I previously started a post regarding the fuel tanks, fuel return, etc. Okay got all that stuff taken care of. Had to order a new fuel pump and switchover valve. Jag has been sitting for two years and you know what happens with that DAMN ALCOHOL FUEL! If only they would outlaw that stupid stuff!! Anyway I now have fuel up to the injection header. But engine seems like it would run if it had fuel. Question if it seems to have a good flow of fuel up to the injection header assy, why won’t it run? I am not as familiar with a fuel injection engine as with a carburated one. I am wondering if the header is building up enough pressure and if not why? There seems to be no access to check on the header pressure on this 1986 XJ6. Confused at this point and wondering if anyone can shine some light to help me with my problem.
Clogged injectors? Can you remove them and see if they are spraying fuel?
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Fuel up to the fuel rail and injectors is worthless without proper pressure, Lee…
With carbs the fuel is ‘sucked’ into the manifold (actually; delivered by atmospheric pressure) - with fuel injection the fuel is forced through the injectors a 36 psi (xk engine).
The usual pressure test is to disconnect the fuel hose to the Cold Start injector and use a pressure gauge to check rail pressure with the fuel pump running. Some 36 psi, regulated by the fuel pressure regulator. A further test is to check ‘raw’ fuel pressure - connecting the gauge to the fuel rail inlet hose; 100+ psi with an ‘as new’ pump. But at least some 60/70 psi…
A crude pressure test; listen at the open filler lids while running the fuel pump. With adequate pressure (functioning pressure regulator) you should hear fuel returning to the selected tank. No fuel return; inadequate fuel pressure - faulty pump or clogged feed lines…
With spec fuel pressure; the injectors may be clogged, as Robin says - or the injectors may not operate. Have you verified that the injectors are ‘clicking’ while cranking…
And further; have you verified if you actually have sparks? And also; bear in mind that excess fuel may also prevent starting. After cranking; have you checked if plug/plugs are wet or dry…?
Frank
xj6 85 Sov Europe (UK/NZ)
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Frank as always you always have a wealth of info. Let me answer each
of your sentences. Boy I was into checking the rail pressure on a
different Jag several years ago but forgot all about how to. Can’t
even remember much about where the cold start injector is. There is
some part on the forward part of the rail. Is that the regulator?
How much pressure should you have from the fuel pump going into the
rail. Did not check the pressure but there seems to be quite enough
fuel there. The auto ran for just a brief period but then quit. If
we spray starting fuel into the air inlet, it wants to start but
will not continue running. I could see no way to check rail
pressure. Would it be the same as the pressure where I disconnected
the rubber hose that was coming from the pump? Where is the
pressure regulator located? Checked all the injectors and they were
dry with the exception of the rearmost injector seemed a little wet.
Yes I must have spark because it will run for just a brief period.
I will try to dig more into the literature to bring myself a little
up to speed again. Do you have any suggestion of a write-up or
anything in the forum which would describe the part of the fueling
system (rail etc) that I apparently am having trouble with? How is
the rail pressure obtained. Is the fuel pump capable of providing
36 psi? Have to find out where the cold start injector is according
to your message. So rusty on this.
Lee Noga
Lee, the regulator is at the front of the fuel rail (or pre-82 the can-looking item). It looks like a can, has fuel in, fuel out and vacuum connections and should hiss a little if the pump runs.
The cold start injector has the blue connector. disconnect the fuel pump and crank the engine (although, in your case…)
Then, use the spigot to feed the cold start injector to connect the gauge instead, ideally with a longer hose.
Reconnect the pump
Put the transmission in drive
Turn the key to crank for a few seconds, listen for the pump, look for pressure.
If none is obtained and no flow into the tank, but the pump runs, disconnect the feed to the fuel rail in the rear of the car. Dry?
Then disconnect the fuel filter in the trunk. Dry?
Check pump polarity.
Disconnect the battery.
Clamp the hose between changeover valve and fuel pump. Disconnect the fuel pump. Have a rag ready. Dry? If so, fill tanks. If wet, trial run the fuel pump and see if it pumps anything.
Should the pump run, disconnect the white bullet connector that is part of the same wiring loom that feeds the 6 injectors. About in the middle of the water rail (black). With ignition on, listen for it clicking sporadically when you dis-and reconnect that wire to see if the 6 fuel injectors would inject. What you have sounds like no fuel and is probably easily rectified. Or all injectors are in fact clogged.
