XJ-C 4.2L 1977
Good day, I have next problem with my car. Cold start is OK, driving on flat roads no problem, when driving uphill (even small slopes) car is loosing power considerably, coming back on flat roads and the problem is gone. Pick up normal again, although over 120 km/h not perfect and doesn't feel to have all power.

 

Firstly welcome to the Forum.

When time permits, please do an Intro in the New Members Area.

Being as it is a Carby car, is it fitted with SU or Stromberg Carbies???, this will make a difference to answers.

I suspect SU, in Belguim, but not sure.

My few thoughts based on SU is:

Pistons are not moving freelly inside the carby bellchamber. Remove those top bellchambers, one at a time, and clean the inner bore, and the circumference of the piston with a solvent soaked rag.

Timing, it sounds like it may a few degrees out, maybe too far advanced. Lack of power in the top end is usually too much advance, but not always, so check the timing very carefully.

The fact it now starts fine cold, eliminates spark plugs for now.

Check the trans fluid, make sure is is full when HOT and engine running in Park.

After the that is all checked out, the list gets long.

Good luck, and keep us informed.

 

Is it lack of engine power or a delivery to the rear wheels issue, aka transmission slippage ?


Clue, the tachometer. Rpm's drop on the load added by the hills ?
Or remain the same or even increase?


The former, lack of HP and torque !. The latter, slippage in the converter or transmission.


In my opinion, basic engine health must be determined before the state of tune, either ignition or fueling.


Two great tools:


1. Test the compression, wet and dry with a proper guage.


2. A vacum guage on a convenient spigot, behind the throttle plate/s


Interpretation of each subject to he comments of others.


A bit at a time philosophy !!


Carl

 

Coming from a different direction here but....

Have you owned the car long and what are you accustomed to driving? Compared to modern cars these old Jags are a bit....um...leisurely in the power department

Cheers
DD

 

I'd also be interested in the answer to this since comparisons are relative to the individual's personal experience.

Although we know the 4.2 isn't a modern V8 or turbocharged unit, in good fettle it's no slouch either. I alternate continually between the Jag and two modern cars (one is near new and turbocharged) and the Jag never feels lacking under any conditions when compared with her stable mates.

 

+1 on Grants suggestion, plus maybe make sure if they are SUs that the oil in the dashpot dampers is a light low viscosity oil.

Heavier engine oils (or a glugged up mess) can slow the operation of the piston and inhibit throttle opening when you need it most.

 

He lives (bird's eye) some 45 miles from where I live.
The Bastogne region has quite a few mountainous roads.

I'm guessing fuel issues (as in Belgium all 95 RON octane fuels contain 10% of alcohol as of april 1st 2017 by law). Would be interesting to see if the problem persists when running on 98 RON octane or higher.

Furthermore, maybe the carbs need a good synching? Can improve performance A LOT...

@TS:
What's the mileage on this particular car and, indeed, for how long have you had it before the problem arose?

 

I'm with Tony's comments...my engine is 43 years old and she doesn't labour up hills at all, in fact I always need to keep an eye on my speed.

 

Higher octane rating, in and of itself, will not add horsepower. Nor will lower octane rating reduce horsepower.

However, if the timing was intentionally retarded to tolerate particularly low octane (or low quality) fuel, that could certainly account for lack of power.

You'll lose about 3% efficiency with E10 gasoline. Not enough to detect, really.



Cheers
DD

 

Right.

I'm not suggesting that the older Jags are deficient or can't climb hills easily.

But, the fact is, you can buy a modern, mundane Toyota family sedan that'll very easily outpower and outrun lots of older cars....including our old Jags.

Cheers
DD

 

This is true. When they first came out, a friend who worked at Toyota, bought home a standard V6 Camry manual for the weekend. As was our habit, we took the new toy out for a bit of a spin. If you gave it some, that thing flew for something that was nominally a shopping trolley.

 

Yes, different stuff abounds.


There is a fairly step hill nearby on one route from my house to the freeway and beyond. My venerable OHV six climbs it decently.
But, my V8 powered Jaguar can fly up it, if urged, just a tad.


The six at 4.0 and the lump a 5.7 . Big difference...


And, a bit ago, in my daughter's much smaller Passat V6, it zipped....


Carl


CAr

 

It's not the octane rating I'm worried about..it's the E10 gasoline.
In Europe it is now widely spread, but is leading to a lot of very strange problems in older vehicles. When in the tanks for too long, strange stuff happens to older rubbers, interior parts of carbs etc. Not to mention the stuff is a lot less stable over time than premium non-alcohol gasoline.

In Belgium the only gas without alcohol nowadays is the high octane version. That's why I recommended that.

I bet if you'd ask Jaguar about using E10 in any of their cars prior to the year 2000, they'd strongly advise against it....

 

Just grow in to E10. In CA, we were alarmed. But, found that it was far better than the MTB laced fuel that preceded it.


True, some "pot metals" seem to react to it and some older fuel hose material. And, yes, old E10 laced fuel may not fire well or not at all.


But, many issues that have existed way before have been laid at the feet of E10.


My two venerable older cars 'eat it up" with relish....


My Honda powered lawn mower insists on fresh E10!!! But, true, my to cycle machines resist it


Carl

 

Not at all. My 1988 Jaguar owners (from my 1988 donor car) manual very plainly states that E10 is perfectly acceptable.

In my neck o' the woods we've had virtually nothing but E10 for at least the last 20 years. I honestly can't think of any fuel systems problems I've had as a result. It works fine in all my cars, lawn mower, hedge trimmer, etc.

There is some kernal of truth to the E10 horror stories but, IMO, they are greatly overblown.

In some circles E10 is summarily blamed for ANY running problem or ANY fuel system problem....without any actual analysis. I would advise against falling into that trap.

There are some storage scenarios where E10 might be a problem....storage in high moisture areas, specifically....but even then it's hit-n-miss.

Cheers
DD

 

Thanks a lot for replies.
(And sorry for my late reply)
Car has SU's, gearbox oil was changed and I'm using 98 Octane.
I will check carbs as suggested (did the points, condensor, rotor + head but problem still there)