XJ6 & XJ12 Series I, II & III 1968-1992

87 xj12 cranks but no spark at plugs

 
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Old 08-21-2011, 01:13 AM
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Red face 87 xj12 cranks but no spark at plugs

my 87 xj12 vanden plas (canada)ran when i picked it up had no alternator belt. got home ordered belt and installed charged battery started right up engine bogged down then wouldnt start.did cei checklist pickup reads 1.5 ohms took of distributor cap had difficulty removing rotor seemed to be stuck on.rotor finally came off but broke rotor hope i didnt damage anything else removed pickup if i understand the cei checklist pickup should show 2.2-4.8 ohms i would appreciate any help. thx.
 
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Old 08-21-2011, 07:43 AM
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Numerous items come to mind in my many years with the mighty V12.

Maybe 2 seperate issues not related, maybe not, some simple checking will quickly find the source.

The fact it fired up, then bogged down sounds like fuel (too much). Pull the 2 vac hoses from the 2 regulators and see if fuel is present. If so there is one problem. If not, then cold start injetors (if fitted), CTS (coolant temp sensor LH thermo backing) is erratic, and causing overfueling.

The NO spark at the plugs may be:

Module INSIDE the ignition amp. They do go legs up suddenly.

That little capacitor looking thing inside the amp may be leaking to earth, mine did loooong ago, and I have had 3 others since, NO SPARK, simply unplug it from the module and try and start the engine. It may be that simple?.

Carbon brush inside the dizzy cap (they dissappear sometimes).

The 2 pin plug on the small loom from the dizzy to the amp may be crudded up inside (common).

The wiring at the coils has broken. The primary coil (in the centre) should be able to start the beast, if the secondary coil (out the front) is dud, and vice versa.

Unplug the HT coil lead from the cap, plug a spark plug in the free end, earth the body of that plug, crank the engine, and see if the coil is actually sparking, if so follow the fault from there. If not, back to the module.

Make sure you have 12+v at the coil +ve post at "ignition" position, AND "start" position, as sometimes it will drop ign signal when you go to "start" due to a cruddy electrical section of the ignition switch.

Of course the lack of spark, or very weak spark, will cause the engine to sort of "bog down", so it may not be overfuelling at all. A number of simple checks as I described will very quickly determine what is actually giving you grief.

Let us know what you find, so more things can be added as we go deeper into firing it up.
 
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Old 08-21-2011, 08:33 PM
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thx.for your reply -i picked car up 3 months ago she ran beautifully but had to swap out battery a few times as alternator belt was broken .parked in garage till i could set time aside to replace belt.replaced belt charged battery used start feature on my charger started right up ,with a slight miss.turned of ignition did inspection of underside incase i disturbed a wire or relay(mighty cramped down there)checked ignition system wires found one on the amp.that was bare and might have grounded tapped up and went for test drive started no problem but still was missing thought maybe fuel issue switched tanks no improvement,switched back accelerated bogged down seemed to have little spark as barely ran at idle pressed accelerator stalled wouldnt start out came the multimeter and test light voltage at coil not at sparkplug wire tested voltage at +&- of coil both same as battery disconnected distributor pickup from the amp.read 1.5 ohms reconnected pickup measured voltage at -post at coil when cranking seemed fine at a loss.towed home,bought haynes manual only had 75-85 but everything seemed similar when reading found i should have disconnected battery posts while charging and never use the start feature as i had done.performed fuel system check seemed fine i disconnected vacuun hoses at regulator seemed fine depressurized system checked fuel filters again seemed fine pump cycles when ignition turned on and when engine cranked fuel gushes out of rear filter also fuel lines at regulator.so book no help i go on line looking for help being mostly computor illiterate a daunting undertaking after many days i stumbled onto this site found a few others have had simmilar problem read dougs replies of 04/14/2010&06/27/2011 rexamined ignition system noticed in his reply the distributor pickup from amp should read 2.2-4.8k ohms removed distributor cap taping &numbering wires had trouble removing rotor tugged and rotor cracked but came loose removed the pickup intending to replace as the ohm reading was so low.am i on the right track i dont know .pls help thx
 
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Old 08-22-2011, 04:43 AM
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OK.

Now a tad clearer.

