Hello
I recently installed a new engine in my 1985 XJ6, I also installed a new fuel injection harness, fuel injectors, thermotime switch, coolant temp sensor and fuel pressure regulator. The problem I am having is no start from fuel delivery. When I spray starter fluid through the air flow meter the the car starts right up and then dies and will not start without spraying fluid again. With that it rules out ignition problems. I checked the pressure in the fuel rail and it holds a steady 35 psi also the injectors are receiving pulse which I checked with my Noid lights. I replaced the fuel pump relay on the bulkhead along with the other two relays alongside it. I also gave the fuel pump direct power and still no luck. Any help would be greatly appreciated, Kevin.

 

Question - At what point in the start cycle did you measure the fuel rail pressure, etc ?

On these L-Jetronic-fuelled engines, there is a small switch inside the MAF meter which is open when the engine is not running and the flap in the MAF is at rest. This switch only closes when the air flap moves as air starts passing. When the MAF flap moves from its rest position, the switch is closed and voltage passes to the fuel pump relay.

So how does engine start work before the flap moves, as the pump cannot run until the relay is closed ? Well, the start circuit, (when the starter motor is activated on the 3rd ignition switch position), directly feeds the fuel pump relay thus allowing the pump to run and the engine to start. As soon as the ignition switch returns to the 'run' position, this direct feed is closed and fuel pump relay control passes to the MAF switch, which should now be closed and thus keep the relay switched.

Try rigging up a light bulb to detect supply of volts to the fuel pump, then look at this light when starting the car. What should happen is that when you turn the ignition switch to "start" the light should come on, and stay on when you release the switch back to "run". If it goes out when you release the switch, then the fuel pump relay is not being switched by the MAF switch. These switches are a couple of very small contacts, and over the years can lose their springiness and hence fail to make contact. On the other hand, it could be a wiring fault or bad connection somewhere.

 

OK, you've got ignition, fuel pressure, and injector pulse. Hmmmm....this is a stumper!

Are the terminals inside the coolant temp sensor in good shape? Jump them with a paper clip and see if anything changes.

Cheers
DD

 

Hi Doug
The coolant temp sensor is new but I will jump it and see what happens, Kevin.

 

Fraser
I measured the fuel pressure at the cold start pipe from the fuel rail. I cranked the engine and measured the pressure which was 32 PSI and it held pressure for quite some time. I had previously given the fuel pump direct power thus taking out the signal to the fuel pump and still no start. Kevin.

 

Hi Kev

Can you expand on how you detected injector pulses. When I had a 1980 4.2, I had, (and still have), a little light that plugs in to an injector lead in place of the injector which lights up as each pulse is detected. Is this what you have ? If so, and it detects the pulses OK, then have you had the injectors cleaned and serviced so they actually allow fuel through.

Also does the cold start injector work OK ? This pours petrol in for a few seconds to start the engine.

Sorry, but it's an awfully long time since I had to do any of this sort of thing, so my memory may be fading.

 

I remembered I had a similar thing with a Mark 2 Jaguar 2.4 litre engine on carburettors. It would not run unless I squirted Easystart into the inlet. This stuff wakes the dead !!

As I remember, I checked the ignition timing and also the valve timing and something was not right, but I am damned if I can remember as it was 1987 !!

Reason I say this is you mention "new engine" - has it been assembled totally correctly ? There is a camshaft setting tool, (I still have mine in the toolbox !). Also have you got good cylinder pressures ??

 

Hi Fraser
Yes the compression is good at 150psi across all cylinders, I did check the valve timing, the tool you are mentioning is a camshaft tool that fits over the camshaft at the front of the engine, it has a notch that fits into the top of the camshaft which must fit into each camshaft whilst being at top dead centre on the compression stroke which it is. The tool I have to check the pulses of the injectors is a noid light, it fits into the injector connector and shows the pulsing. I did fit new injectors along with a new injector harness as the original was brittle and falling apart.
I do agree with you about the starting fluid, it was used to put a man on the moon.
I am in Florida so the temperature never falls below 80 degrees, according to the manual the cold start would not be operative at that temperature. I dont mean to rub it in about the temperature here, I was born in Yorkshire. Cheers Kevin.

 

Still scratching my head with the fuel problem. Just like to throw this one out there, could the problem be in the ECU which is not injecting the fuel when it is supposed to do or it is not giving the injectors enough fuel to start, any thoughts,Kevin.

 

Since your noid light is blinking, indicating that the injectors are pulsing....a function that comes from the ECU.....the ECU is doing its job, fundamentally, at least.

I suppose it is possible that the "pulse width"....the amount of time that the indicators are commanded to stay open....is too short and the cylinders are not getting enough fuel. This could be an ECU fault. The only way I know of to test for that is by swapping in a known good ECU.

Another thing that has a major influence on injector pulse width is the the coolant temp sensor. Did you jump the terminals at the connector? If not, humor me :-)

The primary influence of pulse width, though, is the Air Flow Meter. You could try a known good substitute.

