Need advice here. Fuel injection module check

I am considering buying this car, currently on eBay.

The seller has stated:

Here’s my story…I am a 1986 Jaguar XK-6, series iii, I am a 4 door sedan with dual fuel tanks, both tanks work and the switching valve works as well. I have a black exterior, tan leather interior, power sunroof, windows, locks, a trip computer, cruise control and a rear defogger all in tip top shape.

I crank and spark, my fuel system is functional. My A/C automatic system needs some help. My heater core has a leak, which is probably why my A/C doesn’t work.

I got hot on the way home from work during rush hour traffic. Once I cooled down in an open area I was able to finish my journey. The next day I heated up again, quicker than yesterday.

I am being sold as is. My owner doesn’t have the time to work on me right now.

Unfortunately, even with good fuel pressure, it only runs off of starting-fluid.
Overheating was traced to thermostat being stuck w/scale build-up. being stuck w/scale build-up.
Plugs don’t even show the short period of high heat; piston-tops, chamber, valves have no visible damage.

The heat must‘ve damaged Fuel-injection module under the intake manifold.
It’s located right under the manifold next to the head; a nice spot for baking cookies, but not electronics.

Any comments guys?

That would not be the injecton module, but much rather the ignition amplifier.
If it cranks and sparks, the module is fine!
If it sparks, it should also trigger the injectors; the ECU for which is in the boot.
I don’t see how any electronics would be harmed by the overheating situation. Maybe the injectors are not triggered or something went wrong that is related to the overheating situation - maybe there is no compression.

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if the car runs on starter fluid, why should anything be wrong with the ignition in the first place or the compression in the second - or am I misreading

If he sprays the fluid into the intake and the car starts there is clearly a fuel issue. Maybe a coincidence of a failed fuel pump. I’d check whether the injectors are clicking and then whether there’s sufficient fuel pressure at the rail.

I’d suspect that the overheating relates to a loss of coolant due to the known leak of the heater core. There are no two separate circuits. Besides, the heater core will probably leak into the cabin. Lift the carpets and check for footwell rust. Closely inspect the lower screen corners,

Other than that a nice car! If the body is sound and the original engine inside, the fact that the seller knows about the two tanks and has kept them operating indicates that this is not an abused car.

1200 doesn’t sound bad.

Good luck


75 XJ6L 4.2 auto (UK spec)

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Dave, here.

Yes, module suspected before spark @all plugs OK’d.
Used tester w/clear piece in middle of 6-7" HT-Lead; it’s an off-the-shelf tester from chain parts store.
Tester’s spark looked more orange, so did old-school “hold-plug-against-head” test to confirm blue spark for strength.
I should have set gap to confirm (min) voltage strength from coil (since it’s also right over top of hot motor).

Overheating account for diag:

20 Deg. F outside; 5 Mi @40-45 to I-75 on-ramp;
Stopped @1st 2 of 5 lights; gauge slowly rose to normal by 3rd mile on hwy, then steady.
7th mi on hwy, slow-down to 15-25 mph for 1/2-mile; pull-away past accident was strong;
Second burst 60 up to 70 heard slight ping/knock (about 5), lifted off throttle to just “lead” power, not deep or WOT (too far causes knock).
Gauge up, just above center, needle still touching center-mark.
3 More miles road rose for overpass, heard knocking on-throttle to aim for open lane-change spot ahead, no knock when just holding speed;
Gauge @2/3rds to RED, decide to pull-off; from left lane, across 4 lanes over next mile to catch 2nd exit after overpass;
Still OK except for knocking if accelerating too hard;
Idling @light (top of exit ramp) gauge raises to 3/4;
More knocking as I pull away from light, so I pull into Coney-Restaurant, instead of looking for a service station.
Engine idling OK as I park, but gauge still climbing, not yet to red; no steam out of exhaust, shut off to let it cool;
Busy w/online mtg. kept turning key to “Run” to see temp level;
Gauge below 1/2, hood’s been open to help cool-off, only slight oil seepage @cam-cover gaskets (near front of head) Oil clear-gold on dipstick, no coolant;
Figured safe to re-start; runs for couple secs. sputters out;
Went in for a bite & wait more;
Gauge @1/4, “wants” to start, only sputters-out;
“Mechanic” leaving Coney sniffs tailpipe: declares “You outta GAS, man!” (wasn’t).