Back to what I suggested, is there a spark from the centre post of the primary coil whilst cranking. IF NOT, then the module and or the wiring to the dizzy is highly suspect. All the ohms etc will come into play later, maybe, as the car ran, and ran fine. The 2 wires through the base of the dizzy go through a rubber grommet, and it is well known (eventually) that the wires can fracture INSIDE that grommet. Do a continuity test on the 2 wires, and wiggle them significantly whilst doing the test.

Once you get a good FAT BLUE spark, we are on a winning track. Simply swapping too many things will confuse you and us, it is best to keep it basic, the system is a SIMPLE system, and the fact it is 12 cylinders makes NO difference.

The misfiring is more than likely spark plugs. They can soot up on the HE quite easily. Now when they are sooted they dont spark, so a misfire is obvious, but ALL 12 misfiring, unlikely. That is why I continue to ask if you got spark out of the primary coil, this is the first thing that needs to be RIGHT.

The front 2 plugs are also well documented for NOT being changed, so 10 get new, and 1A and 1B stay as is. NOT funny, but sadly fact. If the spark plugs are of unknown age, replace all 12 and ensure they are gapped to 0.025", or idle quality will be compromised.

The plug leads are an issue on these as age creeps in, and that will cause a misfire, not a non running engine in my opinion.

The charging with the battery connected is fine as long as the ignition switch is OFF. Starting with the start thingy is not advised, but it is similar to starting with jumper cables from another car, so I do not believe yoyu have damaged anything. The main danger there is "spike" that damages ECU's, and alternators.
 

Last edited by Grant Francis; 08-22-2011 at 04:46 AM.
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Old 08-23-2011, 12:37 AM
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thx for your help .checked plugs even 1a&1b had to partially remove a/c all look recent including distributor,cap,coil ,plug wires,tested for spark at coil when cranking good spark.tested distributor pickup from amp.has continuity looks near new will put it all back together tomorrow after work and follow any suggestions you have.thank you for your patience and expertese
 
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Old 08-23-2011, 04:30 AM
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Maurice,

Good so far.

Before you refit that cap, make REAL sure the carbon brush is intact. I have had some over the years wear away, and that cap is NOT a 5 minute job to replace haha.

If you got good spark from the coil, then the next natural progession of that spark is via the carbon brush, to the rotor, then the spark plugs (journeys end).

Take a spark plug, ANY OLD spark plug will do, and plug it into the end of one of the actual plug leads, earth that plug body on something steel, and crank again, and observe the spark at the actual spark plug. I use #2 or #3 leads as they are easy to get to.

If you get spark, OK sort of, coz it only establishes spark at the plug at atmospheric pressure, NOT actual combustion chamber pressure, which on a HE is VERY high.

Remove a spark plug from the engine and observe the colour, it is possibly all black and sooty. This soot is an excellant insulator, and the spark plug simply will NOT spark, in true combustion situations, so a clean is required, or just bite the bullet and fit 12 new ones gapped to 0.025" , with anti sieze on the threads, and then you know you have NEW plugs, and set correctly. Again, the plugs are NOT a simple thing to change, and I always fit new when having this issue with a V12.

Based on all that, and the fact you actually got spark out of the coil, and the track of that spark is good, then it should fire straight up.

If it dont, then we keep diagnosing until it does, but PROPER elimination is the only way, and that takes time, SORRY. That is why I drink, 42 years with Jaguars, something had to give hahaha.
 

Last edited by Grant Francis; 08-23-2011 at 04:45 AM.
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Old 08-25-2011, 01:49 AM
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grant I did damage to the distributor when i pulled off stuck rotor .can I get replacement parts for the inner works eg.the little springs and 1 pawl was broken i will have to wait for parts or a new or rebuilt distributor thx.
 
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Old 08-25-2011, 03:21 AM
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Bugga.

I thought this would come up eventually, especially when I read you had "to pull like hell, and broke the rotor". I hoped you hadnt pulled that inner shaft up too far and buggered those springs and weights, but alas I was wrong.

You should be able to find those items somewhere. Maybe NOT new, but s/h will do.

I have had luck over many years with XK Unlimited in San Loius Obispo with odd bits and pieces.

Wreckers/dissmantlers may be your friend here.

