New owner, 77 xj6 s2 4.2 Engine trouble

Rpms cannot influence fuel pumps, Chris - they are electrically powered, and nominally running at full pressure at all times. Theoretically, with high fuel consumption, a pump may not deliver enough fuel volume. Either caused by restrictions in the pump feed (hoses/filters) or wrong capacity pump fitted (verify) - and, as Paul implies; 4 psi enough to adequately feed the engines. Too high pump pressure may ‘force’ the needle valves, resulting in elevated float levels, which is the opposite of lean. Carb pumps may deliver up to 15 psi, but some carb pumps have adjustments for fuel pressure - there is no other ‘fuel pressure regulator’ on carbed engines.

So checking/adjusting pump pressure is relevant. You can of course feed the carbs directly from an elevated can, bypassing pump and any feed restrictions. To check fuel pressure with the engine running; you can plumb in a ‘T’ between pump and carbs. As an aside; some carbs have tiny inlet filters - which may clog and cause starvation at high(er) consumption. Again, correctly set float levels and properly functioning needle valves are imperative for proper carb function…

The converter ‘input’ axle is always slaved to engine, the ‘output’ axle is hydraulicly coupled to the input, and runs at all times - but in ‘P’ or ‘N’ the ‘output’ axle is freewheeling as the valve body has not engaged any gear. So ‘creep’ in 'P or ‘N’ is impossible unless there is a fault related to selector adjustment or within the valve body…

Failure to drive, forward or in reverse, means slipping bands or clutches - either by maladjustments or worn out linings. These are very thin, and slipping due to adjustment neglect will very quickly wear them out - and a box overhaul/replacement is required.

There are no clutches within the converter, and the only sludge build-up comes from the fluid itself. There is no viable way a disengaged (not in gear) box can stall an engine. A stall test is used to verify engine and box - in gear the engine is reved up, with the wheels suitably chocked, and max rpms is recorded. Typically, rpms will then stall at some 2000 rpms when engine and box is OK; the engine is unaffected - but the converter gets awfully hot, hence test should last max

That’s exactly it; something ‘simple’ is eluding us! We can only propose actions, but are totally depending on your follow-ups at the coal face…:slight_smile:

David’s advice in checking spark plugs is very pertinent; I experienced the same on my Mercedes, two out of four defective plugs. And his pictured set-up is indeed ingenious; with the plugs wired in the ign sequence you can also follow the sparks wandering around! And again; using a vacuum gauge will reveal a lot of faults, like valves, misfiring cylinders - and general vacuum levels revealing weaknesses…

xj6 85 Sov Europe (UK/NZ)

1 Like

Good evening gentleman, again i got home late from work. cold, dark and wet.

Ill endeavour to get out tomorrow afternoon and have another tinker.

I like the plug holder shown above, will be a good way to inspect what maybe happening for is there is still a firing issue.

Ill also track down my vac gauge and also plumb in the inline fuel pressure reg/gauge i have to see what the fuel pumps doing.

As commented above the pump should be transferring the correct volume of fuel, but if for some reason its failing to transfer at certain rpm points in the range and is starving the bowl of fuel, it could look to cause a lean out. somewhat the same idea of efi pumps running out of duty on performance applications.

regarding the bw65, thanks for the addition info regarding the stall. when i first got the car i dropped the fluid and what i saw wasnt pretty, completely full of clutch material and most likely band material also. I source a full rebuild kit from a auto repair mob from sydney. was about $320 delivered. New seals, orings, bands, plates etc etc. Its one of the jobs on the list to do. ill look to have the convertor power flushed also, as im nearly certain itll be full of debris from what was all throughout the fluid.

anyways, many thanks as always for the feedback, ill look to update you all further as i get time to attend the old girl.

enjoy your friday night.

No it couldn’t. It takes far too long to run a fuel bowl down from OK running to misfire level for the symptom to manifest as hiccups at certain rev points during no-load testing. When I had a dual-fuel Series 2 the car would drive a couple of hundred meters on fuel bowls alone before stopping if the propane LPG tank was empty.

Disconnect the fuel line and put it into a container. Run the pump and observe what comes out.

I’m surely not alone in keenly checking for an update on this one?

1 Like

You tube is full of videos of bring long sleeping engines back to life. almost all involve filling the fuel bowl. Just squirt gasoline in via the vent. Run time is amazing on the contents of the bowl alone.