Howdy, i`ve got a very early series 3 XJ with Bosch L-Jettronic EFI. And while the car is otherwise in perfect shape, recently the engine began running lean and suffering a great loss of power, which was seemingly corrected with a tune, a new coolant temp sensor, fuel pump, fuel filter, lambada sensor and inspection of the AFM. However there was a greater problem underneath that, as the car recently died at speed, and refused to run for more than 5 seconds, albeit running seemingly ideally before sputtering out, giving no reason to believe the engine is mechanically suffering. After taking the car home, i took apart all the harness connectors, hitting it with contact cleaner, and sanded down the injector ground contacts on the engine and coolant rail.

After all that, the car will now run for approximately 15 seconds before dying, and will run seemingly indefinitely if the throttle is opened to any significant degree. Albeit still undrivable and stranded in the garage.

If it's of any use, while doing the reading up on the system, i found someone mentioning that with the ignition on but the engine dead, the brown and tan wires to the resistor pack should read a constant 12 volts, as should all injectors. I found that neither show any voltage with the ignition on, but function normally with the engine running. Tested on both the cold start injector and the #4 cylinder injector. However it is a very early S3, well before the modernisation in '83, so presumably the system differs.

Also of note, before the car died, it had extremely strange power characteristics. Particularly in that it was very down on power, but if you kept the throttle open in a static position, the engine would seemingly wake up, and produce full power in a very reliable pattern/behavior.

So yeah, does anyone know what the bugbear could be? Everything i can think of has had a negligible effect at best.

 

Weird. The "could be" list might get a little long with various jumping off points.

My gut feeling is that you have a fuel supply issue. I like doing easy stuff first so I'd begin by emptying the contents of the fuel filter into a clean jar. What you see will dictate your next steps. If ugly, you have some tank cleaning ahead of you.

If the gas is clean I'd bypass the fuel pump control circuit to see if anything changes. Remove the fuel pump relay and locate which terminals in the socket are associated with the white green wire or wires. Use a jumper wire to apply 12v to those terminals. You'll now have direct 12v to the pump.

Any change is behavior?

Just for the heck of it make sure that the ducting between the air flow meter and the throttle body is secure and leak free.

You mentioned lambda sensor so I assume this is a USA/Canada market car?

Also, does yours have the large "combination" relay on the firewall, or the separate pump relay, main relay, and red diode pack? I've never seen the very early 'combination' style unit but they exist at least in theory on some very early cars.

What's the history of the car? Was it in storage, or used very little, for a period of time?

Cheers
DD

 

Welcome.


looks like another smart gal coming aboard.


Carl

 

I replaced everything but the hard line between the fuel tanks and the fuel rail. The filter was pretty old and what bled out was pretty brown. I suppose it's worth flushing the tank. At some point and for some reason someone tack welded the left side gas tank panel onto the car, so getting to it's drain tap is going to suck.

To get at all the wiring under the air intake bits, i've taken the whole assembly out a few times and tightened the hell out of the clamps more than a few times. The rubber is still healthy, though i haven't done a smoke test looking for vaccum/pressure leaks.

I'll try the fuel pump relay bypass.

I'm assuming this is the triple relay, pardon the mess.




As for the history of the car, it's a show/hobby car, although i try to take it out every weekend i can. It's never sat idle for more than a month. previous owner took fantastic care of it, it was #1 in JCNA's north american driven ranking for a time. There's no sign of cracked or abnormally worn wires or anything like that.

 

You have the individual relays rather than the all-in-one combination type.

When these cars don't see much use the tanks tend to get rusty and gunky and sometimes several new filters will become clogged before all the cruddy stuff has managed to work its way through. If it's really nasty then the tanks have to be cleaned.

if the fuel does indeed look brown again you might want to consider adding a filter between each tank and the changeover valve. This way the fuel is filtered before the pump. Your new pump might not be long for the world if the gas in dirty.

Cheers
DD

 

I know i can drain the right hand tank, so i'll try that and see what comes out.

 

Well, was talking to someone and on a hunch the lent me a replacement AFM to try. And that was it.

I thought it was good but apparently not.

