functioning non-return valve will hold rail pressure for days, but over time
pressure will invariably leak down anyway due to dripping/leaking injectors or other leaks. To check; connect pressure gauge to the rail (CSI hose and repeat test…
Adding extra filter will not solve the slow starting, of course - it has other purposes…
I used to have a problem getting my '85 XJ6 to start without some progressively increasing crank time. I found the problem was the dizzy cap and rotor. I thought it was low fuel pressure or a fueling problem, but it was a spark problem.
Thanks for the info. I’ll test with a pressure gauge as you suggest. The thoughts on the extra fuel filters was to directly cure possible tank rust and sediment affecting the working of the non return valve.
I can say that precharging for just a few seconds does always effect both cars starting right up on the first touch of the starter where other wise they take 4 to 5 seconds and sometimes that twice.
I’ve just recently been through both cars with extensive ignition maintenance to good effect; both cars just run great once started, never better!. I checked/rebuilt distributors, checked all wiring, new cap and plugs and leads, dist vacuum hose routing and advance function. I set initial adv. to 17 deg btdc.
As the ign is turned ‘on’ the injectors fire once - and when to ‘crank’ the CSI fire once first time (it needs minutes, depending on temp, to reset before firing again). This ‘pre-charges’ the engine for starting.
Beyond 2 seconds cranking the non-return valve plays no part - so anything less than 4 seconds cranking for starting is ‘good’. Longer cranking implies something amiss - but it be anything. And if just occasionally it may not be worth while pursuing - only consistently slow starting warrants that. Temperature, ambient or engine, and battery status also plays their parts…
Certainly, checking fuel pressure leakdown, ‘raw’ and ‘regulated’, is prudent; it will indicate eventual leaks, non-return or otherwise.
Many moons ago I had an extended-cranking-before-start issue with m XJ6. I did all the fuel system stuff with respect to fuel pressure, non-return valve, etc.
Long story short a new battery solved the problem. I discovered this inadvertently…at 6:00pm on Christmas Eve in a snowstorm. I never sensed that the battery was slightly sub-par but it apparently was.
It isn’t unusual for fuel injection systems to be a bit sensitive to voltage drop. The starter motor consumes tons of amps and a weak-ish battery can’t fully supply both the cranking circuit and the fuel injection system.
One could try cycling the ignition switch ‘on’ for 2 seconds, then ‘off’, wait a few seconds, then repeat.
That should pressurize the fuel rail, and if the pressure begins to leak down through faulty nonreturn check valves, the next cycling of the ignition switch will re-pressurize the fuel rail.
After cycling the ignition switch a few times, on the last cycling turn the swicth to start it.
If it is a fuel pressure issue not holding pressure, the engine should start.
How long does the key need to be ‘off’ before a “second prime”? Minutes, hours, days?
If one drives to fill up with gas, turns off, fills tank, starts, drives 50 feet to park at store instead of stay at the pump, turns off, goes in for a drink (one’s personal preference, of course), then goes to restart … fuel pump doesn’t come back on?
One branch operates from the starter circuit; whenever the starter is engaged the fuel pump runs
The second branch operates from the Air Flow Meter. As air is drawn thru the AFM the air flap opens. This closes a switch to activate the fuel pump circuit.
As mentioned the fuel rail is pressurized very quickly; mere moments assuming a healthy fuel pump. If the cranking goes on for several seconds the fuel rail should be pressurized (a pressure test will confirm) and the hard starting possibly related to some other issue.
I’ll add a bit of emphasis to checking the actual fuel pressure.
Personally I’ve never come across a Series III XJ6 that was an instant starter. A few spins of the starter seems common. An interesting anomaly, never understood as far as I know, is letting the starter spin for maybe 3 seconds then releasing the key. If the key is again turned to start the engine fires on one spin. From my own experience this weirdness is not a fuel pressure issue.
As the decades go by I have to wonder if and how slight degradation of solid state circuits might manifest itself. Perhaps this is something to consider. I dunno.
[quote=“JerryPeck, post:12, topic:444317, full:true”]
…How long does the key need to be ‘off’ before a “second prime”? Minutes, hours, days?
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There is nothing preventing immediate repetitive ‘priming’ rail fuel pressure, Jerry.
For the xk engine; running the pump require the key to ‘crank’ - actual cranking prevented by engaging any gear. In this mode the pump will start every time the key is turned to, or held, in ‘crank’.
Also, the injectors are triggered once when ign is turned from ‘off’ to ‘on’, priming the engine with petrol if there is pressure in the rail. The engine is also primed with petrol by the CSI when ign key is turned to ‘crank’ if warranted by engine temp. This, however, is prevented from subsequent action by the TT (Thermo-timer) - which needs time (minutes) to reset…
If I am understanding you correctly, you ‘lock the starter up’ so it won’t spin/rotate/turn the engine over while you put 12V on it … so you can put 12V on the fuel pump?
By putting the gearshift in D (or any position rather than N or P) the neutral safety switch prevents the starter from engaging
In this scenario turning the key to Start powers-up the primary side of the starter circuit (and thus also powers the fuel pump circuit) while the secondary side (and thus the starter) remains inoperative
It seems then that the triggering of the injectors just prior to cranking provides for an immediate start up but only if there is fuel pressure in the rail. Otherwise one can expect to crank for at least 2 seconds before any fuel is getting to the injectors.
When I isolate the starter relay (by cranking it while in gear) I can pressurize the rail in 2 seconds but if it is fairly cold just what happens to the function of the cold start injector when I next actually crank the engine? I think you are saying that it will not function until the thermo-timer resets some minutes later?
Again it seems I first need a pressure gauge set into the rail to see what is actually happening there. The other good advice I have gleaned is to check the fuel hoses and replace if old and hardened. Adding filters just aft of the tanks seems a good idea if the tanks are old and rusty to better protect the pump and non-return valve.
Since the CSI and Thermotime Switch don’t know that the starter isn’t actually spinning you’ll get the usual spurt of fuel based on coolant temperature. This raw fuel will be waiting in the intake manifold when you DO engage the starter a few moments later.