David
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The cold start injector is the ‘7th’ injector on the inlet manifold, Lee - the pressure regulator is mounted on the front of the fuel rail. Has a vacuum line connected - no electrics…
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Negative - the fuel pump delivers up to 100+ psi to the rail
. The pressure regulator bleeds off fuel to the return lines, reducing pressure to injection spec - 36 psi when tested with the fuel pump running…
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This opens different can of worms…
An engine that starts has fuel and ignition - that it fails to continue idling may have several causes, including a fuel issue…
The invariable first step is to check if the fuel pump continue running when the ign key is returned from ‘crank’ to ‘run’. If the fuel pump stops, the engine may continue to run briefly on residual rail fuel…
To eliminate one factor; remove air filter and prop the AFM flap in the AFM open. the fuel pump should then run whenever the ign is turned ‘on’…
If pump runs as it should in these tests; the problem may be in the engine’s idle settings - an engine that cannot idle will not run on. the xk engine is a ‘feet off’ starter; any use of the gas pedal during cranking may cause engine baulking - and idle settings must be correct for proper starting/idling…
Three factors affects idle rpms. The throttle gap should be checked - and set to 0.002". Disconnect air duct at the throttle body for access, measure throttle gap and adjust as required with the tiny throttle stop screw. (And clean the throttle body - dirt may restrict air flow…
The idle screw can only be adjusted with the engine hot and running - and set to some 800 - 900 rpms…
At cold starting; extra air is provided by the AAV - a square base with a ‘tower’ and an electric contact. (Bolted to the inlet manifold below the AFM).
The extra air increases cold idle rpms to overcome cold engine ‘drag’. If the AAV is not working the engine may stall after stating.
To check AAV; disconnect the air hose on the top of the AAV and peer inside. A slide is moved by a bimetallic spring to open and shut the air passage according to engine temp.
The AAV should be about half open with the engine cold - and shut with engine hot. If your slide is closed cold; use a small screwdriver to move the slide. Over time it may stick in accumulating go - and may be freed with some exercise…
The idle setting checks should be carried out to eliminate the possibilities that this is the cause of the problem. If seemingly OK; David has elaborated on the fuel system checkout to be pursued…
Frank
xj6 85 Sov Europe (UK/NZ)
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So Frank how best to troubleshoot this? Questions from a dummy! If
the pressure from the pump puts out about 36psi, how does it get up
to 100psi? I disconnected the fuel line at the inlet to the rail
and had plenty of fuel there but did not check the pressure. Should
I? What should it be just cranking the engine?
Lee
The pump can produce 100 psi or so.
The regulator keeps the fuel rail pressure at ca. 36 psi and bleeds off the excess, hence the return!
If you measure against the hose that enters the fuel rail, you’ll deadhead the pump - 100 psi.
If you measure at any hose to the 7 injectors, you‘ll see 36 as the regultor can bleed off the rest.
In your case, measure at the cold start injector as I told you and see 36. that should do it for idle.
Thanks David, I’ll try that this morning
Lee
I don’t know what documentation you have, but I found the online product from OTpubs.com proves very helpful. there is a supplement (to the manual) that has the steps to diagnose the fuel injection. The documentation is well worth the price tag.
That being said, my '86 Series III had the exact same issue after I repaired the other issues, alternator over charging, battery, coil, ignition module, all cooked. all said and done, it fired right up, got to the top of the hill on my street - quit. wouldn’t start to save my sole. got it home - long story short - the intake timing chain had a bit of slack. fixed that now the car runs great!
What was the condition of the vehicle when you parked it two years ago?
Have you completely ruled out ignition? more often than not, a Jag that won’t start is ignition - well that’s been my experience. The only time that wasn’t the case is on the Series II where the carbs where clogged with a goo that was a by product of the reaction of the ethanol in the fuel and the metal the carb is made up of.
It’s been my experience if the injectors aren’t completely plugged - even bad gas will fire. not well, but it will fire.
after many attempt to fire the thing up, have you pulled a plug to see if its wet? an indication if there is actually fuel where it’s suppose to be? And consistent between all 6 barrels, then I’d clean / replace the plugs and take a gander at the ignition,
otherwise,
This is how I diagnosed my fuel system. Starting at the engine bay and working backwards. amazon.com has a fairly inexpensive fuel pressure tester has a bunch of different connection types and which works very well. I’ve also used vacuum guage with a mix of fittings fittings to go from fuel hose I popped off the fuel rail, to the inlet to the vacuum guage. Besure to use a longish hose. the fuel will compress the air pushing the vacuum guage backwards, (mine didn’t have a needle stop) pretend you’re dyslexic and count backwards. The reading will be the same.
if check out there, then take a peek at the injectors. Now before you proceed. I would STRONGLY recommend having a set of seals, and replacement injector hoses. because once you pull the injector it will require a new seal in order to keep it from leaking. It’s not uncommon for Jags to burst into flames. Typical cause is fumes igniting. The coil IS sitting just above the injector rail. Just say’n.
If the pressure isn’t what it should be then, head to the boot @Davidsxj6 is spot on.
Hope this helps a bit.
cheers!
Yes 36psi at the injector rail will suffice.
Okay did a little testing this morning. Removed one of the injectors and they were dry and when I turned the engine over nothing came out of the injector. Applied voltage right to the injector and fuel spurted out. Had to quit for the morning since I don’t know where to go next. Hope the ECU is not bad. Everything worked fine when I parked the auto two years ago. But evidence of mice under the hood. Have mice messed me up?
Where should I go next to figure out why the injectors are not firing?
