Weak, intermittent spark

[okey0]

trying to get rebuild started back up. Car wont start. Using same parts that were in place before, car always fired up. getting fuel, so looking at ignition. Get about 2.8 ohms resistance between terminals on the coil, I've read that it should be between 3.1 and 3.5, so i'm not sure if that makes a diference.
I do get good spark from the coil wire when I hold it next to the valve cover.
It looks like the spark is weak, or even intermittent at the points when I crank the engine. My next step is to put new points and a condenser in. Any other thoughts on what could cause this issue?

 

[LSolheim]

Certainly you should also check your cap for a microscopic crack (or a carbon trail leading to ground) & the cap to spark lead connections, particularly if you have changed to carbon core at some time (hint: you can use a straight pin insterted into the wire end core to provide some solidity in the carbon to give the connector screw something to seat against, if necessary).

Defective/failing rotors have also been an issue in the past (kind of hard to believe,.but it happened to me), see THIS thread for some background.

Good luck.

 

[Steve]

I had the exact same symptoms this summer. The cap looked in perfect condition and wasn't more than 3 years old but that was where the problem was. A new cap and wires completely solved the misfiring.

 

[Cap'n John]

Check to see that your cap and rotor are indeed LUCAS parts. The after-market caps are turned 90 deg (this will throw off your firing order if you didn't notice the difference) and they and the rotors are junk. True Lucas caps can be a tough find. A cracked cap may not be visible to the naked eye, but if you happen to grab it while the engine is running or cranking, it will leave no doubt that there is a spark leak. (Don't ask how I know this!). I also put a dab (don't over do it!) of silly-cone sealant on ea wire where it enters the cap for protection.

I highly recommend Pertronics ign module and be sure to get the appropriate coil too for best results. Water won't bother it and it does provide better performance and reliability.

 

[okey0]

sadly, i'm starting to think the timing is out of whack. New points and condenser gave me a more consistent spark, but the engine only cranks. not even a hint of trying to ignite any gas. not even sure where to start with that issue to try to figure it out.

 

[mike_israel]

Start with the basics. I got tripped up on my 914 because I was certain the plug wires were correctly routed to the distributor. I once had a Jaguar specialist who was unable to diagnose my no start until I noticed the distributor (and thus the timing) was completely askew. Here is a rough idea of how dizzy should be positioned.

 

[LSolheim]

Hopefully your rebuilder (or you) aligned the crank & cam properly when installing the chain. The distributor only fits one way in the gear, so also hopefully the distributor gear was dropped in at the correct alignment.

Take out plug #1and rotate crankshaft until mark is vertical (aligned w/ marker tab). Look in cylinder and verify piston is at top of stroke. If not rotate another 360 degrees. When tab is aligned and piston fully up, verify that rotor is pointed at cap contact for #1. If all checks out, rotate crank again to about 10 degrees before Top Dead Center. Then loosen distributor and rotate until points just open.

Hopefully she'll start once you reassemble and you can tweak the timing.

Good luck

Edit: Mike has an excellent point: that 1-3-4-2 firing order is easy to screw up with this cap because the wires look funny as they come off of it.

 

[okey0]

Take out plug #1and rotate crankshaft until mark is vertical (aligned w/ marker tab). Look in cylinder and verify piston is at top of stroke. If not rotate another 360 degrees. When tab is aligned and piston fully up, verify that rotor is pointed at cap contact for #1. If all checks out, rotate crank again to about 10 degrees before Top Dead Center. Then loosen distributor and rotate until points just open.

everything lined up, I did the rotation til the points just open, and all I get is a little backfiring thru the carb and a real gassy smell and some blue smoke out the exhaust. I'm thinking I screwed up the valve adjustment some how, so next i'll be taking off the valve cover.

this is what happens when you let a dummy (ME) rebuild an engine.

 

[LSolheim]

everything lined up, I did the rotation til the points just open, and all I get is a little backfiring thru the carb and a real gassy smell and some blue smoke out the exhaust. I'm thinking I screwed up the valve adjustment some how, so next i'll be taking off the valve cover.

this is what happens when you let a dummy (ME) rebuild an engine.

Before removing the valve cover, take one last look at the plug wires off of the cap per Mike's photo. Note they should be 1-3-4-2 (#1 is to the aft of the car) rotating CCW looking at the top of the cap. #1 & #2 are the upper connections. Like he said, we've all had that issue!

 

[okey0]

I took the valve cover off, as I rotate the crank, the #1 valve starts to open when the bump on the crank pulley is at 180 degrees. As I continue to rotate the crank, #1 valve is closed when the bump is about 5 degrees before indicator on timing cover. Piston is tdc, rotor is pointing at contact for the #1 plug in the dizzy. Does that sound right?

 

[mike_israel]

You have tried a different cap and rotor as others have suggested?

 

[Jon March]

i will be very intersted in hearing how this resolves!

 

[okey0]

You have tried a different cap and rotor as others have suggested?

Different rotor, but don't have a different cap yet. No one has them in stock so won't be til Tuesday. Be nice if it was that simple tho I'm dubious. Car started just fine prior to tear down, and I have a hard time grasping the idea that simply removing and reinstalling the part would cause it to malfunction. But I'll give it a shot-and I PRAY you are right!. Does anyone think the 2.8 reading on the coil is cause to get a new coil? I think the book says it should be between 3.1 and 3.5.

 

[LSolheim]

I took the valve cover off, as I rotate the crank, the #1 valve starts to open when the bump on the crank pulley is at 180 degrees. As I continue to rotate the crank, #1 valve is closed when the bump is about 5 degrees before indicator on timing cover. Piston is tdc, rotor is pointing at contact for the #1 plug in the dizzy. Does that sound right?

That sounds OK as long as you are looking at the correct valve (see here). Shouldn't be an issue if you followed the Maintenance Manual reassembly procedure.

 

[Steve]

everything lined up, I did the rotation til the points just open, and all I get is a little backfiring thru the carb and a real gassy smell and some blue smoke out the exhaust. I'm thinking I screwed up the valve adjustment some how, so next i'll be taking off the valve cover.

this is what happens when you let a dummy (ME) rebuild an engine.

Is it possible the distributor is installed 180 degrees out (firing on the intake)? I did this on a rebuild I did years ago and had to sleep on it before I figured it out. The symptoms sound much the same.

 

[Cameron in UK]

Yes, easy mistake to make, we have an engine here like that. Dad just changed the plug lead order from 1342 to 4213 and it runs fine - just looks a bit odd.

 

[okey0]

Is it possible the distributor is installed 180 degrees out (firing on the intake)? I did this on a rebuild I did years ago and had to sleep on it before I figured it out. The symptoms sound much the same.

DING DING DING the winner. The rotor was pointing at #4 spark plug lead when the piston was at tdc on the compression stroke. So I did what Cameron suggested with the re-wire and it fired right up. THANKS to all for your suggestions. You all helped turn my frown upside down!

 

[Jon March]

all i got is

 

[mike_israel]

Glad you figured it out. Yup, this has happened to many of us. Like I said, I was certain that the wires were correct in my 914 so spent three days chasing gremlins until I realized they were crossed. A professional Jaguar restorer with 40 years experience could not diagnose my no start until I pointed out that the distributor was positioned differently than the other xj6 in his shop.

Have a beer and go rev that engine. (You did use a high zddp break in oil).

 

[LSolheim]

Glad you got it, always a relief! As noted above, although the distributor fits only one way in the gear, the distributor gear itself can be pulled up and dropped into the housing at almost any alignment if you feel the need to reorient.