• Hi Guest!
    If you appreciate British Car Forum and our 25 years of supporting British car enthusiasts with technical and anicdotal information, collected from our thousands of great members, please support us with a low-cost subscription. You can become a supporting member for less than the dues of most car clubs.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

TR5/TR250 No spark... again

Share this page

M

mcqin

Member
Offline
I started work on a TR250 a little over a year ago. It sat under tarps in a driveway here in Chicago for 20+ years before I bought it. Needs a lot. I was able to get the engine running last year with some good advice from this forum, thanks. At the end of the year as I was getting ready to tune everything up, I lost spark. I'm just getting back to it again now. Do you have a checklist of the best suspects or order of things to check first. Last year I put in new plugs, points, wires, coil, and battery. I just started some checking, ran some fine sandpaper over the points, and checked the coil with a meter but haven't gotten any further. Suggestions on what to check next?
Thanks, Bob
 
Perhaps you have covered this since you messed with the points... but have you verified the points gap? Even just sitting the gap can close up if the points set was not secured tightly enough.
 
Check the voltage feeding the coil when the ignition switch is turned to the "ON/RUN" position.
 
Doug,

Your link works for me - I just had to click on the "here" where it says Click here to download your attachment
 
The link worked for me. Thanks, this is just the sort of instruction I was looking for. I'll let you know if I have questions. Thank you!
 
Hi Doug,
I read this over and used your troubleshooting flowchart to try and isolate my issue. I've followed through leading me to test 6 which tells me to examine ground connections inside the distributor. So I used a meter to check voltage from the positive side of the battery to the distributor housing, which showed battery voltage, and then checked the base plate in the distributor the same way, shows battery voltage there also. Am I checking that correctly? Am I missing something else? Maybe I should just get another set of points and condenser and try again..?
 
Looking back at my PDF, test 6 is really looking at the condenser to try and determine if it is functioning. If the condenser is internally shorted or if its wire is incorrectly connected (easily the case with 25 series distributors and probably the DM2) then the circuit will behave like the points never open and there will be no spark.

A footnote about test 6 is that when you are looking for the spark at the plug with no condenser installed, the spark will be weak and hard to see. Be sure to put the plug in the shadows where faint sparks can be seen.

The step after test 6 is the one focused on looking at the wiring inside the distributor. You carry out that test after removing the condenser and not finding a spark. Look for an earth wire between the breaker plate and the dizzy housing. Some Lucas distributors, others not. I believe they were used on the DM2 and 23/25 series distributors. If the wire is missing or broken you may have an intermittent ground connection for the points.
 
Just a quick update. Finally have spark and it is running again! After running through Doug's flowchart with various tests and confirming the ground is good at the distributor, I decided to replace the points, condenser, cap and rotor and see what happens. After doing that, noticed that at some point I had the connections to the ignition coil reversed. Don't know when I did that, but with new components and ignition coil connected correctly it fired right up. I assume that the reversed coil connections were giving me a very weak spark and probably my problem all along. Don't know when I did that... a bonehead move that made my limited time available to work on the car very frustrating. Anyway, that's done now and I can move onto the extensive list of next items. Thanks again everyone for your help, and Doug, your PDF will remain in my catalog of manuals...Thanks. -Bob
 
So I lost spark again! This really has me confused. Not sure if I have something shorted somewhere that is causing a component to burn out or something. So everything was running fine for about a week and I synced the carbs and was going to start tuning the engine next when it wouldn't start... no spark. Going back through the document from Doug and following the flowchart View attachment lucas ignition troubleshooting flowchart.pdf

I've gone through to step 5 and still no spark. I'll continue this weekend, but this has me very perplexed. I thought I was past this... any ideas?
 
If you've made it to step 5 and not resolved the problem yet, skip down one step and disconnect the condenser wire from the points. See if that restores a faint spark at the test plug connected to the coil. If you have a weak spark under those conditions, replace the condenser. If you have no spark under those conditions, look carefully at the wire between the coil and distributor for problems at either end.
 
Yep Doug, plan on going to the next steps this weekend. I ran out of time the other day. Just can't understand how it suddenly lost spark after it was going so well. I'll post how it goes this weekend. Thanks again, Bob
 
Ok, I removed the condenser and still had no spark. I replaced the condenser anyway, just in case, still nothing. Checked wires between coil & distributor and I can't find anything amiss. I'm completely stumped.
 
I would have a look at the ignition switch. Not be the first one to have a short.
I'm sure you checked for voltage at the coil, but try a jumper between the positive side of the battery and positive side of the coil, then there is no doubt it's in the distributor, if no spark.

Wayne
 
Ok, I'm back running again! Noticed this morning that spring loaded contact in the distributor cap was stuck and wasn't contacting the rotor. Replaced with the old one and it fired right up! I'm not sure if it started with something else and the contact in the cap got jammed while I was fiddling with other things. Anyway, I'm running again... whew...
Thanks for the advice!
-Bob
 
Arghhh... so I lost spark again. I must have a short somewhere that I'm missing and my monkeying around is occasionally doing something. So what would I look for with the ignition switch? any suggestions would be good...
Thanks, Bob
 
You can bypass the ignition switch...and if the engine dies or refuses to start, you'll know it's not because of the switch.
Remove the existing wire feeding the coil and tape (insulate) it's end.
Connect the coil directly to the battery. Use the ignition switch to engage the starter.
To kill the engine, remove the wire from the battery.
 
As Poolboy and Wayne said, try running the bypass wire from the battery to the coil (+) terminal. You MUST remember to disconnect that wire not just to stop the engine but also to keep the coil from overheating when the car is parked.

If you can use the bypass wire to drive the car without the loss of spark reoccurring, assume the root cause of the problem to be in the switch or the wire from the switch going to coil (+).

EDIT: This almost certainly would not be the case for you car but I had a similar issue with a car using the Lucas 45D distributor. Sometimes the car would start and run, other times not. The source of the problem turned out to be a poor crimp on the distributor end of the wire going between the points and the coil.
 
Could be a slight rupture of one of the wires causing an intermittent failure. Check the continuity of all wires, wiggling them back and forth to see if there might be an interruption.
 
Back
Top