Problems when doing long steep hill climb 1971 S1 4.2

Hi Gents, today I encountered some new problems when doing hillclimb on the more difficult side of a local mountain. Its east side has a long steep climb section with multiple hair pin bends (takes about 12 mins with my Lexus 4WD). When I was half way through, RPM suddenly dropped to about 1500 and stayed there, even with the accelerator floored. It feels like the fuel supply was not keeping up. The car struggled and went up slowly, lucky there was no car following me. In a normal climbing section the engine revs freely from 2500~4000 RPM in 2nd gear. I then made a u turn when possible. As soon as the car is facing down hill, the engine revs strong and free again.
There were a few times the oil warning light went off for a few seconds when I cut the hair pin bends hard. But the oil pressure was always on 50psi.
Before I left home, the engine oil level was at the middle of the #### section. I checked the oil level again tonight, it got to the bottom of the #### on dipstick. So about 500ml was gone? After checking the engine bay, I noticed quite a bit of oil leak came from the top of the dipstick. Does it mean it is the time to do a PCV cleaning?

Did you try switching tanks?

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Have you made that climb before with better performance ?

I think the engine just ran out of power. Nothing wrong. Lugging at 1500, unable to increase in top gear. time to shift down to 2nd or even low!!!

Lots of crankcase pressure going on during that pull. Your car has no PCV!!! merely a thimble somewhere in the crankcase vent system.

The Lexus has a lot more HP and torque…


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With the accelerator ‘floored’ why didn’t the transmission kick down?

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as long as the tarmac is solid, your SI Jag should be at least as quick uphill as any modern SUV due to its lower centre of gravity and roadholding qualities - in fact the antique 3sp autobox is remarkably well-matched to the torque of the engine and will comfortably shift back in each bend and let you zoom out in second. I was surprised to easily keep pace with current A6 and the like. So, if your engine suddenly loses power, there is something amiss.

As you have dual fuel pumps, Kirberts question is pertinent: maybe one pump wasn’t able - or got clogged by debris being relocated in the tank due to vertical acceleration in the hairpins. Maybe the other one does better? In good nick even the considerable fuel need under such circumstances would be met by a pump in good order.

You don’t mention, but 12 mins driving time indicate you’re not adding some 2000 metres in altitude which might explain why the carbs are leaning out.

What about that oil thing? Do you see any external traces of loss? A friend had a SII E type and for years he could drive the car considerately without any signal of smoking, but when we went out together and his engine was revved up, it would burn oil like a two-stroke engine - no fun following in the open Spitfire (yes, you can keep pace with an E type in a Spitfire:-).

If you say, the revs won’t go over 1500, does this mean the engine goes smoothly, or is it rather lumpy? I just got over a very similar scenario and it was the rear carb that simply wasn’t tuned correctly.

Good luck


75 XJ6L 4.2 auto (UK spec)

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No, I didn’t. I filled up the right tank before the trip, but the left is very low.

You may find that the oil level is back in middle if checked while parked on an incline.

The reciprocation assembly swings very close to the baffle in the sump, which is about the middle of the hatching on the dipstick. Maybe some of that oil made it into you air cleaner housing - this is where crank case pressure (with misted oil) is vented.

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Hi Carl, I have not made the climb with the jag before, but with a Lexus RX350 and a Subaru Impreza. The Subbi has way less horse power but made the climb. I wont say it was easy though.
I kept the gear in 2nd when climbing. Engine ran smoothly in the first half with enough strength. Loss of power happened quite in a a sudden and RPM stayed at around 1500. But as soon as its nose was not pointing upwards, it rev freely again.
By saying PCV, I mean the metal mesh in front. Sorry if I used the wrong term.

Yes, I expect it would kick down (already in 2nd gear when I started the climb). The kick down function works well in this car when I need to overtake.