 

Good news !

Cheers
DD

 

The best of the best....


I may have an AFM that I no longer need. But, I'm not sure if we are "on the same page".


If it is and you are not that far away, that postage would be unreasonable, it is yours. Postage only.


That engine bay sure looks nice and a former JCNA winner, it must be a really nice example.


Carl

 

-whoops, doublepost-

 

Well if you're offering, i'd really appreciate that. If y'all could send along a PM with some information on the thing that'd be great. I could source one from a parts car or from a local shop for a couple hundred bucks, so it depends on how bad the postage is.

And yeah the car's a gem. Currently needs a real good clean and some other stuff but there's always something to do.



Also i ran the car some, and a new set of test plugs show sign of lean running and it still starves under load at low speed. So I think a purge of the tanks and service of the injectors still needs doing after all.

 

Well, the car is still running pretty ugly. So while the new AFM brought it back to life, it still ain't right. pulled the drain plug in both tanks, gas came out clear as glass. Ran my finger around the little rim around the drain plug tap, and felt nothing but metal. The gas tanks are perfectly healthy, and the gas perfectly clean. Pulled the filter too, nothing but nice clean gas came out.

So yeah, whatever it is, it still isn't fixed, and a clogged up fuel line ain't the problem.

 

back to basics...

check fuel pressure. Should be around 40 PSI.

Check Coolant temp sensor. Dont know the spec for this.

Check plugs, made be fouled. Remove and clean with wire brush. "Reading a plug" can really help diagnosis.

Check ignition timing.

Check for air leaks on the intake bellows.

One of the tricks I use on the I6 is to use a spray bottle and spray soapy water on leads and wiring. This can make an electrical issue worse and an air leak better. Listen for a change as you spray around.

Another trick I use is the spay the soapy water round the plugs. The water will collect in the space between plug and the head. If the cylinder is firing good i will be hot and the water will boil off quickly. If the cylinder is misfiring the soapy water wont boil off at all. If the cylinder is week or has low compression the soapy water will boil off slower than the rest.

 

Iso:


Those are really clever.


Stev.


I sent you a PM after "scratching" my memory as to how it is done on this forum.




?


Carl

 

Coolant temp sensor was the first thing i replaced, ignition is the proper 4 degrees static for that year, plugs show signs of lean running, air hoses are very new and unworn with no obvious air leaks, engine is running lean and overly hot so i'm not sure the boil test would produce any noticable results.

I think what i'm going to do is just get some scorched earth tier injector cleaner, run the tanks dry and hit the fuel line with an air compressor and replace the throttle position sensor. The only thing on the fuel line left to replace/check is the hard line itself, and if that doesn't work god only knows what's left to try.

 

The fuel pressure regulators don't last forever. They consist of a piston with a seal that is held against the rail pressure with a spring. To compensate for the need to vary fuel pressure with manifold vacuum, the spring is compensated by a vacuum line to the manifold. I had to replace one on a Series 3. If the engine is running lean it could be low fuel pressure, so check it out.

 

Check you dynamic timing or timing when the engine is running. 4 degrees is not enough when running. At idle the vacuum advance should give you more timing and the mechanical weight should offer advance from cintrifical force. I dont know the spec for your XK engine but its usually around 15 degrees at idle and should increase with RPM.

Vacuum Advance versus Vacuum Retard

 

The manual, all the information i could find and the engine spec label under the hood all stated that 4 degrees static is the correct base advance, with later years going up to 7 and 13. When i first brought out the timing light 4 seemed extraordinarily low, but that's just what they shipped that year.

Maybe i should've specified, it's 4 degrees base, and the vacuum retard works just fine. I don't know the exact upper number because the balancer is only marked up to 15, but it's well past that.

That's a thought. I'll buy a pressure gauge and see what it has to say

 

Brown fuel will haunt you through this whole process. I'm glad they make new replacement tanks, ~275 ea bucks on ebay.

 

Well, hit it with some scorched earth injector cleaner and blew out the fuel line with compressed air. Runs perfect, all the way to redline. I'm guessing all the absent crud in the fuel tanks ended up in the lines.

Thanks everyone