New owner, 77 xj6 s2 4.2 Engine trouble

XJ
41

So, now for the minor update i found out today.

I decided to remove the SUs again and put on the bench, i was watching some interesting SU videos last night on YT and began to question had the needles been changed or perhaps not equal to each other.

I also did as david mentioned is spray the linkages with parts cleaner and see if there was any change. much to my surprise there was a change to the rear carb. i had inspected the linkage for excessive play when i first pulled them off the engine and wouldnt have said it was excessive, but clearly there was an air leak.

i had the CSK38 service kits from Midel that came with replacement shaft seals etc, so i went about pulling it all down again and cleaning the shafts up and resealing with the new type viton seals. most definitely that has helped steady the idle. but more to come as i found.

i removed the pots and did the drop test of the slides blocking the holes, both sus drop at the same rate so that was good.

i also found from the video i saw, that when the pots are internally vented the caps dont need to be vented with the tiny hole, my front SU doesnt have a vented cap, where the rear one does. I thought i would trial sealing the hole and see what happens. More to comeā€¦

I also removed the needles to see what they were. Both were UM needles which the book states are STD needles for HD8. but, one needle was half a mm further protruding. i got the verniers again and reinstalled them equally and moved on with the reassembly stage.

installed back onto the engine and with semi happy news the erratic/irregular/hard to chase, idle has improved.

i actually manage to have the engine idle at 900 rpm, for a short while smoothly before it would develop a little choke and shake about a little, but noooo where near as bad as it used to.

i also managed to check static timing again with the vac hose off, it was about 8-9 degrees BTDC.

attempted to then slowly bring it up in RPM, where like always, it would fart around and start backfiring through the carbs at 2500 rpm, push it to 3000 rpm it would go off all the time, flames out the carbs.

fiddled with mixtures and it makes no change at all. its as if theres a limiter set for antilag at 2500 rpm. good for my rally car, not the jag haha.

which brings me back to wondering if the Goss replacement coil someone prior to me has installed, it actually breaking down under load. as ive gone around the moon 4 times now and still the engine farts around at that rpm rangeā€¦

if its not mechanical mistiming it has to be something in the distributor timing and or components.

open for suggestions, im still trying to find my box with my datsun coils and dizzys so i can use one of those for a test

1 Like
42

Flames shooting out of the carbs is surely a very clear sign that the timing is way out?

1 Like
43

Maybe bent valve sticking valve, to much advance at RPM
Fuel pressure in no particular order
Do a leak down and listen at the intake, exhaust and breather
Ck the fuel pressure

44

I had all this last week on a 4.2 with twin HD8s. The car had newly rebuilt carbs and electronic ignition statically timed to 10 degrees BTDC. The engine was also fresh and the cam timing tool just dropped in perfectly.

It was not starting easily, it was also dropping a cylinder or two, then cutting out. When it was running it was also backfiring dangerously through air filter.

This turned out the be 2 problems that, luckily took minutes to fix and 1 problem that took a bit longer.

Old fuel that was contaminated with water had been mistakenly added to the petrol tank. I would say 5 liters of old fuel had been added in a tank containing 20 liters of new fuel. The water had gone to the bottom then been sucked up into the engine immediately. Water doesnā€™t burn very well.

Once the tank had been drained into a bucket it was obvious a layer of water was at the bottom, you could see the interface.

I unscrewed the dash pots, one was empty!. I put in some light oil and bingo, all fixed.

The AED was also leaking, annoying as it has just been rebuilt. Took me 3 attempts to seal it.

From underneath the car I undid the 2 drilled bolts. The front float bowl had a damaged float bowl thread where the drilled bolt had been over-tightened. New float bowl ebay Ā£30. The red seals and aluminum ring just would not work. I had to assemble it all with Wynns black gasket making sure to paste the threads.

The car now starts on the button, idles cold, the thermostat turns off the AED and it then idles on the warm idle control perfectly with the butterflys completely closed. No dripping AED either.

All a bit of a ball ache though!

2 Likes
45

I note a very important point. Olds spark plug leads, wrog plugs, incorrectly gapped!!!

Did you fix that? Poor ignition will mean no run or poor ruyn at best.

tis not a hard engine to time. Usae a roid in the #1 bore. nearest the fire wall. Establsh top dead center. Verify that the rotor ponts to that cylinderā€™s post in the distributor cap.

Verify that the centrifugal weights in the distributor arefree. Verify that the diaphram is intact and advances the timionmg.

Nice find.

Carl

46

You sound very thorough and competent; Iā€™m sure youā€™ll sort it. Good luck.

47

Hi Chris!

In your case you just have to search and search till you find what you need.

Did you get in touch with David Boger, eeuroparts.com, eurojag.com, treeysjag.com

etc.

Walter

48

I agree.
If fattening it more doesnā€™t help (I still think it should) itā€™s time to look at the sparks again etc.
Intake backfiring can also be lean? To a degree!
Fresh fuel helps. Empty dampers run okay until you open the throttle, then youā€˜d get backfiring because itā€™s lean for a second.