Thanks Jochen,
I selected 2nd gear before doing a climb. The engine normally rev happily and provide enough power. But that suddenly stopped and not possible to rev up.
The altitude may not be a problem in my area. The peak would be nearly 1000m which I did not expect to affect the mixture too badly. I had only one tank filled up that day, so could not switch tanks to try out. The loss of power happened in a sudden, so getting clogged by debris is quite possible. And the engine did not run smooth after the loss of power. It struggled and coughed a bit. As soon as I turned around, it was back to life again. So I suspect something happened with the fuel system when the car was pointing uphill.
About the oil leak, I have not noticed any oil burning issue so far. When cruising on high way, if I make a strong acceleration, there is a slight puff of smoke at the moment when the accelerator is pushed down. Then it looks clean after that. But to be honest, I could only observe it from the rear view mirror, the guy following me may have suffered all the way. It is a bit difficult to run the engine hard with a speed limit of 100~110kph.
From my observation, it does not burn much oil but I can see oil leak from the top of dipstick tube almost every time after doing hill climb.

I had exactly the same problem 2 weeks ago and had to get towed home.I wrote on this forum"engine running rough" a few days ago.
Both my tanks were full of crap and the tank filters were blocked.I cleaned both of them by removing sender units and drain plugs,filter screens and diconnecting the fuel pipes to the pump and flushing the tanks with a garden hose.I let tanks dry for a few days before refitting filters and refuelling,plus a 1/2 litre of metho in each tank.I had to also blank of the purge line and vacuum hose to the charcoal canister and open the vent valve to make the engine run a lot smoother.I have been driving the car around for the last 4 days and its like a new car.You may have the same problem.

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Thanks Felix. I saw your post and another post in XJ section talking about the same problem when going uphill. For my car, the previous owner had both tank linings done several years back, but it may get contaminated again now. I may stop doing hillclimb on the steep side for now. There is no mobile signal in that part of road. I can not even get a tow if I break down there. Only cruising and mild climbs for now, until I can find out if the intank screen is clogged or there are other problems.

At 1500 rpms, the xk engine can barely turn itself, Fan Yi - there is little left to propel the car…:slight_smile:

Things to remember; if a car won’t accelerate up hill - you need a lower gear. So did the box actually shift down - and did you try manual downshift to ‘1’?And when the road flattens out; engine will recover at a higher gear…

Also; all manufacturers make sure that fuel and oil delivery is not impaired with up-hill running - ref carb bowls placing and oil pick-up at the rear of the sump. It’s a bit odd that the oil warning light came on with the gauge still showing normal pressure - but the sensor are placed at different points…

Finer details; the xk quickly burns off oil at high oil levels - and uphill the oil level at the rear is indeed very high. But it still takes some time for the oil to burn off to the extent you noticed. The sump ventilation is there to vent out excess sump pressure mainly caused by piston blow-by, worn engine. High pressure may increase oil consumption by excess oil being forced to the manifold/carbs - or may indeed, and more rapidly, force oil out of the dipstick, or wherever…

Incidentally; how did the temp gauge react - if you had time to watch it…:slight_smile:

All that said; neither points eliminates the possibility of a fuel feed fault, of course…

xj6 85 Sov Europe (UK/NZ)

A couple of more points.

  1. The coating in the tank is peeling off and clogging the screen.

  2. The Subie enjoys a better power to weight ratio/ And a lower gear ratio in the diferential .

The Jag is a heavy beast…

Re: Frank
You may well be right. I did not manually shift it down to 1st. The car ran well in the first 5mins of climbing, so I did not bother shifting it down. The oil pressure gauge takes a bit of time to respond to the change of OP, so I guess it is not as sensitive as the oil level sensor?
I did notice more oil leaks if the oil level is filled up higher than the middle of #### on dipstick. Also after some long and hard pull, there are more oil leaks found on the garage floor.
About the temperature, Yes, I kept watching the changes in all gauges when the loss of power happened. It pointed at “o” of “Normal” and rarely at “r” even when climbing hard.

Re: Carl

  1. That would be possible. I may use a little fibrecam to observe the internal condition of the fuel tank.
  2. Agree, I saw some local guys use van or cross over tyres to race their xj6s with high weight ratings.

The gauge is a bit slower than the warning light sensor, which is just an 'on/off switch, Fan Yi…

But the latter is triggered by oil pressure, it is not for oil level. This may constitute a warning; warning lamp reacts instantly, but the delay for the gauge is not that long - so the gauge should show up drop. It’s just a bit curious…

At high/full throttle setting the cylinder pressure is very high, nearing some 600 psi - which accentuates any blowby due to ring/bore wear. So the crankcase ventilation has some bearing on leaks. Have you recently done a ‘dry’ and ‘wet’ compression test?

xj6 85 Sov Europe (UK/NZ)