A couple other things: there should be a white/black wire from the "-" post of the coil heading aft along the water rail. Make sure it's there and in good shape. This is the "trigger" wire to the ECU that wakes the ECU up. Also, check the bundle of wires at the rear of the water rail. Make sure all the wires are securely grounded and that none of them are danglisng free behind the cylinder head. In theory (ha ha) if the grounds were loose here, or there was a problem on the white/black wire, you wouldn't get an injector pulse at all....but, hey, you never know.

Make sure the ductwork between the AFM and the throttle body hasn;t come adrift or been broken in some way.

I'm running out of ideas.....


Good luck,
DD

 

Yes, this post really brings back memories !! The trigger to the ECU comes as Doug says, from the coil pulses which come, (of course), from the distributor. As I remember, the injectors operate all together and twice per engine revolution. Thing I cannot get over is the "noid" light is illuminating so fuel must be getting there. Only other thing I can think of if the engine runs on Easystart, is the spark at the plugs is too poor to ignite petrol but OK for ether, (which is what Easystart contains).

I would take a couple of plugs out and check them out.

Also check the engine-body earthing strap. If this is high resistance it can have a marked effect on the engine electrics.

 

Kevin, don;t take this wrong but are you *absolutely sure* about the 35 psi fuel pressure? The spec is 36.25 but 35 is certainly good enough.

With 35 psi in the rail and the injectors pulsing you really should be getting fuel into the cylinders (as though we don't know that, eh?).

Cheers
DD

 

If you take a plug out after an abortive start attempt, it should be wet with fuel.

Check the ignition high volts side - cap for tracking, leads etc, and that there is a "healthy" spark at the plug. Under compression the gap becomes effectively 10 times wider, and the HT can leak away at weak points giving a very weak spark in the cylinder.

 

Hi Guys
Thanks for staying with me on this one. I tried the jumping across the coolant sensor and no joy, it is a new one. The injector harness is new and the black and white wire coming from the coil is pulsing. I did put a ground from the negative side of the battery to the ground wires at the back of the head. The 2 big connectors from the new harness are plugged in all the way.
One thing I notice is that there is a small harness next to these 2 big connectors which look like 2 whites and a pink and white wire which all go to the sensor on the head which is all the way to the rear of the head. I think this sensor is something to do with the air pump.
I will check the big ground to the engine as I have replaced the engine and maybe that is not connected. Also the terminal on the large oil pressure sending unit is broken away, I dont think that would cause a problem though.
Tomorrow I will check the fuel pressure again, sparkplugs, and after that I am going to remove the injectors and make sure they are all spraying.
I really do appreciate everybodys help, Kevin.

 

Hang on in there, Kevin. Believe me, I have been to Hell and back with one of these cars, but eventually came out into sunlit uplands, (to use a Churchill expression).

 

Gentlemen, I have finally cracked it. Initially before installing the engine I took out both drain plugs to drain the gas tanks, the left had gas in it and the right had none. I then put new gas in the right tank and carried on with the install. As you all know the problems I was having I will keep it brief. After taking out the injectors and laying them out I found them all to be spraying nicely, that ruled out the supply of fuel.
I decided to drain the tank and see if the fuel had become dirty. I took out the drain plug and found no fuel coming out, which was strange because the tank showed half full. I then took a screwdriver and pushed it up and down several times and low and behold out comes the fuel, which was full of water. I could have kicked myself but didn't because the problem is solved. The car had been outside for about a week and had taken in water because the drain hole for the tank was blocked.
God I feel good today. Thankyou for all your help and put this one in the archives. Kevin.

 

My son has a 1985 XJ6 that was running well last fall but it will only fire for a few seconds and then stops firing. I am wondering if the cold start is working but then when it should switch to the normal running position it isn't making the transition... i have not seen this much plumbing and circuitry in a car before- I drive an MGB and it is much simpler. Any feedback would be apprciated. My son is going for his license next month and would love to be taking the test in his Jag!

 

Read my 2010 post on how the fuel pump is kept running after engine start.

 

Mr Mitchell,
Thank you for the response. In this thread I only see posts that are in 2009. Can you please be more specific? I can read back through the entire thread but I wasn't sure if there is one thing in particular you had in mind. I did see the final post from Exectivkev stating the clog in the bottom of the fuel tank. This car has 73,000 miles on it and it did sit for a few years after my friend passed away-- before his wife gave it to my son. We drove it last summer/fall with no ill effects but at the end of the season before we put it away for the winter it would not start. I have checked the fuel pump and changed the fuel filter and the spark plugs. It will start momentarily and even a second time and then it will not gain ignition again- this is what has me thinking the cold start(12 second spray) may be what allows it to start initially but not allow it to remain running. There is also spark at the plugs. I have not checked any relays yet as the sequence is not something I am familiar with. I will look for a "Chilton" type guide to maintenance for the car later this week.

 

My car misses at idle no check engine light