Did you look at the plugs you took out - anyone sooty/oily or all the correct light brown? Part of the puzzle is of course that it came on suddenly - and does it hesitate when reving up in ‘P’ or ‘N’?
Did you check that petrol does not leak out of the pressure regulator’s vacuum connection?
Two things to ponder; the engine has never been run up to operating temperature, always for cold and for shortish times - which may or may not have a bearing on symptoms. Secondly, if there is a misfire it reduces engine power - which may cause hesitation at take-off - at higher revs, there is enough power to prevent hesitation. It’s a characteristic of the xk that it’s smooth as silk and responsive even with serious issues. As throttle is opened the cylinder pressure increases, putting higher demands on the ignition system.
The xk also produces a lot of heat…
At the quoted air temps the engine should certainly reach operating temps even in idle. You can watch the temps at the top hose’s connection at the radiator with the temp of the water rail. In principle, there should be no hot water flowing through the closed thermostat - possibly apart from the ‘jiggle pin’ if fitted.
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Wise moves - to be followed in due time with a level check with the box hot after a good drive…
You do not deserve more water pump leaks (where exactly?) - or the hesitation, which may be very elusive to find…
70° water rail, 69° top hose, his thermostat opens way too soon OR doesn’t close fully and overcools at idle. He can check if the hose stays cold until it approaches 70°… and then he can replace the thermostat.
I mean the little rubber hose piece that connects the 2 rigid lines at the front of the engine are clamped to the cylinder head so close. That part gets so hot! Good thing the fuel flows by very quickly
I did and so can you… The picture of the plugs is posted above. #1 was a bit darker but all pretty clean. Remember these plugs were in the super rusty engine. All things considered I am suprised they work at all.
You have long days… I recall this taking me 19 months and counting! Funny how I was just planning on changing the fluids, replace a few rubber parts and go for a drive… If I had known…
I will give you a free tip, having 26 and 53 year old vehicles
between these ages, many items will be due for renewal, items such as alternators, brakes, suspensions, exhausts, ventilation systems, radiators, vacuum parts, fuel pumps, electrical parts etc etc
I have rebuilt or replaced all these parts on my '69 420G, including IFS and IRS rebuilds
I have rebuilt or replaced most of the above parts on my 26 year old vehicle, albeit quite recently, but thats why they are cheap, and you dont see many around, as people dont want to spend $2k repairing a $4k vehicle, but I do it all myself, and am judicious in selecting parts. It would cost me several times what my vehicle is worth to get one as capable
No water leaks so far. It was a fuel leak! Since it is located behind the fuel regulator it wouldn’t have made a difference. I think it’s taken care of.
The hesitation I do not know. Idle seems fine. As far as I can tell it will rev fine in N. It only does it under load. It also does it if you let her roll out at 15-20km/h and then try to accelerate some more. So only at low RPMs and only under load. It was pretty bad backing into the garage to get over the garage lip but of course with the car in the garage the misfire sounds louder.
I checked for the full load switch. Disconnected and reconnected it. I have not done the CAP-MOD.
I read up on it a bit and it seems that it should be visible in form of black smoke and running rich if this was in fact the issue. I am thrilled with the exhaust gases. Clear no smoke.
Lean is usually arrhythmic uneven splashy idle, light plugs, briefly weak when accelerating, running hot.
Rich is rhythmic uneven idle, even black smoke, dark plugs, and it bogs down when accelerating if it’s really rich.
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They would likely be, Max - the car has been running a comparatively short time on your hands.
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But fuel leaking out of the regulator’s vacuum port does - it is sucked into the engine from the rail. Check; which only takes some seconds - a negative is good enough. The actual fuel pressure is kept by a spring - the vacuum only lowers rail pressure in accordance with manifold vacuum…
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So it basically happens from a closed throttle at low revs?
If so; first check that the throttle gap is at 0,002" - and that the throttle body is clean. If so, you may have an AFM issue - which is difficult to assess. However, locate the AFM bypass screw (5 mm hex), screw it closed - then open it some 2 - 3 turns. The screw adjusts the mixture - which at present may be set too lean, causing the hesitation. The effect of the bypass is more pronounced around idle…
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The symptoms of cap-mod need is restricted to a cold/warming up engine and only during acceleration - no symmptoms in idle or with a steady throttle. With the engine warmed up (say some 40C) - there are no symptoms what soever…
The symptoms are identical for both FI and carbs - it is just the cause that differs. Either system has the same purpose; to deliver the correct mixture - and if incorrect, the engine reacts the same way…
Ok. So I misread the fuel pressure gauge the pressure is actually a bit higher. I am ruling out fuel pressure. I an guessing with fuel pressure confirmed I can rule out a clogged fuel filter as well.