Lee
When I had (almost) no fuel, it behaved like this - might start, won’t run, so we are dead on as far as I can see. I would think idle should be checked later; as we all know it won’t catch at all if there is too much air, and so on.
Now we know it’s not the issue. We have (some) fuel pressure!
Lee, turn the ignition on and find the wire with the bullet connector that runs along and joins the harness that also feeds the injectors. This goes from coil to ECU in the trunk/boot.
Verify the wiring is good (mice).
Dis-and reconnecting the connector should yield clicking injectors, all at once every third time. Don’t overdo it, a few times maximum.
Alternatively, crank and listen for same.
If so, the ECU fires them.
If nothing, check for spark.
If no spark, rectify.
If still no clicking, the ECU - but that one can take a beating and is unlikely.
If they fire as they should, return to fuel pressure. Good luck, waiting for results.
David
Les, That is backwards. A healthy pump provides 100 PSI + as Frank states.The regulator bleeds off enough to the return line so that the injectors see about 36 PSI.
A guage as mentioned earlier is used to verify those numbers… One past lister used a plumber water pressure guage to o that.
My house gets about 100PSI from the water meter… But, a “new tech” water heater bled off at about 60 PSI!!! A plumber friend and I detrected that and installed a regulator and adjusted to just under 60 PSI. It took some getting used to !!!
Carl
Hello Frank, My problem is I don’t know where anything is very
well. Don’t know where the ECU is. Is it really in the trunk area?
I don’t know where that bullet connector is that feeds the
injectors. But I turned the key on and I have voltage at both pins
on one injector that I removed. Since I have voltage there, the
problem must be with the ECU not grounding the injectors is that
right? I am lost at this point of what further to do. Is there any
way to determine if the ECU is working at all? Wondering if I have
voltage to the ECU? If I have voltage on both injector pins does
that tell me that I have voltage to the ECU? My problem now is no
longer a fuel problem but some kind of electrical problem as the
injectors are not firing.
Lee
Keep going!
Forget the ECU (which is in the trunk - all the way forward, hidden with carpet).
Watch this video.
This is the wire. And the clicking.
Ignore the (probably hotwired) fuel pump which should only run for two seconds or while the key is turned to ‚crank‘. Shouldn’t hiss, but if you ‚crank‘ in ‚D‘ it would.
Voltage on both sides is correct and it is correct that the ECU grounds one side to open the injectors.
If doing the bullet connector trick (key to run!!) doesn’t make them click your problem is electrical but as I said before it is probably NOT the ECU. More likely the wire or ignition.
I am familiar with older autos and the points system that grounds the coil to produce a spark. But in a fuel injection system, what initiates the timing of the grounding pulse that comes out of the ECU to the injectors. Where can I troubleshoot this to see if the ECU is getting the proper signal etc. Lost!
Lee
The wire!
The distributor has a magnetic pickup instead of points. The signal is sent to an external box (amplifier) down by the intake manifold next to the distributor that cuts the current to the coil instead of the points opening. From the coil to the plugs everything is as it used to be. Just treat it as if it were a points system.
The signal for the ECU is taken from the coil via „the wire“. Another wire is for the tachometer. If there is spark, there should be a signal via the wire.
Don’t feel lost, just follow our troubleshooting advice and report back.
As David says, Lee - the pump output pressure may reach 100+ psi…
The pressure regulator is, crudely, a spring that is compressed at 36 psi - to open ports to the return line.
With a suspected fuel problem; both the ‘raw’ (at the rail inlet hose), and the ‘regulated’ pressure (at the injector hose) should be checked. The point of this is that the test are unambiguous - pressures are either correct or incorrect…
However, as David also says; all testing is is a matter of deciding priorities - if you are really lucky, the first test you make may reveal the culprit…
Frank
xj6 85 Sov Europe (UK/NZ)
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I know you’re typing up a response, Frank, but he seems to have fuel pressure and decent spray from the injectors, so I would focus on the probability of a lacking pulse.
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Indeed, Lee - both wires on the injector connector(!) should show 12V with ignition ‘on’, It is important that voltage are checked on the connector, disconnected from the injector…
One wire powers the injector from the main relay,injector resistor pack - the other is connected to the ECU, receiving voltage from that item. This confirms that the respective connections/wires are intact and the ECU is powered up.
And your concept is perfectly right; the ECU grounds the injector briefly once every engine revolution - and grounding the (connected) injector directly opens the injector.
The ECU grounds the injector by signal from the ign amp (coil neg) - via one white/black wire (the other white/black goes to the ign amp) - connected to the ECU through the mentioned bullet connector.
The standard test is to connect a test lamp between the two wires on the connector(!). With ign ‘on’ the lamp should be ‘off’ - while cranking; the lamp should flicker - indicating that the ECU grounds the injector in step with engine turning…
A special injector test lamp is cheaply available, designed to connect directly to the injector connector - but any test lamp will do.
As an aside; a faulty ign amp may affect both the ignition and the injection…
Frank
xj6 85 Sov Europe (UK/NZ)
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