Starter slowing, called flatbed to get it home.

I Need compression tester.

In a previous life, I opened up the fuel pump. I don’t remember why, assumably because I suspected it faulty for some reason (duh!). I seem to remember it being rebuildable, with points(?), I just can’t remember. Heck, it may have been almost 50 years ago when I had my first Jag, a '63 E-Type Roadster {that inhaled every weekly paycheck I got for 2 years!}. Or maybe it was my Series I XJ6. :thinking: Come to think of it, I do recall hearing the fuel pump “pumping up”, so maybe it did have something resembling points.

Since the motor gets fuel starved, it seems to me that the problem could well be a flaky, intermittent fuel pump. Or maybe a plugged fuel filter, or squeezed line somewhere.

Looking forward to hearing back from “Dave”. I definitely would want to know the compression readings, dry and squirted, before deciding whether to buy it anyway. I’m feeling more than a little positive about it at the moment. :+1:

I don’t know of anyone successfully rebuilding the efi fuel pump in one of these cars. They look to be sealed units and most folks just replace them. Very different to the kind of fuel pump you had in your E-Type.
It does sound like a fuel supply problem and the fuel filter in the spare wheel well would be the first candidate for replacement.
Take a look at the strainers on the pickup pipes inside the fuel tanks too, and replace them too - they aren’t expensive and once you’re in there… The strainers often fall apart on removal anyway after years immersed in gasoline.
I’d do all this before deciding to replace a fuel pump.

A compression test would be wise before going any further though.



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Indeed, Don - your memory is probably right…:slight_smile:

However, his is a fuel injected set-up - and they are not ‘rebuildable’. Though sometimes ‘reverse’ cleaning may work…for a time…

xj6 85 Sov Europe (UK/NZ)

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More history just received from the owner:

1st owner drove until ill, then passed, 9-97 Penn. Inspection stickers
Wife left it parked moderately protected (car-port?), not properly prepped for long-term storage.
When she went to assisted-living, nephew as 2nd owner got it running just to sell it.
Heater hoses bypassed valve/heater core.

Fuel pump, tank-selection solenoid & return valves/solenoids looked new (filter, also, but not 100% sure).
Had fuel flow to engine, but only used RH tank, then only filled it half-way.
He didn’t say what happened if put more in, just used half-at-a-time.

I filled it on the way home & as forum would expect, it promptly pumped to wrong return & over-flowed @LH cap.
Switching tanks stopped overflow a while, then started over @RH cap.
I corrected the orientation of the tank selection valve, all works as intended, drove until overheat.
Pressure @rail verified; key in run position, part-opening of throttle butterfly kicks on pump (simulates intake flow while cranking/running).

Functionally, all fuel-flow is working from tanks to engine & back to (proper) tanks.

I don’t have “noids” to test signals to injectors, need to find alt. test method & diag. steps to pinpoint, if not clicking.

Have smart-charger on bat. to go listen for injector clicking.
All cranking so far has left chambers & plugs dry, no fuel odor at tailpipes since I turned it off when hot.
Perhaps not enough injected to leave evidence just from cranking speed & gone by the time I pull a plug.
Sputtering-running on starting-fluid eliminates spark/ignition/cap/rotor/etc. concerns.

Reminder: no sweet smell of coolant when I stopped it, @tailpipes or pressure cap; it didn’t blow steam @cap when overheated, either.
Temperature differences between engine & rad. barely warm to touch was indicator to ‘stat or pump.
Coolant was cloudy, too, suspected deposit dislodged from passages, crud on ‘stat not all “grown” on ‘stat.
No coolant in oil.
Will update with comp. test #s, too.

Bullet connector along water rail, connect and disconnect with ign. on; all 6 should click on every 3rd contact. Make sure the pump is running and the pressure regulator at the front hissing. You said so, so it must be the signal from the coil to the ECU, the ECU, the resistor pack connector below the air filter (longish, on fender, silver, Lucas 2CU power resistor), or the wiring in between. You might want to wiggle the connector there.

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Great reply David! I’ll pass it right on!

also, this should read AFM and according to this description the switch in there is fine. Just turn the key to crank in ‚D‘ to check the fuel pump and pressure. With ignition on, while testing the injectors, it should not run of course. Glad if I can help!