Someone nearer to you should come up with options on this.

Not sure what access you got up there, but we have a few "specialist" auto electricians here from the real OLD days that have ways and means of getting near any auto electrical item repaired and working again. Some serious "outside of the box thinking" is required, but results are all we want.
 
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Old 09-12-2011, 01:43 AM
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Unhappy I got those steadely depressing low down mind messing working on my jaguar blues

well found and ordered my replacement distributor removed the old one to send as exchange when looked in hole and saw teeth are stripped on jackshaft pulled a/c and throttle tower there is an inspection cover now to my question can you remove the jackshaft through this hole I notice there is a tool to lock the jackshaft gears in place my car is a 1987 xj12 vandenplas ser#SAJBN104XHC476416 I now need a jackshaft had to get a distributor that would work from a xjs lots of surfing before i found distributor wonder if the jackshaft will be the same maybe some v12 expert may have a suggestion as i would really rather not remove the front of the car. THX
 
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Old 09-12-2011, 04:42 AM
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UM, take a seat, strap yourself in, REAL TIGHT, alcohol, LOTS OF IT.

Getting the message. BUGGA, as we say down here, the rest is un-printable.

The front of the engine MUST come off, and you will be messing with that "plastic" timing chain tensioner (real big $$), and the rest is basic engine rebuilding stuff.

The jackshaft itself is the same right through the V12 5.3ltr range. So basicallay from early '70's, to about 1992.

That distributor you just done a deal on is more than likely NOT required, so see if a cancellation is possible if it is not too late.

I have never seen one of them do that, but I have read about it here quite a lot, maybe its the top half of the globe versus the bottom bit haha, you are going to have to learn how to laugh, trust me.

I have had V12's for 20+ years, and a few engines apart for rebuild in that time (mega miles on all but 1). Reasons for failure of that gear elude me, but I reckon oil (rubbish el-cheapo), distributor siezing, come to mind.
 
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Old 09-14-2011, 02:35 AM
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Red face A hobbies a joy to find "hic"

needed distributor as old had broken pawl&spring. Found jackshaft,it's in the mail also schematic of front of jackshaft I see the bolts go through chain tensioner into jackshaft gears and thats why front of car must come off.Now to find the time to disassemble would have rather been working on body work but looks like I'm to learn how to work on the v12 good place to start.Any tips on chain tensioner removal as that is $295 if there's anything I shouldn't do I'd like to know now before disassembly.I see in my haynes manual there is a tool for locking the jackshaft gears so it won't move when unbolting can't seem to find this tool, manual also mentions using a couple of bolts if tool unavailable but no discription on how to go about it.Hopeing a little planning and research will prevent anymore surprises.
 
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Old 09-14-2011, 05:04 AM
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The chain tensioner is a seperate item, and not related to the jackshaft other than the chain itself.

At those $$ I would NOT mess with that tensioner, just replace it. Over $650 last time I asked down here. There is a "hook" thingy that is used to pull the tenmsioner straight prior to removal of the timing cover. However the plastic part usually snaps when straightened, BUT, you may be lucky. That is due to the lower pivot pin is supported in the block AND the timing cover, and unless that tension is removed things can "pop" and then the vocabulary will expand significantly. Mind you I have never used one, could not find one at the time, and nothing stupid happened, BUT, my tensioner was broken.

I am thinking of the locking of that jackshaft, and I really dont remember it being THAT special. Basically I think I used a screwdriver through the spare holes and simply tightened those bolts, not rocket science really. I dont think that movement is going to be your issue here, as the chain will be removed from that gear to get the gear out of the way so the shaft lock plate can be undone and the shaft slid out.

When assembling make REAL SURE you get the cam timing CORRECT. If its out DO NOT turn that engine backwards, coz the chain can possibly pick up the top edge of the tensioner and break it, haha, you need that, NOT. So if you wind that engine by hand and go "too far", bad luck, keep going until the timing marks come up again, and be more careful this time , mmm.

Inside that timing cover is NOT that scary, it is quite basic really. It just sounds worse than it is because its got 12 cylinders, big deal, its an internal combustion engine of 1960's design.
 

Last edited by Grant Francis; 09-14-2011 at 05:07 AM.
 
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