I live on a small hill, if I coast down with the asc killed (after 1-2 minutes of running) it will idle okay so not the top priority. But of course get it sorted some time soon etc.

The S3 ignition is generally reliable and straightforward so if going over it the 5th time including second opinion itā€™s parts time.

I have to say it, carbs are much easier than fuel injection and I had to learn both from scratch, S3 first and then S1. The HD8 are brilliant. Fuel injection doesnā€™t do much for me.

49

**
The purpose of the ignition sequence is to ensure that the rotor points to the plug lead to the cylinder ready to fire as coil discharges, Chris - as the dist rotates counterclockwiseā€¦

The trick is to find which cylinder is ready to fire; set to TDC mark on the damper, itā€™s either the #1 or #6 - and deciding which on is the trick. Itā€™s the cylinder that comes up on the compression stroke that is the reference cylinder - and the rotor must point to that. So, depending on the reference cylinder; ign sequence is either 1-5-3-6-2-4 or 6-2-4-1-5-3 when starting on placing plug leads on the dist lid. The important thing is to hand track each lead from the dist to the plug and back - placing each lead ccv next to the one already in place, in in the ign sequence.

All this is of course as familiar to you as to anyone, including me - and I still managed on occasion, to get it wrongā€¦:slight_smile:

Itā€™s not that I doubt you; I quite agree with Kevin; you sound indeed thorough and competent - itā€™s just incomprehensible that your endeavors hasnā€™t fixed the problem! Noticing that engine is shaking in idle - as opposed to the well known xk ā€˜uneven idleā€™ - the idle varying some 30 rpms in a ā€˜regularā€™ way.

Backfiring is an indication that the mixture is leaning out at higher revs, which may, as Jim mentioned, be lack of fuel fuel supply (unusual with carbs) - or indeed incorrect float levels, which is suppose you have checked? It is also essential that the carb bowls are vented; it is ambient air pressure in the bowls that forces fuel into the carb.

Or indeed ign mistiming, as mentioned by others - including, of course, crossed plug leads. The problem may of course be lack of centrifugal and/or vacuum advance sticking, also mentioned frequently. This can be checked, up to a point by watching timing changes as rpms increase. Remember that ā€˜staticā€™ advance refers to a stationary engine - easily checked with mechanical points. With electronic ignition it is checked by setting the desired advance on the damper, then loosening the dist clamp and move the dist slowly either way to provoke sparking in a test plug - the reclamp the dist.

ā€˜Dynamicā€™ setting means engine is idling, and the ā€˜normalā€™ setting is around 5 deg BTDC at 800 rpms - vacuum disconnected. However, this is when ā€˜manifoldā€™ vacuum is used; when ā€˜portedā€™ vacuum is used - the ā€˜normā€™ is around 17 deg BTDC. Itā€™s therefore important that a vacuum gauge is used to verify what vacuum the dist is getting - wrong initial timing plays havoc with the advance. And a vacuum gauge is indeed a valuable diagnostic tool; dig it out or get a new one - while vacuum readings require some interpretations, it is really worth while in your struggleā€¦

As an aside, there is little gain and a lot of trouble to convert to EFI - to the point of being sort of pointless pointlessā€¦:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)

50

Chris!
If you need any printed manual pages, let me know I have a 400 page
manual XJ6 69 thru 87 and XJ12 1973 thru 79.
I can e mail.
Walter

51

Good evening all, i didnt get any time today to continue playing with the jag. got home late from work and family duties.

To answer some of the above comments;

Fuel quality and condition, i have installed a brand new boat fuel tank in the boot and have a new facet style fuel pump. all new rubber hoses and the steel lines were blown out. All new filters also. One in the boot and one in the engine bay. Have also only used new 98 Premium fuel in it. The factory fuel tanks are another mission, as theyre full of pin holes. Ive had the RHS tank out about 5 times chasing pinholes. I just keep silver soldering them up. thinking of using tank urethane coating the insides. and or cutting off the bad area and folding new sheet work and tig welding the tank halves back togetherā€¦ as said, mission for another day.

The plugs are brand new as of two days ago, gapped to correct spec as per the manual.

Leads have been replaced also.

I did read another thread ā€¦ [xk-engine] no power and backfire through carbs ā€¦ which ironically sounds all the same as what im experiencing, but of coarse theres no conclusion reportedā€¦

it does speak of perhaps a lack of fuel pressure in the the delivery bowls at certain rpm ranges. I have a spare fuel pressure regulator i can plumb in to see whats happeningā€¦

I just find it so odd that theres possibly a fuel starvation issue happeningā€¦ this setup isnt all that different to my old dato engine when i ran SSS twin carbs on it. Albeit Hitachi SU carbs. But very similar in design.

I do own a AFR gauge which i traditionally use for tuning cars, but like always when you lend it to a friendā€¦it goes missing. Kinda of pissed off about it as its $400 worth of diagnostic tooling thats priceless in these situations. Will endeavour to get that back as itll give me allot of data.

regarding the comments about oil in the dampers, thats all been squared away again since i had the SUs on the bench and rechecking all the fine details on the carbs.

without knowing if fuel pressure if dropping off at increase of rpm creating a lean out to occur (again my AFR meter would be a wonderful tool for this), i would be nearly convinced im back looking at timing and distributor/coil performance.