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It appears we may finally be ‘circling the wagons’. The mystery’s resolution may be revealed soon, thanks to Dave’s and David’s detailed posts.

From David:

Air Flow Metre :wink:
As a one person dance, it was easier to open up with a popsicle stick to trigger the pump to run, check pump in trunk & hop back to see pressure, without the noise & load of the cranking (and no helper in the driver’s seat).

I haven’t gotten back to checking more, yet.
A Semi turned left in front of me at an intersection Monday; I stopped before hitting the side of the drive axles’ wheels, but as he straightened out he rolled the trailer’s axles right over the hood of my Focus!

Good thing I love working on cars, but that one might be beyond anyone’s depth. :slight_smile:


Thankfully he is ok!

Trailer over the hood sounds like that Focus is now a pancake… Must have been a bit of a shock.
Agree that is easier when alone - however it would not actually crank in gear, but it will run the fuel pump. The AFM can be fixed, as with most components in the engine bay. Anyways.

When you check the injectors, ignition on.
If they do click, try to start the engine after maybe ten clicks and see if it’ll catch shortly.
If you only hear faint clicking you can single them out, but be careful as the connectors can be brittle according to some.

Good luck!

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Indeed, Don - propping open the AFM is recommended for all tests that requires the pump to run.

The pump should then run whenever the ignition is turned on. And can easily be stopped by pulling the prop - if an emergency occurs…

And ‘no pump’ with the AFM flap open is a test in itself…

xj6 85 Sov Europe (UK/NZ)

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Well folks, I just closed the deal for $1200. “Winslow” is going to be waiting for me when I return to Michigan from Thailand sometime in the summer. Hopefully Dave will have had enough free time to get Wins running. Not important, I just want want the car and will deal with whatever issues may have at the time. Wins is identical to my '82, just 4 years newer. My favorite car ever! Now I have the incentive to return to the states sooner and stay longer. I am thinking about 6 months or so each time. In the meantime, I’ll keep this thread open to update on progress toward resolving the problem. Comments or ideas still welcome!

Some perspective: my r/t airfare will most likely cost more than the Jag!

Congratulations Don, and best of luck once you get started!

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Hi Don,
I have many clapped out XJ6’s I seem to gravitate to the no runners. the last one I purchased had a similar issue.
As someone state above (I’m lazy and didn’t read the whole thread - Sorry) :blush: a compression test is always good place to start. It will give you an indication on who much life is still in Winslow (right?). If this is a north American car the compression should be within 10% of 145lbs. That’s what the good book states for a Federal spec XK 4.2 if its less, start looking for a donor; if it’s more WhoooHooo!!
If that checks out, and it sounds like you have spark. be it weak? maybe?
fuel pull the fuel line to the rail, then through a fuel pressure guage on it; their fairly cheap. it should register somewhere around 35psi. If that checks out, listen to see if you can here the injectors clicking on and off. This one may be a bit tough to hear on a cold XK 4.2 the intake valves may be rattling away (on a cold engine). A Fuel injector testor aka NOID’s are also very handy. they plug into the injector plug and light up if the injector is getting a signal.
If no signal, then look in the boot for moisture or signs of moisture. The Fuel system braniac (ECM) is back of the backseat (area). They electronics are well potted, but the connectors tend to respond badly to moisture. Unlike the domestic FI rides, the fuel pump only comes on when during a crank and when the car is running. It’s triggered by the key position - crank or on and the potentiometer burried in the massive mass air flow sensor. pop the air box… no tube off, put a screw driver to hold the flap open, put the car in reverse, and turn the key to the ON POSITION. this will fake the system into waking up the fuel pump. You’ll hear it. Also, the fuel systems on these cars are a return system unlike the modern stuff where once the pressure is reached the pump turns off. While the pump is running pop the fuel cap open, you should hear the fuel returning into the tank.

In my case it was a couple of things - mostly the cam chain was loose allowing the valve timing to change at random. Made for an exciting drive until I figured it out.

keep coming back :slight_smile:

Rule out the basics. A compression check is a good place to start

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Thanks much Mark. I haven’t spoken to Dave lately because he has been very busy with other things but I will pass your comments on to him for consideration. Will keep everyone updated, we all learn something from these diag topics!

Mark agree on the compression check (throttle open), but for the injectors the method I (surely, I‘m lazy too) described above is entirely sufficient.