Side note, again spit balling ideals now, the BW65 auto and convertor. At what rpm range does the convertor start to come in? i question this as i know the auto box does need a rebuild, the previous owner ran it low on oil and cooked the plates and then topped it up with dex III instead of type F, which has further affected any real opportunity for forward drive, reverse seems to work ok if i can keep the engine revved up and not stalling out. I also know even in Park the car will on odd occasion want to creep forward if i can get it to rev past the backfire period. Its rare but does happenā€¦what my minds thinking is if the convertor is full of sludge and clutch material, that after sitting at the farm for 3-4 years unmoved, could the convertor be trying to stall up an loading up the engineā€¦ around this magic 2500-3000 RPM range?

Ive played with tuning cars before using ECU software and when presented with a high engine load situation you do have to cater for it on the VE map and timing maps.

hence why im wondering if this maybe a situation not yet consideredā€¦

52

Ah, not running the SU fuel pumps, another possible issue. Does the Facet deliver the correct fuel pressure?

53

So my jag came with the fuel pumps internally installed in the tanks. Needless to say they were both shagged. Socks were pretty much non existent and or clogged.

Ive used the facet style pump many times over. I even have one installed on my patrol to act as a low pressure pusher pump for the td42 turbo injection pump (yes another car thats well beyond standard haha)

im tempted to buy a carter fuel pump and use once i knew the engine was healthy and running rightā€¦ I used to have a carter pump on my datsun as a tranfer pump to a surge tank that had a bosch 044 on it to send fuel to the z18et under the bonnet. Never once skipped a beat.

What is everyone else using when not using OEM pumps?

54

Also regarding going EFI one day, its something im not shy on as i was fortunate to learn the basics of carby engines from my old man from a young age, but when he bought a Z32 300zx that sent me into the world of EFI. From that time on, i learnt all i could and have build many project cars and worked on many styles of performance cars over the years. From building my own megasquirt ecu for a project car, through to rewiring complete engine harnesses so a factory ecu could be made to work on a engine that was pre efi.

The final idea of going efi with the jag would be something for when i have a spare engine and think of going down the forced induction route. Use the standard jag manifold, but use the abundance of parts from previous builds to control it. As classic as blow through carbies and a twin spark distributor using a two way diaphragm valve to control boost timing sounds, a tuning VE table is far simpler.

Anyways i digress.

Wish to thank everyone so far for their attendance and help in solving what no doubt will be something rather crude, yet time consuming.

So thankyou all!

55

How about a broken valve spring or cracked something
Some vacuum leaks only show up when itā€™s hot
Does this car have some sort of EGR valve

56

You should use the correct SU pump,

either lash out and buy one new or get used off Ebay

ā€¦or join the Australian Jaguar Parts Facebook page, you will easily get one on there, or advertise wanted on the ā€œclassifiedsā€ section here on J-L

I have a lot of SU fuel pumps, but I dont think I have any working ones for S2 XJ6
( have a few for XJ12)

If you want the vehicle to run properly it needs to have correct parts

Using another fuel pump with regulator is just two more things not right

The SU has a specific very low pressure (specified in the FSM)

Fix known faults first :grinning:

The stall speed of a BW trans is lower than 3000RPM

1 Like
57

As long as the fuel pump doesnā€™t provide more than four PSI pressure, any pump will do. Iā€™ve used Facet pumps for years on cars with SUs and Strombergā€™s.

58

Dex 3 is no Problem in the 65 (more wear because it shifts softer thats all). Bw65 and 66 are dirt cheap. There canā€™t be debris in the converter, is enough fluid in there and is the tv cable hooked up because it has to be and it likely isnā€™t - if it isnā€™t transmission pressure will be way low and reverse is the last function to stop working. If it creeps forward in park something is really wrong because as all transmissions it should lock the output shaft in park!!
Pull the kickdown cable out to the first detent and see what happensā€¦

I would get new fuel tanks or try the sealant. And pumps of course. SU are the best but hardi is an option you donā€™t need. But that facet should work for now. A used SU will set you back $20-30 and itā€˜ll be reliable if you set it once.

The piston lift test should tell you if itā€™s lean or rich. Donā€™t stop trying until itā€™s really rich and still not better.

1 Like
59

If you havenā€™t checked pull the plugs and see if they spark at all (duds exist) and in order for the final conclusion

image
image1920Ɨ3413 457 KB

Thats the nice version obviously a bit of wire does the job - two of the brand new champion plugs (not pictured) did not fire.

60

My lump project began in 2001/ My first and only adventure in to the guts of EFI. This after many decades in carb cars and trucks. Teh prohect before the Jaguar was a ford Hot rod.
Three, then two carbs ona flat heac V8.

EFI light years better. Never moind the engine management, AKa computer.

The LT1 engine in my 83 jaguar transformed the car.

Sorta made it the car, it should have been.